Loss of the hSNF5 gene concomitantly inactivates p21CIP/WAF1 and p16INK4a activity associated with replicative senescence in A204 rhabdoid tumor cells

hSNF5, the smallest member of the SWI/SNF chromatin remodeling complex, is lost in most malignant rhabdoid tumors (MRT). In MRT cell lines, reexpression of hSNF5 induces G, cell cycle arrest, elevated p16(INK4a), and activated replicative senescence markers, such as beta-galactosidase (beta-Gal) and plasminogen activator inhibitor-1. To compare the replicative senescence caused by hSNF5 in A204 cells to normal cellular senescence, we examined the activation of both p16(INK4a) and p21(CIP/WAF1). Analogous to normal cellular senescence, both p16(INK4a) and p21(CIP/WAF1) were up-regulated following hSNF5 restoration. Furthermore, we found that hSNF5 bound the P16(INK4a) and p21(CIP/WAF1) promoters, suggesting that it directly regulates transcription of these genes. Using p16(INK4a) RNA interference, we showed its requirement for the replicative senescence caused by hSNF5 but not the growth arrest. Instead, p21(CIP/WAFI) remained activated by hSNF5 in the absence of high p16(INK4a). expression, apparently causing the growth arrest in A204. Interestingly, we also found that, in the absence of p16(INK4a), reexpression of hSNF5 also increased protein levels of a second cyclin-dependent kinase (CDK) inhibitor, p18(INK4a). However, our data show that lack of hSNF5 does not abrogate cellular responsiveness to DNA damage or growth-inhibitory factors. In summary, our studies suggest that hSNF5 loss may influence the regulation of multiple CDK inhibitors involved in replicative senescence.