title: Cx43 mediates TGF-beta signaling through competitive Smads binding to microtubules.
abstract: Transforming growth factor-beta (TGF-beta) superfamily members play an important role in growth, differentiation, adhesion, apoptosis, and development in many species from insects and worms to vertebrates. Recently, TGF-beta signaling has been demonstrated to be negatively regulated by microtubules (MTs), which anchor endogenous Smad2/3 to cytosol and also directly interact with connexin43 (Cx43), and the activity of TGF-beta is mediated by Cx43. However, the mechanism underlying the intracellular regulation of TGF-beta activity by Cx43 remains unknown. Here, we found that the functional link between TGF-beta activation and Cx43 is mediated by interactions among Smad2/3, MTs, and Cx43. We confirmed that Cx43 competes with Smad2/3 for binding to MTs, which Cx43 specifically induces release of Smad2/3 from MTs and increases phospho-Smad2 and which, as a result, Smad2/3 and Smad4 are accumulated in the nucleus, leading to activation of the transcription of target genes. Consistently, knockdown of the endogenous Cx43 activity with double-strand RNA (dsRNA) in HL1 cardiomyocytes and Cx43 knockout mice cardiomyocytes consistently show the opposite effect. Our findings demonstrate a novel mechanism for Cx43 positive regulation of TGF-beta function.
authors.affiliation: Department of Pathology and Cell Regulation, Kyoto Prefectural University of Medicine, Kawaramachi Hirokoji, Kamigyo-ku, Kyoto 602-8566, Japan. dping@koto.kpu-m.ac.jp
authors.forename: Ping
authors.initials: P
authors.lastname: Dai
authors.forename: Takuo
authors.initials: T
authors.lastname: Nakagami
authors.forename: Hideo
authors.initials: H
authors.lastname: Tanaka
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Hitomi
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Takamatsu
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology; D000818:Animals; D002478:Cells, Cultured; D018031:Connexin 43 / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008870:Microtubules / Q000378:metabolism*; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D051899:Smad2 Protein / Q000235:genetics / Q000378:metabolism*; D051900:Smad3 Protein / Q000235:genetics / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D014404:Tubulin / Q000378:metabolism
chemical_list: D018031:Connexin 43; D011993:Recombinant Fusion Proteins; D051899:Smad2 Protein; D051900:Smad3 Protein; D016212:Transforming Growth Factor beta; D014404:Tubulin