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1 Department of Urology, Veterans Affairs Medical Center and University of California at San Francisco, San Francisco, California and 2 Department of Urology, Kagoshima University, Kagoshima, Japan
Requests for reprints: Rajvir Dahiya, Urology Research Center (112F), Veteran Affairs Medical Center and University of California at San Francisco, 4150 Clement Street, San Francisco, CA 94121. Phone: 415-750-6964; Fax: 415-750-6639; E-mail: rdahiya{at}urology.ucsf.edu.
Wnt inhibitory factor-1 (WIF-1) has been identified as one of the secreted antagonists that bind Wnt protein. WIF-1 has been described as a tumor suppressor in various types of cancer. However, the molecular function of WIF-1 gene has never been examined in human renal cell carcinoma (RCC). Therefore, we hypothesized that WIF-1 functions as a tumor suppressor gene and overexpression of this gene may induce apoptosis and inhibit tumor growth in RCC cells. Immunohistochemistry and real-time reverse transcription-PCR revealed that WIF-1 was significantly downregulated in RCC samples and RCC cell lines, respectively. Bisulfite sequencing of the WIF-1 promoter region in RCC cell lines showed it to be densely methylated, whereas there was no methylation of WIF-1 promoter in normal kidney. Significant inhibition of cell growth and colony formation in WIF-1–transfected cells compared with controls were observed. WIF-1 transfection significantly induced apoptosis and suppressed in vivo tumor growth. Also, Wnt signaling activity and β-catenin expression were reduced by WIF-1 transfection. In conclusion, this is the first report documenting that the WIF-1 is downregulated by promoter methylation and functions as a tumor suppressor gene by inducing apoptosis in RCC cells. [Cancer Res 2009;69(22):8603–10]
Key Words: RCC • WIF-1 • methylation • tumor suppressor
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