BMB 252 Exam 3
How does myc become an oncogene?
By amplification
What cancer is associated with Rb?
Retinoblastoma
How do antibodies block cancer's inhibitory signals?
By binding to proteins on T cell surface which prevents the cancer proteins from activating themH
How is the EGF receptor become consistently active?
By deletion of the extracellular part of the receptor- Common in brain tumor, glioblastoma
How can DNA damage affect Mdm2?
By either inducing phosphorylation of Mdm2 or decreasing the production of it, both of which cause an increase in p53
What kind of changes can cause cancer?
- Genetic gene inactivation- Epigenetic gene inactivation
What causes genetic instability that leads to cancer?
- Defect in DNA repair - Inability to maintain chromosome integrityExample: Translocation in breast cancer cells
In what ways can a proto-oncogene be converted to an oncogene?
- Deletion or point mutation coding sequence- Regulatory mutation - Gene amplification- Chromosome rearrangement
Effects of child-bearing on the risk of breast cancer
- Increases with age - Increases with exposure to hormones - First full-term pregnancy changes differentiation state of breast cells The relative probability of breast cancer developing at some time in a woman's life increases with age at which she gives birth to her first child. The longer the period of exposure to reproductive hormones up to birth of the first child, the greater the risk. It is thought that the first full-term pregnancy may result in a permanent change in the state of differentiation of the cells of the breast, altering their subsequent responses to hormones. Several other lines of epidemiological evidence also support the view that exposure to certain combinations of reproductive hormones, especially estrogen, can promote development of breast cancer.
Loss of contact inhibition in cell culture
- Most normal cells stop proliferating once they have carpeted the dish with a single layer of cells- Proliferation seems to depend on contact with the dish- Proliferation is inhibited by contacts with other cells- Cancer cells ignore these restraints
What factors can cause cancer?
- Mutagens such as chemical carcinogens, ionizing radiation, and viruses. - Genetic predispositions like an increased rate of mutations in some individuals (DNA repair defect)
What influences the rate of evolution of cancer?
- Mutation rate- Number of individuals- Rate of reproduction- Selective advantage of mutants over the normal
How do proto-oncogenes become cancerous?
- Mutations in the proto-oncogene - They turn into oncogenes- Oncogenes gain function and turn into cancer
How do tumor suppressor genes become cancerous?
- Mutations in tumor suppressor gene - Loss of function
What happens in the formation of hereditary retinoblastoma?
- Occasional cell inactivates it's only good Rb gene copy, leading to excessive cell proliferation- Result: Tumors in both eyes
Why are many mutations needed in the evolution of a tumor?
- To break control systems- To survive with limited amounts of oxygen and nutrients
Domains AND STRUCTURE of p53
- Transcription-activation domain which activates transcription factors - Apoptotic domains (2) - DNA-binding domain - Oligomerization domain (forms tetramers before binding to DNA) - Nuclear localization domains
Cancer-critical genes
- Unstable/many mutations - Repeatedly altered in human cancers - Total number is about 300, which is 1% of the genes in human genome - They include signal proteins, receptors, transcriptional regulators, DNA repair enzymes, CAMs, metabolic enzymes, etc.
Gap junction functions
-Electrical coupling of neurons, which is faster than synapse -synchronous contractions of heart and smooth muscle cells -coordination of the responses (liver cells) -development of egg (follicle cells)defect in certain connexin causes deafness
Integrins Recruit Intracellular Signaling Proteins at Sites of Cell-Matrix Adhesion
-Focal adhesion kinase (FAK) is recruited to integrins. It results in recruitment and phosphorylation of signaling proteins since FAK serves as a scaffold
Fibronectin and other multidomain glycoproteins help organize the matrix
-Glycoproteins contain multiple copies of protein interaction domains-bind to integrins on cells surfaces-Help organize the matrix and help cells attach to it-guide cell movement-Glycoproteins are proteins decorated with polysaccharides, around half polysaccharide; proteoglycans are 99% polysaccharides at the expense of long GAGs.
integrin binding to ECM changes in response to intracellular signals (inside-out regulation)
-Integrins Must Interact with the Cytoskeleton to Bind Cells to the Extracellular Matrix-Cells can regulate the activity of their integrins-In white blood cells, integrins are normally in a conformation that does not bind to the matrix.-This allows cells to move around until a signal triggers them to stick-Signals emanating from damaged tissue bind to cell surface receptors and elicit an intracellular signal transduction cascade that results in activation of integrins.-white blood cell then stick around the damaged tissue longer.-Similar mechanism induces platelets to aggregate.
