ISR activator A8 is a specific small molecule activator of integrated stress response (ISR) through the binding of the cytosolic pattern recognition receptor RIG-I, subsequently activates the heme-regulated inhibitor (HRI) ISR kinase independent of an interferon response.
A8 promotes lipid droplet clearance with an EC50 of ~100 to 500 nM across multiple cell lines.
A8 activates an ATF4-firefly luciferase (FLuc) ISR reporter stably expressed in HEK293T cells with EC50 of 10 uM, which could be blocked by ISR inhibitor ISRIB.
A8 induces expression of ISR target genes CHAC1 and CHOP in HEK293T cells and MEF cells.
A8 activates ISR signaling through the noncanonical activation of the HRI kinase.
A8 binds to RIG-I with KD of 0.764 uM in HTRF assays, induces HRI-dependent ISR signaling in HEK293T cells, but independent of interferon signaling associated with RIG-I–dependent MAVS activation.
A8 robustly increases lipid droplet clearance in both MEFWT and MEFA/A cells with an EC50 of ~500 nM.