ER stress and its PERK branch enhance TCR-induced activation in regulatory T cells

Although accumulating evidence indicates participation of endoplasmic reticulum (ER) stress pathway or the unfolded protein response (UPR) in immunity, there still exists little information linking ER stress to regulatory T cells (Tregs). To evaluate the potential contribution of the UPR, we tested the effects of thapsigargin (TG), an ER stress inducer, on the function of Tregs. Here we reported that TG stimulation induced the up-regulation of the endoplasmic reticulum (ER)-stress chaperon Glucose-Regulated Protein 78 (GRP78), which is a master regulator of the UPR, the phosphorylation of eukaryotic initiation factor 2 alpha (elF2α) and the induction of activating transcription factor 4 (ATF4), which are both protein kinase R (PKR)-like ER kinase (PERK) downstream targets in Tregs. Simultaneously, we demonstrated that, under ER stress conditions, Tregs presented enhanced functional activity upon TCR stimulation, as illustrated with forkhead box transcription factor (Foxp3) expression, interleukin-10 (IL-10) and transforming growth factor-β (TGF-β) production and suppressive functional analysis. Notably, pretreatment with GSK2656157, a potent and selective PERK inhibitor, markedly diminished the TG-induced hyperresponsiveness of Tregs upon T cell antigen receptor (TCR) stimulation. Therefore, our findings illustrated the inter-connection and coordination of the evolutionarily conserved ER stress response and TCR signaling in Tregs and uncover a critical new role of the PERK branch of UPR in the regulation of Tregs function.