Prostaglandin F2 alpha mediates ovarian sterol carrier protein-2 expression during luteolysis.
In the corpus luteum, prostaglandin F2 alpha (PGF2 alpha) appears to be a physiological agent with both antisteroidogenic and luteolytic actions. It is hypothesized that the antisteroidogenic action of PGF2 alpha acts through altered transport of cholesterol to the mitochondrial cytochrome P450 side-chain cleavage enzyme (P450scc). However, the effect of PGF2 alpha on the expression of the putative cholesterol transport protein, sterol carrier protein-2 (SCP2; 13.2 kilodaltons), has not been examined. In this study, the decline in serum progesterone after PGF2 alpha injection was examined in parallel with altered ovarian SCP2, P450scc, and 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) protein and messenger RNA (mRNA) levels. Rats (28 days old) were treated with 8 IU PMSG to induce follicular development and ovulation. Ten days after ovulation, animals were treated with PGF2 alpha (single or multiple injections; 100-250 micrograms each) or left untreated. Ovarian SCP2, P450scc, and 3 beta HSD protein and mRNA levels were examined 0 (time zero), 4, and 8 h post-PGF2 alpha treatment using Western and Northern blot analysis. SCP2 mRNA levels were also examined using a highly sensitive ribonuclease protection assay that detects a 429-base pair SCP2-mRNA specific sequence. The results indicate that serum progesterone was significantly reduced 4 and 8 h after PGF2 alpha injections (P < 0.001; n = 6/time point). The decline in progesterone paralleled a 50-60% reduction in 3 beta HSD protein and mRNA levels by 4 h post-PGF2 alpha. Protein and mRNA levels for 3 beta HSD returned to control values by 8 h post-PGF2 alpha treatment. P450scc expression was also reduced at 4 h (44-54%), but by 8 h, both protein and mRNA levels had increased above the normal control levels (P < 0.02). In contrast, the 0.8-kilobase SCP2-specific mRNA transcript was reduced to 50% and 80% of the pre-PGF2 alpha treatment level at 4 and 8 h, respectively (P < 0.01). SCP2 ribonuclease protection assay analysis also indicated that SCP2 mRNA levels were reduced 65% (P < 0.03) and 85% (P < 0.01) by 4 and 8 h post-PGF2 alpha treatment compared to those in time zero ovarian tissue. Consistent with the loss of SCP2 mRNA expression, Western blot analysis indicated that a 15-kilodalton SCP2-immunoreactive protein (presumably the pro-SCP2 form) was significantly reduced or absent in the PGF2 alpha treated animals (P < 0.04).(ABSTRACT TRUNCATED AT 400 WORDS)
McLean
M P
MP
Department of Obstetrics and Gynecology, University of South Florida College of Medicine, Tampa 33606, USA.
Billheimer
J T
JT
Warden
K J
KJ
Irby
R B
RB
D015096:3-Hydroxysteroid Dehydrogenases / Q000235:genetics; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D015153:Blotting, Western; D002352:Carrier Proteins / Q000235:genetics*; D002786:Cholesterol Side-Chain Cleavage Enzyme / Q000235:genetics; D015237:Dinoprost / Q000494:pharmacology*; D005260:Female; D015870:Gene Expression / Q000187:drug effects*; D008969:Molecular Sequence Data; D010053:Ovary / Q000378:metabolism*; D010940:Plant Proteins; D011374:Progesterone / Q000097:blood; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
D002352:Carrier Proteins; D010940:Plant Proteins; D012333:RNA, Messenger; C072087:sterol carrier proteins; D011374:Progesterone; D015237:Dinoprost; D015096:3-Hydroxysteroid Dehydrogenases; D002786:Cholesterol Side-Chain Cleavage Enzyme