A carboxyl terminal domain of connexin43 is critical for gap junction plaque formation but not for homo- or hetero-oligomerization

We have initiated a series of experiments to analyze the biosynthesis and oligomerization of Cx43 in cells containing other connexins through the expression of site-directed mutants and chimeric connexin polypeptides. Here we report studies concerning a mutant of Cx43 (Cx43tr) that has been truncated after amino acid 251 to remove most of the Cx43 carboxy-terminal region. In stably transfected HeLa cells, full length Cx43 localized primarily to appositional membranes while much more Cx43tr was observed in the cytoplasm. Both Cx43 and Cx43tr showed similar oligomerization profiles based on centrifugation through sucrose gradients. HeLaCx43tr cells showed limited transfer of microinjected Lucifer Yellow but did show electrical coupling. Co-expression of Cx43tr with Cx43 or Cx45 led to Cx43tr localization at appositional membranes and co-localization with the other connexins. Moreover, cells co-expressing Cx43tr with Cx43 or Cx45 showed extensive intercellular dye coupling. Thus, Cx43tr was able to oligomerize and form functional channels when expressed alone or with a compatible connexin, but it only formed plaques when co-expressed. These results suggest that the carboxyl tail of Cx43 is not important for oligomerization, but they implicate critical residues in the formation of gap junction plaques.