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. perinatal death (13). Although this congenital cardiac defect was unexpected and its occurrence remains unexplained, recent studies support the hypothesis that loss of function of Cx43 in cells of neural crest origin may account for this phenotype (14).One potential regulator of gap junction expression and function that may have important implications for developmental processes as well as for normal function in adult stages is the Wnt family of genes. Wnt genes encode a large family of secreted polypeptides that can influence cell-cell communication, both during embryonic development and in adult life (15). Wnt proteins are thought to act via the Frizzled class of cell-surface proteins. Receptor activation leads to inhibition of glycogen synthase kinase 3β (GSK3β), resulting in stabilization and accumulation of nonphosphorylated β-catenin within the cytosolic compartment. Increased abundance of this pool is associated with entry of β-catenin into the nucleus, where the protein complexes with Tcf transcription factors and modulates the expression of specific target genes (16). β-Catenin also is associated with the plasma membrane, where it acts as a component of the cell-cell adhesive junction. Wnt-1 has been shown to enhance gap junctional communication between ventral cells of the developing Xenopus embryo (17, 18). In addition, ectopic expression of Wnt-1 in the limb mesenchyme of transgenic mice increases the local accumulation of...

Cdon deficiency causes cardiac remodeling through hyperactivation of WNT/β-catenin signaling

“…Cx43 localization is regulated through a variety of mechanisms, including protein trafficking following translation and overall stabilization of intercalated discs. Recently the role of Wnt in expression of Cx43 has been established (24,49). Consistently, we confirmed that Wnt inhibitor reversed up-regulation of Cx43 level and cell-cell coupling in Cdon-knockdown neonatal cardiomyocytes.…”

The Second PDZ Domain of Zonula Occludens-1 Is Dispensable for Targeting to Connexin43 Gap Junctions

“…Alternatively, the presence of low levels of ZO-1 at the edge of Cx43-GFP plaques could result indirectly via macromolecular associations between GJs and other cell-cell junctions that incorporate ZO-1. Adherens junctions are logical candidates in this respect as they are known to play a pivotal role in GJ stability (Hertig et al 1996;Jongen et al 1991;Li et al 2005;Meyer et al 1992;Musil et al 1990;Wei et al 2005) and cadherin-associated catenin complexes have been shown to bind both Cx43 (Ai et al 2000;Wei et al 2005) and ZO-1 (Itoh et al 1997).…”

Gene array analysis of macronodular adrenal hyperplasia confirms clinical heterogeneity and identifies several candidate genes as molecular mediators

“…In addition, other genes that may be affected by Wnt-1 signaling and were observed in the data set produced by the GIP-dependent AIMAH microarray analysis included the gap junction gene connexin43, a molecule that is also induced by Wnt-dependent increase of b-catenin in cardiomyocytes (Ai et al, 2000) (data not shown).…”