Regulation of Cx37 channel and growth suppressive properties by phosphorylation

Abstract

Connexin 37 (Cx37)-mediated growth suppression requires interaction between its carboxyl terminus (CT) and functional pore-forming domain. Using rat insulinoma cells, we show that Cx37 induces cell death and cell cycle arrest as well as slowed cell cycling. Whether differential phosphorylation might regulate intramolecular interactions and consequently growth suppressive phenotype is unknown. Protein kinase C inhibition increased the open probability of low conductance gap junction channels (GJCh) and reduced GJCh closed state probability. Substituting alanine at serine residues 275, 302, and 328 eliminated Cx37-induced cell death and cell cycle arrest, and reduced the GJChs closed state probability. With additional alanine for serine substitutions at residues 285, 319, 321 and 325, Cx37-induced cell death was eliminated and the growth arrest period prolonged, and GJCh closed state probability restored. With aspartate substitution at these seven sites, apoptosis was induced and the open probability of large conductance GJChs (and hemichannels) was increased. These data suggest that differential phosphorylation of the CT regulates channel conformation and, thereby, cell cycle progression and cell survival.