Role of the GTPase Rab22a in the recruitment of ER components to dendritic cell phagosomes and endosomes.

CROCE, CRISTINA; ZALAZAR, ALEJANDRO; DINAMARCA, SOFÍA; MAYORGA, LUIS; CEBRIÁN, IGNACIO

Buenos Aires

Congreso; Reunión Conjunta de Sociedades de Biociencias; 2017

Cross-presentation is the process by which antigen presentingcells (APCs) expose exogenous antigens-derived peptides in associationwith MHC class I molecules to CD8+ T lymphocytes in orderto trigger cytotoxic immune responses. In this context, dendriticcells (DCs) are the most potent APC able to achieve cross-presentationefficiently. Several studies have focused on deciphering themolecular mechanisms underlying this process, but the connectionbetween the endocytic network and endoplasmic reticulum (ER)-derivedcompartments is still poorly understood. In this study, we haveinvestigated the role of the small GTPase Rab22a during the deliveryof ER resident proteins to DC endosomes and phagosomes. Ina previous work, we have shown that Rab22a is crucial to regulateantigen cross-presentation, the phagosomal acquisition of MHC-Iand the recycling of these molecules to the cell surface in DCs.Now, we show that the knock-down (KD) of Rab22a expression inDCs impairs the normal delivery of ER components exclusively toendosomes but not to phagosomes, suggesting a differential role ofRab22a in these compartments. We have validated these observationsby performing a biochemistry assay (phagosomal purification),immunofluorescence and confocal microscopy, and a flow cytometry-based approach. Furthermore, we evidenced that endosomalmaturation is drastically altered in Rab22a KD DCs, as comparedto control cells. Interestingly, this phenomenon was not observedduring the process of phagosomal maturation. Altogether, our resultsindicate that Rab22a displays major regulatory functions inendosome maturation and is important to guarantee the proper recruitmentof ER components to DC endosomes.