Modification of glycan chains as a mechanism to regulate SOCE (P1156)

Abstract

Abstract T cell receptor mediated activation requires the influx of calcium from the extracellular medium. Here, the endoplasmic reticulum (ER) Ca2+ sensor STIM1 reports the decrease in luminal [Ca2+] caused by IP3 receptor activity, clusters and directly binds and activates Orai1 channels, providing Ca2+ influx (store-operated, SOCE) essential for immune cell activation. We are interested in the regulation and modulation of this pathway. Because alterations of glycosylation of several T cell epitopes are implicated in immunsenescence and cancer, we investigated N-glycosylation site mutants of STIM1 and Orai1 and describe a STIM1 mutant (NN/DQ) which results in a strong gain-of-function. The mutant leads to a significant increase in the number of active channels despite a concomitant decrease in Orai1 protein, uncovering a novel CRAC channel regulatory mechanism. While we have already shown that the STIM1 mutant phenotype is mainly due to an increased rate of STIM1 oligomerization, we now investigate the specificity of this effect by analysing Ca2+ influx mediated by Orai2 and Orai3 and also started delineating the mechanism of Orai1 protein reduction. In addition, we are investigating the complex glycosylation pattern of primary human T cells and its effect on SOCE. Our findings indicate that the cell type specific repertoire of N-glycoslytransferases modifies the influence of the Orai1 glycan chains on Ca2+ influx.