Genetic variants disrupt human RGS14 binding to NHERF1 and regulation of NPT2A-mediated phosphate transport

Abstract

RGS14 is a multifunctional scaffolding protein that integrates G protein, MAPK, and Ca++/CaM signaling pathways. RGS14 contains an RGS domain, tandem Ras/Rap-binding domains, and a G protein regulatory motif. Human/primate RGS14 differ from rodent proteins by possessing a carboxy-terminal extension encoding a Type I PDZ ligand. RGS14 has been implicated in disordered phosphate metabolism. The human RGS14 gene is adjacent to SLC34A1 that encodes the NPT2A sodium-phosphate cotransporter. Hormone-regulated NPT2A requires the PDZ protein NHERF1 which contains two PDZ domains (PDZ1 and PDZ2). NHERF1 binds the PDZ ligand carboxy tail of NPT2A to regulate phosphate uptake, and this NPT2A:NHERF1 complex is inhibited by parathyroid hormone (PTH). Studies here define roles for RGS14 in NHERF1-dependent, PTH-sensitive phosphate transport. We found that RGS14 binds to NHERF1 via the PDZ2 domain. PTH inhibits NPT2A-mediated phosphate transport and RGS14 blocked this action. Several rare human mutations have been reported in the RGS14 PDZ ligand located at residues 563 (D563N, D563G) and 565 (A565S, A565V). D563N disrupted RGS14 binding to NHERF1 and did not interfere with PTH action, whereas D563G, A565S, and A565V bound NHERF1 and were functionally equivalent to wild-type RGS14. Computational analysis and molecular dynamics modeling of NHERF1 PDZ2 binding to the RGS14 C-terminal PDZ ligands refined the structural determinants of this interaction. Additional studies demonstrated that RGS14 is expressed in human kidney proximal and distal tubule cells. Together, our findings are consistent with the view that RGS14 contributes to PTH-sensitive phosphate transport in humans. RGS14 coding variants may cause disordered phosphate metabolism.