Cell cycle regulation in H2O2-induced premature senescence of human diploid fibroblasts and regulatory control exerted by the papilloma virus E6 and E7 proteins

Many biomarkers of replicative senescence appear in stress-induced prematur e senescence (SIPS) of human diploid fibroblasts (HDFs). The mRNA level of key cell cycle regulators was studied in H2O2-induced premature senescence of HDFs expressing or not the papillomavirus E6 and E7 proteins, which enha nced, respectively, the proteolysis of p53 and Rb. The CdKI's p21(waf-1) an d p16(Ink-4a) were found overexpressed in H2O2-induced premature senescence , while p19(Ink-4d)and p27(Kip-1) were repressed. The results obtained in E 6 HDFs suggest that p21(waf-1) and p16(Ink-4a) over-expressions are p53-ind ependent, while p27(Kip-1) and p19(Ink-4d) down-regulations are p53-depende nt. E6 regulated Rb, p130, p53 and p16(Ink-4a) mRNA level in non-stressing conditions, and regulated p130, p107, p53, p19(Ink-4d), p27(Kip-1) mRNA lev el in SIPS. SIPS modified the E6-mediated regulatory control on p107, p16(I nk-4a), p19(Ink-4d) and p27(Kip-1) mRNA level, when compared to normal cond itions. E7 regulated the mRNA level of all the genes studied, in all condit ions, suggesting that the Rb family or other E7-interacting proteins might modify the expression of these genes. SIPS modified strongly the E7-mediate d regulatory control on p107, p16(Ink-4a), p19(Ink-4d), p27(Kip-1), p21(Waf -1) and Rb mRNA level, when compared to normal conditions. Further work is ongoing to test whether this E7-mediated regulatory control takes place thr ough interactions with Rb or other E7-interacting proteins. (C) 2000 Elsevi er Science Inc. All rights reserved.