Nova-1 Mediates Glucocorticoid-induced Inhibition of Pre-mRNA Splicing of Gonadotropin-releasing Hormone Transcripts

Eonyoung Park,Mi Sun Lee,Sun Mi Baik,Eun Bee Cho,Gi Hoon Son,Jae Young Seong,Kun Ho Lee,Kyungjin Kim

doi:10.1074/jbc.m807386200

Abstract

Glucocorticoid (GC) is known to affect the reproductive system by suppressing the gonadotropin-releasing hormone (GnRH) gene expression in the hypothalamus. However, the mechanism of this effect is poorly understood. We show here that the GC-induced reduction of GnRH mRNA is due to attenuation of a post-transcriptional process i.e. splicing of intron A. Treatment of dexamethasone (DEX), a synthetic GC, lowered GnRH mRNA transcripts and was accompanied by reduced excision of the first intron (intron A) from the GnRH pre-mRNA both in vitro and in vivo. While seeking to identify the splicing factors involved in GC-inhibited GnRH pre-mRNA splicing, we found that DEX down-regulated neuro-oncological ventral antigen-1 (Nova-1) mRNA and protein and that knockdown of Nova-1 reduced intron A excision from GnRH pre-mRNA. Nova-1 overexpression reversed the DEX-induced reduction of intron A excision. Nova-1 appears to promote intron A excision by binding to the distal region of exon 1 of the GnRH pre-mRNA. Taken together, our findings indicate that the intron A excision by Nova-1 is a target of GC for down-regulation of GnRH gene expression, and more importantly, we characterized Nova-1, a brain-enriched splicing regulator responsible for GnRH pre-mRNA splicing.

Highlights

GC secretion from the adrenal gland in turn suppresses activity of the hypothalamic-pituitary-gonadal axis [3, 4]
Administration of the synthetic GC homolog, dexamethasone (DEX), decreases gonadotropin-releasing hormone (GnRH) mRNA levels, probably by lowering GnRH promoter activity [8, 9]. This inhibitory effect of GC on GnRH gene expression and secretion may be mediated by the GC receptor (GR), which is expressed in GnRH neurons of the hypothalamus and in GnRH-producing GT1 cells [8]
We determined levels of both mature GnRH mRNA and its intron A-containing variant in GT1-1 cells treated with DEX

Summary

Introduction

GC secretion from the adrenal gland in turn suppresses activity of the hypothalamic-pituitary-gonadal axis [3, 4]. To verify the impaired excision of the intron A by DEX, we used a splicing reporter (named p1A234-GFP) mimicking the intron A-containing GnRH gene transcript under the control of the GC-insensitive cytomegalovirus promoter (Fig. 4A) and a strong SV40 poly(A) signal as previously described [13].

Results

Conclusion