Unit 8 Cell Cycle and 9 Cancer

ubiquitin mediated degradation

proteasome mediated. destroy cyclins so the cell cannot go backwards. degradation essential to move out of mitosis.

caretaker genes

protect integrity of the genome but when inactive --cells accumulate mutations faster, including mutations on other regulatory genes

p21cip, p27kip, p57kip2

inhibit G1/s phase CDKs. must be degraded so DNA replication can begin. p21cip important for responses to DNA damage.

kinesin-4

(+) end directed motor- pulls chromosome to center. alignment regulator.

c-Cbl

An E3 ubiquitin ligase that negatively regulates EGF receptor HER 1. has EGFR and RING finger domains. binds to phosphorylated EGF receptor and RING domain recruits ubiquitin conjugated enzymes to transfer ubiquitin onto receptor as a tag. Cell would be too sensitive without regulation. Only for HER 1!

separase (ESP1 gene)

Before Anaphase, it is bound to inhibitory securin. when the appropriate tension on the spindle is reached, APC/C-Cdc20 ( activated by mitotic CDK, but inhibited by check point pathway until mitotic spindle is correct) ubiquitinylates securin to free separase. Separase then cleaves a subunit of cohesin (Scc1 or Rad21). Sister chromatids are allowed to segregate. irreversible. Also regulated by phosphorylation- inhibited by CDKs in prophase and metaphase. When Mitotic CDK activity declines, APC/C-cdc20 activates and triggers this process.

G1/S phase CDKs

CDK 2. binds cyclin E. works with D-CDK4/6 to trigger START. accumulate in late G1, peak as cell enters S1, and decline during S phase. trigger transition into cycle. CDK4 can be inhibited by p15 to arrest the cell in G1 from the Smad pathway induced by TGF-beta

G1 phase CDKs

CDK 4 and CDK 6. binds cyclin D. Lynchpin for coordinating with extracellular events. Regulated by signal transduction. Levels gradually increase during cell cycle.

CAK

CDK activating kinase. not rate limiting. phosphorylates threonine 160 residue to increase activity. constant level throughout cycle. phosphorylates as soon as CDK complexes are formed.

Sic1

CDK inhibitor (holds S phase in check). Works with Cdh-1 to inhibit CDKs. CDKs inhibit them too, but Cdc14 turns the switch to promote CDK inhibitions during anaphase to start ending mitosis.

CKI

CDK inhibitors. bind to CDK-cyclin complexes to inhibit activity. prevent S and M phase premature activation. G1 CDK inhibitors-- G1 arrest. often mutated in cancer cells.

CDK- cyclin dependent kinases

CDK region present throughout the cell cycle, but only active when bound to a cyclin subunit. proper progression dependent on cyclin. oscillate in activity- only active during phase they promote. Positive feedback- CDKs promote own activation. negative feedback- inhibit self indirectly or with a delay. Serine/Threonine kinases. Humans have 9, 4 of which are known. Much more active when Threonine 160 is phosphorylated.

Mitotic CDKs

CDK1. cyclin A (for S when bound to 2) and cyclin B. promote entry and progression through mitosis. synthesized in S and G2, but activity held back until after DNA synthesis (inhibitor phosphorylation on T14 and Y15). inactivated during anaphase.

S phase CDKs

CDK2. bound to cyclin E (the G1/S phase cyclin) and cyclin A. CDKs phosphorylate proteins that activate DNA helicases and load polymerases onto DNA. high levels until mitosis, synthesized with G1 cyclins.

centrosome disjunction

Centrosomes (MOTCs) duplicate in S phase. in G2, triggered by mitotic CDKs, centrosome ties with daughter centrioles are severed. (now two sets of centrioles, or two centrosomes) The two matured centrosomes (mitotic asters in prophase) make MT and move away from one another, pulled by dynein motor proteins ( anchored into cell membrane) and pushed by bipolar kinesin-5 motors. two is important-- some cancer cells have more than two, which results in aneuploidy.

benzo(a)pyrene

in smoke, coal tar. activated in lung. causes 60% of lung cancers. potent mutagen of guanine--> thymine (transversion mutation) at positions 175, 248, and 273 codons of p53 in 1/3 of lung cancers. inactivating mutations.

Rb proteins

E2F regulation. transcriptional repressor. Recruits chromatin- modifying enzymes to promote deacetylation and methylation of histone lysines. Chromatin condenses, inactive. Rb inactive in almost all cancers. regulated by G1 CDKs- phosphorylated in multiple sites, which promote its exportation out of the nucleus. E2F then activates transcription for movement into S phase. newly translated G1/S CDKs further phosphorylate Rb. when there is fall in cyclin CDK, then Rb dephosphorylates and rebinds to E2F. loss of Rb function- cancers later in life. critical for retinal cancer- regulation only by Rb. other tissues have other regulators. HPV encodes E7, which inhibits Rb.

