Angiotensin II (Ang II) has multiple sites of action and induces diverse types of tissue responses. Although the action of Ang II is believed to be mediated by transmembrane signal transduction mechanisms, accumulating evidence suggests that Ang II may also have a direct nuclear effect. This nuclear action may account, at least in part, for some of the delayed, long term effects of Ang II. The overall goal of this proposal is to study the mechanism of the nuclear effects at the molecular level. We have characterized nuclear Ang II binding sites in the rat liver. In the absence of detergent, Ang II binding sites appear to be a soluble protein that can be released from nuclei by freezing and thawing and which is distinct in physicochemical properties to the membrane bound receptor. Preincubating cAMP activated nuclear extract with Ang II resulted in generation of specific retarded bands after interacting with the regulatory region of renin gene, as revealed by gel retardation assay. The nuclear Ang II effects may be the result of binding of the hormone-receptor complex to a specific DNA sequence, leading to changes in expression of target genes, like that of thyroid and steroid hormones. We will study the regulation of expression of this nuclear receptor. Perturbations which are known to regulate plasma Ang II receptors will be employed to determine if plasma and nuclear receptors are regulated in parallel. The sequence necessary to confer angiotensin responsiveness to a gene will be determined using molecular biological techniques. We will also study the origin of intracellular Ang II which binds to the nuclear receptor. The results of these studies should greatly increase our understanding on the mechanism of action of this important peptide.
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