cancer bio exam 2

tumor suppressor inactivation

loss of proteins that positively regulate cell death and DNA repair; resisting cell death, genome instability and mutation

evading growth supressors

loss of proteins that negatively regulate proliferation

expressed and regulated appropriately

proto-oncogenes and tumor suppressor genes

too much protein expressed (myc) or hyperactive form (ras)

mutations in proto-oncogenes lead to oncogene activation

loss of protein expression or inactive form of protein

mutations in tumor suppressor genes

oncogenes

dominant, mutation of one allele is sufficient to transform a normal cell into a cancer cell

tumor supressors

recessive, require mutation of both alleles to transform a normal cell into a cancer cell

positively regulate opposing cell processes

tumor suppressor genes encode for proteins that… (cell cycle arrest, apoptosis, DNA repair, differentiation)

positively regulate cell growth and survival

proto-oncogenes are genes that encode for proteins that… (proliferation and cell survival)

gatekeeper

directly suppress growth, cell cycle regulator genes, checkpoint control genes, apoptosis related genes

caretaker

maintain overall genetic stability, DNA repair genes

Retinoblastoma

loss of genetic material on chromosome 13 (area that includes Rb gene)

somatic mutations

not heritable, occur in nongermline cells

germline mutations

mutation in egg or sperm, can be inherited, cause cancer familial syndromes, all cells affected in offspring

bilateral retinoblastoma

only one mutation required for development, familial retinoblastoma (one mutant Rb allele inherited, second mutation is somatic, leading to formation of retinoblastoma)

unilateral retinoblastoma

two mutations required for development (sporadic form of retinoblastoma, both mutations are somatic)

mechanisms for loss of function of tumor supressors

loss of heterozygosity, methylation of promoter, point mutation

loss of heterozygotsity

genetic alteration that results in two nonfunctional alleles, genetic crossing over, nondisjunction, gene conversion

methylation of promoter

DNA methylation in promoter regions, regulates gene expression

cancer phenotypes

discovered they are mostly recessive, so called ‘tumor suppressors’ for genes that ‘inhibit’ tumor formation

LOH are

cells already have a nonfunctional allele, likely due to point mutations but could be result of other genetic alterations, most often due to chromosomal changes rather than a second somatic mutation

low probability of

second somatic mutation leading to LOH, first somatic mutation (10-6/cell division) then second somatic mutation (10-12/cell division)

G0

most cells exist in

S-phase

cells replicate DNA during

mitosis

phase of cell cycle during which the cell divides into two identical daughter cells, chromosomes need to be evenly separated between daughter cells

mitotic recombination

homologous chromosomes and during s-phase there is a double stranded break which causes a homologous recombination, uses the template to repair break. not a translocation because it is the same chromosome

non-disjunction during mitosis

chromosomes do not segregate correctly during mitosis, chromosomes being separated by one and three instead of two and two

gene conversion

error in DNA polymerase, begins replication on template strands of one chromosome, then moves up to the other chromosome, then continues back one the original chromosome. can also be repaired during a double stranded break by homologous recombination

LOH in retinoblastoma

loss of DNA: faulty DNA repair, replication errors, non homologous end joining, unequal crossover, chromothripsis

chromothripsis

fragment of chromosomes dropping, like a glass or plate shattering

DNA methylation

another mechanism of inactivation of tumor suppressor genes because it blocks the binding of transcription factors and decreasing expression

GpG islands

regions in promoter with G or C

altering chromatin structure

decreasing access to DNA and DNA methylation may also… (decrease transcription by condensing chromatin and making it harder for transcriptional machinery to access the DNA)

histone deacetylase

enzymes bind to CpG islands, alter histone tails leading to chromatin remodeling, remove acetyl groups from lysine residues in histone tails, leads to stronger interactions between positively charged histones and negatively charged DNA

smoking

is the most preventable cause of death, in current and former smokers 44% of cultured cells showed hypermethylation of TSG promoter in normal bronchial epithelial cells

growth factor receptors

Her2, EGFR, Ras, Src, myc, cells integrate information from outside and inside the cell, which direction the cell goes is orchestrated by changes in gene express or changes in protein

S phase checkpoint

DNA damage checkpoint, DNA replication halted if genome is damaged (ATR)

G1 phase checkpoint

DNA damage checkpoint, entrance into S is blocked if genome is damaged (Rad17)

G2 phase checkpoint

entrance into M blocked if DNA replication is not completed

M phase checkpoint

anaphase blocked if chromatids are not properly assembled on mitotic spindle (BUB1)

disruption of checkpoints

benefits cancer cells because it increase chances of mutation, inactivating one or more checkpoints because permits mistakes, increase expression to help cancer cells manage genetic instability and replication stress

restriction point

decisive moment a cell decides to enter the cell cycle or not, once beyond normal and cancer cells proceed in similar fashion (Rb!)

cyclin dependent kinases

phosphate target, serine/threonine kinases that function in complex with cyclins (recognition of targets) to coordinate progression through the cell cycle

Rad17

DNA damage/stalled forks, deletions, increase expression in SCLC

BUB1

alignment, germline mutations (loss of function), increase risk of CRC at younger age, increase expression in aggressive cancer