HPV

E5 protein makes a membrane dimer. forms stable complex with PDGF-- causes them to aggregate. mimics hormone- mediated receptor dimerization, causing sustained receptor activation and eventually cell transformation. Also codes for other proteins that act to inhibit tumor suppressing genes

Hedgehog

Hh. For development. Sonic Hedgehog stimulates division by binding and inactivating Patched1 (Ptc1) [a tumor suppressor]. loss of function Ptc1= proliferation without Hh signals. one defective allele inherited--higher risk of cancer. complete loss leads to fetal death. Only cancer cells have homozygous loss of function of Ptc1. Dominant active cancers of Hh turn on its targets inappropriately

XMAP215

MT associated stabilizer. inhibited by phosphorylation during mitosis, when the tubule dynamcis increase. increased catastrophe events in mitosis

Mitosis

Interphase, Prophase (nuclear envelope retracts into ER and golgi), prometaphase (chromosome congression), metaphase (chromosomes all aligned, tension on spindle), anaphase (triggered by the loss of cohesins, chromosomes pull apart), telophase (spindle breaks down and nuclear envelope reforms), cytokinesis. Most cells are in G0 though.

S phase

Interphase. Synthesis phase where chromosomes are actively replicated. Followed by G2. Then mitosis

G1

Interphase. cell grows in size, replicates RNA, can enter cell cycle from here (START)

Ras

Kinase cascade after RTK/JAK. binds N terminal of Raf. bound to membrane. mutant- glycine at position 12 sub to valine. RasD.

dimerization--> asymmetric kinase dimer

Ligand binding causes a conformational change that promotes dimerizing of extra cellular RTKS. Extracellular loops push out and clamp onto one another. One RTK (activator)'s C lobe binds to receiver's juxtamembrane segment above its N lobe to unblocks its activation lip-- localize "on." active kinase site then phosphorylates tyrosine residues on C terminal tails .

MEN

Mitotic Exit Network. GTPase signaling pathway that responds to spindle position and only active in anaphase. Reversal of CDK phosphorylation changes activities back to interphase states, ending mitosis. (ex. dephosphorylation of condensins, histone H1, etc--> chromosome decondensation)

Cdc25

Opposes Wee1. necessary to start mitosis from G2. Cdc25A-- activated in late G1 to remove phosphorylation on Y15 of G1/S and S CDK catalytic subunits. Cdc25C-- active in G2 to remove phosphorylation on mitotic CDKs. rapid switch from Wee1 to Cdc25 causes entry into mitosis.

Myc

Over expression can lead to cancer. Proto-oncogene. Onocogene addiction. Interruption in myc feed can stop cancer formation. encodes a basic helix loop helix zipper than can dimerize in various combinations. Mad, Max, and Mnt part of the same protein set. Myc-Max dimers regulate genes that control proliferation (like cyclins). Mad proteins inhibit Myc. Mcy affects transcription by recruiting chromatin-modifying complexes containing histone acetyltransferase to target genes. Mad and Mnt work with Sin3 co repressor proten to bring in histone deacetylases to block transcription. overall, production of Myc tips the scales in favor of cell division and proliferation. mutations in myc can also cause dramatic changes in cell size.

GTP-ase activating protein (GAP)

Ras has low intrinsic activity, so GAP helps it deactivate by hydrolyzing GTP to GDP. 100X more activity

Tet (exogenous controlled promoter)

Tet operon promoter- regulates expression of a gene. transactivator tTA (for Tet off) and reverse transactivator rtTA (for Tet on)--> both controlled by tetracycline, which inhibits tTA from binding (turns off for Tet-off) and can induce rtTA binding to promoter (turns on for Tet on)

RTK's

Tyrosine kinase enzymes that function as allosteric enzymes with an extracellular effector. Stimulated by growth factors. Monomeric, but dimerize to activate. # domains: extracellular with ligand binding and loop to connect to other monomer, membrane spanning alpha helix, and cytosolic area with flexible activation lip with tyrosine kinase activity. (We're focusing on HER human EGF receptors)

Raf

activated by Ras. Inactive- bound to 14-3-3 by phosphorylation of N terminus. When it binds to Ras, the 14-3-3 releases from N terminus and the C terminal kinase domain can phosphorylate and turn on. Serine/threonine kinase. then phophorylates and activates MEK. Oncogene w/o it's N terminal-- not regulated by 14-3-3 and it constitutively active

C-Cdh1

binds to APC/C during telophase. destroys mitotic cyclins to promote exit from cell cycle. Together with Sic1-- inhibit CDKs. conversely, CDKs inhibit them too. Cdc14 pushes in favor of Sic1 and C-Cdh1 during anaphase though.

MAP

activation lip destabilized by MEK and then tyrosine-185 and threonine-183 are phosphorylated. exposes catalytic site. pY185 also helps binding substrates. Dimer goes to the nucleus to regulate transcription of c-Fos and c-Jun, which are early response genes needed for the cell cycle. Directly phosphorylates transpiration factor TCF, which is bound to c-fos's promoter, SRE.

GRB2

adaptor protein that binds RTK or JAK and Sos. no enzymatic activity. has a SH2 domain that binds to a phsopho-tyrosine on RTK or JAK. Two SH3 domains that bind Sos. Binds simultaneously on both ends.

