A novel role for Rab23 in the trafficking of Kif17 to the primary cilium

Abstract

The small GTPase Rab23 is an antagonist of Sonic hedgehog (Shh) signaling during mouse development. Since modulation of Shh signaling depends on the normal functioning of the primary cilium, and overexpression of Rab23's putative RabGAP, Evi5L, led to reduced ciliogenesis, Rab23 could have a role at the primary cilium. Rab23 wild-type and constitutively active Rab23 Q68L mutant were found enriched at the primary cilium. In testing Rab23's role in the ciliary targeting of known cargoes, ciliary localization of a kinesin-2 motor protein Kif17 was disrupted in Rab23 silenced cells. Co-immunoprecipitation and affinity binding studies revealed that Rab23 exists in a complex with Kif17 and Importin β2 (Kif17's putative ciliary import carrier), implying that Kif17 requires binding to regulatory proteins like Rab23 for its ciliary transport. Although a ciliary-cytoplasmic gradient of nuclear Ran is necessary in regulating Kif17's ciliary transport, Rab23 and Ran appear to have differing roles in ciliary entry of Kif17. Our findings have uncovered a hitherto unknown effector of Rab23 and demonstrated how Rab23 could mediate Kif17's transport to the primary cilium.