Rab22A recruits BLOC‐1 and BLOC‐2 to promote the biogenesis of recycling endosomes

Abstract

Recycling endosomes ( REs) are transient endosomal tubular intermediates of early/sorting endosomes (E/ SEs) that function in cargo recycling to the cell surface and deliver the cell type‐specific cargo to lysosome‐related organelles such as melanosomes in melanocytes. However, the mechanism of RE biogenesis is largely unknown. In this study, by using an endosomal Rab‐specific RNAi screen, we identified Rab22A as a critical player during RE biogenesis. Rab22A‐knockdown results in reduced RE dynamics and concurrent cargo accumulation in the E/ SEs or lysosomes. Rab22A forms a complex with BLOC‐1, BLOC‐2 and the kinesin‐3 family motor KIF13A on endosomes. Consistently, the RE‐dependent transport defects observed in Rab22A‐depleted cells phenocopy those in BLOC‐1‐/ BLOC‐2‐deficient cells. Further, Rab22A depletion reduced the membrane association of BLOC‐1/ BLOC‐2. Taken together, these findings suggest that Rab22A promotes the assembly of a BLOC‐1‐ BLOC‐2‐ KIF13A complex on E/ SEs to generate REs that maintain cellular and organelle homeostasis.