Genes & Cancer Test 1

Slowly Transforming Retroviruses

- Do not carry oncogenes. _proviral DNA integrates next to proto-oncogenes, causing inappropriate activation. Ex: ALV can cause avian leukemia by inserting within the c-myc gene. note- insertional mutagenesis must happen in the right spot to have a proliferative advantage

Alternate Ras Signaling Pathways

- MAPK/ERK - P13K - Ral/Rac

Cyclin/CDK kinases phosphorylate Rb protein.

- The R-point gatekeeper. - When Rb hyperphosphorylated, triggers progression through the R point. -Rb related proteins may control different parts of the cell cycle.

Chronic Myelogenous Leukemia

- example of a translocation that creates fusion proteins with novel structures and function. - caused by a translocation between chromosome 9 and 22 - the Philadelphia chromosome - creates Bcr-Abl fusion protein

Nude Mice

- note that nude mice are especially helpful in studying cancer. - can easily see where tumors form.

Tumor Viruses

Both RNA & DNA viruses. Viruses that cause cancer in humans (or animals).

Positive Feedback Control of RTK Signaling

If the RTK is not activated, NF1 helps keep Ras in the off state. If RTK is activated, signaling via PKC results in degradation of NF1.

Medical Terminology for Cancer

Malignant neoplasm. Cells have acquired: - the ability to grow in an uncontrolled fashion - the ability to invade local tissues and spread throughout the body

Negative Feedback Control of RTK Signaling

Sprouty activated via activation of Erk. Sprouty feeds back and inhibits Grb2 from inhibiting Sos. Also inhibits Raf.

Cancer Statistics

1 in 4- number of American deaths due to cancer. Lung cancer accounts for 27% of all cancer deaths. 1 in 3- cancer deaths related to obesity, physical inactivity, and nutrition. 86%- percentage of all cancers that are diagnosed in people age 50 or older.

How do we get mutations in both copies of tumor suppressor genes?

1) 1st mutation is either inherited or sporadic. - probability of a random mutation inactivating one copy is 10^-7 per cell - chance of two independent mutations inactivating both copies is 10^-14 per cell 2) Loss of heterozygosity (LOH) - the second copy can be inactivated by a different mechanism that does not require an independent mutation - mitotic recombination - nondisjunction - gene conversion - chromosomal deletion 3) If you inherit one mutant allele, then the chance that the other allele will be lost due to LOH is higher than would be expected from 2 independent random mutations.

4 Major Types of Cancer

1) Carcinomas 2) Sarcomas 3) Leukemias & Lymphomas 4) Neuroectodermal Tumors

Proto-oncogenes and Oncogenes

1) First oncogenes were isolated from cancers caused by retroviruses. 2) Found that non-virally induced human tumors also have activated forms of some of the same oncogenes. 3) All oncogenes had a corresponding normal cellular form (proto-oncogene) whose expression is tightly controlled.

Caveats to the Ames Test

1) High number of false positives. 2) Not all chemicals that increase cancer risk act as mutagens0 tumor promoters- increase cancer risk but do not cause mutation. - ex: estrogen, testosterone, ethanol 3) Ames Test needs to be followed by other tests: - measure the ability of a carcinogen to cause chromosomal breakage, cause mutations in human cells in culture, cause cancer in lab animals and epidemiological evidence. - ex: Saccharin- positive mutagen in Ames Test, causes cancer in lab rats, but no evidence from epidemiology that it causes cancer in humans.

Identifying Mutant Genes Involved in Cancer

1) Isolate suspect gene. 2) Test for ability to transform cells in culture. 3) Make transgenic mouse (or knockout mouse). - determine whether this gene promotes tumor formation in mice. 4) Test for ability to interact with other genes to promote cancer. 5) Microarray Analysis- identify common sets of genes activated or repressed in cancer.

