Facilitation of gap junctional communication and gap-junction formation in mammalian cells by inhibition of glycosylation

The effect of inhibition of glycosylation on basal and cAMP-induced homologous and heterologous gap-junctional communication was studied in various normal and transformed cell lines that express mRNA and protein for the gap junction-forming gene, connexin43. In communication-incompetent Morris hepatoma cells, inhibition of glycosylation alone did not induce junctional communication, but enhanced cAMP-induced junctional communication several fold. This enhancement correlated with the presence of more gap junctions at the membrane appositions, but not with an increase in connexin43 mRNA or protein in these cells. In several other normal and transformed cell lines, inhibition of glycosylation enhanced both basal as well as cAMP-induced junctional communication. Furthermore, both basal and cAMP-induced heterologous junctional communication between nontransformed RL-CL9 and several other nontransformed and transformed cells was also enhanced when glycosylation was inhibited. Our data suggest that the formation of gap junctions between cells of the same type or different types is subject to local constraints imposed by the oligosaccharide moieties of the glycoproteins of the plasma membranes of the gap-junction-forming cells and that inhibition of glycosylation abrogates such constraints. Our findings thus suggest a new basis for the communication deficiency observed in several types of transformed cells and between transformed and normal cells.