New causal relationship between PLA2g6, store-operated Ca2+ entry, refilling of Ca2+ stores and ER stress in mouse embryonic fibroblasts.

Store-operated Ca2+ entry (SOCE) is essential for maintenance and timely refilling of Ca2+ stores in the endoplasmic reticulum (ER). Here we used molecular, imaging and genetic approaches to unmask new determinants of this process and their role in ER stress and the unfolded protein response (UPR). Analysis of endogenous SOCE in primary embryonic fibroblasts (MEF) from a new knockout mouse model revealed that constitutive genetic impairment of interaction of specific plasma membrane-associated phospholipase A2 (PLA2g6) with STIM1 (ER-resident Ca2+ sensor) leads to impairment of endogenous SOCE. Such deficiency resulted in sustained depletion of intracellular Ca2+ stores, and more than 50% reduction in ionomycin-induced Ca2+ release from the stores. We found that PLA2g6 and SOCE-deficient MEF cells experience significant ER stress: qRT-PCR analysis of ER stress markers showed a 2–4 fold increase in mRNA expression levels of BiP, CHOP, and TXNIP. Discovery of a new causal relationship between PLA2g6, SOCE, ...