TBC1D24 regulates recycling of clathrin-independent cargo proteins mediated by tubular recycling endosomes.

Many plasma membrane proteins enter cells by clathrin-independent endocytosis (CIE). Rab family small GTPases play pivotal roles in CIE and following intracellular trafficking of cargo proteins. Here, we provide evidence that TBC1D24, which contains an atypical Rab GAP domain, facilitates formation of tubular recycling endosomes (TREs) that are a hallmark of the CIE cargo trafficking pathway in HeLa cells. Overexpression of TBC1D24 in HeLa cells dramatically increased TREs loaded with CIE cargo proteins, while deletion of TBC1D24 impaired TRE formation and delayed the recycling of CIE cargo proteins back to the plasma membrane. We also found that TBC1D24 binds to Rab22A, through which TBC1D24 regulates TRE-mediated CIE cargo recycling. These findings provide insight into regulatory mechanisms for CIE cargo trafficking.