Wnt-1 regulation of connexin43 in cardiac myocytes
Zhaowei Ai, … , Anthony M.C. Brown, Glenn I. Fishman
Zhaowei Ai, … , Anthony M.C. Brown, Glenn I. Fishman
Published January 15, 2000
Citation Information: J Clin Invest. 2000;105(2):161-171. https://doi.org/10.1172/JCI7798.
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Article

Wnt-1 regulation of connexin43 in cardiac myocytes

Abstract

Gap junction channels composed of connexin43 (Cx43) are essential for normal heart formation and function. We studied the potential role of the Wnt family of secreted polypeptides as regulators of Cx43 expression and gap junction channel function in dissociated myocytes and intact hearts. Neonatal rat cardiomyocytes responded to Li+, which mimics Wnt signaling, by accumulating the effector protein β-catenin and by inducing Cx43 mRNA and protein markedly. Induction of Cx43 expression was also observed in cardiomyocytes cocultured with Rat-2 fibroblasts or N2A neuroblastoma cells programmed to secrete bioactive Wnt-1. By transfecting a Cx43 promoter-reporter gene construct into cardiomyocytes, we demonstrated that the inductive effect of Wnt signaling was transcriptionally mediated. Enhanced expression of Cx43 increased cardiomyocyte cell coupling, as determined by Lucifer Yellow dye transfer and by calcium wave propagation. Conversely, in a transgenic cardiomyopathic mouse model that exhibits ventricular arrhythmias and gap junctional remodeling, β-catenin and Cx43 expression were downregulated concordantly. In response to Wnt signaling, the accumulating Cx43 colocalized with β-catenin in the junctional membrane; moreover, forced expression of Cx43 in cardiomyocytes reduced the transactivation potential of β-catenin. These findings demonstrate that Wnt signaling is an important modulator of Cx43-dependent intercellular coupling in the heart, and they support the hypothesis that dysregulated signaling contributes to altered impulse propagation and arrhythmia in the myopathic heart.

Authors

Zhaowei Ai, Avi Fischer, David C. Spray, Anthony M.C. Brown, Glenn I. Fishman

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Figure 9

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Biochemical association between Cx43 and β-catenin and repression of tra...
Biochemical association between Cx43 and β-catenin and repression of transactivation. Triton X-100 (1%) soluble lysates were prepared from myocytes grown in the absence (C) or presence of 20 mM LiCl (Li) and immunoprecipitated with irrelevant IgG (–) or with specific antisera, and the recovered proteins were immunoblotted with the indicated antibody. (a) Lysates immunoprecipitated with anti-Cx43 antisera and probed for β-catenin. (b) Lysates immunoprecipitated with β-catenin antisera and probed for Cx43. (c) Neonatal myocytes were treated with LiCl and transfected with 2 μg of either pTOPFLASH or pFOPFLASH, 9.8 μg of either a Cx43 expression plasmid (filled squares) or its parental vector (open squares), and 0.2 μg of a β-galactosidase expression plasmid to normalize transfection efficiency. Transactivation of the pTOPFLASH reporter gene was significantly reduced by forced expression of Cx43.