Abstract
We have shown that the transient changes in the expression of luteinizing hormone/choriogonadotropin receptor (LHCGR) messenger RNA (mRNA) during the ovarian cycle occurs, at least in part, through a posttranscriptional mechanism involving an LHCGR mRNA-binding protein (LRBP). Eukaryotic initiation factor 5A (eIF5A), an LRBP-interacting protein, participates in this process. eIF5A undergoes hypusination, a unique posttranslational modification that is necessary for its functions. This study examined the role of eIF5A in follicle-stimulating hormone (FSH)-induced LHCGR expression during follicular growth. Treatment of primary cultures of rat granulosa cells with FSH and 17β-estradiol (E2) showed a time-dependent increase in LHCGR mRNA expression. Conversely, inhibition of endogenous hypusination of eIF5A using N1-guanyl-1,7-diaminoheptane (GC7), a hypusination inhibitor, showed a greater increase in LHCGR mRNA expression over that produced by FSH and E2 alone. Further studies were carried out to determine the mechanism by which inhibition of hypusination of eIF5A causes an increase in LHCGR mRNA expression. Because LHCGR expression is negatively regulated by LRBP, the effect of inhibiting hypusination of eIF5A on LRBP expression was examined. The results showed a decrease in the expression of LRBP mRNA and protein when hypusination of eIF5A was inhibited by GC7. Because LRBP promotes LHCGR mRNA degradation, the results of this study support the notion that by inhibiting eIF5A hypusination, FSH reduces the expression of LRBP. This increases LHCGR mRNA expression by abrogating the inhibitory action of LRBP.