Department of Pharmacy, Health and Nutritional Sciences, University of Calabria, CS, 87036, Arcavacata di Rende, Italy.
BMC Cancer. 2019 Nov 4;19(1):1038. doi: 10.1186/s12885-019-6262-4.
Androgens, through their own receptor, play a protective role on breast tumor development and progression and counterbalance estrogen-dependent growth stimuli which are intimately linked to breast carcinogenesis.
Cell counting by trypan blu exclusion was used to study androgen effect on estrogen-dependent breast tumor growth. Quantitative Real Time RT-PCR, western blotting, transient transfection, protein immunoprecipitation and chromatin immunoprecipitation assays were carried out to investigate how androgen treatment and/or androgen receptor overexpression influences the functional interaction between the steroid receptor coactivator AIB1 and the estrogen- or androgen receptor which, in turn affects the estrogen-induced cyclin D1 gene expression in MCF-7 breast cancer cells. Data were analyzed by ANOVA.
Here we demonstrated, in estrogen receptor α (ERα)-positive breast cancer cells, an androgen-dependent mechanism through which ligand-activated androgen receptor (AR) decreases estradiol-induced cyclin D1 protein, mRNA and gene promoter activity. These effects involve the competition between AR and ERα for the interaction with the steroid receptor coactivator AIB1, a limiting factor in the functional coupling of the ERα with the cyclin D1 promoter. Indeed, AIB1 overexpression is able to reverse the down-regulatory effects exerted by AR on ERα-mediated induction of cyclin D1 promoter activity. Co-immunoprecipitation studies indicated that the preferential interaction of AIB1 with ERα or AR depends on the intracellular expression levels of the two steroid receptors. In addition, ChIP analysis evidenced that androgen administration decreased E-induced recruitment of AIB1 on the AP-1 site containing region of the cyclin D1 gene promoter.
Taken together all these data support the hypothesis that AIB1 sequestration by AR may be an effective mechanism to explain the reduction of estrogen-induced cyclin D1 gene activity. In estrogen-dependent breast cancer cell proliferation, these findings reinforce the possibility that targeting AR signalling may potentiate the effectiveness of anti-estrogen adjuvant therapies.
雄激素通过其自身受体在乳腺癌的发生和发展中发挥保护作用，并拮抗与乳腺癌发生密切相关的雌激素依赖性生长刺激。
采用台盼蓝排斥法检测细胞计数，研究雄激素对雌激素依赖性乳腺癌生长的影响。采用实时定量 RT-PCR、Western blot、瞬时转染、蛋白免疫沉淀和染色质免疫沉淀检测，研究雄激素处理和/或雄激素受体过表达如何影响甾体受体共激活因子 AIB1 与雌激素或雄激素受体之间的功能相互作用，进而影响 MCF-7 乳腺癌细胞中雌激素诱导的 cyclin D1 基因表达。数据采用方差分析进行分析。
本研究在雌激素受体α（ERα）阳性乳腺癌细胞中证实了一种雄激素依赖性机制，即配体激活的雄激素受体（AR）降低了雌二醇诱导的 cyclin D1 蛋白、mRNA 和基因启动子活性。这些效应涉及 AR 和 ERα 与甾体受体共激活因子 AIB1 的相互作用竞争，AIB1 是 ERα 与 cyclin D1 启动子功能偶联的限制因素。事实上，AIB1 的过表达能够逆转 AR 对 ERα 介导的 cyclin D1 启动子活性诱导的下调作用。共免疫沉淀研究表明，AIB1 与 ERα 或 AR 的优先相互作用取决于两种甾体受体的细胞内表达水平。此外，ChIP 分析表明，雄激素给药降低了 E 诱导的 AIB1 对 cyclin D1 基因启动子中含有 AP-1 位点的募集。
综上所述，所有这些数据支持这样一种假设，即 AR 对 AIB1 的隔离可能是解释雌激素诱导的 cyclin D1 基因活性降低的有效机制。在雌激素依赖性乳腺癌细胞增殖中，这些发现增强了靶向 AR 信号的可能性，可能增强抗雌激素辅助治疗的有效性。