Selectins are named according to cell type
-L-selectin: leukocytes- P-selectin: platelets -E-selectin: endothelial cells (blood vessel lining)
Examples of regulation of integrin binding activity
-Platelets are induced to bind to matrix protein fibronectin for blood clotting-T-cells binding to antigen activates their integrins to bind and activate other immune system cells-During development, when cells should disintegrate from the matrix and migrate
integrin binding to ECM increases its binding to intracellular filaments
-To regulate the cell movement along the surfaces the integrin binding should be regulated -When cell attaches to some outside components, alpha and beta chains move away from each other, exposing the binding site to protein talin that recruits actin filaments. -As a result, an intracellular network of filaments is formed inside the cell- integrins bound to the matrix may induce localized cytoplasmic changes this is particularly true in axon guidance in developing nerves where local interactions of TM adhesion proteins affect the placement of actin fibers and the plasma membrane
Cell-cell anchoring junctions are mostly mediated by Cadherins
-Transmembrane proteins-mediate cell-cell junctions-in all animals-depend on Ca2+ (Ca2+ +adherins) •There are hundreds of different cadherins •Each vertebrate cell expresses one or more cadherins, according to the cell type •Differentially expressed by different cell types and in different tissues
Cell-Matrix Adhesions Respond to Mechanical Forces
-When there is a pulling force at integrins, talin unfolds revealing the vinculin binding site that results in recruitment of extra actin filaments
Two types of cell-matrix anchoring junctions
-actin-linked cell-matrix adhesions (focal adhesions): link actin filaments to ECM; use integrins attached to actin filaments-hemidesmosomes: link intermediate filaments to ECM; use integrins attached to intermediate filaments
Two types of cell-cell anchoring junctions
-adherins junctions: link actin filaments-desmosome junctions: link intermediate filaments
Structure of GAP junctions
-assembled from TM connexins-connexin hexamer forms a half-channel called connexon-different connexins can form heteromeric connexons- when 2 channels align they form a continuous channel-channel opening and closing can be regulated- There are many semi-channels connexons in the membrane which are in closed conformation. They are used for remodeling the channels
Integrins activate intracellular signaling pathways
-attachement to matrix is important to stem cells-When they lose the matrix connection they can't proliferate (defense from cancer)-Some cells (epithelial cells, endothelial cells) die by apoptosis unless they are attached to matrix
Different forms of ECM
-bones and teeth (calcified)-transparent cornea-tendons (ropelike)
Anchoring Junctions
-cadherins proteins: link cells together-intergrin proteins: link cells to ECM
Extracellular matrix
-can be in form of fibrous polymers (collagen, fibronectin, etc.) A network of proteins and polysaccharide chains that are secreted by cells
How do the cells move inside the ECM?
-cells that need to move secrete proteases-ex: branching growth of epithelial structures, such as glands, migration of WBC out of the blood vessel (need to digest their way through basal lamina)-proteases spread locally-many cells have proteases bound to receptors-portease inhibitors are produced where proteases aren't needed
types of cadherins
-classic: named according to tissues where they were found; related in sequence; both extra- and intra-cellular; N-Cadherin (nerve, muscle and lens cells, fibroblasts), P-cadherin (placenta, epidermis), E-cadherin (epithelial, parts of brain)-non-classical: not so close in sequence to classical; in desmosome; in neurons (protocadherins)
Roles of main components of basal lamina
-collagen: provides basal lamina the tensile strength-laminin: responsible for the sheet structure-proteoglycans, collagen, and laminin: important for filtering functions-integrins: provide binding to the cell membranes
Two main ways in which cells in a tissue are held together
-epithelial tissue: attached to basil lamina and to each other; lines cavities and surfaces of structure throughout body; skin, inside of lungs, GI tract, reproductive and urinary tracts, exocrine and endocrine glands -connective tissue: inside of ECM; connections between cells are scarce; matrix provides most of mechanical strength; bone, cartilage, adipose tissue, blood
Elastin
-gives tissues their elasticity- hydrophobic protein-cross-linked-skin, blood vessels, lungs, bladder lining need to be both strong and elastic
Laminin is the primary organizer of the sheet structure of the basal lamina
-heterotimer molecule-glycoprotein-interact with each other, other basal lamina components, and integrins
Proteoglycans and hyaluronan forms hydrating gels
-hyaluronan is very negatively charged so it attracts positively charged ions into it- influx of sodium is followed by influx of water because of osmotic pressure- hyaluronan is a component of joint fluid and is massively produced in wound healing Even though GAGs take less than 10% of the connective tissue, they attract massive amount of water and fill all the space. This creates a substance that can withstand compressive forces
Adherens Junctions respond to forces generated by the actin cytoskeleton
-if cells are pulling away from each other, alpha-catenin is stretch, revealing a domain for vinculin binding, which attaches more actin filaments so that the cells stay connect with a stronger bond
beta-catenins indirectly link classical cadherins to actin filaments
-intracellular domain of cadherin provides anchorage to cytoskeleton -anchorage to actin depends on cluster of intracellular anchor proteins, mainly beta-catenin
structure of selectin
-lectin domain binds oligosaccharides -selectins are calcium dependent
Hemidesmosomes
-link intermediate filaments to ECM type of intermediate filament attached to desmosomes/hemidesmosomes depends on cell type keratin filaments in most epithelial cells desmin filaments in heart muscle
Desomosome junctions
-link to intermediate filaments-button-like spots provide epithelia with mechanical strength abundant in epidermis contain non-classical cadherins family proteins that attach to intermediate filaments such as keratin filaments. Connect Intermediate Filaments from Cell to Cell similar in structure with adherence junction
More on basal lamina
-made by cells on each side of it: epithelial cells and stroma (cells of connective tissue) provide some components-made of fibrous proteins, mostly glycoproteins, which have oligosaccharide chains attached (laminin, collagen and others)-made of proteoglycans-associated with fibronectin of the connective tissue-connects with epithelial cells thru integrins-the content of basal lamina varies from tissue to tissue
Collagens
-major proteins of ECM-25% of protein mass in skin and bone-3-stranded; 3 alpha chains-every 3rd residue is glycine (-H)-25 alpha chains, 20 types of collagen-stiff; assemble into fibrils outside the cell-fibrils often assemble into fibers-resist tensile forces
More on cadherins
-most are single-pass glycoproteins-cadherin (tandem) repeats are structurally related to antibodies-in cell junctions connect to actin or intermediate filaments
Cell junctions in small intestine epithelium cells
-occluding, adherens, and desmosome junctions organized by scaffold to form a junctional complex in order from apical end to basal end: tight junction, adherens junction, desmosome, gap junction
cadherins mediate homophilic interactions
-only bind to same or closely related subtype of cadherins on other cells bind by insertion of terminal knob into the pocket bind to each other only in presence of Ca2+, and then they become rigid-arrayed in parallel, functioning like Velcro: each binds by a weak bond but all together they form a strong interaction junction can be easily peeled apart In the absence of Ca2+ , cadherin molecules become floppy and their interaction fails Ca2+ binding stabilizes structure of flexible hinge region, required for binding
GAP junctions
-present in most animal tissues, including connective and epithelia- allow cells to communicate with e/o-are channels bn cells-allow small water-soluble molecules (inorganic salts, sugars, amino acids, nucleotides, vitamins, cAMP, IP3) to pass bn cells-molecules larger than 1000 dalton (1000g/mol) can't pass
Why are cell junctions important?
