DNA Damage

DNA Damage

1. Cancer: -Cause -Therapeutic -Side efects (hair loss; Gastrointestinal toxiaties; Bone marrow suppression)

2. Causes: Endogenous, Exogenous Effects: Damage bases, break the phosphodiester backbone

3. Affect: -Cell cycle progression -Programmed cell death

4. CELL STRESS

   • Free oxygen radicals
     • Break the phosphodiester bonds
     • External source of ionizing radiation
   • Alkylating chemical moleties
     • Purine bases
     • Size of the adduct
     • Inter-strand or intra-strand cross-links
   • Inhibits of DNA topoisomerases
     • Lead to enhanced single or DSBS
   • ATM
     • Homodimer kinase domain = blocked
       • DSB
         • Dissociation of the homodimer
           • Monomer
             • Change in higher-order chromatin structure
             • Release of blocked ATM Kinasa domain
             • ATM can sense
             • Phosphorylate substrates
               • P53
               • DNA breaks
     • ATM actived
       • Recruitment of: MRN (MRE11/RAD50/NBS1); BRCA1; 53BP1; MDC1
         • Localization; timing and velocity, signalling
     • CHK2
       • P53
         • Independent mechanism are sufficient to sustain G2 arrest
   • ATR
     • Arrest of DNA replication folk. Cell can’t survive without this
     • ATRIP+RPA=Arrest
     • + RAD17 RSR RAD9-RAD1-HVS1 (9-1-1) Sliding clamp Claspin protein
       • Substrate phosphorylation
       • Claspin is a mediator/adaptor protein that is structures
     • CHK1
       • Phosphoryllation of CDC25s
         • CDKs Cyclins
           • Delayed sustained
           • Rapid; transient
         • Abundance of CDC25S through its ubiquitin during unperturbed proliferation
       • Conplete absence of either ATR or CHK1 results in early embryonic lethality
       • In response to genotoxic stress, increased activity of CHK1 and CHK2
         • Inhibition of cyclin E(A)/CDK2 complexes
           • Delays the G1/S transition
     • Serine/Threonine Kinasas
   • Checkpoint
     • Before Replication
       • ATM-CHK2,CHK-P53/MDM2-P21-CDKs,Ciclins
         • Stop between G1 and S
           • G1 arrets
         • ATM/ATR phosphorylate the p53 transcription factor (serine 15, threonin 18, and serine 20)
           • Target of p53+MDM2 is the p21CIP1/CHK1
             • Silences the G1/S
             • Inability DNA si synthesis
             • Preserves the RB/E2F pathway
               • G1 blockade
     • S-phase checkpoint pathways
       • Activated by genotoxic
       • Intra-s-phase
         • Reflects the impact of ATM-mediated phosphorylations of NBS1 (serine 343, 957, 966) of the cohesin protein SMC1
         • BRCA 1 and FANCD2
         • Responses to both ionizing radiation and UV
       • “Replication checkpoint”
         • Activated by stalled replication
           • Protect the integrity of the stalled replication forks
     • G2 checkpoint
       • Prevents cell from initiating mitosis
         • When they experience DNA damage with some unrepaired damage
       • Target is the mitosis-promoting activity of the cyclin B/CDK1 kinase
       • Activation various stresses is inhebited by ATM/ATR, CHK1/CHK2 and/or p38
         • Degradation and/or inhibition of the CDC25 normally activate CDK1 at the G2/M boundary
       • B/CDK1, Polo-like kinases (PLK3, PLK1)

5. Normal: cells with an intact DNA-damage response frequently arrest or die in response to DNA damage

6. However, can permit the survival or the continued growth of cells with genomic abnormalities

7. Oncogenes

   • BRCA1, BRCA2
     • Breast and ovarian cancers

8. Tumour suppressor genes

   • Chk1
   • CHECK2- breast and prostate cancer

9. Pathway steps are important

   • Loss of ATM predisposes to lymphoma development
     • The deletion of the Rad52 protein, which is required for homologous recombination

10. Patients with mutations in NBS1 or MRE11 are predisposed to develop cancer

11. Disruption in ATR causing embryonic lethality

12. H2AX or 53BP1 is a cancer predisposition

    • Absence p53