Hitomi Toshiaki, Matsuzaki Youichirou, Yasuda Shusuke, Kawanaka Mayumi, Yogosawa Shingo, Koyama Makoto, Tantin Dean, Sakai Toshiyuki
Department of Molecular-Targeting Cancer Prevention, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kawaramachi-Hirokoji, Kamigyo-ku, Kyoto 602-8566, Japan.
FEBS Lett. 2007 Mar 20;581(6):1087-92. doi: 10.1016/j.febslet.2007.01.092. Epub 2007 Feb 14.
p15(INK4b) functions as a tumor suppressor and implicated in cellular senescence. Here, we show that the Oct-1 binding site in the human p15(INK4b) gene promoter functions as a silencer. Oct-1 specifically interacts with this binding site in vitro and in vivo and SMRT and HDAC1 are present in the p15(INK4b) proximal promoter region. Moreover, mouse embryo fibroblasts (MEFs) lacking Oct-1 have shown significantly increased levels of p15(INK4b) protein compared to their normal counterparts. Treatment with a histone deacetylase (HDAC) inhibitor has activated the expression of p15(INK4b) in wild-type MEFs but has no effect in MEFs lacking Oct-1, suggesting that Oct-1 represses p15(INK4b) gene expression in an HDAC-dependent manner. Finally, we show that the expression of Oct-1 protein significantly decreases, whereas p15(INK4b) protein significantly increases with the cellular aging process. Taken together, these results suggest that Oct-1 is an important transcriptional repressor for p15(INK4b) gene and the transcriptional repression of the p15(INK4b) gene by Oct-1 may be one of the regulatory mechanisms of cellular senescence.
p15(INK4b)作为一种肿瘤抑制因子，与细胞衰老有关。在此，我们表明人类p15(INK4b)基因启动子中的Oct-1结合位点起着沉默子的作用。Oct-1在体外和体内均特异性地与该结合位点相互作用，且SMRT和HDAC1存在于p15(INK4b)近端启动子区域。此外，与正常的小鼠胚胎成纤维细胞（MEFs）相比，缺乏Oct-1的MEFs显示出p15(INK4b)蛋白水平显著升高。用组蛋白去乙酰化酶（HDAC）抑制剂处理可激活野生型MEFs中p15(INK4b)的表达，但对缺乏Oct-1的MEFs没有影响，这表明Oct-1以HDAC依赖的方式抑制p15(INK4b)基因表达。最后，我们表明随着细胞衰老过程，Oct-1蛋白表达显著降低，而p15(INK4b)蛋白显著增加。综上所述，这些结果表明Oct-1是p15(INK4b)基因的重要转录抑制因子，Oct-1对p15(INK4b)基因的转录抑制可能是细胞衰老的调控机制之一。