Metaphase

all chromosomes aligned on a metaphase plate. Tension

conditional systems

allele is wild type until activated or inactivated by exogenous chemicals or virus in tissue or time specific matter. Ex. Cre and FLP recombinases that promote homologous recombination between loxP and FRT sites. If it's a tissue specific promoter, then the oncogene or tumor suppressor will only occur in that tissue. there are two main mechanisms for inducing cancerous genes conditionally: recombinase can flank an exon-- results in exon loss and gene inactivation for tumor suppressors, esp in tissue specific cases (inactivating system). other way is to remove a stop codon from the exon, which makes it non-functional (activating system). If the exon is flanked by recombinase targets though, the oncogene will be produced when recombinase is introduced (activated). pg. 1132

sis oncogene

alter PDGF gene- can continuously stimulate proliferation. It's rare for a growth factor to become cancerous though. Cancerous, hyperactive growth signal

APC/C

anaphase-promoting complex or cyclosomes. controls exit from mitosis. degrades S phase and mitotic cyclins. controls onset of chromosome segregation (metaphase to anaphase). activated by phosphorylation. active through rest of mitosis and through G1 for cyclin and mitotic regulator degradation. Substrate specificity from association with Cdc20 and Cdh1. Activates dephosphorylation of CDK cyclins to leave mitosis when associates to Cdc20. (since mitotic CDKs activate APC/C, this means in also activates own destruction). cuts remaining cohesins holding sister chromatids together at onset of anaphase.

Sos

binds to SH3 domains of GRB2 and to inactive Ras. functions as a guanine nucleotide exchange factor (GEF) for Ras, which will accelerate its activity by promoting GDP dissociation by causing switch I and II to open. GTP replaces and activates Ras

imatinib (Gleevec)

binds to the Abl active site and inhibits kinase activity. Highly lethal to cancer cells, but leaves healthy cells alive. Problem-- cells can become resistant over time

programmed cell death

apoptosis. three protein functions: killer, destruction, and engulfment. engulfment part of death process. A halo of actin triggers Rac. Stimulates neighboring cells to start engulfment death in response to tissue damage-- necrosis inflammation- swell and burst pathway: Ced-3, Ced4, Ced9, egl1 Ced-3: needed to destroy cell components ced-4: is a protease-activating factor that causes autocleavage of and by the ced-3- "killer" ced9: bcl-2. suppresses apoptosis. tethered to mitochondria. forms complex with ced4, preventing ced3 from binding. large contact surface egl1: binds to ced-9 to catalyze release of ced-4. ced9 and egl1 have BH3 domains- key contact surface. gives ced9 a different formation, which releases ced4 ced4+ced3=accelerated autocatalysis +ced9=inhibition +egl1=ced3 function restored

kinetochore

assemble in centromeric-specific (constricted DNA) region marked with H3 histone variant CENP-A (which will recruit Aurora B [in CPC] when phosphorylated, on chrom) . Many other proteins associate. 3 sections: centromeric DNA, inner kinetochore layer, outer kinetochore layer (where + end of MT will terminate with about 30 connections in humans)

gamma- TuRC and augmin

associated complexes. bind to sides of existing spindle MT to nucleate additional MT- contributes to polar MT and anaphase B

chronic myelogenous leukemia

associated with bcr-abl mutations. cancer arises when another mutation occurs in one of those cells, usually in a gene for transcription regulation-- like Hox. Hox is a group of transcription factors needed for cell proliferation and differentiation

Kinesin-7 (CENP-E)

associates with the free kinetochore after dynein-dynactin pulls one side if not captured on the other side yet. It will start moving the chromosome back towards the other side to be captured. Towards (+) end of an already formed kinetochore MT. Also a regulator for alignment

dynein-dynactin

associates with the kinetochore to move the duplicated chromosome down the microtubule towards the spindle pole. results in end-on attachment of MT to kinetochore. Helps orient the kinetochore so the unoccupied kinetochore on opposite wide faces the distal pole. eventually, a MT from the other side will capture it and then it will be bi-oriented. Now under tension.also a regulator for alignment. Releases from kinetochore MT after alignment.

HER 1

binds EGF, HB-EGF, TGF-alpha. homodimerizes. can be targeted for lysosomal degradation.

Cdc20

binds to APC/C during anaphase. ubiquitinylates proteins (securin) leading to chromosome segregation (freeing separase).

PP1

binds to the outer kinetochore. dephosphorylates Ndc80, which stabilizes it.

Cdc14

brings 2nd step in mitotic CDK inhibition. Switches the dynamics of CDK v Sic1/Cdh-1 toward Sic1/Cdh-1 to stop CDKs to end mitosis during anaphase. Inactive during most of the cycle. Activated in anaphase by GTPase signaling pathway- MEN (mitotic exit network)

Burkitt's lymphoma

c-myc transcription factor gene is translocated to a site near the heavy-chain antibody genes, which are normally active in antibody producing white blood cells. rare aberration in the normal DNA. myc now continuously expressed. localized amplification.

oncogenesis or tumorigenesis

cancer forming process-- interplay of genetics and environment- most cancers from mutations fro carcinogens or errors in copying and repair. a damaged cell will give rise to a cline, which can eventually become a tumor. when cells from a primary tumor migrate and forma new tumor-- metastasis. tumors produce own growth factors and angiogenesis factors (to bring blood vessels to promote growth and migration). tumors are characteristically hypoxic (oxygen starved)

