Liu Guilai, Honisch Sabina, Liu Guoxing, Schmidt Sebastian, Pantelakos Stavros, Alkahtani Saad, Toulany Mahmoud, Lang Florian, Stournaras Christos
a Department of Physiology ; University of Tübingen ; Tübingen , Germany.
Cancer Biol Ther. 2015;16(1):52-9. doi: 10.4161/15384047.2014.986982.
Functional membrane androgen receptors (mAR) have previously been described in MCF-7 breast cancer cells. Their stimulation by specific testosterone albumin conjugates (TAC) activate rapidly non-genomic FAK/PI3K/Rac1/Cdc42 signaling, trigger actin reorganization and inhibit cell motility. PI3K stimulates serum and glucocorticoid inducible kinase SGK1, which in turn regulates the function of mAR. In the present study we addressed the role of SGK1 in mAR-induced apoptosis. TAC-stimulated mAR activation elicited apoptosis of MCF-7 cells, an effect significantly potentiated by concomitant incubation of the cells with TAC and the specific SGK1 inhibitors EMD638683 and GSK650394. In line with this, TAC and EMD638683 activated caspase-3. These effects were insensitive to the classical androgen receptor (iAR) antagonist flutamide, pointing to iAR-independent, mAR-induced responses. mAR activation and SGK1 inhibition further considerably augmented the radiation-induced apoptosis of MCF-7 cells. Moreover, TAC- and EMD638683 triggered early actin polymerization in MCF-7 cells. Blocking actin restructuring with cytochalasin B abrogated the TAC- and EMD638683-induced pro-apoptotic responses. Further analysis of the molecular signaling revealed late de-phosphorylation of FAK and Akt. Our results demonstrate that mAR activation triggers pro-apoptotic responses in breast tumor cells, an effect significantly enhanced by SGK1 inhibition, involving actin reorganization and paralleled by down-regulation of FAK/Akt signaling.
功能性膜雄激素受体（mAR）此前已在MCF-7乳腺癌细胞中被描述。特定睾酮白蛋白结合物（TAC）对其刺激可迅速激活非基因组FAK/PI3K/Rac1/Cdc42信号通路，引发肌动蛋白重组并抑制细胞迁移。PI3K刺激血清和糖皮质激素诱导激酶SGK1，而SGK1又反过来调节mAR的功能。在本研究中，我们探讨了SGK1在mAR诱导的细胞凋亡中的作用。TAC刺激的mAR激活引发了MCF-7细胞的凋亡，当细胞同时与TAC以及特异性SGK1抑制剂EMD638683和GSK650394孵育时，这种效应显著增强。与此一致的是，TAC和EMD638683激活了caspase-3。这些效应对经典雄激素受体（iAR）拮抗剂氟他胺不敏感，表明是不依赖iAR的、mAR诱导的反应。mAR激活和SGK1抑制进一步显著增强了MCF-7细胞的辐射诱导凋亡。此外，TAC和EMD638683在MCF-7细胞中触发了早期肌动蛋白聚合。用细胞松弛素B阻断肌动蛋白重组消除了TAC和EMD638683诱导的促凋亡反应。对分子信号的进一步分析揭示了FAK和Akt的晚期去磷酸化。我们的结果表明，mAR激活在乳腺肿瘤细胞中触发促凋亡反应，SGK1抑制可显著增强这种效应，涉及肌动蛋白重组，并伴随着FAK/Akt信号通路的下调。
