Androgens regulate SMAD ubiquitination regulatory factor-1 expression and prostate cancer cell invasion

Background: Prostate cancer (PCa) is the most commonly diagnosed male cancer in the United States and is a hormone-driven disease. Androgens have been recognized as a major promoter of PCa development and progression. However, the mechanism of androgen action in PCa, especially in PCa cell invasion and metastasis remains largely unclear. SMAD ubiquitination regulatory factor-1 (SMURF1) is a C2-WW-HECT-domain E3 ubiquitin ligase that plays important roles in cancer cell metastasis. Whether there is a relationship between androgens and SMURF1 expression is not known.

Methods: The effect of androgens on the expression of SMURF1 in PCa cell lines was examined by Western blot analyses and reverse transcription-polymerase chain reaction (RT-PCR). Gene transfection was performed by electroporation to manipulate the expression levels of proteins studied. The binding of AR to the SMURF1 gene enhancer was determined by chromatin immunoprecipitation (ChIP) assay. Cell migration and invasion was measured by wound healing and Matrigel invasion assays, respectively.

Results: We found that expression of SMURF1 is upregulated by androgens in PCa cell lines and that this effect of androgens is mediated through the androgen receptor (AR). We further showed that androgens regulate SMURF1 expression at transcriptional level and provided evidence that AR transcriptionally activates SMURF1 by binding to its enhancer that contains a canonical half androgen responsive element (ARE). Finally, we demonstrated that SMURF1 is important for androgen-induced invasion of PCa cells.

Conclusions: We demonstrate for the first time that SMURF1 is a bona fide target gene of the AR. Our findings also suggest a potential role of SMURF1 in PCa metastasis.