2 General Types of Mutations in Human Cancers

1) Oncogenes- encode proteins that provide an excessive or uncontrolled growth-promoting signal. Derived from normal cellular genes- proto-oncogenes. - conversion of a proto-oncogene into an oncogene usually involves a gain-of-function mutation 2) Tumor Suppressor Genes- encode proteins that inhibit cell proliferation or metastasis - loss-of-function mutations contribute to cancer

Ames Test

1) Rat liver homogenized. 2) Test compound (procarcinogen) added to homogenized rat liver. 3) Metabolic activation of test compound by rat liver enzymes leads to metabolically activated compound (ultimate carcinogen). 4) Add to Salmonella bacteria unable to grow without added histidine in culture medium. 5) Count number of bacterial colonies that have undergone mutation enabling them to grow without added histidine.

6 Phenotypes of Cancer

1) Self-sufficiency in growth signals. - cancer cell is providing own signal to undergo mitosis 2) Insensitivity to antigrowth signals. 3) Evasion of apoptosis. 4) Limitless replicative potential. - cancer cells are immortal if provided with enough glucose and O2. 5) Tissue invasion and metastasis. - what generally makes cancer lethal 6) Sustained angiogenesis. Some consider genetically instability a 7th phenotype of cancer.

Phenotypes of Cancer

1) Self-sufficiency in growth signals. 2) Insensitivity to antigrowth signals. 3) Evasion of apoptosis. 4)Limitless replicative potential. 5) Tissue invasion and metastasis. 6) Sustained angiogenesis. - need at least one of these mutation for each of these.

TGF-B Signaling

1) TGF-B ligand binds Type II TGF-B receptor. 2) Brings Type II, I receptors together and phosphorylates Type I. 3) Type I phosphorylates (Ser/Thr) cytosolic Smad 2 or 3, Smad 2/3 binds Smad4. 4) Translocates to nucleus, complexes with transcription factors; gene expression (p15, p16). note- that because of this, cell needs enough mitogenic signals to overcome inhibitory signals.

Properties of Transformed Cells

1) altered morphology (rounded shape, refractile in phase-contrast microscope). 2) loss of contact inhibition (ability to grow over one another). 3) ability to grow without attachment to solid substrate (anchorage independence). 4) ability to proliferate indefinitely (immortalization). 5) reduced requirement for mitogenic growth factors. 6) high saturation density (ability to accumulate large numbers of cells in culture dish). 7) inability to halt proliferation in response to deprivation of growth factors 8) increased transport of glucose 9) tumorigenicity 10) increased motility

Tumor Progression

1) benign epithelial tumor 2) a cell becomes transformed and loses contact inhibition 3) malignant invasive tumor (carcinoma) 4) metastasis

Life Cycle of a DNA Virus

1) viral DNA maintained as an independent episome 2) viral DNA integrated into host chromosomal DNA 3) viral DNA replicated as part of host chromosomal DNA 4) assembly of new virions

Identifying Chemicals that Induce Cancer

1761- first connection between use of tobacco (snuff) and nasal cancer. 1775- first report of the connection between occupation and cancer. - scrotal cancer in chimney sweeps. - Danish chimney sweepers guild recommended its members take daily baths. 1800's- documented high number of lung cancer cases among silver miners in Bohemia 1839- report of 6X higher incidence of breast cancer among nuns as compared to women who had children 1950- two groups reported a 20X higher risk of lung cancer in smokers. 1915- first direct evidence that chemicals can induce cancer - Yamagiwa painted rabbit ears with coal tar over several months period. - resulted in skin cancers in the rabbits. - shown that animal models could be useful.

Tumor Virus History

1911- Peyton Rous reports on an infectious agent that causes sarcomas in chickens. - The infectious agent can pass through a filter. - Named RSV virus. 1930s- isolated a virus that caused papillomas on rabbits. - DNA virus. 1960s- RSV was shown to transform tissue culture cells. - transformed cells form foci in tissue culture. - the transformed cells in a focus were derived from a single infected progenitor cell. - cancer could be studied at the level of individual cells. 1970s- temperature sensitive RSV mutant isolated. - at 37 degrees Celsius, virus transformed cells. At 42 degrees celsius, the transformed cells reverted to normal. - this continued action of RSV virus was required to transform cells. - RSV is an RNA virus.

Historical Theories on the Cause of Cancer

A disease of improper differentiation. - change in cell behavior as cells move up or down the differentiation pathway inappropriately A viral disease. - prompted by the discovery in the 70's of cancer causing viruses. -20% of tumors worldwide. A disease of mutant genes. - the mutation was present in the cancer cell and not imported by a virus. - mutations are caused by carcinogens. - the field of cancer genetics is born.