-provide strength of the body -support the shape of the body -providing the way for the cells to exchange signals and nutrients
How is aflatoxin converted into a carcinogen?
Aflatoxin is first produced by a mold that grows on grain and peanuts. It is then converted to a mutagen that binds to DNA by metabolic processes
GAGs
-repeated disaccharide, unbranched -highly negatively charged- fairly stiff and don't fold into globules like proteins do -ex: hyaluronan, heparan sulfate- attract a lot of water and fill all the space, creating a substance that can withstand compressive forces •Hyaluronan consists of about 25,000 sugar monomers
Basal Lamina
-same as basement membrane- present in all multicellular animals- underlies all epithelia-surrounds individual muscle cells, fat cells, and Schwan cells (wrap around perpheral nerve cell axons to form myelin)- functions as a selective filter in kidney-determines cell polarity- influences cell metabolism- organizes proteins in adjacent cells' membranes-promotes cell survival- promotes proliferation and affects differentiation- serves as highway for cell migration in regeneration of the epithelium tissue
Where does ECM come from?
-secreted by cells of fibroblast family mostly- chondroblasts make cartilage- osteoblasts make bone
Additional cell adhesion molecules (CAMS) provide a weaker binding between cells
-selectins are involved in immune response-they direct immune system cells to the point of infection -bind to oligosaccharides on other cell surfaces (heterophilic binding)
Selectins and Integrins and white blood cells in blood stream
-selectins make WBC roll along the blood vessel walls-integrins allow a stronger binding and penetration of the WBC into the tissue for an immune response
How are cells of the body held together?
-some are connected to each other -some are connected to the extracellular matrix (ECM)
Paracellular transport through the tight junctions
-tight junctions can be transiently changed to allow the passage of water and small molecules like amino acids and monosaccharides-paracellular transport is a passive passage of small molecules in case their concentration in the lumen is very high-does not require ATP
ZO proteins serve as a scaffold for tight junctions
-zonula occludin proteins have multiple domains serving as scaffold that can bind to diff components of tight junctions and actin
Tight (occluding) junctions
-•More than 60% of the cell types in vertebrate body are epithelial All epithelia are structurally polarized: basal side is attached to the basal lamina and apical surface is bathed in extracellular fluid epithelia serve as permeability barriers;occluding junctions seal cells together to prevent leakage •Occluding junctions are also called tight junctions in vertebrate epithelia
How is cancer derived from a single mutated cell?
1) Chromosomal translocation analysis2) X-chromosome inactivation analysis in female tumor cells
What are the 6 key properties of cancerous cells
1) Disregard external/internal signals regulating cell proliferation (including those for replicative senescence) 2) Avoid apoptosis/suicide 3) Are genetically unstable (aids tumor evolution) 4) Are invasive (can move out of primary tissue) 5) Are metastatic (survive & proliferate in secondary tissues) 6) Able to recruit adequate blood supply (many tumors show enhanced production of angiogenic factors)
What two groups of protein kinases activate p53?
1) MAPK family which responds to membrane damage, oxidative stress, osmotic shock, heat shock, etc 2) ATR, ATM, CHK1, CHK2 - Oncogenes also stimulate p53 activation along with UV light
2 functions of tight junctions in epithelium of small intestine
1) junctions provide a selective permeability barrier between cells: selective molecules can pass through, depending on tissue and condition 2)prevent mixing of plasma membrane components-active transporters pump glucose in cell on apical surface-passive transporters pump glucose in tissue on basolateral side The transport through the cell is called transcellular transport
Components of ECM
1) proteoglycans and glucosaminoglycans (GAGs) 2) fibrous proteins (mostly collagen) 3) glycoproteins
Two stages of cancer development
1)neoplasm - cells start to divide uncontrollably 2) metastases - Cells gain the ability to invade surrounding tissues and form secondary tumors
What is the "hot spot" regarding CML?
100-1kb region
A single mutation is not enough to cause cancer
10^16 cell divisions per human body Probability of mutation in each gene in one cell division is 10^-6 For each single gene there were 1010 divisions where it got mutated in a lifetime Direct analyses of tumors: one mutation - benign tumors Malignant tumors - 10 or more mutations
-basil lamina
= flexible, thin mat of specialized ECM that underlies epithelial cell sheets and tubes
Myc
A gene regulatory protein that promotes cell division. Overproduction causes cancer- Myc is amplified/fused with a stronger promoter due to a chromosomal translocation which results in cancer formation
carcinoma
A malignant tumor that occurs in epithelial tissue
What are characteristics of low grade of epithelial neoplasia?
A mix of mature and immature cells, cells with larger nuclei, and white blood cells
Underactivity mutation (loss of function)
A normal cell undergoes a mutation event that inactivates tumor suppressor genes then undergoes a second mutation event which inactivates the second gene copy. These two inactivating mutations eliminate the tumor suppressor genes and promote cell transformation
PARP
A polymerase involved in DNA repair, along with BRCA1 and BRCA2
What happens in the absence of the Wnt signal?
