Phosphoinositide 3-Kinase-C2α Regulates Polycystin-2 Ciliary Entry and Protects against Kidney Cyst Formation

Signaling from the primary cilium regulates kidney tubule development and cyst formation. However, the mechanism controlling targeting of ciliary components necessary for cilium morphogenesis and signaling is largely unknown. Here, we studied the function of class II phosphoinositide 3-kinase-C2 alpha (PI3K-C2 alpha) in renal tubule-derived inner medullary collecting duct 3 cells and show that PI3K-C2 alpha resides at the recycling endosome compartment in proximity to the primary cilium base. In this subcellular location, PI3K-C2 alpha controlled the activation of Rab8, a key mediator of cargo protein targeting to the primary cilium. Consistently, partial reduction of PI3K-C2 alpha was sufficient to impair elongation of the cilium and the ciliary transport of polycystin-2, as well as to alter proliferation signals linked to polycystin activity. In agreement, heterozygous deletion of PI3K-C2 alpha in mice induced cilium elongation defects in kidney tubules and predisposed animals to cyst development, either in genetic models of polycystin-1/2 reduction or in response to ischemia/reperfusion-induced renal damage. These results indicate that PI3K-C2 alpha is required for the transport of ciliary components such as polycystin-2, and partial loss of this enzyme is sufficient to exacerbate the pathogenesis of cystic kidney disease.