Caveats to the Monoclonal Theory

A tumor that started out as polyclonal could contain cells that have a shorter cell cycle (enter mitosis more often) -over time these cells would outgrow the other cells, making the tumor appear monoclonal. A tumor that started out monoclonal could become heterogenous due to the continued acquisition of new mutations, making the tumor appear polyclonal.

Alterations of the Cell Cycle

All (or almost all) cancers have altered G1/S transition. - they have lost control of the R-point. High cyclin E levels can increase genetic instability.

Cytokines, STATs, and Cancer

Altered cytokine expression may help cancers evade the immune system. - increased concentrations of cytokines MIF, TNFa, interleukin 6, interleukin 8, interleukin 10, interleukin 18 observed in many cancers. Stat 3 is constitutively activated in many melanomas and breast cancers. - in these cancers Stat3 is often activated by a constitutively activated Src. - if Src is inhibited, the cancer cells undergo apoptosis. Potential avenue for an anti-cancer drugs that inhibit Stat3 or Src. Or drugs that neutralize specific cytokines.

Example of Aberrant Proteins that Have a Gain-of-Function

Amino acid substitutions. - ex: H-ras- constitutively active ras protein found in many cancers - ex: ErbB2/Her2/Neu oncogene found in many breast cancers Truncations - ex: ErbB oncogene found in many breast cancers (truncated receptor emits signals even in absence of ligand binding) Over-expression (increased protein levels) resulting from gene amplification or chromosomal translocations. - ex: ErbB2 amplification in breast cancer - ex: myc amplification in leukemias and neuroblastomas - ex: myc activation in Burkitt's lymphoma Chimeric proteins resulting from chromosomal translocations. - ex: Bcr-Abl fusion protein in CML.

Neurofibromatosis

Benign tumors of the Schwann cells in the peripheral nervous system. Neurofibromas can progress to neurofibrosarcomas. Increased risk of glioblastomas, pheochromocytomas and leukemias. 1:3500 live births. Tumor suppressor (autosomal dominant).

Tumors

Benign~ localized to the tissue of origin - usually slow growth rate - well differentiated - rarely life threatening - well defined "encapsulated" tumor boundary Malignant~ spreads by invasion and metastasis - usually rapid growth rate - variable in differentiation state - if they are poorly differentiated, termed anaplastic - often life threatening - poorly defined tumor boundary

Tumor Progression

Between the two extremes of normal cells and metastatic cells, there is a broad spectrum of tumor phenotypes. Hyperplastic~ cells that deviate minimally from normal. Metaplastic~ one type of cell is displaced by normal cells that are not normally found in this location. - not all tumors do this. Dysplastic~ abnormal cytology (changes in nuclear size and shape- a pre-malignant stage) Adenomas, Polyps, Papillomas~ large growths of dysplastic epithelial tissue. Do not invade the basement membrane Neoplasia~ abnormal cytology, increased mitosis. Can be a benign neoplasm or a malignant neoplasm (cancer). Anaplastic~ cell have lost all differentiated traits Metastatic~ cancer cells migrate and establish new tumors

Cyclins

Bind cyclin-dependent kinases. Without cyclins, Cdks are inactive. The cyclins were found in yeast. Yeast is advantageous experimentally because you can mutate easily and found when cell cycle in mutations were blocked. Cyclin levels fluctuate during the cell cycle. Cdk levels do not fluctuate. Control of Cyclin D1 levels via extracellular signals. - period during which cells are responsive to mitogenic GFs and to TGF-B.

Ability of RSV to Cause Cancer Requires the SRC Gene

Bishop and Varmus- 1970's- discovered that src was a normal cellular gene present in all vertebrates. The precursor of the RSV virus must have integrated next to the normal cellular src (c-src) and a viral RNA containing a c-src was packed into a virus, creating the viral form of src (v-src). Because c-src was precursor to a cancer gene it was called a proto-oncogene, whereas v-src was capable of transforming chicken cells, it was called an oncogene. 1978- c-src was shown to be a tyrosine kinase - 1st tyrosine kinase identified and sequenced

Expression of Immediate Early Genes

Can tell which genes are expressed early by looking at a microarray analysis. Works well as you can look at whole-cell changes in the expression of genes.

