Maximal activity of the luteinizing hormone beta-subunit gene requires beta-catenin.
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.
Salisbury
Travis B
TB
School of Molecular Biosciences, Fulmer 639A, Washington State University, Pullman, Washington 99164-4660, USA.
Binder
April K
AK
Grammer
Jean C
JC
Nilson
John H
JH
D000818:Animals; D002478:Cells, Cultured; D051766:Early Growth Response Protein 1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology / Q000502:physiology*; D018398:Homeodomain Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D047468:Immunoprecipitation; D037101:Luteinizing Hormone, beta Subunit / Q000235:genetics*; D051379:Mice; D009154:Mutation; D051761:Paired Box Transcription Factors / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000187:drug effects; D017434:Protein Structure, Tertiary / Q000235:genetics; D034741:RNA, Small Interfering / Q000494:pharmacology; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D054339:Steroidogenic Factor 1; D014157:Transcription Factors / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D051176:beta Catenin / Q000378:metabolism*
D051766:Early Growth Response Protein 1; C486109:Egr1 protein, mouse; D018398:Homeodomain Proteins; D037101:Luteinizing Hormone, beta Subunit; D051761:Paired Box Transcription Factors; D034741:RNA, Small Interfering; D018160:Receptors, Cytoplasmic and Nuclear; D054339:Steroidogenic Factor 1; D014157:Transcription Factors; D051176:beta Catenin; C101485:homeobox protein PITX1; C515058:steroidogenic factor 1, mouse; D007987:Gonadotropin-Releasing Hormone