A protein complex destabilizes beta catenin
What happens after p53 is phosphorylated?
After Mdm2 is removed, p53 begins to accumulate and stimulates transcription of the gene that encodes for the CKI protein p21
Smad4
A transcription factor that is activated by TGFbeta signaling molecule.- When Smad4 is mutated, the cells start to uncontrollably proliferate
To get cancer, both alleles of____ should always get mutated A. RB B. TP53 C. Both TP53 and Rb
A. Rb -TP53 is dominant negative or recessive. one mutated receptor is enough to cause cancer -Rb is recessive. Both alleles need to be mutated to get cancer
adherens junctions in epithelia form a continuous adhesion belt
Actin bundles are linked into a transcellular network This network can contract through myosin motor proteins, which can lead to folding of epithelial sheet
Active/Inactive conformation of integrin
Active/Inactive conformation of integrin -inactive state: (not bound to extracellular ligand) intracellular parts of alpha and beta chains adhere to one another -when integrin is stimulated from inside or outside, its conformation changes -alpha and beta chains no longer bind to each and become available to bind filaments inside and outside the cell
What are closer to the basal end?
Additional desmosomes and gap junctions
Adherens junctions coordinate actin based motility of adjacent cells
Adherens belt of epithelial cells in small intestine= ring of adherens junctions encircling each of the cells Intracellular contractile bundles of actin filaments are tethered by intracellular anchor proteins to cadherin Cadherins of one cell bind homophilically to those of adjacent cell actin filament bundles of adjacent cells are tied together
Proteoglycans can form aggregates
Aggrecan aggregate Consists of about 100 aggrecan molecules linked non-covalently to a hyaluronan molecule via two linkage proteins Each aggrecan consists of a 3000 amino acid core protein that is linked to >100 GAG molecules
Occluding Junctions Form a Selective Permeability Barrier Across Epithelial Cell Sheets
Also called tight junctions in vertebrates. The 'zip-lock' seal prevent molecules and cells from permeating between cells from the gut of an animal. Actually cells regulate this too, to let certain molecules (like amino acids, certain ions) past. The tight junctions also prevent transmembrane carrier proteins on basal and lateral side of the cell from migrating over to the luminal side (apical surface).
What does loss of p53 most often result in?
An aneuploidy phenotype
Mitogens
An extracellular signal molecule that stimulates cell proliferation
How are tumor suppressors identified?
Analyzing fragments and representative difference analysis •More difficult, than to identify an oncogene: you have to find something, which is missing in cancer cell •A lot might be missing because a lot of non cancer-related mutations are produced as a side effect •It's easier for some rare cancers that have small number of mutations •Example of such cancer: retinoblastoma. The tumor suppressor gene, which was discovered - Rb (from retinoblastoma) •Sometimes it's obvious that a fragment of chromosome was lost. Then researches look if another allele has any mutations. •There are new powerful techniques to identify the difference between normal and cancer cells total mRNA: Representative Difference analysis
Cancer cells avoid apoptosis
Apoptosis is a default developmental program of a normal cell Cells in the human body only survive and proliferate if they receive survival signals or signals to proliferate from other cells If there are no survival signals, cells turn on apoptotic program and die, no proliferation signals - cells stop proliferating Cancer cells override control signals There are mutated cells that manage to override apoptotic program and survive when they were supposed to die, or proliferate in the absence of signals
What happens in normal cells when PARP is inhibited? A. BRCA proteins can compensate for the loss of PARP because it has a similar structure B. BRCA proteins repair DNA in an alternative pathway
B. BRCA proteins repair DNA in an alternative pathway
Mutations in which domain of p53 require both alleles to be mutated in order to cause cancer (recessive loss-of function mutations)? A. Oligomerization domain B. DNA binding domain C. Both types are recessive
B. DNA binding domain
Which cytoplasmic tyrosine kinase is always in the "on" conformation, independent of cytokine signaling?
Bcr-Abl fusion protein
Why do many carcinogens act with a delay?
Because many mutations are needed for a tumor to become metastatic and the natural selection process within cancer cells takes time
Why are cancer cells more susceptible than normal cells to the damaging effects of ionizing radiation?
Because they lack an ability to arrest the cell cycle and make necessary repairs
Explain the difference between benign and malignant tumors in breast cells
Benign: Tumor takes up space in the lumen Malignant: Tumor ruptures the basal lamina causing it to spread
Leukemia
Blood condition of white (hemopoietic) cells; malignant (cancerous) condition.
What mechanisms can inactivate tumor suppressor genes?
Both genetic and epigenetic mechanisms
How does HPV cause cancer?
By integration in basal cells genome in benign infection (warts) the HPV chromosomes are stably maintained in the basal cells of the epithelium as plasmids Integration of a fragment of a plasmid into chromosome, which interferes with control of cell division
How can immortal cell lines be further transformed?
By introducing various oncogenes which may transform them into fully malignant/tumorigenic cells- This supports the multiple hit theory for cancer
How is E2F un-inhibited and what does this allow?
By phosphorylation of Rb protein by Cyclin/CDK which allows it to activate transcription of S-phase geneS
How can "immortal" cell lines be established?
By selecting for transformed cells that defy programmed replication senesence (lose chromosomes/genes required for rep. sen.)
How does papillomavirus activate cell proliferation?
By using two viral proteins, E6and E7, to sequester the host cell's p53 and Rb. E6 protein binding leads to ubiquitylation of its p53 partner, inducing p53 proteolysis
Viruses cause cancers by_____ A. Promoting excessive proliferation B. Introducing mutations C. Both
C. Both
Which of the following metabolically activates carcinogens in the Ames test? A. Liver extract B. Salmonella C. Test compound
C. Test compound
The matrix can be diverse in function.
