Nephrocystin-4 Regulates Pyk2-induced Tyrosine Phosphorylation of Nephrocystin-1 to Control Targeting to Monocilia

Abstract

Nephronophthisis is the most common genetic cause of end-stage renal failure during childhood and adolescence. Genetic studies have identified disease-causing mutations in at least 11 different genes (NPHP1–11), but the function of the corresponding nephrocystin proteins remains poorly understood. The two evolutionarily conserved proteins nephrocystin-1 (NPHP1) and nephrocystin-4 (NPHP4) interact and localize to cilia in kidney, retina, and brain characterizing nephronophthisis and associated pathologies as result of a ciliopathy. Here we show that NPHP4, but not truncating patient mutations, negatively regulates tyrosine phosphorylation of NPHP1. NPHP4 counteracts Pyk2-mediated phosphorylation of three defined tyrosine residues of NPHP1 thereby controlling binding of NPHP1 to the trans-Golgi sorting protein PACS-1. Knockdown of NPHP4 resulted in an accumulation of NPHP1 in trans-Golgi vesicles of ciliated retinal epithelial cells. These data strongly suggest that NPHP4 acts upstream of NPHP1 in a common pathway and support the concept of a role for nephrocystin proteins in intracellular vesicular transport.

The Cleaved Cytoplasmic Tail of Polycystin-1 Regulates Src-Dependent STAT3 Activation

“…In this regard, NPHP1-a protein mutated in the renal cystic disease nephronophthisis-binds via its SH3 domain with the PXXP motif in the PC1 tail. 39 Because NPHP1 has been shown to be phosphorylated by Src, 64 it is possible that Src acts on the complex of PC1 and NPHP1. In addition, EGFR interacts with the C-terminal part of the cytoplasmic tail of PC2, the same domain that interacts with the PC1 tail.…”

The extracellular matrix and ciliary signaling

“…Deficient cilia-based signaling from polycystins and/or nephrocystins mutated in ciliopathies may contribute to altered integrin, ECM, and MMP activity based on indirectly transduced signals (see also [68–70]). However, besides their function at cilia, both polycystins and nephrocystins associate with proteins that regulate focal adhesion and cell-cell junctions, and have been reported to localize to these structures [23,25–27,71–77]: hence, it is possible that part of the fibrotic phenotype may arise from actions at these locations. Supporting a specific role for cilia, fibrosis also occurs in mouse models with experimentally induced defects specific to cilia [78–81].…”

The Ciliary Protein Nephrocystin-4 Translocates the Canonical Wnt Regulator Jade-1 to the Nucleus to Negatively Regulate β-Catenin Signaling

“…Monoclonal mouse anti-NPHP4 was generously provided by Sophie Saunier. Monoclonal mouse anti-NPHP1 was described previously (32).…”

“…Nephrocystin-4 (NPHP4) has been shown to localize to the basal body (27,31) and, furthermore is thought to be involved in docking and organizing ciliary traffic at the transition zone (32,33). Recently, NPHP4 has been reported to be a negative regulator of canonical Wnt signaling (34), acting in a similar manner to inversin (NPHP2) to regulate Dsh localization.…”