Rab22a Regulates the Recycling of Membrane Proteins Internalized Independently of Clathrin

Abstract

Plasma membrane proteins that are internalized independently of clathrin, such as major histocompatibility complex class I (MHCI), are internalized in vesicles that fuse with the early endosomes containing clathrin-derived cargo. From there, MHCI is either transported to the late endosome for degradation or is recycled back to the plasma membrane via tubular structures that lack clathrin-dependent recycling cargo, e.g., transferrin. Here, we show that the small GTPase Rab22a is associated with these tubular recycling intermediates containing MHCI. Expression of a dominant negative mutant of Rab22a or small interfering RNA-mediated depletion of Rab22a inhibited both formation of the recycling tubules and MHCI recycling. By contrast, cells expressing the constitutively active mutant of Rab22a exhibited prominent recycling tubules and accumulated vesicles at the periphery, but MHCI recycling was still blocked. These results suggest that Rab22a activation is required for tubule formation and Rab22a inactivation for final fusion of recycling membranes with the surface. The trafficking of transferrin was only modestly affected by these treatments. Dominant negative mutant of Rab11a also inhibited recycling of MHCI but not the formation of recycling tubules, suggesting that Rab22a and Rab11a might coordinate different steps of MHCI recycling.

RAB-10 Is Required for Endocytic Recycling in theCaenorhabditis elegansIntestine

“…The accumulation of endocytic tracers in these enlarged endosomes indicates that the internalization step of endocytosis is not significantly impaired in rab-10 mutants, but rather the recycling of the fluid back to the body cavity is defective. We also found that basolaterally localized transmembrane cargo proteins thought to be endocytosed by both clathrin-mediated and clathrin-independent mechanisms label the enlarged endosomes, consistent with the proposal that rab-10, like rme-1, regulates endocytic recycling but not endocytosis per se and that clathrin-dependent and clathrin-independent cargo are likely to meet in the endosomal system, as has been suggested in mammalian cell systems (Naslavsky et al, 2004;Weigert et al, 2004). Because all exogenous tracers that we have identified for studying endocytosis in C. elegans are sent to lysosomes when internalized apically but not recycled back to the intestinal lumen, we have not been able to determine if rab-10 or rme-1 mutations also affect apical recycling in the worm intestine.…”

“…In MDCK cells Rab4 has also been reported to associate with early endosomes and a later compartment named the common endosome, where is promotes apical delivery of transcytotic cargo (Mohrmann et al, 2002). Rab11 is primarily associated with recycling endosomes and has been reported to act after Rab4 in nonpolarized cells, mediating recycling endosome to PM transport of clathrin-dependent and clathrin-independent recycling cargo (Sheff et al, 1999;Weigert et al, 2004). In polarized cells Rab11 is primarily associated with the ARE and is thought to function in the transport of cargo from the ARE to the PM (Casanova et al, 1999;Sheff et al, 1999;Brown et al, 2000).…”

“…GDP-bound Rab proteins are primarily found in the cytoplasm bound to GDP dissociation inhibitor (GDI; Seabra and Wasmeier, 2004 (Seabra and Wasmeier, 2004). A number of Rab proteins have been implicated in the endocytic recycling pathway including Rab4, Rab11, and Rab15 in the clathrin pathway, and Rab22 and the more distantly related Arf6 in the recycling of cargo internalized independently of clathrin (van der Sluijs et al, 1992;Ullrich et al, 1996;Sheff et al, 1999;Zuk and Elferink, 2000;Kauppi et al, 2002;Naslavsky et al, 2004;Weigert et al, 2004). In nonpolarized cells Rab4 is primarily associated with early endosomes and is thought to contribute to direct transport from early endosomes to the plasma membrane as well as early endosome to recycling endosome transport (Sheff et al, 1999).…”

SEC-10 and RAB-10 coordinate basolateral recycling of clathrin-independent cargo through endosomal tubules in Caenorhabditis elegans

“…Many CIE cargo proteins, such as the major histocompatibility complex class I (MHCI), the α-chain of the IL-2 receptor (TAC), CD59, CD44, and CD147, have been confirmed to follow the Arf6-associated CIE pathway, which is highly conserved from Caenorhabditis elegans to mammalian cells (3). Several players, including Rab10, Rab22, Rab35, Hook1, ALX-1, and RME-1/EHD-1, have been identified to modulate the recycling of CIE cargoes through different itineraries (3)(4)(5)(6)(7)(8).…”

Disruption of key GTPase regulators of endocytic recycling compartment does not interfere with soluble antigen crosspresentation in dendritic cells

“…Rab11a, a defining marker of ERC, interacts with many Rab11 family interaction proteins and regulates ERC traffic. 9 These three GTPases are therefore regarded as key regulatory components of trafficking to and from ERC, and presumably participate in crosspresentation. However, most of the work on the regulatory functions of these proteins was performed in cells deficient in crosspresentation; a definitive association thus remains speculative.…”