Submitted on September 18, 2007
Accepted on February 1, 2008
Intracellular angiotensin II induces in vitro transcription of TGF-
1, MCP-1 and NHE3 mRNAs in rat renal cortical nuclei via activation of nuclear AT1 receptors
Xiao C Li1 and Jia L Zhuo2*
1 Division of Hypertension and Vascular Research, Henry Ford Hospital, Detroit, Michigan, United States
2 Division of Hypertension and Vascular Research, Henry Ford Hospital, Detroit, Michigan, United States; Department of Physiology, Wayne State University School of Medicine, 5374 Scott Hall, Detroit, Michigan, 48202, United States
* To whom correspondence should be addressed. E-mail: jzhuo1{at}hfhs.org.
The present study tested the hypothesis that intracellular angiotensin II (Ang II) directly induces transcriptional effects by stimulating AT1 receptors in the nucleus of rat renal cortex. Nuclei were freshly isolated and transcriptional responses to Ang II were studied using in vitro transcription assays and RT-PCR. High power phase contrast micrographs showed an intact envelop encircling the nuclei, which were strongly stained by the DNA marker DAPI but not by the membrane or endosomal markers. [125I]-Val5-Ang II receptor binding confirmed a predominance of AT1 receptors, whereas RT-PCR showed that AT1a mRNA expression was 3-fold greater than AT1b receptor mRNAs in the nuclei. Ang II increased nuclear [
-32P]CTP incorporation in a concentration-related manner and the effects were confirmed by autoradiography and electrophoresis. Ang II markedly increased in vitro transcription of mRNAs for TGF-
1 by 143% (p<0.01), MCP-1 by 89% (p<0.01), and NHE-3 by 110% (p<0.01). These nuclear effects of Ang II were completely blocked by the AT1 receptor antagonist losartan (p<0.01). By contrast, Ang II had no effects on angiotensinogen and GAPDH mRNA expression. Since these transcriptional effects of Ang II in the nuclei were induced by Ang II in the absence of membrane receptor-mediated signaling and completely blocked by losartan, we concluded that Ang II may directly stimulate nuclear AT1a receptors to induce transcriptional responses that are associated with epithelial sodium transport, cellular growth, and proinflammatory cytokines.
