The asthma-associated ORMDL3 gene product regulates endoplasmic reticulum-mediated calcium signaling and cellular stress

Alterations of protein folding or Ca2+ levels within the endoplasmic reticulum (ER) result in the unfolded-protein response (UPR), a process considered as an endogenous inducer of inflammation. Thereby, understanding how genetic factors modify UPR is particularly relevant in chronic inflammatory diseases such as asthma. Here we identified that ORMDL3, the only genetic risk factor recently associated to asthma in a genome wide study, alters ER-mediated Ca2+ homeostasis and facilitates the UPR. Heterologous expression of human ER-resident transmembrane ORMDL3 protein increased resting cytosolic Ca2+ levels and reduced ER-mediated Ca2+ signaling, an effect reverted by co-expression with the sarco-endoplasmic reticulum Ca2+ pump (SERCA). Increased ORMDL3 expression also promoted stronger activation of UPR transducing molecules and target genes while siRNA-mediated knock-down of endogenous ORMDL3 potentiated ER Ca2+ release and attenuated the UPR. In conclusion, our findings are consistent with a model in which ORMDL3 binds and inhibits SERCA resulting in a reduced ER Ca2+ concentration and increased UPR. Thus, we provide a first insight into the molecular mechanism explaining the association of ORMDL3 with proinflammatory diseases.