Abstract
1843
Bmi-1 is a polycomb group transcriptional repressor that plays an oncogenic role in carcinogenesis. Previously, we showed that exogenous Bmi-1 can enhance the replicative capacity of normal human oral keratinocytes (NHOK). To determine the mechanisms underlying the extension of replicative life span mediated by Bmi-1 overexpression, we performed microarray analysis with or without Bmi-1 in NHOK. Among genes that are differentially regulated by Bmi-1 are the genes involved in the TGF-β pathway which has been shown to induce senescence. In serially subcultured NHOK, we found that the TGF-β pathway was activated; Smad2/3 became phosphorylated as cells senesced, and this was followed by upregulation of p15 and p57, CDK inhibitors that are known to be involved in the TGF-β-mediated cell cycle arrest. When exogenous Bmi-1 was expressed in NHOK, no phosphorylation of Smad2/3 or the upregulation of p15 or p57 were observed, suggesting that the expression of Bmi-1 and the activation of the TGF-β pathway are inversely correlated. To confirm this finding, we utilized siRNA to knockdown Bmi-1 expression, and found that Smad2/3 became phosphorylated followed by increased expression of p15 and p57. Transient transfection with different amounts of vectors containing Bmi-1 showed decreased p3TP-Lux activities in dose-dependent manner, indicating that Bmi-1 may have a direct role in regulating the TGF-β pathway. Taken together, our study shows that Bmi-1extends the replicative lifespan of NHOK, in part, by disrupting the TGF-β-mediated senescence program. This study was supported by NIDCR/NIH (DE14147 and DE15316).
99th AACR Annual Meeting-- Apr 12-16, 2008; San Diego, CA