Karmakar Sudipan, Foster Estrella A, Smith Carolyn L
Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas 77030, USA.
Endocrinology. 2009 Apr;150(4):1588-96. doi: 10.1210/en.2008-1001. Epub 2008 Dec 18.
Each of the three members of the p160 steroid receptor coactivator (SRC) family of coactivators (SRC-1, SRC-2 and SRC-3) stimulates estrogen receptor (ER)-alpha function in trans-activation assays. Consequently, we sought to elucidate their contributions to the ER-regulated processes of cell proliferation, apoptosis, and the expression of ERalpha target genes in MCF-7 breast cancer cells. The small interfering RNA depletion of SRC-2 or SRC-3 but not SRC-1 inhibited growth of MCF-7 cells, and this was reflected in decreased cell cycle progression and increased apoptosis in SRC-2- or SRC-3-depleted cells as well as a reduction in ERalpha transcriptional activity measured on a synthetic reporter gene. However, only SRC-3 depletion blocked estradiol stimulated cell proliferation. Depletion of SRC-1 did not affect these events, and together this reveals functional differences between each of the three SRC family coactivators. Regulation of the endogenous ERalpha target gene, c-myc was not affected by depletion of any of the p160 coactivators although depletion of each of them decreased pS2 mRNA expression in estradiol-treated MCF-7 cells. Moreover, progesterone receptor and cyclin D1 gene expression were decreased in SRC-3 small interfering RNA-treated cells. Expression of mRNA and protein levels for the antiapoptotic gene, Bcl-2 was dependent on SRC-3 expression, whereas Bcl-2 protein but not mRNA expression also was sensitive to SRC-1 depletion. Together these data indicate that the closely related p160 coactivators are not functionally redundant in breast cancer cells because they play gene-specific roles in regulating mRNA and protein expression, and they therefore are likely to make unique contributions to breast tumorigenesis.
p160类固醇受体辅激活因子（SRC）家族的三个成员（SRC-1、SRC-2和SRC-3）中的每一个在反式激活试验中都能刺激雌激素受体（ER）α的功能。因此，我们试图阐明它们对MCF-7乳腺癌细胞中ER调节的细胞增殖、凋亡以及ERα靶基因表达过程的作用。SRC-2或SRC-3而非SRC-1的小干扰RNA缺失抑制了MCF-7细胞的生长，这反映在SRC-2或SRC-3缺失的细胞中细胞周期进程减慢、凋亡增加，以及在合成报告基因上测得的ERα转录活性降低。然而，只有SRC-3的缺失阻断了雌二醇刺激的细胞增殖。SRC-1的缺失不影响这些事件，这共同揭示了三种SRC家族辅激活因子之间的功能差异。内源性ERα靶基因c-myc的调节不受任何p160辅激活因子缺失的影响，尽管它们各自的缺失都会降低雌二醇处理的MCF-7细胞中pS2 mRNA的表达。此外，SRC-3小干扰RNA处理的细胞中孕激素受体和细胞周期蛋白D1基因的表达降低。抗凋亡基因Bcl-2的mRNA和蛋白水平的表达依赖于SRC-3的表达，而Bcl-2蛋白而非mRNA的表达也对SRC-1的缺失敏感。这些数据共同表明，密切相关的p160辅激活因子在乳腺癌细胞中并非功能冗余，因为它们在调节mRNA和蛋白表达中发挥基因特异性作用，因此可能对乳腺肿瘤发生做出独特贡献。
