Poster Presentation CD1-MR1 2024

The novel role of calcium-sensing synaptotagmins in MR1 antigen presentation of Mycobacterium tuberculosis (#108)

Se-Jin (Joyce) Kim 1 2 3 , Jessie Peterson 3 , Andrew Olive 4 , Elham Karamooz 1 3 , David Lewinsohn 1 2 3
  1. Department of Pulmonary and Critical Care Medicine, Oregon Health and Science University, Portland, OR, USA
  2. Department of Molecular Microbiology and Immunology, Oregon Health and Science University, Portland, OR, USA
  3. VA Portland Health Care System, Portland, OR, USA
  4. Department of Microbiology & Molecular Genetics, Michigan State University, East Lansing, Michigan, USA

Antigen presentation is crucial for the immune system to detect pathogens such as Mycobacterium tuberculosis (Mtb) and prime T cells for an immune response. MHC class I-related (MR1) molecule presents Mtb-derived riboflavin metabolites and induces production of IFN-γ and TNF-α by MR1-restricted T cells. Cellular mechanisms of MR1 antigen presentation from the endoplasmic reticulum to the cell surface using small ligands are well-defined. However, we have defined a role for trafficking of the MR1 molecule within endosomal compartments during intracellular microbial infection. Our lab has identified a unique role of calcium signaling in MR1 antigen presentation of Mtb, suggesting a role of calcium-sensing proteins in translocating the MR1-Mtb antigen complex to the cell surface. Synaptotagmins (Syts) are calcium-sensing membrane trafficking proteins that mediate vesicle fusion and exocytosis. Using IFN-γ release from human MR1-restriced T cells as an indicator, I found a 50% and 34% reduction in MR1 antigen presentation of Mtb when Syt1 and Syt7 was knocked out in airway epithelial BEAS-2B cells. Moreover, knocking out both Syt1 and Syt7 showed an interdependent relationship in regulating MR1 antigen presentation of Mtb. Interestingly, live-cell imaging showed that Syt1 and Syt7 co-localizes with lysosomes (Lamp1) and vesicles containing MR1 (Syt1: 55% and Syt7: 64%) and Mtb, indicating their potential role in the antigen loading of MR1 and/or translocation of loaded MR1 to the cell surface. The binding partners of Syt1 and Syt7 are synaptosome-associated protein (SNAP) 25 and SNAP23, respectively, for synaptic vesicle exocytosis. Knocking out SNAP23 in BEAS-2B cells showed a 75% reduction in presentation of Mtb and a 56% decrease in MR1 surface expression when induced with 6-formylpterin. These findings elucidate a potential mechanism that Syts regulate MR1 antigen presentation of Mtb by closely interacting with their SNAP binding partner.