Cholesterol Metabolism in Human Cancer Cells in Monolayer Culture. V. The Effect of Progesterone on the Regulation of 3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase Activity by Low Density Lipoprotein*

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Abstract
The effect of progesterone on the regulation of 3- hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase activity by low density lipoprotein (LDL) was studied in eight gynecological cancer cell lines maintained in monolayer culture. In the absence of LDL and progesterone, the specific activity of HMG CoA reductase varied widely from one cell line to another (range, 200–2500 pmol mg microsomal protein−1 min−1). As in noncancerous cells, LDL suppressed the activity of HMG CoA reductase in all cell lines. Progesterone (40 JUM) attenuated or abolished the decrease in specific enzyme activity normally brought about by LDL. Progesterone, in the absence of LDL, stimulated HMG CoA reductase activity in some of these cell lines. Other steroids (cortisol and estradiol) had no effect on the specific activity of HMG CoA reductase. The mechanism by which progesterone stimulates HMG CoA reductase activity is not clear, but since progesterone receptors were not detectable in these cells a mechanism independent of the classic hormone receptor-mediated phenomenon is likely to be involved.

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