The sorting nexin 3 retromer pathway regulates the cell surface localization and activity of a Wnt-activated polycystin channel complex

Abstract

Autosomal dominant polycystic kidney disease (ADPKD) is caused by inactivating mutations in PKD1 (85%) or PKD2 (15%). The ADPKD proteins encoded by these genes, polycystin-1 (PC1) and polycystin-2 (PC2), form a plasma membrane receptor-ion channel complex. However, the mechanisms controlling the subcellular localization of PC1 and PC2 are poorly understood. Here, we investigated the involvement of the retromer complex, an ancient protein module initially discovered in yeast that regulates the retrieval, sorting, and retrograde transport of membrane receptors. Using yeast two-hybrid, biochemical, and cellular assays, we determined that PC2 binds two isoforms of the retromer-associated protein sorting nexin 3 (SNX3), including a novel isoform that binds PC2 in a direct manner. Knockdown of SNX3 or the core retromer protein VPS35 increased the surface expression of endogenous PC1 and PC2 in vitro and in vivo and increased Wnt-activated PC2-dependent whole-cell currents. These findings indicate that an SNX3- retromer complex regulates the surface expression and function of PC1 and PC2. Molecular targeting of proteins involved in the endosomal sorting of PC1 and PC2 could lead to new therapeutic approaches in ADPKD.