STING dampens the unfolded protein response to enable the presentation of self antigens on MHC-I during inflammation

A growing body of evidence supports the contribution of the long-lasting adaptive immune system in Parkinson’s disease (PD). We showed that the PD-associated protein PINK1 negatively regulates the presentation of mitochondrial antigens (MitAP) on MHC-I molecules. *In vivo* evidence indicated that MitAP activation in mice, in the absence of PINK1, led to cytotoxic CD8+ T cell stimulation and severe motor impairments, reversible by L-DOPA. We show here that following TLR4 activation, MitAP is engaged through a pathway involving cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING), which acts as a rheostat to dampen the unfolded protein response (UPR). Without STING, the stress response is amplified, leading to a translational attenuation that inhibits the expression of XBP1s, a transcription factor required for MitAP. STING activity also regulates the repertoire of peptides displayed at the cell surface during inflammation, highlighting a potential role in immunosurveillance. These findings establish STING and the UPR as key immune regulators targetable for therapeutic intervention during autoimmune diseases and PD.