RasD

cannot hydrolyze GTP to GDP. Point mutation. dominant active activity. substitution for the glycine at position 12. GTP state maintained. In bladder, colon, mammary, skin, and lung cancers. GAP mutations can also cause over active Ras. GAP is supposed to help hydrolyze GTP to GDP. Loss of function= sustained Ras activity, similar to RasD. NF1= GAP type protein for Ras. 1 mutant allele in Neurofibromatosis (individuals get cancer when the other allele mutates). tumor suppressor gene. hydrolyzez bound GDP very slowly- not enough to cause cancer alone in the body, but it is enough in T3T cells, which already have some mutations

malignant tumor examples

carcinomas= epithelial sarcoma= mesoderm leukemia= individual blood cells lymphoma= mass of lymphocytes glioblastoma= glial cells in brain

Cdc13

cdc13 required for telomere replication. when absent- large stretches of incompletely replicated telomere DNA persist (incomplete replication). RAD9 gene part of machinery to convey cell cycle arrest signals, not essential but cells are vulnerable to DNA damage without. without RAD9- cell cycle won't stop when CDC13 malfunctions-- cell dies because it undergoes mitosis with incomplete gene replication

checkpoints in yeast example

cell growth and division are separate processes, but have to coordinate to maintain size. Yeast coordinate in G1. activity of G1CDKs dependent on growth- controlled by protein synthesis. G1 cyclin Cln3 esp sensitive to protein synthesis rate. highly plastic system-- critical cell size- size at which cells enter cell cycle- changes in nutrient availability.

type II receptor for TGF-beta

commonly mutated in colon cancer. has 1- adenines in a row which are often changed with polymerase slips- frame shift stops function. resists growth inhibition from TGF-beta

myosin II

concentrated around contractile ring for cytokinesis. Myosin I is towards poles. cytokinesis cannot happen without myosin II

SCF

controls G1-S phase transition by degrading G1/S phase cyclins and CDK inhibitory proteins. Only recognizes substituents when they are phosphorylated though. always active

p16

cyclin-CDK inhibitor important for regulating cell cycle. loss of function p16 cannot inhibit D-CDK4/6 kinase activity common in several cancers --mimics overproduction of cyclin D1. usually a tumor suppressor. sometimes inactivated by hypermethylation of promoter, preventing transcription. p16 locus codes for 3 tumor suppressor genes- highly vulnerable. INK4a, INK4b (p15) key for p53 activation p14ARF controls stability of p53 page 1140-1

c-abl

cytosolic tyrosine kinase- promotes actin and cell processes. hybrid formed by chromosome translocation (chimeric protein with dangerous properties)--> bcr-abl. forms tetramer with unregulated activity. activates many signal transduction proteins (some not even normally its substrates). Activates JAK5 kinase and STATS transcription factors (which normally only bind to transcription factors). Philadelphia chromosome= diagnostic, generated by involved in bcr-abl formation. loss of function in a bcr-abl cell can lead to acute leukemia or chronic myelogenuos leukemia if loss of function

mitosis

dependent on completion of chromosome replication.

PTEN gene

dephosphorylates a second messenger of Akt- activates it. loss--> excessively active Atk, which promotes proliferation

Hedgehog, Wnt and TGF-beta

direct cells into their fates in development- regulate growth to the correct time and place. restraint mechanisms: intracellular antagonist, receptor blockers, and competing signals. malfunction=oncogene

HER 2

does not directly bind to a ligand. Pre-activated RTK on membrane with loop already pushed out. Forms heterodimers with HER 1,3,4. Increased presence on the membrane increases sensitivity. Over expressed in some breast cancers. Can be targeted with antibodies. Only homodimerizes at extremely high quantities.

nuclear envelope

double membrane extension of the ER with many pore complexes. Associated with the nuclear lamina- a meshwork of lamin filaments adjacent to the inside face of the envelope. Mitotic CDKs promote its break down. nucleoporins phosphorylated and dissociate. Retracts into the ER.

Ran- GTP

drives nuclear import and export. Important in reforming the nuclear envelope while exiting mitosis. Stimulates fusion of ER projections to form daughter nuclear envelopes and reassembly of nuclear pore complexes (NPCs). concentration is highest near decondensing chromosomes because the Ran- guanine nucleotide-exchange factor (Ran-GEF) is bound to chromatin. Membrane fusion is stimulated at the surfaces of decondensing chromosomes, forming sheets of nuclear membrane with inserted NPCs. Also induces association of cytosolic MT stabilizing factors. its hydrolysis enzyme (Ran-GAP) is evenly distributed in the cytosol, so it creates a gradient in the cell- which causes biased growth of MT from the spindle towards the chromosomes.

MEK

dual specific kinase activated by Raf. phosphorylates one threonine and one tyrosine on MAP activation lip- starts its catalytic activity

Prophase

duplicated centrosomes from S phase more active- become poles in mitotic spindle. asters move apart using bipolar kinesin-5 motors (also later help in Anaphase B to move poles further apart). protein synthesis becomes CAP-independent. internal order of membrane disassembled. endo/exocytosis halted. rearrange to a round cell. nucleolus breaks down. chromosomes condense. cohesins holding sister chromatids together degrade except for the center. kinetochores associate. coordinated by rapid increase in M CDK activity, which phosphorylates many proteins.

carcinogen

exposure from environment can also cause mutation. loss of DNA repair enzymes-- accumulating mutations. chemical that causes cancer: mutations that reduce tumor suppressor (loss of function), make oncogenes (gain of function) or damage DNA repair systems. insertions, deletions, substitutions, amplifications, translocation. damage to DNA repair systems compromises integrity. Some cancers have specific carcinogens associated.