ATR

stalled replication forks or DNA damage, CHK1, often frameshift

RB

represses gene transcription by binding to transactivation domain of E2F, promotes inhibition of transcription by recruiting HDAC (chromatin compaction and repressed transcription)

hypophosphorylated Rb

inhibits growth and division

hyperphosphorylated Rb

decreased growth inhibition activity

dysregulation of R-point

almost all human cancers exhibit hyperactivity of factors that promote this point transition or inactivation of factors that prevent this transition

HPV

E7 binds to and sequesters Rb and tags it for ubiquitylation (degradation)

knockout mouse models

Rb -/-: embryonic lethality while p53 -/-: die around five months from often cancer

missense mutations

vast majority are in the DNA binding domain of p53

p53

a homotetramer, transactivation domain, DNA binding domain, tetramerization domain

transactivation domain

recruits RNA polymerase

DNA binding domain

binds to regulatory sequences of target genes

tetramerization domain

how p53 molecules interact to form tetramer

p53 monitors

a huge array of signals and coordinates response to alarms

homotetramer

p53 is a transcription factor that must have the same four proteins to activate expression of genes that inhibit cancer phenotypes

ubiquitin ligase

an enzyme that attaches a small regulatory protein called ubiquitin to a target protein substrate

mdm2

it blocks p53-driven transcription initially by binding to p53 and then targets p53 for polyubiquitylation and sends p53 to the cytoplasm for proteolytic degradation (acts as oncoprotein and increases survival and proliferation)

tetramers of WT p53

function as transcription factor to drive gene expression of target genes, regulated appropriately by MDM2

tetramers of WT/mutant p53

does not function as transcription factor to drive gene expression of target genes (including MDM2), may not be regulated appropriately by MDM2

acute DNA damage and hyperproliferative signals

how do alarms in the cell increase p53 levels

phosphorylation of p53

prevents MDM2 binding and subsequent inhibition, the sites are concentrated in the same part of the protein where MDM2 binds

deregulated growth signals

also stabilize p53 through ARF (p14ARF) because it inactivates MDM2

regulation of apoptosis by ARF

elevated activity of E2F signals to the cell that Rb regulatory pathway may not be functioning correctly, E2F can actually increase expression of pro-apoptotic genes

myc and ras

oncogene signaling actually activates ARF which then frees up p53 to counteract the oncogene signaling

neddylation

NEDD8 protein, lysine, decrease transcription activity and increase ubiquitin activity

apoptosis

p53 plays a significant role in regulating this, through changes in the mitochondria, there are specific death receptors

p53 levels increase in response to alarms

DNA damage (activates kinases, hyperphosphorylation and MDM2 cannot bind) and hyperproliferation (increases ARF, which binds to MDM2)

regulation of apoptosis by ARF

elevated activity of E2F signals to the cell that Rb regulatory pathway may not be functioning correctly, E2F can actually increase expression of pro-apoptotic genes)

senenscence

permanent exit from cell cycle, irreversible growth, never divide again, refractory to mitogenic signals but metabolically active (influence their neighbors), have distinctive phenotype changes, limits growth potential but not survival

phenotype changes of senescence

flattening of cell, changing in chromatin structure (senescence-associated heterochromatic foci or SAHF), senescence-associated secretory phenotype (SASP, secretion of pro-inflammatory cytokines), increase in B-galactosidase

prevent progression

oncogene-induced senescence

tumor suppressor inactivation

changes to proteins that positively regulate cell death (p53)

oncogene activation

mitogenic signaling independent of external signals

enabling replicative immortality

as cells divide they can only go through so many time before going into senescence

immortal

tumor cells must be this to form clinically detectable tumors

exponential

cancer cell growth are NOT this, usually some go through apoptosis

mechanisms that regulate replicative capacity

cumulative physiological stress and crisis (telomeres shortening)

telomeres

non coding, repetitive sequences at the ends of chromosomes, they protect the ends of chromosomes from fraying and sticking to each other, consist of thousands of TTAGGG, crucial for maintaining genomic integrity of cells, anchor chromosomes to the periphery of the nuclear membrane

main functions of telomeres

help to organize chromosomes in the nucleus, protect the ends of our chromosomes by forming cap, allow DNA to be replicated properly during cell division (no loss of genes)

shelterin complex

telomeric sequences are complexed with proteins, involved in T-loop and D-loop formation in telomeres

replicative senescence

until telomere reaches critical length, signals to the cell to stop proliferating

cells that bypass senescence

bypass p53 and will eventually encounter crisis

DNA damage reponse

critically short telomeres lose shelterin complex and protective T-loop, telomere dysfunction signals to p53 to induce apoptosis

DNA damage reponse activation

senescence or cell death (Rb and p53 functioning) OR aneuploidy or genomic rearrangements, deletions, amplifications (deregulation of p53 or Rb pathways)

erosion of telomeres

leads to end-to-end chromosomal fusion in cells because of unprotected chromatid ends, shelterin proteins can’t effectively form T and D loops

fused sister chromatid

form anaphase bridges during mitosis, as cells continue to divide, this process of fusions and breaks continues, breakage-fusion-bridge cycles

hTERT

appears to be regulated by C-myc, can inhibit senescence, Ras is able to suppress apoptosis by activating P13K pathway