Multi-Step Pathway of Cancer

Cancer arises due to several independent mutations in both oncogenes and tumor suppressor genes. 1) A mutation in one cell gives it a slight growth advantage. 2) One of the progeny cells undergoes a second mutation that allows it to grow more uncontrolled, producing a benign tumor. 3) Another mutation in one of the tumor cells allows its progeny to overcome contact inhibition (transformed cell). 4) Additional mutation(s) allows cells to invade neighboring tissue (cancerous). 5) Additional mutation(s) allow tumor cells to gain access to new blood supplies. 6) Additional mutation(s) allows cells to metastasize. 7) Ability to colonize and grow in new sites (secondary tumors) may involve still more mutations.

Warburg Effect (Aerobic Glycolysis)

Cancer cells exhibit altered glucose metabolism. Utilize glucose differently than normal cells. Can be seen in PET scans. Utilized to visualize tumors via glucose uptake. Cancer cells bring in a lot more glucose than normal cells. Change pyruvate kinase 1 (PK-M1) into PK-M2. Turn pyruvate into a lactic acid cycle. Approximately 80% of cancer cells do this. One hypothesis is that cells choose lactic acid ferementation to get more building blocks to make DNA and RNA so they can keep undergoing mitosis

What is Cancer?

Cancer is group of diseases characterized by the uncontrolled growth (mitosis) and spread of abnormal cells. If the spread (metastasis) is not controlled, it can result in death. Cancer is caused by external factors, such as tobacco, infectious organisms, diet, and internal factors, such as inherited genetic mutations and immune conditions. These factors may act together or in sequence to cause cancer.

Human Papillomavirus

Causes cervical, penile, anal cancer. Infects 50% of men and women. HPV genome encodes two viral proteins, E6 and E7. - E6 binds to p53 and promotes degradation (p53 normally functions to promote apoptosis in damaged cells). - E7 binds to Rb protein and blocks its function (Rb normally functions to inhibit the cell cycle at G1 to S stage). Only some HPV types cause cervical cancer. - termed high risk strains - the HPV vaccine (Gardasil) targets HPV types 6, 11, 16, and 18 Low-risk strains do not cause cancer as they do not integrate into host chromosome whereas high-risk HPV causes cancer by integrating into host chromosome (allows many more E6 and E7 oncoproteins to be synthesized). Other DNA viruses use a similar mechanism. - i.e. SV40

H-ras Oncogene

Cloned from a human bladder cancer. Point mutation in proto-oncogene results in an amino acid substitution that converts it into oncogene. When Gly changes to Val, GTP gets locked into binding site and Ras is always on. Especially prevalent in the pancreas.

Geographical Variation in Cancer Incidence Rates

Colon highest in Australia (love red meat).

Cytokine Receptors

Cytokines involved in hematopoietic system and trigger these: 1) Erythropoietin (Epo) - acts to save progenitor from cell death - progenitor serves as quicker pathways to RBCs than HSCs 2) Interleukins 3) Interferon 4) Thrombopoietin Still have transphosphorylation but kinases are separate proteins and not part of the receptor domain.

Overview of Carcinogenesis

DNA exposed to radiation, chemicals, infectious agents, and heredity. Mutations come in form of oncogenes and inactivated tumor suppressor genes. Leads to genetic instability that can lead to additional mutations. Accumulation of genetic and epigenetic changes.

Immediate Early vs Delayed Early Genes

Delayed- come on a early but a bit later than immediate early.

Hematopoietic Tumors

Derive from blood forming tissues. Erythrocytes, T and B lymphocytes. About 10% of cancer deaths. Leukemias~ malignant blood cells that move freely through the circulatory system. Lymphoma~ tumors of B and T lymphocytes that aggregate to form solid tumors in the lymph nodes.

Neuroectodermal Tumors

Derive from the neural ectoderm. Comprise approximately 2-3% of cancer deaths.

Carcinomas

Derived from epithelial tissues. Cancers of the colon, pancreas, skin, liver, lung, ovary, bladder, breast. 80% of cancer-related deaths. Most common type of cancer.

