Maximal Activity of the Luteinizing Hormoneβ-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 beta-catenin, a transcriptional coactivator and member of the canonical Wnt signaling pathway. For instance, targeted reduction of beta-catenin attenuates activity of a GnRH-primed LHB promoter. Additional gene reporter assays indicate that overexpression of beta-catenin, or its targeted reduction by small interfering RNA, modulates activity of both SF1 and EGR1 as well as their functional interaction. beta-Catenin coimmunoprecipitates with SF1. Moreover, an SF1 mutant that lacks a beta-catenin binding domain has compromised transcriptional activity and fails to interact synergistically with EGR1. Finally, GnRH promotes beta-catenin colocalization with SF1 and EGR1 on the endogenous mouse Lhb promoter-regulatory region. Taken together, these data suggest that beta-catenin binds to SF1 and that this interaction is required for subsequent functional interaction with EGR1. Thus, these data identify beta-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.

ANE syndrome caused by mutated RBM28 gene: a novel etiology of combined pituitary hormone deficiency

“…Interestingly, recent data have established a major role for the Wnt/ b-catenin signaling pathway in regulating pituitary development and growth (21). These studies demonstrated that b-catenin plays an essential role in transducing the GnRH signal by interacting with multiple DNA-binding proteins in gonadotropes (22)(23)(24). In addition, in a mouse model, b-catenin acts as a cofactor for a number of pituitary transcription factors that control pituitary cell specification and exert both stimulatory (prop1 in regulating expression of pit-1) and inhibitory (Hesx1) effects (21,25,26).…”

Targeted disruption of β-catenin in Sf1-expressing cells impairs development and maintenance of the adrenal cortex

“…Of interest, proposed target genes of both β-catenin and Sf1 include a number of genes that regulate proliferation, providing plausible candidates for this coregulation (Doghman et al, 2007;Gummow et al, 2003;Jordan et al, 2003;Mizusaki et al, 2003;Parakh et al, 2006;Salisbury et al, 2007). Moreover, mutations and/or amplification of both Sf1 and β-catenin have been linked to adrenocortical tumorigenesis in humans, again suggesting that these two genes play key roles in adrenocortical cell proliferation in vivo (Figueiredo et al, 2005;Tissier et al, 2005).…”

“…Inside the nucleus, β-catenin interacts with members of the lymphoid enhancer-binding factor/T-cell factor (Lef/Tcf) family of transcription factors to activate expression of target genes. β-Catenin has also been shown to interact functionally with Sf1 to activate target genes synergistically, including Nr0b1 (Dax1), Inha (inhibin-α), Star (steroidogenic acute regulatory protein), Hsd3b1 (3β-hydroxysteroid dehydrogenase), Cyp19a1 (aromatase) and Lhb (β-subunit of luteinizing hormone) (Gummow et al, 2003;Jordan et al, 2003;Mizusaki et al, 2003;Parakh et al, 2006;Salisbury et al, 2007). These studies raised the possibility that β-catenin also plays important roles in adrenocortical development and function.…”

Targeting mediators of Wnt signalling pathways by GnRH in gonadotropes

“…Indeed, several recent studies have demonstrated that GnRH, acting at the GnRH receptor, can target mediators of the Wnt/b-catenin signalling pathway in both a heterologous HEK293 model cell line and the LbT2 gonadotrope cell line (Gardner et al 2007, Salisbury et al 2007, 2009, Gardner & Pawson 2009). …”

“…An important study highlighting the role of b-catenin as a member of a transcription factor complex that drives maximal activity of the Lhb subunit promoter in response to GnRH was published (Salisbury et al 2007). This study by Nilson et al demonstrates the co-localisation of b-catenin with SF1 and EGR1 on the promoter of the Lhb subunit gene in response to GnRH, and suggests that endogenous SF1 and b-catenin can physically associate in LbT2 cells (Salisbury et al 2007). A role for GnRH targeting of b-catenin/TCF activity to regulate the expression of JUN-responsive genes including Cga, Fshb and Gnrhr, which additionally require SF1, is yet to be demonstrated.…”