Gap junction-microtubule associations in rat alveolar epithelial cells.

Connexin 43 (Cx43) is a predominant gap junction (GJ) protein expressed by alveolar epithelial cells (AEC) in primary cell culture. Cx43 trafficking, assembly, and turnover are regulated by multiple mechanisms, including those mediated by integrins, by extracellular matrix, and by the cytoskeleton. Immunocytochemical double labeling demonstrates association of microtubules with internalization of Cx43-positive GJ plaques. Antibodies against the alpha 5-integrin subunit block cell-matrix interactions without effect on tubulin expression, whereas inhibition of MAP kinase kinase by PD-98059 reduces tubulin expression, based on both Western blot and immunostaining. To examine direct association of microtubules (MT) with GJ plaques, we treated day 3 AEC for 0.5-24 h with colchicine, an inhibitor of tubulin polymerization. After 60 min, MTs were disassembled, whereas Western blot analysis showed no change in tubulin expression. In parallel, colchicine initiated redistribution of immunopositive Cx43 from the membrane to the cytosol. These observations support the premise that direct association of the cytoskeleton with gap junctions plays a significant role in regulation of Cx43 expression and distribution through integrin-mediated signal transduction pathways.