OVEREXPRESSION OF OCCLUDIN, A TIGHT JUNCTION-ASSOCIATED INTEGRAL MEMBRANE-PROTEIN, INDUCES THE FORMATION OF INTRACELLULAR MULTILAMELLAR BODIES BEARING TIGHT JUNCTION-LIKE STRUCTURES

Occludin is an integral membrane protein localizing at tight junctions with four transmembrane domains. When chicken occludin was overexpres sed in insect cells by recombinant baculovirus infection, peculiar mul tilamellar structures accumulated in the cytoplasm, Partial isolation of these structures indicated that the introduced chicken occludin was highly enriched in these structures, Thin section electron microscopy revealed that each lamella was transformed from intracellular membran ous cisternae whose luminal space was completely collapsed, and that i n each lamella, outer leaflets of opposing membranes appeared to be fu sed with no gaps, like tight junctions, Furthermore, in the freeze-fra cture replicas of these multilamellar structures, short tight junction -like intramembranous particle strands were occasionally observed, whi ch were specifically labeled by anti-occludin mAb. These observations favor the idea that occludin plays a key role in the formation of tigh t junctions.