Evidence that Human Chorionic Gonadotropin/Luteinizing Hormone Receptor Down-Regulation Involves Decreased Levels of Receptor Messenger Ribonucleic Acid*

Abstract

Injection of pseudopregnant rats with pharmacological doses of hCG leads to a characteristic decrease in LH/hCG binding by the isolated luteal cells. The steady state levels of LH/hCG receptor mRNA were determined in rat ovaries during hCG-induced down-regulation of the receptor. Northern blots were performed using a 20-mer probe corresponding to a guanine cytosine-rich carboxyl-terminal untranslated region of the LH/hCG receptor cDNA. The hybridization of the probe to LH/hCG receptor mRNA was highly specific, since the probe hybridized only to rat luteal cell RNA fraction, with no signal detected in nontarget tissues. The LH/hCG receptor level was quantitated by [125I]hCG binding to the isolated membrane fractions from the corresponding treatment and control groups. Examination of mRNA levels of the receptor during hCG-induced down-regulation showed a steady decrease from 0-24 h, followed by a gradual increase to control levels from 24-72 h corresponding to days 8-9 of pseudopregnancy. The [125I]hCG-binding activity during down-regulation paralleled the mRNA profile in both the experimental and control groups. Examination of the levels of mRNA for alpha-actin showed no change during this period, suggesting that the loss of LH/hCG receptor mRNA at 24 h was not due to a general loss of mRNA in luteal cells. These results suggest that hCG-induced down-regulation of the LH/hCG receptor in luteal cells involves regulation of the receptors at the message level.

Regulation of luteinizing hormone receptor mRNA expression by a specific RNA binding protein in the ovary

“…This was followed by a gradual recovery to control levels by 72 h, as shown in the solution hybridization analysis data presented in Fig 1. The loss of mRNA was rather unexpected, since the decrease of cell surface receptor expression was thought to occur through rapid internalization of the ligand-bound receptor. In the control samples an increase in LHR mRNA expression was seen during the time-course of the experiment, since our previous studies have shown that in pseudopregnant rat ovary the expression of LHR mRNA increased up to day 8 (Hoffman, et al 1991). The in situ hybridization pattern confirmed the Northern blot data and further suggested that the same corpora lutea that were depleted of the receptor mRNA reacquired the receptor (Peegel et al, 1994).…”

“…The in situ hybridization pattern confirmed the Northern blot data and further suggested that the same corpora lutea that were depleted of the receptor mRNA reacquired the receptor (Peegel et al, 1994). The loss of LH receptor mRNA was specific, as other LH/hCG responsive mRNAs such as Cytochrome p450scc remained at a level significantly higher than the saline treated controls (Hoffman, et al 1991). The loss of LH receptor mRNA occured through post-transcriptional mechanisms as the transcription rate, determined by nuclear run on assays, remained identical in hCG treated group compared to the control.…”

“…Previous studies have shown that in the rat, preovulatory LH surge produces a rapid decline in LH receptor expression as well as an uncoupling of LH receptor from the cognate G proteins (Hoffman, et al 1991, Lapolt, et al 1990, Lu, et al 1993. The loss of LH receptor from the cell surface may be explained on the basis of the rapid endocytosis of the LH-receptor complex, causing its depletion.…”

“…Ovaries were collected at different time intervals up to 72 h (Hoffman, et al 1991, Lu, et al 1993, Peegel, et al 1994) and were processed for Northern blot analysis for the expression of LH receptor mRNA, for in situ hybridization analysis in tissue sections to visualize the changes in mRNA expression, and for solution hybridization assay to quantitate changes in mRNA levels. The results showed that within 6 h of hCG injection, there was a steady decline in the expression levels of LH receptor mRNA that reached almost non-detectable levels by 24 h (Hoffman, et al 1991, Lu, et al 1993, Peegel, et al 1994). This was followed by a gradual recovery to control levels by 72 h, as shown in the solution hybridization analysis data presented in Fig 1. The loss of mRNA was rather unexpected, since the decrease of cell surface receptor expression was thought to occur through rapid internalization of the ligand-bound receptor.…”

Isolation and Characterization of a Novel trans-Factor for Luteinizing Hormone Receptor mRNA from Ovary

“…The cell surface expression of LHR varies during different stages of the ovarian cycle. Its expression in granulosa cells and luteal cells is greatly decreased by an endogenous preovulatory LH surge or by the administration of a pharmacological dose of human chorionic gonadotropin (hCG), a placental counterpart of LH (5)(6)(7)(8). We have shown that the decline in cell surface LHR expression seen after hCG administration is paralleled by a specific loss of all four LHR mRNA transcripts (6.7, 4.4, 2.6, and 1.8 kb) in the ovary (9).…”