Gap junctions contain intercellular channels that enable intercellular communication of small molecules while also serving as a signaling scaffold.
Connexins, the
proteins that form gap junctions in vertebrates, are highly regulated and typically have short (<2 h) half-lives.
Connexin43 (
Cx43), the predominate
connexin in the myocardium and epithelial tissues, is phosphorylated on more than a dozen
serine residues and interacts with a variety of
protein kinases. These interactions regulate
Cx43 and gap junction formation and stability.
Casein kinase 1 (CK1)-mediated phosphorylation of
Cx43 promotes gap junction assembly. Using murine knock-in technology and quantitative PCR, immunoblotting, and immunoprecipitation assays, we show here that mutation of the CK1 phosphorylation sites in
Cx43 reduces the levels of total
Cx43 in the myocardium and increases
Cx43 phosphorylation on sites phosphorylated by
extracellular signal-regulated kinase (ERK). In aged myocardium, we found that, compared with WT
Cx43, mutant
Cx43 expression increases ERK activation, phosphorylation of Akt substrates, and protection from
ischemia-induced injury. Our findings also uncovered that
Cx43 interacts with the
hypoxia-inducible
protein N-Myc downstream-regulated gene 1 protein (NDRG1) and that
Cx43 phosphorylation status controls this interaction and dramatically affects NDRG1 stability. We propose that, in addition to altering gap junction stability,
Cx43 phosphorylation directly and dynamically regulates cellular signaling through ERK and Akt in response to ischemic injury. We conclude that gap junction-dependent NDRG1 regulation might explain some cellular responses to
hypoxia.