p300 Regulates the Synergy of Steroidogenic Factor-1 and Early Growth Response-1 in Activating Luteinizing Hormone-β Subunit Gene

Abstract

Tight regulation of luteinizing hormone-β subunit (LHβ) expression is critical for differentiation and maturation of mammalian sexual organs and reproductive function. Two transcription factors, steroidogenic factor-1 (SF-1) and early growth response-1 (Egr-1), play a central role in activating LHβ promoter, and the synergy between these two factors is essential in mediating gonadotropin-releasing hormone stimulation of LHβ promoter. Here we demonstrate that the transcriptional co-activator p300 regulates this synergy. Overexpression of p300 results in strong stimulation of LHβ promoter but only in the presence of both SF-1 and Egr-1, and not in the presence of other Egr proteins. Mutation of the binding sites for either SF-1 or Egr-1 completely abolishes the synergy between these two factors, as well as the influence of p300. Importantly, LHβ promoter is precipitated using p300 antibodies in a chromatin immunoprecipitation assay with LβT2 gonadotropes, and this effect is enhanced by gonadotropin-releasing hormone. The influence of p300 on LHβ promoter is potentiated by steroid receptor co-activator, as well as by E1A proteins, and attenuated by Smad nuclear interacting protein 1. Taken together, these results suggest that p300 is recruited to LHβ promoter where in coordinates the functional synergy between SF-1 and Egr-1.