INHIBITION OF GLYCOSYLATION INDUCES FORMATION OF OPEN CONNEXIN-43 CELL-TO-CELL CHANNELS AND PHOSPHORYLATION AND TRITON X-100 INSOLUBILITY OF CONNEXIN-43

We transfected the cDNA for the cell-to-cell channel protein connexin 43 (Cx43) into Morris hepatoma H5123 cells, which express little Cx43 and lack gap junctional communication (open cell-to-cell channels). We found that cells overexpressing Cx43 nonetheless lacked open cell-to- cell channels, but that inhibition of glycosylation by tunicamycin ind uced open channels in these cells. Tunicamycin also induced biochemica l changes in Cx43 protein; the level increased, and a considerable fra ction became phosphorylated and Triton X-100 insoluble, in contrast to untreated cells where Cx43 was non-phosphorylated and Triton X-100 so luble. Although tunicamycin caused the formation of open channels, cha nnels were not found aggregated into gap junctional plaques, as they a re when they have been induced by elevation of intracellular cAMP. The results suggest that although Cx43 itself is not glycosylated, other glycosylated proteins influence Cx43 posttranslational modification an d the formation of Cx43 cell-to cell channels.