Sarcomas

Derived from mesenchymal cells. Cancers of the bone, muscle, blood vessel endothelia. Only about 1% of tumors.

Microarray Analysis of Human Cancers

Detect the different patterns of gene expression. Permit complex phenotypes to be defined at the molecular genetic level. Can help identify the type and classification of a tumor. Can help improve decisions about treatment and prognosis.

Burkitt's Lymphoma

Discovered in 1950's. Traced to mosquito-infested areas of Africa. Caused by Epstein-Barr virus (EBV), a DNA virus., First example of a DNA virus that can cause cancer in humans. Now know to contribute to several cancers in immuno-compromised people. Burkitt's Lymphoma cells contain a chromosomal translocation of myc onto heavy-chain IgH gene. - translocation of a portion of chromosome 8 to 14 brings the myc oncogene next to the immunoglobulin promoter.

ErbB Oncoprotein

EGF receptor and the ErbB oncoprotein create a truncated receptor. RTKS can be activated by ligand or mutations that facilitate dimerization of receptors (i.e. point mutation or deletion). This activates MAPK proliferation.

Oncogenes

Encode proteins (oncoprotein) that provide excessive or uncontrolled growth-promoting signals. Derived from normal cellular genes, called proto-oncogenes. Conversion of a proto-oncogene into an oncogene usually involves a gain-of-function mutation. - growth factors and their receptors - signal transduction proteins - transcription factors

Tumor Suppressor Genes

Encode proteins that inhibit cell proliferation or metastasis. Loss-of-function must occur to get cancer. - proteins that regulate the cell cycle (Rb, NF1 protein) - proteins that promote apoptosis (p53) - proteins that participate in DNA repair (BRCA1) - proteins involved in cell adhesion (cadherins) Loss of function can be due to: - missense or nonsense mutations - deletions - loss of heterozygosity - promoter methylation

First 3/4s of G1

Extracellular signals propel the cell through G1. Period during which cells are responsive to mitogenic GFs and to TGF-B. After R pint, cell cycle is not responding to extracellular signals.

Test for the Ability of Cancer Cell DNA to Form Tumors in Animals

Extract DNA from human cancer & apply to culture of normal mouse fibroblasts or transfect suspected gene directly into mouse fibroblasts via plasmid containing suspected gene. Observe culture for transformed Cells. Inject transformed cells into mouse to confirm capacity of cells to form tumors.

What is the link between the histological progression of cancer and the theory that cancer results from the accumulation of several independent mutations (multistep progression)?

First described in colon cancer. Reference Lecture 7 slide 8.

What does environment include?

Food Air Water Lifestyle (i.e. tobacco usage, alcohol, exercise) Occupation Reproductive Habits Healthcare Availability

Cell Fusion Experiments

Fusogenic agent can be utilized on normal cells with cancer cells. Allows us to determine whether cancer alleles are dominant or recessive. -tumorigenic means they are dominant. - non-tumorigenic means they are recessive.

Immediate Early Genes

Genes whose transcription is upregulated immediately after signaling via a growth factor receptor. ex: Genes activated by ERK MAP kinases. Activated MAPK/ERK enters the nucleus and phosphorylates transcription factors. - ERK will phosphorylate specific transcription factors, which will bind to SRE (serum response-elements) to activate transcription.

Adaptor Proteins Used by RTKs

Grb2 recognizes TK and allows Sos to bind. Binding of Grb2 and Sos allows Ras to hydrolize GDP and bind GTP. - note that Ras is membrane-bound. SHC also recognizes TK and has a domain that SH2 can bind (i.e. insulin receptor uses this additional protein).

Environment vs Heredity

Having a inherited susceptibility does not guarantee that you will get cancer- requires other factors be present. Environment includes air, water, soil, diet, tobacco, alcohol, sunlight, radiation, exposure to chemicals. Work place exposure to chemicals has provided a lot of information on the mechanism by which chemicals cause cancer. Individuals vary in their susceptibility to environmental factors.

Where do mutant genes come from?