Calcification of the matrix gives rise to bones and teeth. It can become transparent to give rise to the eye cornea Rope-like organization gives rise to tendons.
What results from an increased amount of p53?
Can cause premature aging
Effect of ionizing radiation on normal and cancer cells
Cancer cells tend to be more susceptible than normal cells to the damaging effects of ionizing radiation because they lack an ability to arrest the cell cycle and make the necessary repairs. Unfortunately, the same genetic defects may render some cancer cells resistant to radiation treatment, as they may also be less adept at activating apoptosis in the face of DNA damage.
Sarcoma
Cancer of connective tissue/muscle
Cancer critical genes fit into two broad categories:
Cancer-critical genes fall into two readily distinguishable categories, dominant and recessive. Oncogenes act in a dominant manner: a gain-of-function mutation in a single copy of the cancer-critical gene can drive a cell toward cancer. Tumor suppressor genes act in a recessive manner: the function of both alleles of the cancer-critical gene must be lost to drive a cell toward cancer. a. oncogenes: their mutant proteins (oncoproteins) are overactive; cells to proliferate when they shouldn't't; usually dominant mutations b. tumor suppressors: normally, their protein products suppress cancer; their genes are DELETED or INACTIVATED in cancer cells; usually recessive mutations
How do cancer cells display an altered control of growth?
Cells of the contact-inhibited monolayer become transformed and lose contact inhibition, thus resulting in an accumulation of uninhibited transformed cells
Most human cancers are showing increased mutation rate: they are genetically unstable
instability -inherited -acquired as a result of mutations
Proteoglycans
Consist of polysaccharide GAG linked to protein Polysaccharide is linked to serine amino acid
Cytochrome P450 oxidases
Convert ingested toxins into excretable metabolites, some of which are mutagenic - Examples of such metabolites: benzopyrene in tobacco smoke
What are the proto-oncogenes associated with E2F activation?
Cyclin D1/Cdk4 in both non-proliferating and proliferating cells
How are oncogenes identified?
DNA is extracted from tumor cells and broken into fragments which are introduced into a mouse-derived cell line which already has cancer mutations. If any of the fragments contains an oncogene, then small colonies of abnormally proliferating cells will appear. The fragment will then be sequenced to be identified.- Oncogene Ras was first to be identified (mutated in 30% of tumors)
What does p53 activate when DNA is damaged?
DNA repair proteins
Are oncogenes dominant or recessive?
Dominant- They gain function from mutations- Oncoproteins are overactive which causes cells to proliferate when they shouldn't
What can act as a cell-cycle inhibitor independent of Rb?
E2F
Dissociated Vertebrate Cells Can Reassemble into Organized Tissues Through Selective Cell-Cell Adhesion Experiment:
Embryonic liver cells and embryonic retina cells: Cell interactions destroyed by trypsin-EDTA Cells combined Cells gradually sort out according to tissue of origin
Mutations in the p53 Pathway
Enable Cancer Cells to Survive and Proliferate Despite Stress and DNA Damage
How is the ECM formed?
Extracellular matrix (ECM) formed from secreted macromolecules (fibronectin, collagen, etc.)
Hyaluronan is a ________
GAG
What drug inhibits Bcr-Abl kinase?
Gleevec (imatinib) by preventing the signal for cell proliferation and survival which results in leukemia
What else is needed for cell cycle progression besides mitogens?
Growth factors, as they are necessary to signal the presence of nutrients required
What types of HPV are mostly responsible for causing cancer?
HPV 16 and 18 - Only persistent HPV infections lasting for years cause cancer - test via pap smear 70% of HPV are caused by HPV 16 and HPV 18
Fibronectin and Other Multidomain Glycoproteins Help Organize the Matrix
Has many domains that bind different parts of matrix and also bind to integrins on cells surfaces
Ras-GTPase
Helps transmit signal to enter the cell cycle- A mutation causes it to transmit signal on it's own, which leads to cancer
What does deletion or point mutation coding sequence result in?
Hyperactive protein made in normal amounts- Ras, truncated EGFR, src, erbB, neu,
How are telomeres involved in cancer cells?
In cancer cells there are high levels of telomerase and the telomeres do not shorten, and the cells can divide uncontrollably (Selective advantage)
What does abnormal activation of the RTK/PI3 kinase/Akt/mTOR pathway lead to?
Increased rate of glycolysis in cancer cells
TGFbeta
Inhibits cell growth
p16
Inhibits formation of CDK/cyclin complex and Rb is dephosphorylated and bound to E2F (inhibits it)- Occurs in stressed cells
How is cancer treated with antibodies?
Injections of antibodies against receptors that are overexpressed on the surface of cancer cells- Can also be linked to toxins
How do cancer cells escape immune response?
Mutant proteins on surface of cancer cells are recognized by immune system and attack, however cancer cells develop resistance by expressing inhibitors. - Treatment is by removing the immunosuppressive environment
Integrins
Integrins -link cells to ECM: matrix receptors -in ECM, they mostly bind to laminin, fibronectin, and collagen -important for epithelial and connective tissue architecture -important as signaling molecules, which can transmit the signals in both directions: into and out of cell -can serve as cell-cell adhesion molecules, bind to Ig-like CAMs -bind with low affinity, strong binding is achieved by integrin clustering Ca2+ or Mg2+ dependent -affinity can be regulated
What are the disruptions in the genome of cancers?
Intrachromosomal rearrangement (most common) Interchromosomal rearrangement- Copy number- Highly amplified regions
What are characteristics of high grade intraepithelial neoplasia?
