Cingulin, a Cytoskeleton-Associated Protein of the Tight Junction

Abstract

Cingulin is a Mr?140 {kDa} phosphoprotein component of the cytoplasmicplaque of vertebrate tight junctions {(TJ),} and was identified asan actomyosin-associated protein. The cingulin sequence predictsthat the molecule is a parallel homodimer, each sub-unit consistingof a coiled-coil ?rod? domain separating a large globular N-terminal?head? domain from a small globular C-terminal ?tail?. The head domainmediates direct in vitro interaction with {ZO-1,} {ZO-2,} {ZO-3}and actin, and is critical for the junctional recruitment of cingulinin transfected cells, whereas the rod domain mediates dimerization.Cingulin forms complexes with {ZO-1,} {ZO-2} and the immunoglobulin-likeadhesion molecule {JAM-1.} These complexes are only detected in Triton-insolublecell fractions, suggesting that one function of cingulin is to link{TJ-associated} proteins to the actomyosin cytoskeleton during {TJ}biogenesis and regulation. In fact, purified cingulin acts in vitroas an actin-binding and -bundling protein. Cingulin shows a cortical,apical localization in early vertebrate embryos, and {inXenopusembryos}is recruited into nascent {TJ} starting at the 2-cell stage, suggestingthat cingulin may play an important role in the development of vertebrateepithelia. Cingulin may represent the first member of a family ofproteins, since a novel protein, paracingulin, with similar domainorganization and significant sequence homology to cingulin has recentlybeen identified.