Two mechanisms underlying the loss of p16(Ink4a) function are associated with distinct tumorigenic consequences for WS MEFs escaping from senescence.

[werner syndrome]

Werner syndrome (WS ) mouse embryonic fibroblasts (MEFs ) can spontaneously escape from senescence and become immortalized , either tumorigenic or non-tumorigenic . Our data revealed a single p 53 (N 236 S ) point mutation in the tumorigenic cell lines , which was correlated with the down-regulation of p 21 (Waf 1 /Cip 1 ). p 16 (Ink 4 a ) expression was significantly decreased in all immortalized cell lines . Bisulfate sequencing indicated that the p 16 (Ink 4 a ) gene was methylated in the tumorigenic cells . Exogenous overexpression of p 21 (Waf 1 /Cip 1 ) demethylated p 16 (Ink 4 a ) and restored its expression , which induced cell growth arrest and senescence . While in non-tumorigenic immortalized cells , the Ink 4 a loci and adjacent genomic DNA were found to be deleted . These data suggest that the loss of p 16 (Ink 4 a ) function by either genomic DNA deletion or methylation have been adopted by senescent WS MEFs escaping from senescence , with distinct tumorigenic consequences . The fact that cells that had escaped senescence via the spontaneous biallelic deletion of the Ink 4 a loci could not form tumors suggests that the functional loss of p 16 (Ink 4 a )per se might not be sufficient for tumorigenesis ; most likely , it is a byproduct and passenger mutation . The mutations in factors regulating p 16 (Ink 4 a ) methylation might be the driver mutation . These findings shed light on the strategy of anti-aging by regulating p 16 (Ink 4 a ) expression .