A scaffold protein that connects plasma membrane proteins and regulatory components, regulating their surface expression in epithelial cells apical domains. May be involved in the coordination of a diverse range of regulatory processes for ion transport and second messenger cascades. In complex with SLC9A3R1, may cluster proteins that are functionally dependent in a mutual fashion and modulate the trafficking and the activity of the associated membrane proteins. May play a role in the cellular mechanisms associated with multidrug resistance through its interaction with ABCC2 and PDZK1IP1. May potentiate the CFTR chloride channel activity (By similarity). Required for normal cell-surface expression of SCARB1. Plays a role in maintaining normal plasma cholesterol levels via its effects on SCARB1. Plays a role in the normal localization and function of the chloride-anion exchanger SLC26A6 to the plasma membrane in the brush border of the proximal tubule of the kidney. May be involved in the regulation of proximal tubular Na(+)-dependent inorganic phosphate cotransport therefore playing an important role in tubule function. Interacts with PDZK1IP1 and ABCC2. Binds to the C-terminal region of SLC26A3. Interacts (via C-terminal PDZ domain) with SLC26A6 (via C-terminal domain). Interacts (via C-terminal PDZ domain) with SLC9A3 (via C-terminal domain) (By similarity). Component of a complex, composed of PDZK1, SYNGAP1, KLHL17 and NMDA receptors. Interacts (via PDZ1 domain) directly with KLHL17; the interaction is important for integrity of actin cytoskeleton structures in neurons (By similarity). Forms a heterodimeric complex with SLC9A3R1. Interacts with AKAP2, BCR, CFTR, SLCO1A1, SLC22A12, SLC22A4, SLC22A5, SLC26A6, SLC9A3R2 and SLC17A1. Interacts (via the first PDZ domain) with PTGIR (via non-isoprenylated C-terminus). Interacts (via PDZ domains 1 and 3) with SCARB1 (C-terminal domain). Localized in the brush border membrane of renal proximal tubule cells (PubMed:11051556, PubMed:16141316). Associated with peripheral membranes (By similarity). Localizes to the apical compartment of proximal cells and to sinusoidal liver membranes (By similarity). Expressed in kidney, liver, small intestine. brain, lung, and testis (at protein level). The PDZ 2 and 3 domains seem to be involved in the interaction with SLC26A3. Interaction with the C-terminus of CFTR could be mediated through independent binding of PDZ 1, 3 and 4 domains. The PDZ 1 and 3 domains seem to be involved in the interaction with SLCO1A1. The PDZ 1 domain interacts with BCR. The PDZ 2 and 4 domains do not interact with the C-terminal region of SCARB1. Disruption of the gene was not associated with abnormal growth and development or redistribution of interacting proteins. However, a modulation of expression of selective ion channels in the kidney, as well as increased serum cholesterol levels were observed. Belongs to the NHER family. The frameshift causes a read through of the stop codon.