Tumor suppressor gene p53 prevents carcinoma by?
DNA repair
Cell cycle arrest
Apoptosis induction
All of the above
Ans. is 'd' i.e., All of the above * p53 gene is located on chromosome 17 & acts as molecular policeman that prevents the propagation of genetically damage cell. p53 gene product, i.e. p53 protein is a DNA binding protein in the nucleus, when called into action, it controls the transcription of several other genes.* When there is DNA damage due to irradiation, UV light or mutagenic chemicals, there is rapid increase in p53 levels.* p53 causes :-a) Cell cycle arrest: p-53 induces transcription of p21, a CDK inhibitor. p21 inhibit cyclin DCDK- 4 complex and there is arrest of cell cycle late in G1 phase. This allow time for DNA repair.b) DNA repair: p-53 also helps in DNA repair directly by inducing transcription of GADD 45 (growth arrest and DNA damage). GADD 45 encodes a protein that is involved in DNA repair.* If DNA damage is repaired successfully, p53 activate MDM-3 and this MDM-3 induce degradation of p-53 - Relieve in cell cycle block. If DNA damage cannot be successfully repaired, p53 induces apoptosis by inducing the activation of apoptosis inducing gene BAX. So p-53 prevents replication of cell with defective DNA - p53 functions as a critical gatekeeper against formation of cancer. Mutation in p53 leads to carcinogenesis because of loss of above protective mechanism.
Neoplasia