Regulation of cytochrome P450scc synthesis and activity in the ovine corpus luteum.
The rate-limiting step in luteal biosynthesis of progesterone consists of cleavage of the side chain of cholesterol by mitochondrial cytochrome P450 side-chain cleavage enzyme (P450scc) to form pregnenolone. Luteal mRNA encoding P450scc, quantitated on selected days of the 16-day ovine estrous cycle, was similar on days 3 and 6, increased by 2-fold on day 9 (P < 0.05) and remained elevated on day 15. Levels of P450scc mRNA on day 15 of pregnancy were not different from those found on any day of the cycle (P < 0.05). To determine whether levels of mRNA encoding P450scc are hormonally regulated, ewes on day 10 of the estrous cycle were injected with hCG or prostaglandin F2 alpha (PGF2 alpha). P450scc mRNA was not increased for up to 36 h after injection of hCG, nor decreased within 8 h after injection of PGF2 alpha (P < 0.05). An assay for P450scc activity was developed which utilized ovine small and large luteal cells in the presence of 22R-hydroxycholesterol and ovine high density lipoprotein. Enzyme activity was quantitated by measurement of progesterone production. In small luteal cells activation of the protein kinase A (PKA) second-messenger system by treatment with LH resulted in 910% increase in progesterone production without altering activity of P450scc. Activation of the protein kinase C (PKC) second-messenger system with phorbol 12-myristate 13-acetate caused a 51% reduction in progesterone secretion from large luteal cells but did not alter activity of P450scc. These findings suggest that in mature luteal tissue steady state levels of mRNA encoding P450scc, and enzyme activity are independent of acute regulation by activation of PKA or PKC second-messenger systems.
Belfiore
C J
CJ
Department of Physiology, Colorado State University, Fort Collins 80523.
Hawkins
D E
DE
Wiltbank
M C
MC
Niswender
G D
GD
D000818:Animals; D002786:Cholesterol Side-Chain Cleavage Enzyme / Q000096:biosynthesis / Q000378:metabolism*; D006063:Chorionic Gonadotropin / Q000494:pharmacology; D003338:Corpus Luteum / Q000201:enzymology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D015237:Dinoprost / Q000494:pharmacology; D004971:Estrus / Q000378:metabolism*; D005260:Female; D015971:Gene Expression Regulation, Enzymologic; D066298:In Vitro Techniques; D011493:Protein Kinase C / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D012756:Sheep / Q000378:metabolism*
D006063:Chorionic Gonadotropin; D012333:RNA, Messenger; D015237:Dinoprost; D002786:Cholesterol Side-Chain Cleavage Enzyme; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C