Polycystin-2 traffics to cilia independently of polycystin-1 by using an N-terminal RVxP motif

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Abstract
Primary cilia play a key role in the pathogenesis of autosomal dominant polycystic kidney disease (ADPKD). The affected proteins, polycystin-1 (PC1) and polycystin-2 (PC2), interact with each other and are expressed in cilia. We found that COOH-terminal truncated PC2 (PC2-L703X), lacking the PC1 interaction region, still traffics to cilia. We examined PC2 expression in several tissues and cells lacking PC1 and found that PC2 is expressed in cilia independently of PC1. We used N-terminal deletion constructs to narrow the domain necessary for cilia trafficking to the first 15 amino acids of PC2 and identified a conserved motif, R6VxP, that is required for cilial localization. The N-terminal 15 amino acids are also sufficient to localize heterologous proteins in cilia. PC2 has endogenous cilia trafficking information and is present in cilia of cells lining cysts that result from mutations in PKD1.