Channel-forming tight junction protein that mediates paracellular chloride transport in the kidney. Plays a critical role in the paracellular reabsorption of filtered chloride in the kidney collecting ducts. Claudins play a major role in tight junction-specific obliteration of the intercellular space, through calcium-independent cell-adhesion activity. Directly interacts with TJP1/ZO-1 (PubMed:16236711). Interacts with TJP2/ZO-2 and TJP3/ZO-3 (By similarity). Interacts with EPHA2; phosphorylates CLDN4 and may regulate tight junctions (PubMed:16236711). Interacts with CLDN1 (PubMed:20375010). Interacts with CLDN8 (By similarity). (Microbial infection) Interacts (via both extracellular domains) with Clostridium perfringens enterotoxin CPE; the interaction may disrupt claudin assembly in tight junctions. CLDN4 is required for tight junction localization in the kidney. Phosphorylated. Phosphorylation by EPHA2 is stimulated by EFNA1 and alters interaction with TJP1. CLDN4 is located in the Williams-Beuren syndrome (WBS) critical region. WBS results from a hemizygous deletion of several genes on chromosome 7q11.23, thought to arise as a consequence of unequal crossing over between highly homologous low-copy repeat sequences flanking the deleted region. Belongs to the claudin family.