Novel Functional Complexity of Polycystin-1 by GPS Cleavage In Vivo: Role in Polycystic Kidney Disease

Polycystin-1 (Pc1) cleavage at the G protein-coupled receptor (GPCR) proteolytic site (GPS) is required for normal kidney morphology in humans and mice. We found a complex pattern of endogenous Pc1 forms by GPS cleavage. GPS cleavage generates not only the heterodimeric cleaved full-length Pc1 (Pc1cFL ) in which the N-terminal fragment (NTF) remains noncovalently associated with the C-terminal fragment (CTF) but also a novel (Pc1) form (Pc1deN ) in which NTF becomes detached from CTF. Uncleaved Pc1 (Pc1U ) resides primarily in the endoplasmic reticulum (ER), whereas both Pc1cFL and Pc1deN traffic through the secretory pathwayin vivo . GPS cleavage is not a prerequisite, however, for Pc1 traffickingin vivo . Importantly, Pc1deN is predominantly found at the plasma membrane of renal epithelial cells. By functional genetic complementation with fivePkd1 mouse models, we discovered that CTF plays a crucial role in Pc1deN trafficking. Our studies support GPS cleavage as a critical regulatory mechanism of Pc1 biogenesis and trafficking for proper kidney development and homeostasis.