Cochrane Dawn R, Wang Zhou, Muramaki Motosugu, Gleave Martin E, Nelson Colleen C
Department of Genetics, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada.
J Biol Chem. 2007 Jan 26;282(4):2278-87. doi: 10.1074/jbc.M608162200. Epub 2006 Dec 4.
Clusterin mRNA levels were shown to increase dramatically in rat ventral prostate following castration, and clusterin was therefore originally thought to be repressed by androgens. It was later discovered that the increased clusterin levels are most likely due to castration-induced apoptosis of the prostatic epithelium rather than direct action of the androgen receptor (AR). In the studies presented here, LNCaP cells in culture and rat prostate organ culture were treated with androgens. Clusterin mRNA and protein are shown to increase with androgen treatment in a time- and dose-dependent manner. This induction of clusterin requires AR and can be inhibited by casodex, an AR antagonist. We have found that the first intron of the clusterin gene contains putative androgen response elements. The intronic region is shown to be bound by AR in chromatin immunoprecipitation assays and is transactivated by AR in reporter assays. Two isoforms of clusterin result from alternate transcriptional start sites. Both isoforms are cytoprotective; however, Isoform 1 has the capacity to produce a splice variant that is apoptotic. Real time PCR was used to determine the response of the two isoforms to androgens. Intriguingly, these results illustrated that Isoform 2 was up-regulated, whereas Isoform 1 was down-regulated by androgens. Isoform 2 was also increased as the LNCaP xenograft tumor progressed to androgen-independence, whereas Isoform 1 was unaltered. This androgen regulation of clusterin may underline the cytoprotective role of androgens in normal prostate physiology as well as play an antiapoptotic role in prostate cancer progression.
去势后大鼠腹侧前列腺中的簇集素mRNA水平显著升高，因此最初认为簇集素受雄激素抑制。后来发现，簇集素水平升高很可能是由于去势诱导的前列腺上皮细胞凋亡，而非雄激素受体（AR）的直接作用。在本文所展示的研究中，用雄激素处理培养中的LNCaP细胞和大鼠前列腺器官培养物。结果显示，簇集素mRNA和蛋白随着雄激素处理呈时间和剂量依赖性增加。这种簇集素的诱导需要AR，并且可被AR拮抗剂比卡鲁胺抑制。我们发现，簇集素基因的第一个内含子含有假定的雄激素反应元件。在染色质免疫沉淀试验中，该内含子区域显示与AR结合，并且在报告基因试验中被AR反式激活。簇集素的两种异构体由不同的转录起始位点产生。两种异构体均具有细胞保护作用；然而，异构体1有能力产生一种具有凋亡作用的剪接变体。采用实时PCR来确定这两种异构体对雄激素的反应。有趣的是，这些结果表明，雄激素使异构体2上调，而异构体1下调。随着LNCaP异种移植瘤进展为雄激素非依赖性，异构体2也增加，而异构体1未改变。簇集素的这种雄激素调节可能突显了雄激素在正常前列腺生理学中的细胞保护作用，以及在前列腺癌进展中发挥的抗凋亡作用。
