Induced p21(waf) expression in H1299 cell line promotes cell senescence and protects against cytotoxic effect of radiation and doxorubicin

The CDK inhibitor p21(waf) is a principal mediator of p53 function but can also be transactivated by many p53-independent stimuli leading to cell growth arrest or differentiation. In order to study the function of p21(waf) in a p53-deficient environment, we established an inducible expression of p21(waf) in the p53-null lung cancer cell line H1299, based on the muristerone-regulated system. Overexpression of p21(waf) led cells to growth arrest which after several days became irreversible and the arrested cells acquired a senescent phenotype as judged by cell shape, the senescence-associated β-gal marker and inhibition of colony formation. The effect of p21(waf) overexpression, in the absence of p53, on the cytotoxicity caused by irradiation, doxorubicin and taxol was studied. Expression of p21(waf) provided protection against the cytotoxic effect of radiation and doxorubicin but not of taxol. These results are relevant to treatment of cancer when p53 is inactive.