The Groucho-related Gene Family Regulates the Gonadotropin-releasing Hormone Gene through Interaction with the Homeodomain Proteins MSX1 and OCT1

Naama Rave-Harel,Nichol L.G Miller,Marjory L Givens,Pamela L Mellon

doi:10.1074/jbc.m502315200

Naama Rave-Harel, Nichol L.G Miller + Show 2 more

Open Access

https://doi.org/10.1074/jbc.m502315200

Copy DOI

Abstract

Gonadotropin-releasing hormone (GnRH) is exclusively expressed in a unique population of hypothalamic neurons that controls reproductive function. GnRH gene expression is highly dynamic. Its transcriptional activity is regulated in a complex spatiotemporal manner during embryonic development and postnatal life. Although a variety of transcription factors have been identified as regulators of GnRH transcription, most are promiscuous in their DNA-binding requirements, and none are solely expressed in GnRH neurons. Their specific activity is probably determined by interactions with distinct cofactors. Here we find that the Groucho-related gene (GRG) family of co-repressors is expressed in a model cell line for the GnRH neuron and co-expresses with GnRH during prenatal development. GRG proteins associate in vivo with the GnRH promoter. Furthermore, GRG proteins interact with two regulators of GnRH transcription, the homeodomain proteins MSX1 and OCT1. Co-transfection experiments indicate that GRG proteins regulate GnRH promoter activity. The long GRG forms enhance MSX1 repression and counteract OCT1 activation of the GnRH gene. In contrast, the short form, GRG5, has a dominant-negative effect on MSX1-dependent repression. Taken together, these data suggest that the dynamic switch between activation and repression of GnRH transcription is mediated by recruitment of the GRG co-regulators.

Highlights

The formation of unique transcription factor complexes determines the intricate spatial and temporal expression of genes during development as well as in terminal differentiation [1]
We show that Grouchorelated gene (GRG) family members physically and functionally interact with the homeodomain proteins MSX1 and OCT1 to regulate Gonadotropin-releasing hormone (GnRH) gene expression
Having identified GRG5 in our yeast two-hybrid screen, we looked for the presence of GRG family members in the GT1-7 cells

Summary

Introduction

The formation of unique transcription factor complexes determines the intricate spatial and temporal expression of genes during development as well as in terminal differentiation [1]. These model cell lines provided the first insight into the transcriptional regulation of GnRH expression Using these models, evolutionarily conserved enhancer and promoter elements conferring neuron-specific activation in culture were identified (Ϫ1863 to Ϫ1571 and Ϫ173 to ϩ1, respectively, in the rat sequence) (6 –9). Such cofactors can enhance or, alternatively, inhibit the interactions between the homeodomain proteins and the transcriptional machinery as well as the chromatin template and alter the function of the transcription factors themselves [23] In line with this concept, the POU domain protein OCT1, an essential activator of GnRH transcription in the GT1-7 cells [20, 24], was shown to function as a downstream regulator in hormone-induced repression of the GnRH gene [25,26,27]. The dynamic exchange between activation and repression, observed with OCT1 and DLX2/MSX1 is probably facilitated by specific coengrailed homology domain; GRG, Groucho-related gene; HSD, honestly significant difference; NLS, nuclear localization signal; Q, glutamine-rich domain; RSV, Rous sarcoma virus; TLE, transducin-like enhancer of split; GST, glutathione S-transferase

Methods

Results

Conclusion