Heredity: - germline mutations are passed from parent to children. - results in "inherited susceptibility" ex: retinoblastoma, familial breast cancer - this type of mutation does by itself cause cancer, but can increase the chance of cancer Environment: - exposure to cancer-promoting factors results in mutations. - exposure varies by person. - often depends on length of exposure and some environmental factors may interact. Also depends on individual susceptibility.

What is the link between carcinogens and cancer?

How does a chemical agent alter a cell, making it cancerous? 1914- Theodor Boveri- suggested that chromosomes within cancer cells are aberrant- creating mutant cells. 1927- Hermann Muller- discovered that X-rays could induce mutations in the genome of fruit flies. 1960- discovery of an aberrant chromosome (Philadelphia chromosome) in chronic myelogenous leukemia (CML). 1957- Bruces Ames- direct demonstration that chemicals cause genetic mutations (Ames test).

Some Assumption

Human body contains great than 10^13 cells. Humans actually produce 10^16 cells over a lifetime. 10^7 cells undergo mitosis each second. Each time a new cell is formed and differentiates there are many things that could go wrong- thus the chance for the formation of a cancerous cell is great.

Human Cells are Highly Resistant to Immortalization and Transformation

Human cells grown in culture usually die after several passages. Introducing a single oncogene or even two oncogenes fails to transform human cells. At least 506 distinct cellular regulatory circuits must be altered to transform human cells.

4 Major Types of New Tissue Growth

Hypertrophy~ increase in cell size, normal organization - muscle cells swelling response to working out Hyperplasia~ increase in cell number, normal organization - can be normal (mammary glands in pregnant women) or abnormal Dysplasia~ disorganized growth - generally considered a pre-malignant stage (pre-cancer) - a pre-malignant tissue composed of abnormally appearing cells, forming a tissue architecture that is not normal Neoplasia~ disorganized growth and net increase in number of dividing cells. - gives rise to cancers -tissue composed of cells having an abnormal appearance and abnormal proliferation - neoplasia results in tumors

Autocrine Signaling

In a normal cell, activation of GF gene via autocrine signaling.

Promoter Methylation

Inactivates many tumor suppressor genes. Expression of the DNA methyltransferase anzyme (DNMT3B) in colon carcinomas as detected by an anti-DNMT3B antibody.

Conclusions from the Work on c-src and RSV

Inappropriate activation of a normal cellular gene could transform cells. - not just viruses but perhaps other mechanisms could lead to gene activation and transformation. Cancer may be caused by mutation (leading to inappropriate activation) of just a small number of normal cellular genes. RSV may serve as a model for the other retroviruses linked to cancers. -other proto-oncogenes waiting to be discovered

Are tumors monoclonal or polyclonal?

Look to see if all tumor cells share a common genetic or biochemical marker: - the gene for glucose-6-phosphate hydrogenase (G6PD) is located on the X-chromosome- look for the presence of certain alleles in tumors - 30% of African American women are heterozygous for G6PF and the different alleles code for slightly different enzymes - results from studies of uterine tumors in African American women demonstrated that each tumor had only one G6PD allele

Rb -/- Mouse

Mice that lack both copies of Rb show increased proliferating cells in the retina.

Retinoblastoma

Most common malignant ocular tumor of childhood. One of the most common of all pediatric solid tumors. 300 new cases every year in the US. Clinical signs include leukocoria (white pupil) and 25% of cases have crossed eyes as 1st sign. Tumor of the retina can lead to loss of eyesight due to displaced retina, thickening of optic nerve is indicative of possible progression to brain.

Examples of Oncogenic Mutations

Mutations that cause structural changes in the protein. - point mutations, deletions, insertions Elevated expression. - gene duplications and chromosomal duplications - result in increased copy number Chromosomal translocations. - result in inappropriate activation

Gene Amplification Causes a Gain of Function

Myc oncogene- originally identified in avian myelocytomatosis virus. Later found to be amplified in a variety of human cancers. - 10-20 extra copies of the gene. - Common in many leukemias. - 30% of childhood neuroblastomas ErbB2 (HER2) oncogene- gene amplified in 30% of breast cancers. - amplification correlates with poorer prognosis as extra HER2 receptors lead to increased chance for dimerization even in the absence of getting a ligand - makes cell more mitotically active and potentially more resistant to apoptosis

Neurofibromatosis Type 1 Gene

NF1 gene cloned in 1990. NF1 encodes a GTPase activating protein (GAP) called neurofibromin. - neurofibromin normally binds to Ras-GTP, forcing hydrolysis of GTP to GDP. Ras-GDP is then inactive. NF1 highly expressed in CNS and PNS. NF1 protein levels normally decrease as cells undergo mitosis, then increase after mitosis. When NF1 is nonfunctional, Ras stays activated and the cell over-proliferates.

