Palangat M, Roy D
Department of Environmental Health Sciences, University of Alabama, Birmingham 35294, USA.
Carcinogenesis. 1995 May;16(5):1017-21. doi: 10.1093/carcin/16.5.1017.
We have previously shown that stilbene estrogen (diethyl-stilbestrol, DES) covalently binds to nonhistone nuclear proteins both in vivo and in vitro. In this study, we demonstrate the differential effects of DES exposure on in organelle transcriptional activity in nuclei isolated from kidney (target organ of cancer) and liver (non target organ) of hamsters. Kidney RNA polymerase (RNA pol) I and III activities were significantly inhibited by 50% at days 8 and 15 of DES exposure compared to that of controls. Liver RNA pol I and III activities were only modestly inhibited (17 and 22%, respectively) by 2 and 8 days of DES exposure, respectively. However, longer exposure of DES to animals did not produce any significant effects on RNA pol I activity. The activity of RNA pol II was affected by DES exposure in both liver and kidney. DES treatment for two days resulted in an increase in RNA pol II activity in kidney. The enhanced enzyme activity was decreased to 50% of that of the control at 15 days of DES treatment. Unlike RNA pol I and III, RNA pol II activity in the liver was inhibited in a time-dependent fashion in response to DES exposure. To understand the mechanism of transcriptional inhibition by DES, we analyzed the effect of DES exposure on the expression of hepatic RNA pol II at both mRNA and protein levels and also phosphorylation of hepatic RNA pol II. The total amount of transcripts or protein contents of hepatic RNA pol II was not altered in response to DES exposure to hamster for 15 days. Total phosphorylation of hepatic RNA pol II was also not affected by 15 days DES exposure. However tyrosine phosphorylation of hepatic RNA pol II was lowered by 2.8-fold compared to that of control enzyme in response to DES exposure for 15 days. An inhibitory effect of DES on the total RNA polymerase activity in both kidney and liver nuclei in the presence of endogenous template was observed in vitro. No inhibitory effect of DES was observed in vitro on transcriptional activity in the presence of exogenously added DNA template. Based on these data it appears that the in vivo inhibition of transcription by DES may be due to alterations in chromatin template or the level of transcription regulating proteins and not due to decreased availability of the chromatin template and/or RNA polymerase. Whether DES related inhibition of transcriptional activity plays a role in the development of kidney cancer is not clear.
我们之前已经表明，芪类雌激素（己烯雌酚，DES）在体内和体外均能与非组蛋白核蛋白共价结合。在本研究中，我们证明了DES暴露对从仓鼠肾脏（癌症靶器官）和肝脏（非靶器官）分离的细胞核中的细胞器转录活性具有不同影响。与对照组相比，在DES暴露的第8天和第15天，肾脏RNA聚合酶（RNA pol）I和III的活性显著抑制了50%。肝脏RNA pol I和III的活性在DES分别暴露2天和8天时仅受到适度抑制（分别为17%和22%）。然而，DES对动物的长期暴露并未对RNA pol I活性产生任何显著影响。RNA pol II的活性在肝脏和肾脏中均受到DES暴露的影响。DES处理两天导致肾脏中RNA pol II活性增加。在DES处理15天时，增强的酶活性降至对照的50%。与RNA pol I和III不同，肝脏中RNA pol II的活性在DES暴露后呈时间依赖性抑制。为了理解DES转录抑制的机制，我们分析了DES暴露对肝脏RNA pol II在mRNA和蛋白质水平的表达以及肝脏RNA pol II磷酸化的影响。在仓鼠暴露于DES 15天的情况下，肝脏RNA pol II的转录本总量或蛋白质含量未发生改变。肝脏RNA pol II的总磷酸化也不受15天DES暴露的影响。然而，在DES暴露15天的情况下，肝脏RNA pol II的酪氨酸磷酸化与对照酶相比降低了2.8倍。在体外观察到，在存在内源性模板的情况下，DES对肾脏和肝脏细胞核中的总RNA聚合酶活性具有抑制作用。在存在外源添加的DNA模板的情况下，未观察到DES对转录活性的体外抑制作用。基于这些数据，似乎DES在体内对转录的抑制可能是由于染色质模板或转录调节蛋白水平的改变，而不是由于染色质模板和/或RNA聚合酶的可用性降低。DES相关的转录活性抑制是否在肾癌的发生中起作用尚不清楚。
