Cell Growth and Diff Flashcards

Question

Role of Retinoblastoma, what it is?, which parts of the cycle it acts on and what it does?

Answer 1

RB – retinoblastoma – tumor suppressor The retinoblastoma protein is a key substrate ofentry into G1 and G1/S cyclin-dependent kinases The retinoblastoma protein is a key substrate ofentry into G1 and G1/S cyclin-dependent kinases Cells that are in G0, G1 is binding the TF called E2F E2F in this scenario is inhibited These cells in G0 receive a signal Signal activates the expression for cyclin D or Cyclin E  one of the targets of the CDK is the RB protein Kinases will phosphorylate substrate In this scenario we have a phosphorylated RB protein When RB is phosphorylated it can no longer bind to E2F Now you have dissociation of this inactive complex Phosphorykated RB and E2F dissociation E2F can now bind the promoter of doff genes and induce the expression of target genes.

Answer 2

Released E2F stimulates increased expression of more Cyclin E and S-phase proteins e.g. DNA polymerase (need to copy the DNA), thymidine kinase (required for expression of thymidine), PCNA (protein involved in DNA rep.) etc. DNA replication starts.

Answer 3

Inhibit cell cycle progression 1 - CDK Inhibitory Protein/Kinase Inhibitory Protein (CIP/KIP) family (now called CDKN1) Expression of members of this family stimulated weakly by TGF  and strongly by DNA damage (involving TP53) Inhibit all other CDK-cyclin complexes (late G1, G2 and M) Are gradually sequestered by G1 CDKs thus allowing activation of later CDKs 2 - Inhibitor of Kinase 4 family (INK4) (now called CDKN2) Expression stimulated by TGF Specifically inhibit G1 CDKs (e.g. CDK4 the kinase activated by growth factors)

Answer 4

CDKN1 Inhibit cell cycle progression Some induced at the level of transcription by TGF beta – inhibits cell growth by inhibiting expression of CDKN1 Another strong regulator of CDKN1 – TP53 – tumor suppressor protein involved in DNA damage Guardian of the genome It activates the expression of these inhibitors of kinases

Answer 5

Growth factor binding to the growth factor receptor Start activating a series of intracellular signal transducers As a result of activating these signalling pathways Effect in nucleus In the nucleus end up activating either expression of p21 or expression of cyclin/cdk4 Induce response in nucleus in response to growth factors

Answer 6

Growth factor signalling activates early gene expression (transcription factors – FOS, JUN, MYC) Early gene products stimulate delayed gene expression (includes Cyclin D, CDK2/4 and E2F transcription factors) E2F sequestered by binding to unphosphorylated retinoblastoma protein (RB) G1 cyclin-CDK complexes hypophosphorylate RB and then G1/S cyclin-CDK complexes hyperphosphorylate RB releasing E2F E2F stimulates expression of more Cyclin E and S-phase proteins (e.g. DNA polymerase, thymidine kinase, Proliferating Cell Nuclear Antigen etc.) S-phase cyclin-CDK and G2/M cyclin-CDK complexes build up in inactive forms. These switches are activated by post-translational modification or removal of inhibitors, driving the cell through S-phase and mitosis.

Answer 7

DNA damage can acc be detected at diff. checkpoints Cell first arrests in response to dna damage Stop cell cycle -Stop the cycle (cyclin dependent kinase inhibitors, CHEK2 etc.) Attempt to repair DNA - Attempt DNA repair (nucleotide or base excision enzymes, mismatch repair etc.) 2 outcomes Fully repaired – cell re enters the cell cycle and starts dividing If DNA repair not acahieved the DNA obvs contains mutations  cell doesn’t want to transmit thei mutation into daughter cell Can produce cancer If DNA not properly reapired - undergoes programmed cell death or apoptosis - Programmed Cell Death if repair impossible (BCL2 family, caspases)

Answer 8

Tumor suppressor P53 All cell types express it and make protein However in the absence of damage the p53 is destroyed by proteasome Look at cell pop.  detect RNA for p53  it is expressed  however if you want to detect protein it is unlikelya s it is constantly being degraded So cells with p53 but its not active In response to DNA damage Let’s say you have a mutagen Incorporate a mutation in that part of the DNA This DNA damage can be read and detected by kinases Mainly ATM ATR kinases Kinases become active and one of the substrates for the kinase is p53 Kinase adds phosphate or more than 1 phosphate group to p53 so as a result of this the p53 can no longer be degraded so therefore as a result of DNA damage you start accumulating P53 in cells P53 is a TF It will activate the expression of different genes Cdkn1 inhibitor of CDK and as a result of that p53 stops cells from dividing by expressing the CDKN1 P53 will aslso try to repair the DNA by activating the expression of quite a few different genes that come from proteins that are involved in DNA reapir for instance quite a few proteins involved in acquisition of that protein there are actually regulated by p53 protein If DNA reapir outcome is good  repair DNA and cell cycling again If not possible then P53 will induce expression of genes required to promote apoptosis

Answer 9

Growth factors binding to receptors induce gene expression G1 and G1/S Cyclin-CDK complexes phosphorylate RB in the absence of inhibition by CKIs (expression of these is regulated by TP53 or TGF) E2F released, stimulating expression of genes required for S-phase Cell replicates DNA (expression of S-phase Cyclin-CDK complexes) If all DNA replicated, G2/M Cyclin-CDK complexes cause cell to enter mitosis. If chromosomes aligned on spindle, exit from mitosis is triggered If process fails, TP53 initiates apoptosis