Background:
Several years ago, we have identified a number of genes that are differentially regulated in response to androgens and had enriched expression in the prostate, a major target organ for androgens. Three of the genes that we identified in this work are Six TrAnsMembrane Protein of prostate 1 and 2 (STAMP1 and STAMP2) (Korkmaz et al., 2002, 2005; Wellen et al., 2007; Wang et al., 2010; Lindstad et al., 2010), and Kallikrein 4 (KLK4) (Xi et al., 2004; Klokk et al., 2007; Jin et al., 2013).
Confocal immunoflourescence microscopy and live cell imaging techniques have shown that STAMPs fused to Green Fluorescent Protein (GFP) are localized in the Golgi/ER and shuttle between these organelles and the plasma membrane. In addition, STAMPs are targeted to the endocytic pathway and may be receptors for a ligand. Furthermore, STAMP1 is highly enriched to prostate for expression and is expressed only in AR positive prostate cancer cell lines whereas STAMP2 is more widely expressed, but exquisitely androgen regulated. Consistent with a role in cancer development, both STAMP1 and STAMP2 expression is increased in prostate cancer compared with normal prostate. Overexpression of STAMPs in prostate cancer cells increases their proliferation whereas siRNA-mediated knockdown decreases cell growth. Furthermore, both STAMP1 and STAMP2 inhibit apoptosis in prostate