3T3 cells

for culture. grow only when they are attached to a plastic surface and are at a low density. Stop growing when they contact each other--> quiescent G0 phase. They have some mutations- loss of function p19ARF and/or p53- so they can grow an unlimited number of times, immortal. when bladder cancer cells are added to a 3T3 culture-- progeny are rounded, do not adhere to one another, and form 3D clusters that grow unattached to the plate.

Aurora kinase

for mitotic spindle and attaching to chromosomes correctly. ex. Aurora B (associated with chromosal passenger complex CPC)-- sits between kinetochores on the sister chromatids, makes sure they are bi-oriented (one attached to a tubule from one centrosome, one attached to a tubule form the other-- tension sensed) [amphitelic attachment] the pulling of MT is resisted by cohesin complexes holding the chromatids together until anaphase. can sever an incorrect MT connection to allow it another chance to attach correctly. Aurora B phosph Ndc80 to destabilize it until it's pulled away from the center under correct bi-orientation. recruited by phosphorylated CENP-A.

Polo kinase

for mitotic spindle formation and chromosome segregation. ex. Plk4-- promotes centrosome duplication

heterocyclic amines (HCAs)

from cooking meat at high temperatures. point mutations in colon and breast cancers

Aflatoxin

fungal metabolite in moldy grains can induce liver cancer-- mutates p53

proto-oncogenes

genes that normally promote cell growth, but mutation to oncogenes makes products that are excessively active in growth promotion- increase expression or overactive product. oncogenes are derived from normal cellular genes. (ex. ***ras= encodes an intracellular signal transduction protein to promote cell cycle progression. rasD= uncontrolled growth promotion)

Chk1 and Chk2

halt the cell cycle. phosphorylate Cdc25 and inactivate it. inhibition also of G1/S phase CDKs and S phase CDKs= no DNA replication.

xeroderma pigmentations (XP)

hereditary non-polyposis colorectal cancer (HNPCC) or lynch syndrome-> propensity to accumulate mutations. skin cancer at 1000sX the normal rate. 7 or 8 known genes for excision-repair- absence of mutations in cell growth an death regulators. encodes part of the mismatch repair systems (mutations in mismatch repair system can be inherited)

ATM and ATR

homologous protein kinases that get recruited to sites of DNA damage. initiate recruitment of adaptor proteins. Also recruit Chk1 and Chk2, which activate repair mechanisms and cause cell cycle arrest or apoptosis. ATM= double strand breaks ATR= stalled replication forks, damaged nucleotides, and double- stranded breaks. -- all contain single stranded breaks

tumor-suppressor genes

normally restrain growth, but mutations allow inappropriate divisions. developmental regulators determine cell growth, not cell type

mitogens

induce receptor tyrosine kinase linked signal transduction. stimulate transcription of multiple genes- either early response or delayed response. early- response within a few minutes of growth factor introduction by signal cascade that stimulate pre-existing transcription factors (ex. c-Fos and c-Jun early response- transcription factors that stimulate transcription of delay response) (ex. AP-1 and myc-- stimulate G1 cyclin and CDK gene transcription) some mitogens inhibit CKIs (CDK inhibitors), like [p15INK4b]

Anaphase

induced by APC/C sensing the correct metaphase tension. destruction of the cohesins and chromosome centers. A) chromatids separate to poles. B) movement of spindle poles further apart

INK4

inhibitor of kinase 4. binds to CDK 4/6 to block Cyclin D interactions and kinase activities. often mutated in cancer.

Wee1

inhibitory phosphorylation of Mitotic CDKs on Tyrosin 15. defective Wee1 means the cell will center the cycle prematurely and not have enough time to grow- smaller. Regulates entry into mitosis. inhibits CDK1 by phosphorylating Tyrosine 15. cells remain in G2 until they reach the right size because Wee1 inhibits when nutrients are low. inhibited by Cdr2. Both localize in patches to cell cortex middle. Pom1 prevents Cdr2 from inhibiting Wee1 when cells are small, mitosis prevented. As cells grow, local Pom1 concentration in middle declines, so Cdr2 becomes active and inhibits Wee1. cell can enter mitosis. cell length measured by the protein gradient.

Transforming growth factor beta (TGF-beta)

inhibits proliferation. epithelial and immune cancers. binds to cytosolic receptors to induce Smad. induces p25, which inhibits CDK4. arrests cell in G1. also induce plasminogen activator inhibitor 1 (PAI-1)- reduces degradation of matrix (reduces metastisis). loss of function- promotes proliferation. Smad 4 deletion- in pancreative cancer. lack of TGF-beta receptors= unresponsive to TGF-beta inhibition-- in retinoblastoma and colon cancer

prometaphase

initiated by nuclear envelope beak down. disassembly of the nuclear lamina. MT form spindles- search and capture for chromatid kinetochores. chromosome congression.

