During the estrus cycle and early gestation, estrogen and progestin secretion control rates of DNA synthesis in specific tissues of the mammalian endometrium. 3-Hydroxy-3-methylglutaryl-CoA reductase (HMG-CoA reductase, EC 1.1.1.34) appears to be an essential enzyme in this control as the rate limiting enzyme in the synthesis of mevalonic acid and cholesterol. Estrogen treatment increases HMG-CoA reductase activity in uterine luminal epithelial cells in close synchrony with increases in DNA synthesis. In other tissues, the activity of this enzyme is controlled by both transcriptional and post-transcription mechanisms, and the goal of the proposed research is to identify and elucidate the mechanisms by which estrogen and progestin control levels of HMG-CoA reductase in the uterus. The following specific aims are proposed: (1) To determine the effect of estradiol and progesterone on HMG-CoA reductase mRNA. Northern blot/dot blot analysis and in vitro translation procedures will be used to determine absolute and functional levels of HMG-CoA reductase mRNA. (2) To study the distribution and concentrations of HMG-CoA reductase mRNA in specific endometrial tissues following hormonal treatments. In-situ hybridization procedures will be performed using 3H-antisense RNA or 3H-cDNAs as probes. (3) To determine the effect of estradiol and progesterone on the rate of synthesis of HMG-CoA reductase. Rates of synthesis will be determined by measurement of the incorporation of labeled amino acid into immunoprecipitable enzyme protein. Changes in enzyme activity resulting from phosphorylation and dephosphorylation of the enzyme protein will also be examined. The proposed measurements of changes in the activity of uterine transcriptional and posttranscriptional mechanisms for HMG-CoA reductase and their correlation with HMG-CoA reductase activity and rates of uterine DNA systhesis should improve our understanding of the control of uterine DNA synthesis by estradiol and progesterone. Better understanding of these cellular control mechanisms in the endometrium should contribute to our fundamental knowledge of uterine physiology during the menstrual cycle and earliest pregnancy.
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