Vitamin A, retinol, is an essential nutrient that serves as precursor to the important hormone, retinoic acid (RA). Relatively little is known of the control of synthesis of RA from retinol in the normal, fully-developed animal and sites of action of RA are inferred, rather than demonstrated. Previous work has identified estrogen as a physiological signal which induces the synthesis of RA in the rat uterus and that coordinately directs cell-specific expression of the three cellular retinoid-binding proteins present in the uterus during the estrous cycle. Proposed studies will: l) Identify uterine genes that are under estrogen control indirectly, via RA stimulation. The techniques of differential display or subtractive hybridization followed by library screening or will be used to identify these genes. Candidate genes will be followed during the estrous cycle to confirm their physiological significance. 2) Demonstrate the site(s) of expression of the estrogen-stimulated RA responsive genes by in situ hybridization and immunolocalization during the estrous cycle. Demonstration of expression/non-expression of candidate genes in cells expressing cellular retinoic acid-binding protein will test the competing hypotheses that this protein either blocks or enhances the RA responsiveness of cells. 3) Establish the mechanism by which estrogen directly regulates cellular retinoic-acid binding protein (II) expression in the uterus. The promoter region of the rat gene will be cloned, dissected and tested using CAT reporter constructs in an estrogen responsive cell line. 4) Demonstrate the mechanism by which estrogen induces RA synthesis in the uterus. Specifically, is this induction a direct effect of estrogen on pre-existing enzymes, does it require transcription, or is it indirect? A novel radioreceptor assay capable of detecting small amounts of RA has been developed for this aim. In summary, the work to be accomplished here will allow dissection of the effects of the demonstrated estrogen-stimulated synthesis of RA signal that is part of a normal physiological process. This will provide important information on retinoic acid action in the unmanipulated, intact animal. Regulation of retinoic acid production by estrogen has direct importance for understanding/treating conditions such as endometriosis, breast cancer, and cancers of the female reproductive system.
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