NEPH1 defines a novel family of podocin‐interacting proteins

TLDR

Mutations in NPHS1 or NPHS2, encoding podocyte proteins nephrin and podocin, cause steroid‑resistant proteinuria, and podocin interacts with nephrin’s C‑terminal domain while NEPH1, a structurally related immunoglobulin superfamily member, is also implicated in podocyte integrity. The study reports that NEPH1 is part of a family of three closely related proteins that bind podocin’s C‑terminal domain. NEPH1‑deficient mice develop nephrotic syndrome resembling NPHS mutations, and the three NEPH proteins share a conserved podocin‑binding motif whose tyrosine residue is critical for affinity; NEPH1 activates AP‑1 like nephrin but requires Tec kinases, indicating that NEPH1 defines a novel podocin‑binding family that may underlie hereditary nephrotic syndromes independent of NPHS1/NPHS2.

Abstract

Mutations of NPHS1 or NPHS2, the genes encoding for the glomerular podocyte proteins nephrin and podocin, cause steroid-resistant proteinuria. In addition, mice lacking NEPH1 develop a nephrotic syndrome that resembles NPHS mutations, suggesting that all three proteins are essential for the integrity of glomerular podocytes. Podocin interacts with the C-terminal domain of nephrin and facilitates nephrin-dependent signaling. NEPH1, a member of the immunoglobulin superfamily, is structurally related to nephrin. We report now that NEPH1 belongs to a family of three closely related proteins that interact with the C-terminal domain of podocin. All three NEPH proteins share a conserved podocin-binding motif; mutation of a centrally located tyrosine residue dramatically lowers the affinity of NEPH1 for podocin. NEPH1 triggers AP-1 activation similarly to nephrin but requires the presence of Tec family kinases for efficient transactivation. We conclude that NEPH1 defines a new family of podocin-binding molecules that are potential candidates for hereditary nephrotic syndromes not linked to either NPHS1 or NPHS2.