Kikuchi Hirotoshi, Uchida Chiharu, Hattori Takayuki, Isobe Tomoyasu, Hiramatsu Yoshihiro, Kitagawa Kyoko, Oda Toshiaki, Konno Hiroyuki, Kitagawa Masatoshi
Second Department of Surgery, Hamamatsu University School of Medicine, 1-20-1 Handayama, Hamamatsu 431-3192, Japan.
Carcinogenesis. 2007 Aug;28(8):1752-8. doi: 10.1093/carcin/bgm120. Epub 2007 May 17.
Cyclin D1 is one of the major enhancers of cell cycle progression and its expression is regulated in several growth stimulatory signaling pathways. ARA54 is an androgen receptor (AR) co-activator that enhances AR-dependent transcriptional activation. Although expression of ARA54 mRNA is observed in a variety of human tissues at low levels, the AR- or androgen-independent function of ARA54 in those tissues remains unclear. In this study, we identified a novel role for ARA54 in the regulation of cyclin D1 expression in the absence of AR stimulation in human cancer cells. Depletion of endogenous ARA54 by small interfering RNA decreased both the protein and mRNA levels of cyclin D1. These changes did not result from a reduction in the half-life of either the protein or the mRNA, but from suppression of cyclin D1 gene transcription. In T98G cells, depletion of ARA54 increased the population of cells in G(1) phase, but reduced the population of cells in S phase, leading to a significant increase in the G(1)/S ratio and impaired cell growth. Furthermore, the amount of ARA54 mRNA appeared to positively correlate with cyclin D1 mRNA levels in specimens of clinical colon carcinomas, indicating that ARA54 is not only involved in the regulation of cyclin D1 expression in cultured cell lines but also in clinical cancer specimens. These results suggest that ARA54 might participate in enhancing cell cycle progression and cell proliferation via induction of cyclin D1.
细胞周期蛋白D1是细胞周期进程的主要增强子之一，其表达在多种生长刺激信号通路中受到调控。ARA54是一种雄激素受体（AR）共激活因子，可增强AR依赖的转录激活。尽管在多种人类组织中均观察到ARA54 mRNA的低水平表达，但ARA54在这些组织中的AR或雄激素非依赖性功能仍不清楚。在本研究中，我们确定了ARA54在人类癌细胞中，在无AR刺激情况下对细胞周期蛋白D1表达调控的新作用。通过小干扰RNA耗尽内源性ARA54可降低细胞周期蛋白D1的蛋白质和mRNA水平。这些变化并非由蛋白质或mRNA半衰期的缩短引起，而是由细胞周期蛋白D1基因转录的抑制导致。在T98G细胞中，耗尽ARA54会增加处于G(1)期的细胞数量，但减少处于S期的细胞数量，导致G(1)/S比率显著增加并损害细胞生长。此外，在临床结肠癌标本中，ARA54 mRNA的量似乎与细胞周期蛋白D1 mRNA水平呈正相关，这表明ARA54不仅参与培养细胞系中细胞周期蛋白D1表达的调控，还参与临床癌症标本中的调控。这些结果表明，ARA54可能通过诱导细胞周期蛋白D1参与增强细胞周期进程和细胞增殖。
