Upregulation of L-plastin gene by testosterone in breast and prostate cancer cells: Identification of three cooperative androgen receptor-binding sequences

L-Plastin is normally a leukocyte-specific actin-binding protein; it is als o expressed in the majority of human cancer cell lines that are derived fro m many types of solid tumors. We have previously reported the isolation of the L-plastin gene promoter, in which we identified several potential stero id receptor-binding sequences. We now obtained evidence that L-plastin gene expression was positively regulated by testosterone in androgen receptor ( AR)-positive prostate and breast cancer cells. DNase I footprint analysis i dentified three AR-binding elements (ARE) located in a 545-bp region approx imately 1.1 kb upstream from the transcription initiation site. However, ea ch of these three AREs exhibited very little testosterone/AR-responsive enh ancer activities toward a test promoter (of the thymidine kinase gene) when tested in MCF-7 breast cancer cells, Their testosterone/AR responsiveness became evident only when two or three of them were combined. In PC3 prostat e cancer cells, cooperation among L-plastin AREs was still evident although individually they had moderate levels of testosterone/AR responsiveness. T hus, the three L-plastin AREs, despite their imperfect sequences compared w ith the consensus ARE, could cooperate with each other to become a potent t estosterone/AR-responsive unit, which was likely responsible for the induci bility of the L-plastin gene by testosterone.