Abstract
Luteinizing hormone (LH) receptor mRNA is post-transcriptionally regulated. An ovarian cytosolic LH receptor mRNA-binding protein (LRBP) identified in our laboratory binds to a polypyrimidine-rich bipartite sequence in the coding region of LH receptor mRNA. The present studies show a role for LRBP in the regulation of LH receptor mRNA. We demonstrated that increased LH receptor mRNA degradation occurs during hormone-induced LH receptor down-regulation. Furthermore, increased degradation of LH receptor mRNA was seen when partially purified LRBP was included in an in vitro mRNA decay reaction. The LH receptor mRNA binding activity of LRBP measured by RNA electrophoretic mobility shift analysis showed an inverse relationship to LH receptor mRNA levels during different physiological states. These results suggest that LRBP is a physiological regulator of LHR mRNA expression in the ovary and provides a novel mechanism for the regulation of LH receptor expression in the ovary.
Highlights
The expression of luteinizing hormone receptors (LHR)1 on the rat ovarian granulosa cells and luteal cells is decreased by an endogenous preovulatory luteinizing hormone (LH) surge or by the administration of a pharmacological dose of human chorionic gonadotropin, a placental counterpart of Luteinizing hormone (LH) (1– 4)
At the end of this incubation period, total RNA was extracted from each fraction, and LHR mRNA was determined by Northern blot using a LHR cDNA probe
The binding activity of LH receptor mRNA-binding protein (LRBP) started decreasing from day 10 but remained higher than the levels seen on days 6 and 8. These results show that the LHR mRNA binding activity of LRBP is inversely related to LHR mRNA expression
Summary
The expression of luteinizing hormone receptors (LHR) on the rat ovarian granulosa cells and luteal cells is decreased by an endogenous preovulatory luteinizing hormone (LH) surge or by the administration of a pharmacological dose of human chorionic gonadotropin (hCG), a placental counterpart of LH (1– 4). Following the injection of a bolus of hCG in female rat, a rapid decline in the steady-state levels of all four LHR mRNA transcripts (6.7, 4.4, 2.6, and 1.8 kb) is seen in luteal cells within 12 h with a complete loss occurring by 24 h. This selective loss is followed by a recovery of receptor mRNA expression between 24 and 48 h (2). A partially purified LRBP causes accelerated decay of LHR mRNA in an in vitro reconstituted mRNA decay system
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