It has only undifferentiated cells, immature cells with large nuclei and little cytoplasm
What do PARP inhibitors do?
Kill cancer cells that have defects in Brca1/2 genes by the inability to seal single stranded breaks forming in replication and the death of cancer cells Normal cells survive PARP inhibitors because alternate pathway
What are the characteristics of the superficial layers of the cervix?
Large, differentiated, cuboidal cells with a small nucleus
What kinds of cancers is Rb missing from?
Lung cancer, breast cancer, and bladder cancer
What happens to p53 under low level normal conditions?
MDM2 (ubiquitin ligase)targets it to be degraded and also promotes its translocationfrom the nucleus to the cytosol
What provides mechanical strength in connective tissue
Matrix
Oncogenes have more ______ ______, while tumor suppressor genes have more _____
Missense mutations, truncatations
Transforming potential of oncogenes
Most normal cells (primary cells) show contact inhibition when crowded in culture and eventually will undergo replicative senesence in culture even if not crowded
Loss of contact inhibition in cell culture
Most normal cells stop proliferating once they have carpeted the dish with a single layer of cells: proliferation seems to depend on contact with the dish, and to be inhibited by contacts with other cells. Cancer cells, in contrast, usually disregard these restraints and continue to grow, so that they pile up on top of one another
What does chromosome rearrangement result in?
Nearby regulatory DNA sequence causes normal proteins to be overproduced and fusion to actively transcribed gene which produces hyperactive fusion proteins- Also myc
Major tissue types in vertebrates
Nerve Muscle Connective Epithelial
Is a single mutation enough to cause cancer?
No, because if a single mutation was enough then the chance of cancer would increase linearly with age. Incidence of cancer increases steeply with age
What tumor suppressor proteins are associated with E2F activation?
Non-proliferating: - p16 (active)- Rb (active)Proliferating:- Rb (inactive)
What do regulatory mutations and gene amplification result in?
Normal protein that is greatly overproduced- myc in Burkett's lymphoma
What cell junctions are not independent and form the junctional complex
Occluding, adherens, and desmosome junctions
What do pathways are altered to promote cancer?
Pathways that respond to the presence of glucosein the blood - Why people with diabetes (type 2) and obesity are more prone to cancer
A structure of basal lamina
Perlecan is a proteoglycan, nidogen and laminin are glycoproteins.
What removes Mdm2 from p53?
Phosphorylation of p53
Replicative senescence
Programmed limits on cell division (like those controlling nr. Cell division that transit amplifying cells can go through)
members of another pathway which stimulates cell division
Proto-oncogenes Myc and Ras
Phosphorylation of Rb protein by cyclin/CDK relieves inhibition of E2F and allows it to activate transcription of S-phase genes
Proto-oncoproteins in green; tumor suppressor proteins in red; E2F is blue because some members of the E2F family can act as cell-cycle inhibitors independent of Rb. In non-proliferating cells, p16 inhibits formation of CDK/cyclin complex and Rb is dephosphorylated and bound to E2F (inhibits E2F). In proliferating cells, p16 is not present, CDK4/cyclinD1 complex forms, phosphorylates Rb freeing E2F to activate S-phase target genes. In stressed cells, p16 inhibits formation of CD4K/cyclinD1 complex, inhibits proliferation
What do mitogens bind to?
RTK receptors
What pathway is insulin involved in?
RTK/PI3 kinase/Akt/mTOR pathway- increased glucose uptake- production of lipids- increased protein synthesis
Frizzled
Receptor for Wnt
Are tumor suppressor genes dominant or recessive?
Recessive- They lose function of both alleles- Tumor suppressing proteins are deleted/inactivated in cancer cell
Selectins Mediate Transient Cell-Cell Adhesions in the Bloodstream
Selectins and integrins mediate the cell-cell adhesions required for a white blood cell to migrate out of the bloodstream into a tissue to fight infection. In case of infection, immune cells exit the blood vessel to enter the infected tissue. At the site of infection, endothelial cells lining the blood vessels start to express selectins that bind to a particular polysaccharide on white blood cells makingthem roll along the blood vessel wall. Integrins allow stronger binding and penetration of the white blood cell into the tissue.
What does colon cancer originate from?
Small polyps that can become malignant •Polyps are initially benign and can be removed during colonoscopy, a routine examination for colon cancer performed each 10 years after age 50. •This usually prevents the colon cancer. However, if colon cancer becomes metastatic, the 5 years survival rate is about 5%.
What do almost all cases of CML have
Spontaneous somatic translocation- Philadelphia chromosome
What happens in the formation of non-hereditaryretinoblastoma?
Starts off the same as in a healthy individual, where the occasional cell inactivates one of it's two good Rb genes, then carries out same process as in hereditary.- Result: Tumor in one eye
Structure of integrins
Structure of integrins -heterodimer: alpha and beta subunits -alpha and beta are glycoproteins (proteins linked to polysaccarides) •At least 24 integrins in humans
Multiple hit theory
The Knudson hypothesis, also known as the two-hit hypothesis or multiple-hit hypothesis, is the hypothesis that cancer is the result of accumulated mutations to a cell's DNA.
What complex is APC a part of and how does it affect it?
The Wnt/beta-catenine destruction complex. Causes accumulation of beta catenin which results in upregulation of genes causing increased cell division
What happens in the presence of the Wnt signal?
The components of the protein complex are recruited at the receptor then beta catenin is stable, enters nucleus, and upregulates transcription of target genes
What are the "drivers" of cancer?
The most common mutations that lead to cancer
APC (adenomatous polyposis coli) gene
The most commonly mutated gene in all of colorectal cancers
What kind of mutations are associated with the DNA binding domain?
