Endocrinology (R.M., A.S., A.Morc., A.B.), Department of Health Sciences, University Magna Graecia of Catanzaro, 88100 Catanzaro, Italy; Endocrinology (S.S.), Department of Clinical and Molecular Biomedicine, University of Catania, Garibaldi-Nesima Hospital, 95125 Catania, Italy; Department of General Pathology (A.Mi.), II University of Naples, Via L. De Crecchio, 7-80138 Naples, Italy; Department of Urology and Biology of Prostate Cancer Program (A.Morr.), Kimmel Cancer Center, Thomas Jefferson University, Philadelphia 19107; and Department of Pharmaco-Biology (M.M.), University of Calabria, 87030 Rende, Italy.
Endocrinology. 2014 Apr;155(4):1207-21. doi: 10.1210/en.2013-1925. Epub 2014 Jan 17.
We have previously demonstrated that, in prostate cancer cells, androgens up-regulate IGF-I receptor (IGF-IR) by inducing cAMP-response element-binding protein (CREB) activation and CREB-dependent IGF-IR gene transcription through androgen receptor (AR)-dependent membrane-initiated effects. This IGF-IR up-regulation is not blocked by classical antiandrogens and sensitizes cells to IGF-I-induced biological effects. Metformin exerts complex antitumoral functions in various models and may inhibit CREB activation in hepatocytes. We, therefore, evaluated whether metformin may affect androgen-dependent IGF-IR up-regulation. In the AR(+) LNCaP prostate cancer cells, we found that metformin inhibits androgen-induced CRE activity and IGF-IR gene transcription. CRE activity requires the formation of a CREB-CREB binding protein-CREB regulated transcription coactivator 2 (CRTC2) complex, which follows Ser133-CREB phosphorylation. Metformin inhibited Ser133-CREB phosphorylation and induced nuclear exclusion of CREB cofactor CRTC2, thus dissociating the CREB-CREB binding protein-CRTC2 complex and blocking its transcriptional activity. Similarly to metformin action, CRTC2 silencing inhibited IGF-IR promoter activity. Moreover, metformin blocked membrane-initiated signals of AR to the mammalian target of rapamycin/p70S6Kinase pathway by inhibiting AR phosphorylation and its association with c-Src. AMPK signals were also involved to some extent. By inhibiting androgen-dependent IGF-IR up-regulation, metformin reduced IGF-I-mediated proliferation of LNCaP cells. These results indicate that, in prostate cancer cells, metformin inhibits IGF-I-mediated biological effects by disrupting membrane-initiated AR action responsible for IGF-IR up-regulation and suggest that metformin could represent a useful adjunct to the classical antiandrogen therapy.
我们之前已经证明，在前列腺癌细胞中，雄激素通过诱导 cAMP 反应元件结合蛋白 (CREB) 激活和 CREB 依赖性 IGF-IR 基因转录，上调 IGF-IR 受体 (IGF-IR)，这是通过雄激素受体 (AR) 依赖性膜起始效应实现的。这种 IGF-IR 的上调不受经典抗雄激素的阻断，并使细胞对 IGF-I 诱导的生物学效应敏感。二甲双胍在各种模型中发挥复杂的抗肿瘤作用，并可能抑制肝细胞中 CREB 的激活。因此，我们评估了二甲双胍是否可能影响雄激素依赖性 IGF-IR 上调。在 AR(+)LNCaP 前列腺癌细胞中，我们发现二甲双胍抑制雄激素诱导的 CRE 活性和 IGF-IR 基因转录。CRE 活性需要形成 CREB-CREB 结合蛋白-CREB 调节转录共激活因子 2 (CRTC2) 复合物，这需要 CREB 的 Ser133 磷酸化。二甲双胍抑制 Ser133-CREB 磷酸化并诱导 CREB 共因子 CRTC2 的核排斥，从而解离 CREB-CREB 结合蛋白-CRTC2 复合物并阻断其转录活性。与二甲双胍的作用类似，CRTC2 沉默抑制 IGF-IR 启动子活性。此外，二甲双胍通过抑制 AR 磷酸化及其与 c-Src 的结合，阻断 AR 向哺乳动物雷帕霉素靶蛋白/p70S6 激酶途径的膜起始信号。AMPK 信号也在一定程度上参与其中。通过抑制雄激素依赖性 IGF-IR 上调，二甲双胍减少了 IGF-I 介导的 LNCaP 细胞的增殖。这些结果表明，在前列腺癌细胞中，二甲双胍通过破坏负责 IGF-IR 上调的 AR 膜起始作用，抑制 IGF-I 介导的生物学效应，并表明二甲双胍可能成为经典抗雄激素治疗的有用辅助手段。
