Multiple domains of occludin are involved in the regulation of paracellular permeability

Tight junctions form selective paracellular diffusion barriers that regulat e the diffusion of solutes across epithelia and constitute intramembrane di ffusion barriers that prevent the intermixing of apical and basolateral lip ids in the extracytoplasmic leaflet of the plasma membrane. In MDCK cells, previous expression experiments demonstrated that occludin, a tight junctio n protein with four transmembrane domains, is critically involved in both o f these tight junction functions and that its COOH-terminal cytoplasmic dom ain is of functional importance. By expressing mutant and chimeric occludin that exert a dominant negative effect on selective paracellular diffusion, we now demonstrate that the extracytoplasmic domains and at least one of t he transmembrane domains are also critically involved in selective paracell ular permeability. Multiple domains of occludin are thus important For the regulation of paracellular permeability, Expression of chimeras containing at least one transmembrane domain of occludin also resulted in an enhanced intracellular accumulation of claudin-4, another transmembrane protein of t ight junctions, suggesting that the two proteins may cooperate in the regul ation of paracellular permeability. (C) 2000 Wiley-Liss, Inc.