Luteinizing Hormone Receptor mRNA Down-Regulation Is Mediated through ERK-Dependent Induction of RNA Binding Protein

Abstract

The ligand-induced down-regulation of LH receptor (LHR) expression in the ovaries, at least in part, is regulated by a posttranscriptional process mediated by a specific LH receptor mRNA binding protein (LRBP). The LH-mediated signaling pathways involved in this process were examined in primary cultures of human granulosa cells. Treatment with 10 IU human chorionic gonadotropin (hCG) for 12 h resulted in the down-regulation of LHR mRNA expression while producing an increase in LHR mRNA binding to LRBP as well as a 2-fold increase in LRBP levels. The activation of ERK1/2 pathway in LH-mediated LHR mRNA down-regulation was also established by demonstrating the translocation of ERK1/2 from the cytosol to the nucleus using confocal microcopy. Inhibition of protein kinase A using H-89 or ERK1/2 by U0126 abolished the LH-induced LHR mRNA down-regulation. These treatments also abrogated both the increases in LRBP levels as well as the LHR mRNA binding activity. The abolishment of the hCG-induced increase in LRBP levels and LHR mRNA binding activity was further confirmed by transfecting granulosa cells with ERK1/2 specific small interfering RNA. This treatment also reversed the hCG-induced down-regulation of LHR mRNA. These data show that LH-regulated ERK1/2 signaling is required for the LRBP-mediated down-regulation of LHR mRNA.

Hypusination of eukaryotic initiation factor 5A via cAMP-PKA-ERK1/2 pathway is required for ligand-induced downregulation of LH receptor mRNA expression in the ovary

“…Our previous studies have established that LRBP is a key component of the post-transcriptional mechanism of LH receptor expression by causing accelerated degradation of LHR mRNA during LHR downregulation [21,22]. The present findings extend this by demonstrating that inhibition of eIF5A hypusination by GC7 reduces the binding of LHR mRNA to LRBP as presented in Fig.…”

“…We have previously shown that LH/hCG-activated cAMP/PKA/ERK1/2 signaling plays an important role in LHR downregulation by increasing LRBP expression [21]. The present study extends this further showing that this pathway is also instrumental in increasing the hypusination of eIF5A.…”

“…Specifically, we examined the role of cAMP/PKA/ERK1/2 signaling pathway, since our previous studies have shown that hCG-induced downregulation of LHR mRNA expression is mediated by this pathway [21]. To examine this, superovulated rats were treated with PKA inhibitor (H-89; 100 mg/kg body weight), ERK1/2 inhibitor (U0126; 10 mg/kg body weight) 1 hour before hCG treatment or eIF5A hypusination inhibitor (GC7; 16 mg/kg body weight) 2 hour before hCG treatment.…”

Role of microRNA-136-3p on the Expression of Luteinizing Hormone-Human Chorionic Gonadotropin Receptor mRNA in Rat Ovaries1

“…Notably, Nair and Menon [11] and Wang and Menon [12] found that Mvk binds to LHR mRNA, resulting in a reduction of LHR mRNA levels by increasing the instability of the transcript [11,12]. They also clarified the fact that the protein kinase A (PKA)-dependent extracellular signal-related kinase (ERK) signaling pathway, activated by LHR stimulation, controls Mvk protein levels, thereby down-regulating LHR mRNA [34]. However, the molecular processes responsible for the down-regulation of LHR mRNA have not yet been defined in detail.…”

Molecular regulation of LHCGR expression by miR-122 during follicle growth in the rat ovary

“…The fold change in gene expression was calculated using the ΔΔCt method with 18S rRNA as the internal control, as described previously [14]. …”