Organ-specific inhibition of types I, II and III transcriptional activity in hamsters exposed to stilbene estrogen.

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.