Ca2+ is an intracellular danger signal promoting STING activation

Calcium release in host cells is essential for viral infection and survival, and mutations disrupting calcium homeostasis are associated with chronic viral infections or autoimmune diseases in patients, yet the biological significance of Ca2+ signaling on STING activation remains unclear. Here we show that cytosolic Ca2+ is sensed by host cells as an immediate-early danger signal. Viral infection-activated Rho GTPases and phospholipase C-β induce ITPR-mediated, while STING translocation induces TRPV2-mediated ER Ca2+ release, both leading to store-operated Ca2+ entry through ORAI channels. Ca2+ influx activates calmodulin (CaM)-dependent protein kinases CaMKK and CaMK1D. Activated CaMK1D phosphorylates STING allowing for TBK1 trans-autophosphorylation. Inhibiting Ca2+ signaling or mutating CaMK1D-phosphorylating STING sites impairs STING activation. Ca2+ signaling is also required for STING-mediated autophagy and lysosome biogenesis, inhibited by CaMKK or CaMK inhibitors, or by deleting CaMKK1/2 or CaMK1D. These results support a two-signal mode for STING activation in which the Ca2+-CaM-CaMKK-CaMK cascade is indispensable.