Kosaka Takeo, Miyajima Akira, Shirotake Suguru, Kikuchi Eiji, Oya Mototsugu
Department of Urology, Keio University School of Medicine, Shinjuku-ku, Tokyo, Japan.
Prostate. 2011 Oct 1;71(14):1510-7. doi: 10.1002/pros.21367. Epub 2011 Feb 14.
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.
越来越多的证据表明肾素 - 血管紧张素系统（RAS）参与肿瘤血管生成的调节。我们之前证明去势抵抗性前列腺癌（CRPC）显示出明显更高的血管紧张素II（Ang II）1型受体（AT1R）表达，并且AT1R阻断（ARB）通过抑制血管生成发挥保护作用。然而，CRPC中AT1R表达增加的详细分子机制尚未完全阐明。
在本研究中，我们使用了C4 - 2和C4 - 2AT6细胞，它们是PTEN缺失、雄激素受体（AR）阳性、产生前列腺特异性抗原（PSA）的CRPC细胞系。我们研究了磷酸化Akt（pAkt）与AT1R表达之间的关联，并使用LY294002作为PI3K/Akt抑制剂。
蛋白质印迹分析显示，尽管总Akt（tAkt）表达没有显著差异，但C4 - 2AT6细胞的pAkt表达明显高于C4 - 2细胞。免疫组织化学（IHC）分析还显示，在去势雄性裸鼠获得的C4 - 2AT6肿瘤中，pAkt表达明显更高。这些结果表明，C4 - 2AT6细胞在体外雄激素剥夺治疗下获得了升高的pAkt状态。用相同剂量的LY294002处理比C4 - 2更有效地降低了C4 - 2AT6的活力，反映了癌细胞对PI3K/Akt途径的依赖性。LY294002以剂量依赖性方式降低了C4 - 2AT6细胞中上调的AT1R表达。另一方面，在C4 - 2细胞中，血清饥饿诱导pAkt上调，这导致AT1R表达增加。
这些发现表明pAkt的上调导致CRPC中AT1R表达升高。
