The role of MHC class I recycling and Arf6 in cross-presentation by murine dendritic cells.

Sebastian Montealegre,Peter Van Endert,Anastasia Abramova,Valerie Manceau,Anne-Floor De Kanter

doi:10.26508/lsa.201900464

Abstract

Cross-presentation by MHC class I molecules (MHC-I) is critical for priming of cytotoxic T cells. Peptides derived from cross-presented antigens can be loaded on MHC-I in the endoplasmic reticulum and in endocytic or phagocytic compartments of murine DCs. However, the origin of MHC-I in the latter compartments is poorly understood. Recently, Rab22-dependent MHC-I recycling through a Rab11+ compartment has been suggested to be implicated in cross-presentation. We have examined the existence of MHC-I recycling and the role of Arf6, described to regulate recycling in nonprofessional antigen presenting cells, in murine DCs. We confirm folded MHC-I accumulation in a juxtanuclear Rab11+ compartment and partially localize Arf6 to this compartment. MHC-I undergo fast recycling, however, both folded and unfolded internalized MHC-I fail to recycle to the Rab11+Arf6+ compartment. Therefore, the source of MHC-I molecules in DC endocytic compartments remains to be identified. Functionally, depletion of Arf6 compromises cross-presentation of immune complexes but not of soluble, phagocytosed or mannose receptor-targeted antigen, suggesting a role of Fc receptor-regulated Arf6 trafficking in cross-presentation of immune complexes.

Highlights

MHC class I molecules (MHC-I) mainly present peptides derived through the degradation of intracellular proteins to CTL, using the so-called direct antigen presentation pathway
Whereas peptide-bound class I molecules can recycle from an early endosome (Zagorac et al, 2012), once β2m has dissociated from the MHC-I heavy chain (HC), the vast majority become targeted to degradation in the lysosomes (Montealegre et al, 2015), a late endosomal recycling pathway has been reported (Mahmutefendicet al, 2017)
Having examined MHC-I recycling in Arf6-sufficient and -depleted murine DCs, we report here the surprising finding that, whereas DC MHC-I engages in a fast recycling pathway, internalized folded and unfolded MHC-I do not reach the endocytic recycling compartment (ERC)-like compartment, suggesting that this compartment does not contain recycling MHC-I which, may not contribute significantly to crosspresentation in murine BM-DCs

Summary

Introduction

MHC class I molecules (MHC-I) mainly present peptides derived through the degradation of intracellular proteins to CTL, using the so-called direct antigen presentation pathway. Work on nonprofessional APCs has shown that upon arrival to the cell surface, MHC-I can divide into different membrane domains according to their peptide-loading status (Mahmutefendicet al, 2011), from where they are constantly internalized to endosomal compartments in a clathrin-independent manner (Eyster et al, 2009; Montealegre & van Endert, 2018) In such cell lines, MHC-I can recycle to the cell surface, in a process regulated by the small GTPases Arf (Radhakrishna & Donaldson, 1997; Jovanovic et al, 2006), Rab (Weigert et al, 2004) and the epsilon homology domain proteins 1 and 3 (EHD-1 and EHD-3). Whereas peptide-bound class I molecules can recycle from an early endosome (Zagorac et al, 2012), once β2m has dissociated from the MHC-I heavy chain (HC), the vast majority become targeted to degradation in the lysosomes (Montealegre et al, 2015), a late endosomal recycling pathway has been reported (Mahmutefendicet al, 2017)

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