DNA viruses

integrate DNA into host instead of RNA. some contain oncogenes (HPV). Integral parts of viral genome, not just borrowed from host and adapted like retroviral oncogenes

lamin

intermediate filaments that make up the nuclear lamina. A and C are alternatively spliced from the same transcription unit. B has fatty acid to anchor into the membrane. form dimers. phosphorylated by CDK phosphorylates them to promote break down of the nuclear envelope, reassemble after mitosis when dephosphorylated.

colon cancer

it has observable stages: polyps, benign adenomes, and carcinomas. Good example of the multihit model of cancer. inherited predisposition: FAP (familial adenomatous polyposis) deregulation of Wnt pathway- formation of polyps. APC (adenomatous polyposis coli) is a negative regulator of Wnt signaling (Wnt promotes cell cycle entry by activatng c-myc genes.) disfunctional APC with inappropriate expression-- leads to polyps. This is the most frequent mutation in early colon cancer. APC is a tumor supressor, so both alleles need mutations for the cancer to start developing. (loss of function) second mutation-- ras. progeny dividing uncontrollably-- adenoma (gain of function) third- p53 inactivation. gradual loss of regulation- malignant. (loss of function)

JAK Kinase

kinases bound to cytokine receptors without kinase activity of their own. starts similar pathways as RTK's.

hallmarks of cancer cells

less well differentiated, high nucleus to cytoplasm ratio, prominent nucleoli, increase in mitosis, little specialized structures, less adherent and form focus clusters, energy metabolism rewired**, PK-M2 (instead of M1) activated by tyrosin kinase signaling [conversion of pyruvate into lactate, usually expressed only in embryonic development], aneuploidy{abnormal chromosome number, usually too many} because checkpoints aren't working, MVA (mosaic variegated aneuploidy) cause increased chromosome mis-segregation, syndrome causes patient to have a predisposition for cancer **use aerobic glycolysis which increases lactate (Warburg effect) and much less efficient with glucose use.

Ndc80 complex

long and flexible, many copies link inner kinetochore with (+) end of MT in outer region. constantly phosphorylated by Aurora B (in CPC) and dephosph by PP1- unstable. When there is correct tension, the complex is pulled away from the center so Aurora B cannot phosph it anymore. Stable when unphosphorylated.

SOC protein

long term signal blocking and protein degradation of JAK2. negative feedback induced by STAT proteins. 1) competitive inhibition of receptor. Inhibits catalytic activity by bindings its SH2 domain to the JAK2 activation lip. 2) promote degradation in proteasomes. box domain opposite of the SH2 domain recruits E3 ubiquitin ligase (same as c-Cbl) for degradation. turns off activity until more proteins can be made.

Mitotic spindle

made of MTs that attach to chromosomes vie kinetochores. Organized by centrosomes and gama tubulin. segregates bi oriented (each attached to opposite poles and pull apart) sister chromatids. During G1 and S, centriole pairs duplicate. 3 types of MT at the spindle: 1) astral, which orient spindle with axis of cell division, go from spindle pole to cell cortex. 2) kinetochore, search and capture to the kinetochores. transport chromosomes to poles in anaphase. 3) polar, interact with opposite pole in antiparallel manner. push centrosomes apart at first and then in Anaphase B.

Spleen focus-forming virus (SFFV)

manipulates a normal developmental signal. Epo and Epo receptor needed for red blood cell proliferation and survival. gp55 (the SFFV oncoprotein) binds to and activates Epo to continuously proliferate. Malignant clones develop after a few weeks as more mutations develop.

Telophase

nuclear envelope reforms and chromosomes decondense

destruction box

motifs on most S and M cyclins. recognizes by APC/C when bound to associates. substrates are ubiquitinated for degradation.

trophic signals

multicellular organisms send cells hormone signals to keep them alive. with out a trophic signal- suicide signal.

multi-hit cancer model

multiple mutations needed to transform a normal body cell into malignant cancer. One mutation can give a slight growth advantage. 2nd mutation- benign tumor. 3rd- outgrowing others and overcoming restraints in the environment. more- metastisis. all the cells in a cancer should have mutations in common because they arise from a single progenitor. (all cancer cells in a woman will have the same inactive X chromosome). 5-6 hits needed for most dangerous cancers to develop. Ex. Myc-c mutations and rasv12 mutations introduced to cells. individually, only a small portion of the cells develop cancer, but they have synergistic effects when the mutations occur together. just a single mutation can lead to senescence, where the cells just stop dividing. more mutations, that response is neutralized genetic instability is a hallmark of cancer

dimeric ErbB oncoprotein

mutations in EGF receptor-- eliminates extracellular domain. constitutively active.

gain of function mutation

oncogene transformation. genetically dominant. 1) point mutation= hyperactive or constitutively active protein product 2) chromosomal translocation= fuse 2 genes together for a chimeric protein, usually constitutive activity 3) chromosomal translocation (another kind)= growth regulation gene under control of different promoter, causing inappropriate expression 4) amplification= numerous copies of a gene exist, overproduction 1 and 2-- "oncoprotein" different from normal 3 and 4-- normal but excessive expression usually achieved when a caretaker is defective. These genes can appear tandem on a single chromosome site- or- as a mini chromosome. --> tandem can be seen with homogenously staining region visible under light microscope overly abundant-- can be seen with DNA microarray or deep sequencing

mdm2

p53 regulator. it is also regulated by p14ARF- coded at locus with INK4 proteins. binds to mdm2 to stabilize p53. normal concentration barely detectible. induced bu E2F transcription factor and induces p53 activation

