Increased stability of the p16 mRNA with replicative senescence.

Expression of p16(INK4a) is elevated during ageing and replicative senescence. Here, we report the presence of an instability determinant within the 3'-untranslated region (UTR) of the p16 messenger RNA in WI-38 human diploid fibroblasts. The p16 3'UTR was found to be a specific target of AUF1, an RNA-binding protein implicated in promoting mRNA decay. Both AUF1 levels and AUF1-p16 mRNA associations were strikingly more abundant in early-passage than late-passage fibroblast cultures. Moreover, short interfering RNA-based reductions in AUF1 levels increased the stability of p16 3'UTR-containing transcripts, elevated the expression of p16 and accentuated the senescence phenotype. Together, our findings show that p16 mRNA turnover decreases during replicative senescence and that the instability-conferring region is located within the 3'UTR of p16, as well as identifying AUF1 as a critical mediator of these regulatory events.