Provides, together with MAGI1, an adhesion machinery at tight junctions, which may regulate the permeability of kidney glomerulus and small intestinal epithelial cells. Mediates calcium-independent homophilic cell adhesion. In testis, it may function as a cell adhesion molecule rather than a tight-junction protein. It may participate in the adhesion between spermatogonia-spermatogonia, spermatogonia-Sertoli cells, and Sertoli cells-Sertoli cells (By similarity). Interacts with MAGI1 at tight junctions, forms a tripartite complex with NPHS1. Interacts with LNX1 isoform 2 via its PDZ 2 domain, it may also interact with other isoforms containing this domain (By similarity). In podocytes, it is mainly found in the apical plasma membrane where no junctional structure is seen. The subcellular location is altered in puromycin amino-nucleoside nephropathy (PAN). A cytoplasmic localization has been observed which may indicate the existence of variants lacking a signal sequence (PubMed:16118391). May be primarily targeted to apical membranes and subsequently recruited to tight-junctions (PubMed:12940823). In kidney, it is found in glomeruli and in the proximal tubules (at protein level). Found at all stages of developing glomeruli and the presumptive proximal tubules in the embryonic kidney. The expression was restricted to the presumptive podocyte. It may be a useful marker for injured podocytes in puromycin amino-nucleoside nephropathy (PAN) since its expression at the apical surface is altered. Belongs to the immunoglobulin superfamily.