Proteinase-induced formation of focal tight junctions in HT 29 adenocarcinoma cells does not require extracellular calcium.

The human adenocarcinoma cell line HT 29 grows virtually without tight junctions, but the formation of focal tight junctions can be induced by brief treatment with proteinases. The freeze-fracture morphology of proteinase-induced tight junctions is not affected by treatment with EGTA or EDTA over a period of 30 min. The induction of tight junctions by trypsin or pronase can proceed in the presence of 3 mM EGTA or EDTA. Neither the formation nor the structure and complexity of the induced tight junctions is affected by the chelators. It follows that no extracellular divalent cations are required for the induced formation and the structural integrity of focal tight junctions in HT 29 cells.