Cancers Associated with HIV Infection

Not directly caused by HIV, but a consequence of immuno-suppression. Underscores the importance of immune system in preventing cancers. ex: Kaposi's Sarcoma

Trends in Cancer Incidence Rates

Note a huge disparity in black and white males. Huge spike in prostate cancer in 1990s due to early detection procedures. Stomach cancer rates have dropped a ton due to the invention of antibiotics. Breast cancer rates have plateaued. Chance of developing cancer in men is 1 in 2. Chance of developing cancer in women is 1 in 3.

Gene Therapy

Orginally based on the idea that retroviruses can carry external genes into a host. Use a retrovirus to shuttle a normal gene into a patient who lacks a functional copy. Works best for hematopoietic diseases. In the first trial, bone marrow from SCID patients were infected with a modified MLV virus containing the normal gene. - SCID patients are severely immuno-compromised, lacking T and B cells. While patients did improve, 4/9 patients developed T-cell leukemia. - Due to insertional mutagenesis, proviral insertions in the first exon of the LMO2 proto-oncogene. Some newer techniques are trying to use lentiviruses or DNA viruses such as adenovirus. - lentiviruses are a sub-category of HIV that are easier to control in regards to where it is expressed. - possible gene therapy for cystic fibrosis.

Cyclin- CDKs as targets for treating cancer.

Palbociclib (Ibrance)- selective inhibitor of CDK4/6. - FDA approved for treatment of ER-positive, HER2-negative breast cancer. - Phase 3 study demonstrated increased progression-free survival. - Numerous other cyclin?CDK inhibitors in various stages of development.

EGF: A Receptor Tyrosine Kinase Example

Phosphorylation of the EGF-R occurs within seconds of adding EGF. EGF binds to monomer EGF receptors, leading them become and active EGF dimer. Transphosphorylation occurs (binding of hormone causes dimerization and phosphorylation of cytosolic receptor tyrosine residues). GRB2 is an example of an adaptor protein and has an SH2 domain subject to phosphorylation that brings GDP. Binding of GRB2 and Sos couples receptor to inactive Ras. Sos promotes dissociation of GDP from Ras; GTP binds and active Ras dissociates from Sos. Active Ras can signal.

Malignant Tumors

Primary Tumor~ the site where the cancer began Metastases~ secondary tumors or new sites where cancerous cells have spread. - most cancer deaths (greater than 90%) are due to metastases - colon cancers often metastasize to the liver - breast cancer often metastasizes to the brain

Alfred Knudsen- 1971

Proposed that the pattern of familial retinoblastoma could be explained by an inherited mutation in one allele of an important gene. Then, early in childhood, another mutation must occur in the other allele of the same gene to develop cancer. - 2-hit hypothesis of tumorigenesis This also explained the rarer sporadic form of retinoblastoma. In these children tumors appeared later (30 months old) only 1 tumor occurred (unilateral). Inherent in Knudsen's theory is that the mutation must occur in a gene that normally acts to prevent cancer- a tumor suppressor gene!

Proteins that Interact with RTKs

Proteins need specific AA adjacent side chain along with phosphotyrosine to bind. Various types of binding domains provide specificity for protein-protein interactions. ex: PDGF-B receptor and EGF receptor.

RNA Viruses

Rapidly transforming retroviruses. - ex: Rous sarcoma virus (RSV) Slowly transforming retroviruses. - ex: mouse mammary tumor virus (MMTV), murine leukemia virus (MLV)

MAP Kinase Pathway

Ras is activated within minutes of adding a growth factor. Ras activated by exchange of GDP for GTP. Active Ras recruits, binds, and activates Raf. GTP hydrolysis leads to dissociation of Ras from Raf. Raf activates MEK. MEK activates MAPK. Dimeric form of active MAP kinase translocates to nucleus; activates many transcription factors. A mutation in RTK pathway that would contribute to the cancer phenotype is loss of function in GAP.

