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

Abstract

<div>Abstract<p>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<sub>1</sub> cell cycle arrest, elevated p16<sup>INK4a</sup>, 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<sup>INK4a</sup> and p21<sup>CIP/WAF1</sup>. Analogous to normal cellular senescence, both p16<sup>INK4a</sup> and p21<sup>CIP/WAF1</sup> were up-regulated following hSNF5 restoration. Furthermore, we found that hSNF5 bound the p16<sup>INK4a</sup> and p21<sup>CIP/WAF1</sup> promoters, suggesting that it directly regulates transcription of these genes. Using p16<sup>INK4a</sup> RNA interference, we showed its requirement for the replicative senescence caused by hSNF5 but not the growth arrest. Instead, p21<sup>CIP/WAF1</sup> remained activated by hSNF5 in the absence of high p16<sup>INK4a</sup> expression, apparently causing the growth arrest in A204. Interestingly, we also found that, in the absence of p16<sup>INK4a</sup>, reexpression of hSNF5 also increased protein levels of a second cyclin-dependent kinase (CDK) inhibitor, p18<sup>INK4c</sup>. 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.</p></div>