STIM1 Deficiency Leads to Specific Down-Regulation of ITPR3 in SH-SY5Y Cells

STIM1 is an endoplasmic reticulum (ER) protein that modulates the activity of a number of Ca(2+) transport systems. By direct physical interaction with ORAI1, a plasma membrane Ca(2+) channel, STIM1 activates the I(CRAC) current, whereas the binding with the voltage-operated Ca(2+) channel Ca(V)1.2 inhibits the current through this latter channel. In this way, STIM1 is a key regulator of Ca(2+) signaling in excitable and non-excitable cells, and altered STIM1 levels have been reported to underlie several pathologies, including immunodeficiency, neurodegenerative diseases, and cancer. In both sporadic and familial Alzheimer’s disease, a decrease of STIM1 protein levels accounts for the alteration of Ca(2+) handling that compromises neuronal cell viability. Using SH-SY5Y cells edited by CRISPR/Cas9 to knockout STIM1 gene expression, this work evaluated the molecular mechanisms underlying the cell death triggered by the deficiency of STIM1, demonstrating that STIM1 is a positive regulator of ITPR3 gene expression. ITPR3 (or IP3R3) is a Ca(2+) channel enriched at ER-mitochondria contact sites where it provides Ca(2+) for transport into the mitochondria. Thus, STIM1 deficiency leads to a strong reduction of ITPR3 transcript and ITPR3 protein levels, a consequent decrease of the mitochondria free Ca(2+) concentration ([Ca(2+)](mit)), reduction of mitochondrial oxygen consumption rate, and decrease in ATP synthesis rate. All these values were normalized by ectopic expression of ITPR3 in STIM1-KO cells, providing strong evidence for a new mode of regulation of [Ca(2+)](mit) mediated by the STIM1-ITPR3 axis.