Examples of Inherited Cancers Linked to Tumor Suppressor Genes

Retinoblastoma - Rb gene Familial Breast Cancer - BRCA1 and BRCA2 genes Familial Colon Cancer - APC and DCC genes Neurofibromatosis Type 1 - NF1 gene

Important Results for the Ames Test

Revealed that known carcinogens were also mutagens. - Essentially revealed that carcinogens also mutated DNA. Chemicals that were potent mutagens were also potent carcinogens, while weak mutagens were weak carcinogens. As bacteria and animal cells have the same genetic substance- DNA, compounds that induce mutations in Salmonella were likely to induce mutations in animals. Cancer cells carry mutated genes which are responsible for the aberrant growth.

Epithelial Tissues

Sheets of cells that line the walls of cavities and channels, and the outside of the body (skin). Epithelial cells secrete and reside upon a specialized ECM called the basement membrane or basal lamina. - basement membrane has both a structural role (scaffolding) and a signaling role.

Relative Frequencies of Cancer

Skin cancer is the most common cancer. Lung cancer is responsible for most deaths. The most common cancers arise in skin, prostate, breast, lung and colon.

Other Evidence for the Monoclonal Nature of Tumors

Some tumor cells exhibit chromosomal aberrations that are visualized in the microscope. Myelomas derive from B-cell precursors. - each B-cell produces only one specific antibody due to a particular immunoglobulin gene rearrangement. - the normal pool of B-cells in your body is polyclonal. - in myelomas, all cancerous cells produce the identical antibody molecule. - this indicates that the myelomas cells derived from a single precursor B-cell.

2 Major Categories of Carcinomas

Squamous Cell Carcinomas~ derive from epithelia that serve to seal a cavity or line a channel. - ex: epithelia of the skin, trachea, esophagus Adenocarcinomas~ derive from specialized epithelial cells that secrete substances into the ducts or cavities - ex: mucus secreting cells int he lung and stomach - lobule and ductal breast cancers

Treatment of Retinoblastoma

Survival of patient most important followed by saving eye and vision. Enucleation (removal of the eye) 65% - 75% of the time. - occurs when tumors involves 50% of the globe - orbital or optic nerve involvement is suspected - anterior segment of eye involved - if it is familial (inherited) enucleation is the only option Chemoreduction with carboplatin, etoposide, and vincristine. External beam radiation. Focal therapies- using laser, thermocautery, cryotherapy, or plaque therapy.

How could you test which is more important: genetics or environment?

Take genetically identical twins to a different environment. Make a bunch of clones and split them up. Realistically... you study immigrants. - cancer incidence rates in citizens of Japan versus Hawaiian Japanese. - See that Hawaiian Japanese hav some types of cancer (i.e. breast) more similar to Hawaiian Caucasian than to Japanese.

How Viral Infections Cause Cancer

The virus carries genes that contribute to transformation. - some RNA and DNA viruses do this. OR The virus causes inappropriate activation of normal cellular genes, leading to transformation. - some RNA viruses do this.

Familial Retinoblastoma

Tumors develop early in childhood (9 months) and in both eyes (bilateral). Average of 3 tumors per eye. Must remove both eye. Appears autosomal dominant. note- retinoblastoma associated with an increased risk of new tumors later in life (36% for bilateral and 6% for unilateral).

Sis Oncogene

V-sis oncogene is encoded by simian sarcoma virus (a retrovirus). C-sis is the normal cellular gene which encodes platelet-derived growth factor (PDGF). PDGF receptor is found on fibroblasts, smooth muscle and adipocytes and endothelial cells. PDGF causes these cells to divide. Simian sarcoma virus causes tumors because extra PDGF (encoded by v-sis) is released by infected cells, which then binds PDGF-R on the same cells and stimulates mitosis.

Normal Mouse Cells are Resistant to Transformation with a Single Oncogene

myc or E1A myc or E1A + ras ras Normal cells transfected with a single oncogene are not transformed. Requires 2 or more oncogenes. note- tissue culture cells are not "normal". They are already immortal.