NAADP-mediated endosomal calcium signaling enables MR1 presentation of Mycobacterium tuberculosis 4464

Abstract Description The immune system has developed specialized mechanisms to recognize intracellular pathogens such as Mycobacterium tuberculosis (Mtb). Major Histocompatibility Complex, Class I-Related molecule (MR1) is a conserved nonclassical antigen presenting molecule that presents ligands derived from Mtb riboflavin synthesis to MR1-restricted T cells (MR1Ts). While endosomal trafficking facilitates MR1 antigen presentation, the exact mechanisms by which MR1 loading of Mtb-derived ligands occurs are not known. We found that endosomal calcium signaling mediates MR1 antigen presentation during Mtb infection. Nicotinic acid adenine dinucleotide phosphate (NAADP) acts as a second messenger for lysosomal calcium release by activating two-pore calcium channels (TPCs). Interference with TPCs via siRNA-mediated knockdown or treatment with a selective NAADP antagonist reduces MR1 antigen presentation of Mtb-derived ligands. NAADP synthesis is catalyzed by NAD glycohydrolases or dual NADPH oxidases. Inhibition of NAD glycohydrolase activity with a quinolone carboxamide inhibitor reduces MR1 antigen presentation of Mtb-derived ligands. These data suggest this enzymatic activity is important. We are investigating candidate proteins that possess this enzymatic activity to further elucidate requirements for MR1 antigen presentation of Mtb-derived ligands. Together, these findings suggest a unique role for endosomal calcium sensing in the recognition of the Mtb-infected cell. Topic Categories Antigen and Dendritic Cell Processing, Presentation, and Biology (AGDC)