Probably plays a role in the formation and regulation of the tight junction (TJ) paracellular permeability barrier. Homodimer (PubMed:11042084). Interacts with TJP1/ZO1 (PubMed:12023291). Interacts with SPEF1 (PubMed:31473225). Localizes to the apical junction complex composed of tight and adherens junctions (By similarity). Colocalizes with SPEF1 at sites of cell-cell contact in intestinal epithelial cells (PubMed:12023291). Localized on the cytoplasmic face of tight junctions of polarized epithelia and some endothelia. Expressed in pancreas, kidney, liver and lung, but not in skeletal muscle, placenta, brain or heart. Deletion of the TJP1/ZO1 interaction motif (ZIM) decreases but does not abolish colocalization with TJP1/ZO1. May be due to an intron retention. Belongs to the cingulin family. It is uncertain whether Met-1 or Met-7 is the initiator. Truncated N-terminus. Extended N-terminus.