Carcinogenesis Advance Access published online on May 17, 2007
Carcinogenesis, doi:10.1093/carcin/bgm120
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ARA54 is involved in transcriptional regulation of the cyclin D1 gene in human cancer cells
1 Second Department of Surgery 1, Hamamatsu University School of Medicine, Hamamatsu, Japan
2 Department of Biochemistry 1, Hamamatsu University School of Medicine, Hamamatsu, Japan
Requests for reprints: Masatoshi Kitagawa, Department of Biochemistry 1, Hamamatsu University School of Medicine, 1-20-1 Handayama, Hamamatsu 431-3192, Japan. Phone: +81-53-435-2322; Fax: +81-53-435-2322; E-mail: kitamasa{at}hama-med.ac.jp
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 G1 phase, but reduced the population of cells in S phase, leading to a significant increase in the G1/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.
Received February 21, 2007; revised April 25, 2007; accepted May 12, 2007.
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