Culig Z, Hobisch A, Cronauer M V, Radmayr C, Trapman J, Hittmair A, Bartsch G, Klocker H
Department of Urology, University of Innsbruck, Austria.
Cancer Res. 1994 Oct 15;54(20):5474-8.
Aberrant activation of the androgen receptor (AR) may be one of the mechanisms which contribute to progression of prostatic carcinoma to an androgen-independent stage. We investigated effects of growth factors on stimulation of the AR-mediated gene transcription in human prostatic tumor cell lines. DU-145 cells, which do not contain endogenous AR, were cotransfected with an androgen-inducible chloramphenicol acetyltransferase (CAT) reporter gene and an AR expression vector. The reporter gene (CAT) was driven either by artificial promoters consisting of one or two androgen-responsive elements in front of a TATA box or by the promoter of the prostate-specific antigen (PSA) gene, a naturally occurring androgen-inducible promoter. Insulin-like growth factor-I (IGF-I), at a concentration of 50 ng/ml, stimulated AR-mediated reporter gene transcription to the same extent as the synthetic androgen methyltrienolone. This growth factor was effective irrespective of the nature of the androgen-inducible promoter. Keratinocyte growth factor (KGF) and epidermal growth factor (EGF), at concentrations of 50 ng/ml, activated CAT reporter gene transcription only in experiments in which the artificial promoter with two androgen-responsive elements was used. Insulin-like growth factor-II and basic fibroblast growth factor displayed no effect on AR-mediated gene transcription. None of the growth factors stimulated reporter gene activity in control experiments when added to cells cotransfected with the CAT gene and an empty expression vector. AR activation by IGF-I, KGF, and EGF was completely inhibited by the pure AR antagonist casodex, showing that these effects are AR mediated. Activation of endogenous AR by growth factors was studied in the LNCaP cell line by determination of PSA secretion. IGF-I, at a concentration of 50 ng/ml, increased the PSA level in the supernatant of this cell line 5-fold. Again, the IGF-I effect on PSA secretion was blocked by casodex. Our results provide evidence that IGF-I, KGF, and EGF directly activate the AR in the absence of androgens, which means that the androgen-signaling chain may be activated by growth factors in an androgen-depleted environment. These findings may have implications for endocrine therapy for metastatic prostatic carcinoma.
雄激素受体（AR）的异常激活可能是促使前列腺癌发展至雄激素非依赖阶段的机制之一。我们研究了生长因子对人前列腺肿瘤细胞系中AR介导的基因转录的刺激作用。DU-145细胞不含有内源性AR，将其与雄激素诱导型氯霉素乙酰转移酶（CAT）报告基因和AR表达载体共转染。报告基因（CAT）由位于TATA框前包含一个或两个雄激素反应元件的人工启动子驱动，或者由前列腺特异性抗原（PSA）基因的启动子驱动，后者是一种天然存在的雄激素诱导型启动子。浓度为50 ng/ml的胰岛素样生长因子-I（IGF-I）刺激AR介导的报告基因转录的程度与合成雄激素甲基三烯醇酮相同。无论雄激素诱导型启动子的性质如何，这种生长因子均有效。浓度为50 ng/ml的角质形成细胞生长因子（KGF）和表皮生长因子（EGF）仅在使用带有两个雄激素反应元件的人工启动子的实验中激活CAT报告基因转录。胰岛素样生长因子-II和碱性成纤维细胞生长因子对AR介导的基因转录无影响。当添加到与CAT基因和空表达载体共转染的细胞中时，在对照实验中这些生长因子均未刺激报告基因活性。IGF-I、KGF和EGF对AR的激活被纯AR拮抗剂卡索地司完全抑制，表明这些作用是由AR介导的。通过测定PSA分泌，在LNCaP细胞系中研究了生长因子对内源性AR的激活作用。浓度为50 ng/ml的IGF-I使该细胞系上清液中的PSA水平升高了5倍。同样，卡索地司阻断了IGF-I对PSA分泌的作用。我们的结果提供了证据表明，在没有雄激素的情况下，IGF-I、KGF和EGF直接激活AR，这意味着在雄激素缺乏的环境中，生长因子可能激活雄激素信号传导链。这些发现可能对转移性前列腺癌的内分泌治疗具有重要意义。