APC

part of the Wnt signaling pathway. mutation connected to colon carcinoma. beta-catenin will also mutate with colon cancer

START

point at which cells are committed to mitosis. G1/S CDKs. D-type cyclins, CDKs, Rb- all regulate passage through START. pathway regulating the entrance to the cell cycle misregulated in 80% of cancers. D-type cyclins induced by mitogens and assemble with partner CDK4/6 to generate catalytic complexes. kinase activity promotes G1. if you withdraw mitogens before the START onset, p15 and p16 accumulate- CDK inhibitors that bind D-CDK4/6 complexes to arrest G1 activity.

Neu oncoprotein

point mutation on HER2- constitutively dimerized, so always active. (val-> gln in membrane alpha helix). activates everything downstream constantly.

cleavage furrow

point of division between the two daughter cells. signals with spindle mid-zone and positioned in respect to the poles. surveillance mechanisms in place to avoid asymmetric cell division. Cells expressing stabilized mitotic cyclins through anaphase do not undergo cytokinesis though.

anti-mitogens

prevent early entry into the cell cycle. most post mitotic cells never re-enter the cell cycle after differentiation unless they are healing. anti-mitogens antagonize G cyclin to prevent accumulation of G1CDKs and they also induce CKIs. (ex. transforming growth factor beta [TGF-beta]- arrest G1 with p15INK4b)

caretaker genes

prevent or repair DNA damage- loss of high fidelity systems leads to cancer

direct-acting carcinogens

reactive electrophiles. (only a few). seek out electron rich centers. react with N and O to modify DNA and distort pattern of base pairings

cohesin complexes

related to condensin process. Most are removed during prophase-- phosphorylation by Polo kinase and Aurora B removes them. But maintained around the centromere to keep the sisters together until they are aligned correctly on the mitotic spindle- protected by protein phosphatase 2A (PP2A). PP2A is recruited to the centromere region by Mei-S332/Shugoshin proteins. Protected cohesins resist tension of bi-oriented chromatids until anaphase.

condensin complex

related to the cohesin complex, but for condensation not holding sister chromatids together. Has two large non- SMC subunits and two SMC subunits (like cohesins). without this complex, the chromosomes do not condense. the two non-SMC units are targeted by mitotic CDKs. phosphorylation by CDK stimulates super coiling by condensin complexes. Removed during prophase.

Telomerase

reverse transcriptase with RNA template to lengthen telomeres, which are the ends of linear chromosomes- tandem DNA sequences. High expression in embryos, germ-line, and stem cells-- also cancer. somatic= low expression when entering S phase. Telomeres shorten with each cycle. extensive shortening (end of cell life) is recognized as a kind of DNA damage- consequent stabilization and activation of p53 protein, leading to apoptosis. Complete loss of telomeres leads to end-to-end chromosome fusions and cell death. can overcome loss of telomere fate with telomerase- cancer. anti telomerase treatments a possibility for cancer (dominant negative telomerase with a modified RNA template can interfere with cell growth).

DNA damage response system

senses DNA damage and activates repair pathways- often apoptosis in multicellular organisms to stop cell mutation accumulations.

surveillance mechanisms

sensor- monitors cellular event signaling cascade- initiates response effector- halts cell cycle and activates repair as needed control kinase activity of CDKs- regulation of synthesis and degradation of cyclins, phosphorylation of CDKs at inhibitory sites, regulation of synthesis and stability of CKIs, and regulation of APC/C ubiquitin-protein ligase

double strand breaks

severe lesion. incorrect joining= rearrangement and translocation. depends on homolog for repair. B and T immune cells particularly in risk. BRCA1 and BRCA2= genes important for repair. without- DNA unable to repair when homolog needed as template. Recognized by ATM. ATM recruits MRN complex, which holds broken ends together. ATM also activates Chk2 and recruits repair proteins. homologous recombination. creates single-stranded overhangs. recruits ATK and effectors also. non-homologous end joining- alternative pathway where broken ends directly fused together. halts cell cycle. (Chk2 inhibition of Cdc25, preventing CDKs)

SHP1

short term deactivation of JAK. Has two SHP2 domains. at rest, one SHP2 binds to the phosphatase domain. stimulated-- binds to specific phosphotyrosine residue in activated receptor. catalytic site dephosphorylates tyrosin at the activation lip. No more kinase activity until more signals come through.

kinesin-13

shortening of MT. regulator in alignment. contributes to movement during anaphase A.

