title: β-Catenin independent cross-control between the estradiol and Wnt pathways in osteoblasts.
abstract: Osteoblasts are controlled by the individual and combined effects of systemic and local growth regulators. Here we show functional and physical interactions between estradiol (17βE) and Wnt activated pathways in osteoblasts. 17βE increased gene promoter activity by the Wnt pathway transcriptional effector T cell factor (TCF) in an estrogen receptor (ER) dependent way. This occurred independently of its activity through traditional estrogen response elements and was not replicated by androgen receptor activation. 17βE also increased the stimulatory effect of LiCl on TCF activity, LiCl increased the stimulatory effect of 17βE through estrogen response elements, and both were further enhanced by a noncanonical Wnt receptor agonist (WAg) that functions independently of β-catenin stabilization. In contrast to LiCl, WAg increased DNA synthesis and reduced relative collagen synthesis and alkaline phosphatase activity in otherwise untreated or 17βE stimulated cells. In addition, WAg suppressed Runx2, osterix, and alkaline phosphatase mRNA levels, and potently induced osteoprotegerin mRNA, whereas LiCl was ineffective alone and inhibitory in combination with 17βE. A definitive intersection between the 17βE and Wnt pathways occurred at the protein level, where ERα physically associated with TCF-4 independently of its β-catenin binding domain. This interaction required ligand-dependent exposure of a TCF binding region that mapped to ERα domain E and was further enhanced by Wnt pathway activation. Our studies reveal highly focused co-regulatory effects between the 17βE and Wnt pathways in osteoblasts that involve activated ERα and TCF-4 and downstream changes in gene expression, osteoblast proliferation, and differentiated cell function.
authors.affiliation: Yale University School of Medicine, Department of Surgery, New Haven, CT, 06520-8041, USA. thomas.mccarthy@yale.edu
authors.forename: Thomas L
authors.initials: TL
authors.lastname: McCarthy
authors.forename: Caleb B
authors.initials: CB
authors.lastname: Kallen
authors.forename: Michael
authors.initials: M
authors.lastname: Centrella
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D049109:Cell Proliferation; D050659:Core Binding Factor Alpha 1 Subunit / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D004958:Estradiol / Q000494:pharmacology*; D005786:Gene Expression Regulation; D018021:Lithium Chloride / Q000494:pharmacology*; D010006:Osteoblasts / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011960:Receptors, Estrogen / Q000378:metabolism; D020218:Response Elements / Q000502:physiology; D051820:TCF Transcription Factors / Q000378:metabolism*; D000073940:Transcription Factor 4; D014157:Transcription Factors / Q000378:metabolism; D051153:Wnt Proteins / Q000378:metabolism*
chemical_list: D050659:Core Binding Factor Alpha 1 Subunit; D004268:DNA-Binding Proteins; D011960:Receptors, Estrogen; C493717:Runx2 protein, rat; D051820:TCF Transcription Factors; C491192:Tcf4 protein, rat; D000073940:Transcription Factor 4; D014157:Transcription Factors; D051153:Wnt Proteins; D004958:Estradiol; D018021:Lithium Chloride