Expression of the steroidogenic acute regulatory protein in the corpus luteum of the rabbit: dependence upon the luteotropic hormone, estradiol-17 beta.
The recent characterization of the mitochondrial protein, Steroidogenic Acute Regulatory (StAR) protein, as a rate-limiting protein in steroidogenesis prompted us to investigate whether StAR is expressed in the rabbit corpus luteum and whether the expression of StAR is responsive to estradiol-17 beta, the luteotropic hormone in the rabbit. In rabbits treated continuously with exogenous estradiol through Day 13 of pseudopregnancy (n = 9), immunoblot analysis revealed that luteal expression of StAR was stable, ranging from 8.5 to 9.7 U of corrected integrated optical density. Plasma progesterone concentration (mean +/- SEM) remained elevated in these rabbits (14.3 +/- 2.1 ng/ml). In contrast, expression of StAR decreased in corpora lutea of rabbits deprived of estradiol for the last 48 and 72 h of the experiment (4.9 +/- 2.2 and 0.3 +/- 0.2 U, respectively, n = 3 per group), and was associated with a decline in plasma progesterone (0.8 +/- 0.1 and 0.5 +/- 0.3 ng/ml, respectively). Replacement of estradiol after 48 h of estradiol deprivation (n = 3) stimulated the reappearance of StAR (10.3 +/- 2.6 U) and the restoration of plasma progesterone (10.4 +/- 4.9 ng/ml). [35S]Methionine labeling of proteins in rabbit corpora lutea revealed that several isoforms of StAR protein were specifically synthesized in response to estradiol treatment. Collectively, these observations are consistent with a proposed role for StAR in the mediation of the luteotropic effect of estrogen to promote the synthesis of progesterone in the rabbit.
Townson
D H
DH
Department of Physiology, University of Michigan Medical School, Ann Arbor 48109-0622, USA. townson@umich.edu
Wang
X J
XJ
Keyes
P L
PL
Kostyo
J L
JL
Stocco
D M
DM
D000818:Animals; D003338:Corpus Luteum / Q000187:drug effects / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D007106:Immune Sera / Q000276:immunology; D008928:Mitochondria / Q000737:chemistry / Q000276:immunology; D010750:Phosphoproteins / Q000097:blood / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D011233:Precipitin Tests; D011374:Progesterone / Q000097:blood / Q000378:metabolism; D011555:Pseudopregnancy / Q000378:metabolism; D011817:Rabbits; D013997:Time Factors; D000098682:Steroidogenic Acute Regulatory Protein
D007106:Immune Sera; D010750:Phosphoproteins; D000098682:Steroidogenic Acute Regulatory Protein; D011374:Progesterone; D004958:Estradiol