PMON56 LH synthesis is regulated by RNA-binding protein ZFP36 bound with AU-rich elements in gonadotropes

Abstract Gonadotropin secretion, which is stimulated by gonadotropin-releasing hormone (GnRH), is a critical feature of reproductive control and maintenance of fertility. GnRH stimulation increases LH secretion 50-100-fold over baseline per pulse, whereas Lhb gene expression increases a modest 1.4-fold. This observation shows that significant post-transcriptional regulation of gonadotropin synthesis and secretion must occur. We have previously shown that GnRH-induced Dusp1 expression, a factor central for feedback control of GnRH signaling in gonadotropes, depends on interaction of the 3'UTR of its mRNA with the RNA binding protein (RBP) ELAVL1, which binds AU-rich elements (ARE) in target mRNAs (1). Recently, using RIP-Chip analysis, we have shown that GnRH receptor (Gnrhr) expression depends on interaction of its mRNA with ELAVL1. Gnrhr mRNA is among the most highly represented ELAVL1-associated mRNAs (2). Further, many mRNAs encoding proteins essential to gonadotropin gene expression, including the immediate-early transcription factor genes Egr1, 2, and 4, Fos, Fosb, Jun, and Junb, as well as Dusp1 and 2, show increased binding to ELAVL1 after GnRH treatment, although gonadotropin Lhb mRNA is not, due to the absence of ARE site to be bound. Typically, association with ELAVL1 stabilize expression of target mRNAs, promoting their translation. Also, of interest is the role of the RBP ZFP36, which competes with ELAVL1 for binding to ARE's but has the opposing effect of directing mRNA to the degradation pathway. Significantly, 5 minutes pulsatile GnRH stimulated ZFP36 protein production in 30-60 minutes in LbetaT2 cells. And, knockdown of ELAVL1 results in the deterioration of Gnrhr expression and of the immediate-early gene Egr1 a transcription factor central to Lhb expression. We have examined the direct role of ZFP36 protein in GnRH-induced gene expression. Interestingly, Gnrhr and Lhb mRNA expression levels were decreased by ZFP36 overexpression in LbetaT2 cells compared with control cells. Also, GnRH-stimulated EGR1 production by was decreased by ZFP36 overexpression. These observations are consistent with previous results with ELAVL1 knockdown showing decreased mRNA stability. We cloned Egr1, Gnrhr and Zfp36 3'UTRs which contain AREs bound by ELAVL1 into luciferase reporter genes in pmirGLO vector to evaluate whether the 3'UTR is directly affected by ZFP36. These Egr1, Gnrhr and Zfp36 3'UTR contained mirGLOs were transfected in both ZFP36 overexpression and control cells and luciferase activity was monitored. The results showed that luciferase expression from reporters bearing the target 3'UTR were significantly reduced in ZFP36 overexpressed cells. Collectively, our studies show that ELAVL1, ZFP36 and their target mRNAs are regulated by GnRH and this indirectly regulates Lhb gene expression in gonadotropes. ) Do MT, T Kim et al. Mol Cell Endocrinology 382 (1): 1346-1357, 2014 ) Terasaka T et al. Endocrinology 160(8): 1999-2014, 2019 Presentation: Monday, June 13, 2022 12:30 p.m. - 2:30 p.m.