The mutations are recessive loss-of-function mutations where both copies of p53 need to be lost to cause cancer
What are the "passengers" of cancer?
The rare mutations, which are unrelated to cancer progression and occur due to genetic instability
The Ames test for mutagenicity
The test uses a strain of Salmonella bacteria that require histidine in the medium because of a defect in a gene necessary for histidine synthesis. - Mutagens can reverse defect, creating bacteria that don't require histidine Bacteria have defect in DNA repair that makes them susceptible to damage - increases sensitivity - Majority of compounds that are mutagenic are also carcinogenic A carcinogen is any substance, radionuclide, or radiation that is an agent directly involved in causing cancer. Many cancer causing agents damage DNA. One test used to help identify mutagenic chemicals: Ames test (Bruce Ames, microbiologist at UC Berkeley)
Which junctions are organized by scaffolding proteins(which also determine the apico-basal cell polarity)?
The tight junctions and adherens junctions
Where does HPV cause cancer?
The uterine cervix
What kind of mutations are associated with the oligomerization domain?
They are dominant mutations that prevent the formation of tetramers necessary for transcription activation.- Have a negative effect on the function of p53
How can cancer overcome PARP inhibitors?
They restore the BRCA proteins by compensatory mutations- Some cancer cells amplify the genes that code for ABC transporters which pump lipophilic drugs out of the cell
How do cancer cells alter sugar metabolism?
They use 10% of glycolysis for building blocks and 85% of lactate
What happens to people who inherit only one functional copy of the TP53 gene?
They will most likely develop tumors in early adulthood
Selective cell adhesion enables dissociated cells or migrating cells to sort out and reassemble into organized tissues
This tells us that: cells expressing diff types of cadherins aggregate separately cells expressing diff amounts of the same cadherin aggregate separately
What is always at the apical end?
Tight junctions
Types of cell junction in small intestine epithelium cells
Tight junctions: seals gap bn epithelial cells-Adherens junction: connects actin filament bundle in one cell with that in the next cell-Desmosome: connects intermediate filaments in one cell to those in next cell-Gap junction: allows passage of small water-soluble molecules from cell to cell
E2F
Transcription activator - when heterodimer with DP1-inhibitor when bound to Rb
Overactivity mutation (gain of function)
When a normal cell undergoes a single mutation event that creates an oncogene. This activating mutation then enables the oncogenes to promote cell transformation
In the cellular regulatory pathways that control growth and proliferation, the products of oncogenes are stimulatory components and the products of tumor suppressor genes are inhibitory components (TRUE or FALSE)
True
Evolution of tumor involves successive rounds of mutation and natural selection
Tumor develops thru repeated rounds of mutation & selection. At each stage, a single cell undergoes a rare mutation than enhances its proliferation relative to rest so its progeny becomes dominant clone in tumor. Proliferation of this clone enhances chances for next mut'n by increasing size of target population at risk for undergoing next mut'n.
PTEN
Tumor suppressor gene
Rb
Tumor suppressor that acts in a recessive manner
SV40 virus
Uses a single dual-purpose protein called large T antigen for same purpose as papillomavirus
Cell cycle arrest by p53 in response to DNA damage
When DNA is damaged, protein kinases that phosphorylate p53 are activated. Mdm2 normally binds to p53 and promotes its ubiquitylation and destruction in proteasomes. Phosphorylation of p53 blocks its binding to Mdm2; as a result, p53 accumulates to high levels and stimulates transcription of the gene that encodes the CKI protein p21. The p21 binds and inactivates G1/S-Cdk and S-Cdk complexes, arresting the cell in G1. In some cases, DNA damage also induces either the phosphorylation of Mdm2 or a decrease in Mdm2 production, which causes an increase in p53
K-Ras
a member of Ras superfamily Upregulates the glucose transporter thereby contributing to the switch to glycolysis metabolic pathways
What kind of gene is APC?
a tumor suppressor gene
Epigenetic gene inactivation
accident causes DNA packaging into heterochromatin
Epigenetic gene inactivation
accident causes methylation of C nucleotides
Genetic gene inactivation
accidental change in nucleotide sequence in DNA
which filaments form a layer close to the cell surface?
actin filaments
Where does p53 arrest the cell cycle?
at the G1/S-phase checkpoint until the DNA damage can be corrected
Connective tissue
bone, cartilage, adipose tissue, blood lots of extracellular matrix, few cells. Matrix provides most of the mechanical strength Cell-cell junctions are rare.
Cadherins bind
by insertion of the terminal knob into the pocket
cell proliferation signals are mostly transmitted through
cadherins
p21
cell cycle regulatory protein that inhibits G1/S-Cdk, arresting the cell in G1. its levels are controlled by p53
What are the stages of metastasis?
