Loss of KIF13B causes time-dependent changes in ciliary polycystin-2 levels and extracellular vesicle release

Abstract

The polycystic kidney disease gene product polycystin-2 (PC2) localizes to and is released from primary cilia in extracellular vesicles (EVs). We report that KIF13B regulates ciliary EV release and PC2 levels in kidney epithelial cells in a time-dependent manner and show that KIF13B itself is released from the ciliary tip. In early stages of ciliation, Kif13b-/- cells displayed excessive ciliary accumulation of PC2 and initially released fewer small EVs than control cells. Over time, ciliated Kif13b-/- cells increased their small EV release rate to control levels, however proteomic analysis identified >50 proteins depleted from mutant EV samples. These included the ubiquitin E3 ligase ITCH and palmitoyl transferase ZDHHC5, which localized to primary cilia. Mature Kif13b-/- cilia exhibited aberrant membrane bulges and decreased PC2 and ALIX, an ITCH substrate that negatively regulated ciliary PC2 levels. Our work provides new insight into the mechanisms of ciliary EV release, which is important for regulating ciliary membrane homeostasis and signalling function.