Rab22a Regulates the Sorting of Transferrin to Recycling Endosomes

Abstract

Rab22a is a member of the Rab family of small GTPases that localizes in the endocytic pathway. In CHO cells, expression of canine Rab22a (cRab22a) causes a dramatic enlargement of early endocytic compartments. We wondered whether transferrin recycling is altered in these cells. Expression of the wild-type protein and a GTP hydrolysis-deficient mutant led to the redistribution of transferrin receptor to large cRab22a-positive structures in the periphery of the cell and to a significant decrease in the plasma membrane receptor. Kinetic analysis of transferrin uptake indicates that internalization and early recycling were not affected by cRab22a expression. However, recycling from large cRab22a-positive compartments was strongly inhibited. A similar effect on transferrin transport was observed when human but not canine Rab22a was expressed in HeLa cells. After internalization for short periods of time (5 to 8 min) or at a reduced temperature (16°C), transferrin localized with endogenous Rab22a in small vesicles that did not tubulate with brefeldin A, suggesting that the endogenous protein is present in early/sorting endosomes. Rab22a depletion by small interfering RNA disorganized the perinuclear recycling center and strongly inhibited transferrin recycling. We speculate that Rab22a controls the transport of the transferrin receptor from sorting to recycling endosomes.

Structural basis for Rab GTPase activation by VPS9 domain exchange factors

“…It is also possible that subcellular localization or other unidentified mechanisms might sharpen the specificity for RAB5 and/or RAB21, or otherwise provide conditions favorable for activation of RAB22. Recent studies indicate that RAB5, RAB21 and RAB22 have overlapping subcellular distributions in the endosomal system and may have distinct functional roles in common or related endocytic processes [28][29][30][31][32]46 . One hypothesis consistent with the structural observations, specificity profiles and currently available cell-biological data is that RABEX-5, RIN1 and potentially other mammalian VPS9 domain GEFs have coevolved with RAB5-subfamily GTPases from common progenitors in lower ancestral eukaryotes to facilitate and coordinate more elaborate control mechanisms required for regulation of complex endosomal trafficking networks in higher eukaryotic organisms.…”

Rabex-5 Is a Rab22 Effector and Mediates a Rab22-Rab5 Signaling Cascade in Endocytosis

“…A previously described shRNA specific for human Rab22 (Magadan et al, 2006) was used in this study and expressed in HeLa cells via the pSIREN-RetroQ-DsRed-Express vector, which simultaneously expressed dsRed-Express, an RFP, for identification of transfected cells by fluorescence microscopy. The effective knock down of Rab22 expression in the cell was confirmed by immunofluorescence microscopy with an anti-Rab22 antibody.…”

“…Rab22 is another Rab GTPase localized on early endosomes and is closely related to Rab5 with 52% sequence identity (Olkkonen et al, 1993;Kauppi et al, 2002). Inhibition of Rab22 function via small interfering RNA (siRNA) blocks recycling of endocytosed cargoes such as transferrin receptor and MHC-I (Weigert et al, 2004;Magadan et al, 2006). Overexpression of Rab22 in the cell leads to enlargement of early endosomes (Kauppi et al, 2002), similar to the effect of Rab5.…”

Engrailed-2 regulates genes related to vesicle formation and transport in cerebellar Purkinje cells

“…Similarly, the transport back to the trans-Golgi-network might be hindered in L7En-2 PCs since expression of genes involved in these processes, gga2 and rab21 (Black and Pelham, 2000;Simpson et al, 2004) were found to be reduced following En-2 overexpression. Finally, genes involved in recycling of endocytic vesicles (rab22a, snx10 and snx15; Magadan et al, 2006;Qin et al, 2006;Phillips et al, 2001) were also reduced in expression. Taken together, the set of differentially expressed genes following En-2 overexpression pinpoint to a dysregulation of vesicle formation, maturation and sorting; such interpretation is fully consistent with the morphologically observed changes in L7En-2 PCs, from the conspicuous absence of the Golgi apparatus from the axonal pole, to the delayed and reduced dendritogenesis in these cells (Jankowski et al, 2004).…”