Involved in the establishment of cell polarity in mammalian epithelial cells (PubMed:12771187, PubMed:14718572). Regulates the morphogenesis of tight junctions (PubMed:12771187, PubMed:14718572). Involved in promoting phosphorylation and cytoplasmic retention of transcriptional coactivators YAP1 and WWTR1/TAZ which leads to suppression of TGFB1-dependent transcription of target genes such as CCN2/CTGF, SERPINE1/PAI1, SNAI1/SNAIL1 and SMAD7 (By similarity). Component of a complex composed of CRB3, PALS1 and PATJ (By similarity). Interacts (via C-terminus) with PALS1 (via PDZ domain) (PubMed:12527193, PubMed:12771187). Interacts with PARD6A (PubMed:14718572). Interacts (via intracellular domain) with EPB41L5 (PubMed:17920587). Localizes primarily to the apical membrane with a small fraction in the upper part of tight junctions of epithelial cells. Preferentially expressed in epithelial tissues (PubMed:14718572). Expressed at high levels in lung, kidney, and colon (PubMed:12527193, PubMed:14718572). Expressed at high levels in retina, colon and mammary glands (PubMed:12527193). Moderately expressed in liver, spleen, pancreas and prostate (PubMed:12527193). Moderately to weakly expressed in the placenta (PubMed:14718572, PubMed:12527193). Weakly expressed in skeletal muscle and small intestine (PubMed:14718572). The PDZ-binding motif is involved in the interactions with PARD6A and PALS1.