Data from Loss of the <i>hSNF5</i> Gene Concomitantly Inactivates p21<sup>CIP/WAF1</sup> and p16<sup>INK4a</sup> 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 G₁ cell cycle arrest, elevated p16^INK4a, and activated replicative senescence markers, such as β-galactosidase (β-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/WAF1 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^INK4c. 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.