Rab6 regulates recycling and retrograde trafficking of MR1 molecules

Abstract

Mucosal-associated invariant T (MAIT) cells are an innate-like T cell subset important in the early response to bacterial and viral lung pathogens. MAIT cells recognize bacterial small molecule metabolites presented on the Class I-like molecule MR1. As with other Class I and Class II molecules, MR1 can likely sample ligands in the intracellular environment through multiple cellular pathways. Rab6, a small GTPase that regulates a number of endosomal trafficking pathways including retrograde transport to the trans-Golgi network (TGN), is involved in the presentation of ligands from Mycobacterium tuberculosis (Mtb) to MAIT cells. The Rab6-mediated trafficking pathway contains endosomal compartments that share features with the Mtb intracellular compartment. Using inducible expression of MR1, this study demonstrates that Rab6 regulates the recycling of MR1 molecules from the cell surface through endosomal trafficking compartments to the TGN. This Rab6-dependent pool of recycled MR1, which is available for reloading with ligands from bacterial pathogens like Mtb, may be important for early recognition of infected cells by MAIT cells in the lung.

Chronic obstructive pulmonary disease and cigarette smoke exposure lead to dysregulated MAIT cell activation by bronchial epithelial cells

“…To examine this possibility, we measured the surface expression of MR1 on primary BEC at basal levels and following induction of MR1 surface translocation through treatment with the ligand 6-formylpterin (6-FP). Consistent with our previous studies, the level of endogenous MR1 surface expression in ex-vivo primary BEC is relatively low compared to cell lines 39 , particularly those that overexpress MR1 40 . As such, we included BEAS-2B cells overexpressing MR1 in each assay as a control to confirm detection and surface translocation of MR1 (Figure S3a-b).…”

“…Little is known about the regulation of MR1 gene expression, although it is known that overexpression of MR1 increases MR1-dependent MAIT cell responses (e.g. Huber et al 40 ). Additionally, genome-wide studies have identified MR1 as a gene with altered expression or methylation status in the context of e-cigarette smoking 49 and COPD lungs 50 .…”

“…Statistical significance was determined as indicated by pairwise t test or two-way ANOVA with Bonferroni's multiple comparisons, using α=0.05. All images were analyzed using Imaris (Bitplane) as in 39,40 . Arrows indicate adherent S. pneumoniae (yellow) enumerated for analysis.…”

Comparative transcriptomes reveal pro-survival and cytotoxic programs of mucosal-associated invariant T cells upon Bacillus Calmette–Guérin stimulation

“…These metabolites function as agonist antigens to be loaded to MR1 protein and presented on antigen-presenting cells for MAIT cell activation ( McWilliam et al., 2020 ). Intracellular bacteria such as BCG and M. tuberculosis provide antigens for MAIT cell activation, likely involving endocytic compartments for antigen loading and presentation ( Huang et al., 2008 ; Harriff et al., 2016 ; Huber et al., 2020 ; Sharma et al., 2020 ). Our MAIT gene profiles in BCG stimulation showed similar alterations to memory CD8 + T cells or PBMCs with intracellular bacterial infections, whereas MAIT cell gene profiles in E. coli stimulation showed reversal association with CD8 + T cells in intracellular bacterial infections.…”

Delivery of loaded MR1 monomer results in efficient ligand exchange to host MR1 and subsequent MR1T cell activation

“…Freezebacks are frozen down during the first 2-3 passages and are routinely tested for mycoplasma. BEAS-2B MR1 -/- , BEAS-2B MR1 -/- : MR1A 20,21 and the BEAS-2B cell lines overexpressing GFP-tagged MR1A constitutively (BEAS-2B.MR1-GFP) 51 or under the tetracycline-inducible promoter 52 were described previously. THP-1 cells were obtained from ATCC.…”