Channel-forming tight junction protein that mediates paracellular chloride transport in the kidney (PubMed:20921420). Plays a critical role in the paracellular reabsorption of filtered chloride in the kidney collecting ducts (PubMed:20921420). Claudins play a major role in tight junction-specific obliteration of the intercellular space, through calcium-independent cell-adhesion activity. Interacts with EPHA2; phosphorylates CLDN4 and may regulate tight junctions (By similarity). Directly interacts with TJP1/ZO-1, TJP2/ZO-2 and TJP3/ZO-3 (PubMed:10601346, PubMed:16236711). Interacts with CLDN1 (By similarity). Interacts with CLDN8 (PubMed:20921420). CLDN4 is required for tight junction localization in the kidney (PubMed:20921420, PubMed:25831548). Expressed primarily in lung and kidney (PubMed:9892664). Present in both cortical and medullar collecting ducts (at protein level) (PubMed:20921420). Phosphorylated. Phosphorylation by EPHA2 is stimulated by EFNA1 and alters interaction with TJP1 (By similarity). Belongs to the claudin family.