Maximal activity of the luteinizing hormone β-subunit gene requires β-catenin

Abstract

GnRH regulates expression of LHB via transcriptional regulation of early growth response 1 (EGR1), an immediate early gene that encodes a zinc-finger DNA-binding protein. EGR1 interacts functionally with the orphan nuclear receptor steroidogenic factor 1 (SF1) and pituitary homeobox 1, a member of the paired-like homeodomain family. The functional synergism of this tripartite interaction defines the maximal level of LHB transcription that can occur in response to GnRH. Results presented herein provide new evidence that the interaction between SF1 and EGR1 also requires β-catenin, a transcriptional co-activator and member of the canonical Wnt signaling pathway. For instance, targeted reduction of β-catenin attenuates activity of a GnRH-primed LHB promoter. Additional gene reporter assays indicate that overexpression of β-catenin, or its targeted reduction by small interfering RNA, modulates activity of both SF1 and EGR1 as well as their functional interaction. β-Catenin coimmunoprecipitates with SF1. Moreover, an SF1 mutant that lacks a β-catenin binding domain has compromised transcriptional activity and fails to interact synergistically with EGR1. Finally, GnRH promotes β-catenin colocalization with SF1 and EGR1 on the endogenous mouse Lhb promoter-regulatory region. Taken together, these data suggest that β-catenin binds to SF1 and that this interaction is required for subsequent functional interaction with EGR1. Thus, these data identify β-catenin as a new and required member of the basal transcriptional complex that allows the LHB promoter to achieve maximal activity in response to GnRH. Copyright © 2007 by The Endocrine Society.