cell detachment invasion of lymphatic and/or blood vessels arrest penetration invasion and growth
Example of an oncogene that results from a deletion in a coding sequence
deletion in EGF receptor can make it active in the absence of a signal •Deletion of the extracellular part makes the receptor consistently active, resulting in uncontrollable proliferation •Common in brain tumor, glioblastoma
Retinoblastoma
eye tumor Cause: lost of tumor suppressor gene Rb Both copies of Rb are lost in cancer Rb is an important tumor suppressor missing in many cancers (lung, breast, bladder)
Paracellular transport requires ATP •A. True •B. False
false
Tumor suppressor genes can also be identified by inserting them in cells and looking for cancer cells (TRUE or FALSE)
false
Cell matrix junctions
focal adhesions and hemidesmosome attachments to the extracellular matrix
Structure of GAP junctions
gap-junction connexon hemi channel consists of 6 transmembrane connexin subunits. Different connexins can form heteromeric connexons Two connexons in adjacent cells form a channel between two adjacent cells. Gap junctions are used for communication via small molecule second messengers In some neurons and heart muscle cells GAP junctions serve to transmit electrical synapses, allowing ionic currents to pass and spread between cells The diameter is not required for memorization
Ig-like CAMs participate in ________ interactions
homophilic and heterophilic
Three ways to convert proto-oncogene to oncogene
hyperactive protein (mutant Ras, truncated EGFR in glioblastomas) elevate protein by gene amplification chromosomal rearrangement that hyperactivates expression of gene ( Myc in Burkett's lymphoma)
which are not Ca2+ dependent? selectins, cadherens, integrins, Ig-like CAMs
integrins
hemidesmosome
integrins link laminin outside the cell to keratin filaments inside the cell
Talin binds to ______domain of integrins
intracellular
Basal lamina
is synthesized by the cells on each side of it: epithelial cells and stroma (cells of connective tissue) provide some components
Oncogenes
many 1st identified as genes fortuitously "highjacked" by retroviruses subsequently rendered oncogenic (causing tumors in infected animals); show dominant transforming activity in cultured cells (e.g., point mutations that hyperactivate Ras, found in many cancers); gene interrupted/altered at chromosomal translocation break points
mutations in E-cadherins promote ________
metastatic cancers
Mutations in E-cadherins and cancer
most cancers originate in epithelia (normal epithelial cells express E-cadherin) to become malignant cancer cells need to escape epithelia and invade other tissues so they turn off expression of E-cadherin, which promotes the change to malignancy
BRCA1 and BRCA2
mutations that increase risk for breast and uterine cancers
Both increased cell division and decreased apoptosis can contribute to tumorigenesis
normal cell division and normal apoptosis -> homeostasis increased cell division and normal apoptosis -> tumor normal cell division and decreased apoptosis -> tumor
How many mutations for a benign tumor? Malignant tumor?
one mutation for a benign tumor and 10+ mutations for a malignant tumor
p53
the main tumor suppressor protein
Examples of lines the cavities and surfaces of structures throughout the body
the skin insides of the lungs, the gastrointestinal tract, the reproductive and urinary tracts, exocrine and endocrine glands
Transformed cells loose contact inhibition in cell culture
they grow on top of each other
p53
tumor suppressor gene that controls cell division/apoptosis, genomic stability, and inhibition of angiogenesis
focal adhesions
use integrins attached to actin filaments
Hemidesmosomes
use integrins attached to intermediate filaments.
tight junction formed by claudins and occludins
•Claudins and occludins are transmembrane proteins that form the tight junctions. •They interact by homophilic interactions -TM proteins that interact by homophilic interaction- each tight junction is composed of a long row of claudins and occludins- claudin molecules can also form paracellular pores (selective channels) that allow specific ions to pass in bn the cells (ex: Mg2+ in kidney)
How to increase a pool of cells available for mutations?
•Destroy cell division controls •Destroy apoptosis pathways •Alter the ability of the cells to differentiate:more than 50% of stem cells progeny should stay the stem cells and less differentiate
Other functions of basal lamina
•Determines the cell polarity •Influences cell metabolism •Organizes the proteins in adjacent cells membranes •Promotes cell survival •Promotes proliferation and affects differentiation •Serves as a highway for cell migration in regeneration of the epithelium tissue
The macromolecules that make the basal lamina
•Fibrous proteins, mostly glycoproteins, which have oligosaccharide chains attached (laminin, collagen and others) •Proteoglycans •Associated with fibronectin of the connective tissue •Connects with epithelial cells through integrins •The content of basal lamina varies from tissue to tissue
Each gap junction is a cluster of a few to many thousands connexons
•Gap junctions between fibroblasts in culture •There are also many semi-channels connexons in the membrane which are in closed conformation. They are used for remodeling the channels •The half life of a connexin is only about half an hour; the new connexons are added from the side and old ones are degraded.
HPV causes cancers by integration in basal cells genome
•In a wart or other benign infection HPV chromosomes are stably maintained in the basal cells of the epithelium as plasmids •Rare accidents can cause the integration of a fragment of such a plasmid into a chromosome of the host, altering the environment of the viral genes. •This (or possibly some other cause) disrupts the control of viral gene expression. •The unregulated production of viral replication proteins interferes with the control of cell division, thereby helping to generate cancer.
HPV causes cancers of uterine cervix
•Only persistent infections by HPV that last for years cause cancer; in most cases the symptoms disappear within a year •Regular testing of women by Pap smear test significantly reduced the occurrence of the uterine cervix cancer
p53 functions in cancer prevention
•Plays a role in apoptosis, genomic stability, and inhibition of angiogenesis. •Activates DNA repair proteins when DNA has sustained damage. •Arrests cell cycle at the G1/S checkpoint (holds the cell cycle until the DNA repair proteins fix the damage). •Initiates apoptosis if DNA damage proves to be irreparable •People who inherit only one functional copy of the TP53 gene will most likely develop tumors in early adulthood •Loss of p53 most often results in an aneuploidy phenotype •Increased amount of p53 can cause premature aging
Studies of Rare Hereditary Cancer Syndromes First Identified Tumor Suppressor Genes
•Rb was first identified in a rare form of the eye cancer, retinoblastoma •Both copies of Rb should be lost to cause cancer •In hereditary retinoblastoma, cancers happen in both eyes (spontaneous loss of the second copy of Rb) •In nonhereditary retinoblastoma, cancers occur in just one eye; happens very rarely (both copies of Rb spontaneously lost in the same cell)
Telomers in normal cells
•no or low levels of telomerase (except germ line and some stem cells) •Telomeres shorten with each division •They can only divide limited number of times (replicative senescence)