Abstract
Phosphorylation regulates connexin43 (Cx43) function from assembly/disassembly to coupling at the plaque. Src is a tyrosine kinase known to both phosphorylate Cx43 (residues Y247 and Y265) and affect gap junction intercellular communication. However, the Cx43 carboxyl-terminal (CT) domain contains additional tyrosine residues and proteomic discovery mass spectrometry data identified Y313 as a potential phosphorylation target. Based upon the study of Lin et al. (2001) J. Cell Biol., which still observed tyrosine phosphorylation by Src when using a Cx43 Y247/Y265F mutant, we addressed the possibility of Y313 phosphorylation (pY313) by Src. In vitro Src phosphorylation of purified Cx43CT followed by mass spectroscopy revealed that Src also phosphorylates Y313. This observation was confirmed by repeating the in vitro phosphorylation using different combinations of Cx43CT Y → F mutants and a general anti-pTyr antibody. Next, a phospho-specific antibody was generated to help characterize the importance of pY313. We established an in cyto experimental system by stably expressing Cx43 WT and mutants (Y247F, Y265F, Y313F, Y247/265F, Y247/313F, Y265/313F, or Y247/265/313F) in Cx43-deficient HeLa cells. Cx43 WT and mutants, in the absence of v-Src, localized to the plasma membrane and formed gap junctions. When v-Src was over-expressed, Cx43 WT localized intracellularly, while all of the single and double mutants remained able to form plaques and transfer dye, albeit variable in number and amount, respectively. Complete Src-resistance was only achieved with the Cx43 Y247/265/313F mutant. Furthermore, Cx43 Y265F inhibited the ability of v-Src to phosphorylate Y247 and Y313 as well as phosphorylation at both Y265 and Y313 was necessary to inhibit the Cx43 interaction with Drebrin. Finally, we observed in diseased cardiac tissue, in which Src is active, an increase in intercalated disc and intracellular localized Cx43 pY313.