Phosphorylated Akt up‐regulates angiotensin II type‐1 receptor expression in castration resistant prostate cancer

Abstract

Accumulating evidences has suggested that the renin-angiotensin system (RAS) participates in the regulation of tumor angiogenesis. We previously demonstrated that castration-resistant prostate cancer (CRPC) showed significantly higher angiotensin II (Ang II) type-1 receptor (AT1R) expression, and that AT1R blockade (ARB) exerted protective effects by inhibiting angiogenesis. However, the detailed molecular mechanisms for the increase of AT1R expression in CRPC has not been fully elucidated yet. In this study we used C4-2 and C4-2AT6 cells, which were PTEN-null, androgen receptor (AR) positive, PSA-producing CRPC cell lines. We investigated the association between phosphorylated Akt (pAkt) and AT1R expression, and used LY294002 as a PI3K/Akt inhibitor. Western blot analysis revealed C4-2AT6 cells showed significantly higher pAkt expression than C4-2 cells, although there were no significant differences in total Akt (tAkt) expression. Immunohistochemical (IHC) analysis also revealed significant higher pAkt expression in C4-2AT6 tumors obtained from castrated male nude mice. These results indicated that C4-2AT6 cells acquired elevated pAkt status under androgen-ablated treatment in vitro. Treatment with LY294002 at the same dose reduced the viability of C4-2AT6 more effectively than that of C4-2, reflecting the dependency of cancer cells on PI3K/Akt pathway. The up-regulated AT1R expression in C4-2AT6 cells was reduced by LY294002 in a dose-dependent manner. On the other hand, in C4-2 cells, serum starvation induced pAkt up-regulation, which led to an increase of AT1R expression. These findings indicated that up-regulation of pAkt contributed to elevated AT1R expression in CRPC.