DNA polymerase

to correct damage. 9 use the same template that is modified, including polymerase B. Each copes with a different kind of lesion= lesion bypass DNA polymerases. inaccurate, but better than nothing- last resort. Polymerase B- over expressed in some tumors. needed for division under heavy mutation burden

p53

transcription factor activated by DNA damage. transcribes CDK inhibitor p21, which binds and inhibits all cyclin-CDK complexes. Arrest G1 and G2. tumor repressor- functions to limit proliferation when there is DNA damage. very unstable. Ubiqitinylation by Mdm2 (ubiquitin-protein ligase) and then degraded by proteasomes. rapid degradation inhibited by ATM and ATR when needed though- phosphorylate p53 at a site to interfere with Mdm2 binding. Also greatly enhance transcription ability of genes that help the damage. P53 enhances CKI p21. can also activate apoptosis when damage is extensive. nearly all cancers have mutations in both alleles or stabilization page1142 central to tumorigenesis. arrest cell in G1 when there is damage. usually in very low levels, but increase in stressful situations (gamma radiation, heat, low oxygen)-- creates lesions on DNA and serine kinase ATM and ATR are recruited to damage sites and activated-- phosphorylate p53 on serine residue in the N terminus, so it can evade ubiquitin-mediated degradation--> higher concentration. stable p53 activates transcription of p21CIP- binds to inhibits cyclin E-CDK2, arrest cell stimulates pro-apoptotic proteins and DNA repair Mdm2 normally keeps activity low- binds p53 and catalyzes ubiquitination to degrade, but ATM or ATR displace mdm2 to stabilize p53- autoregulatory feedback loop. loss of function in most cancers. less p14ARF and more mdm2. active form is a tetramer with identical subunits. point mutation in one allele makes it inactive DOMINANT NEGATIVE mutation. tumor still sometimes loses the other allele though. no p53, no apoptosis

E2F

transcription factor complex that promotes G1/S phase cyclins. activated by CDKs. inactivated in G1 by Rb. CDKs phosphorylate Rb, which inactivates it and sends it out of nucleus. E2F activates genes for DNA synthesis. promotes own transcription too. (growth factors are cyclin D CDK 4/6) Makes cyclin A and E-->START, S phase, positive feedback loop for self. Rb controlled by cyclin D-CDK4/6 phosphorylation. unphosphorylated- binds to E2F transcription factors in cytoplasm. Phosphorylation typically initiated midway through G1 by active cyclin D-CDK4/6 complexes. Finished by E-CDK2 in late G1, allowing E2F to move cycle forward. Complete Rb phosphorylation and E2F dissociation commits the cell to DNA synthesis. Most cancers have mutations to make regulation not work- cell goes into S phase without proper signaling. Increase in D-type cyclin in many cancers. cyclin D translocation in lymphocytes- amplification of cyclin D in many breast cancers

jun and fos

transcription factors found in cancer cells (c-jun and c-fos). Cancer forms can bind into a heterodimer AP1. Can also act independently. Induce transcription of genes encoding proteins that promote progression through the G1 phase of the cell cycle and the G1 to S transition. high levels in cancer cells. In normal cells, they are very unstable, which leads to rapid degradation. cancerous genes have deletions in the sequences that make them short lived.

chronic lymphoblastic leukemia (CLL)

translocated bcl-2 activates it. apoptosis blocker- keeps cells alive when they shouldn't be.

loss of function mutations

tumor suppressing genes. encode for proteins that inhibit cell proliferation. loss of function stops inhibition. genetically recessive, so both alleles must be inactive. if haplo insufficient though-- then dominant

DNA microarray

tumors undergo cascade of changes and become very different. microarray-- analysis of expression of tens of thousands of genes at once. can be used to determine which patients would benefit from which aggressive treatments

indirect acting carcinogens

unreactive compounds that can induce cancer at electrophilic centers. (ex. cytochrome P-450 enzyme- in ER, function to add electrophilic centers (like -oh) to nonpolar foreign chemicals to solubilize them for excretion- can turn chemicals into carcinogens though)

sister chromatid resolution

untangling of the sister chromatids for condensation and segregation. mediated by topoisomerase II

CLN3 (yeast)

upstream open reading frame that inhibits transcription when nutrients are low. sufficient nutrients or TOR pathway-- transcription stimulated. unstable protein-- fluctuates with mRNA level. regulated with nutrient availability

src protein kinase

v-src= constitutively active protein-tyrosine kinase. Cytosolic protein kinase that transduces signals for intracellular signaling pathways. has a catalytic domain, SH2 and SH3. supposed to be inactived by phosphorylation of tyrosine at position 527 (residue on the C terminus). hydrolysis of phosphotyrosine-527 normally activates. but tyrosine 527 is missing or altered in src (C terminus all together gone) oncoproteins that are constitutively active. page 1134

retrovirus

virus whose RNA genome is reverse transcribed into DNA that is incorporated into the host-cell genome. oncogene transforming viruses-- retrovirus that has oncogenes. (ex. Rous Sarcoma Virus RSV- has v-src [wild type is c-src])-- example of transducing retrovirus- contain oncogene derived from a transduced cellular oncogene. dominant onco. turns animal's own gene against them. RSV transduced within a few days, but they are usually slow acting. slow acting-- lack oncogene- incorporate into host DNA near cellular proto-oncogene and activate it Long terminal repeat (LTR)- sequences in integrated retroviral DNA= enhancer or promoter for cellular gene These are slow to activate because integration near cellular proto-onco is random and rare. Additional mutations are also needed before a tumor arises. but much more common than oncogene containing viruses. HTLV (Human T cell leukemia/lymphoma virus)-- only retrovirus known to cause human tumors