STAT5A–α-actinin axis links actin integrity to mitochondrial homeostasis and innate immune activation

STAT5A is unique in its diverse expression in different cells. Here, we show that STAT5A deficiency results in reduced expression of the actin-bundling protein α-actinin-1, which alters cytoskeletal reorganization, including loss of actin bundles, reduction of cellular motility, and clustering of mitochondria and endoplasmic reticulum in the perinuclear region. These changes in cellular architecture led to production of ROS by the mitochondria, which may be explained by reduced peroxisome abundance. This, in turn, results in dsDNA breaks and formation of cytoplasmic micronuclei, and activating the cGAS-STING pathway, and mediating type I IFN production and the expression of IFN-stimulated genes. The ectopic expression of α-actinin-1 or STAT5A in STAT5A knockout cells is sufficient to restore actin bundle formation and nullifies all downstream effects. Conversely, inhibiting downstream steps suppresses only subsequent events in the pathway. STAT5A knockout results in a similar phenotype as seen with cytochalasin B, an inhibitor of actin polymerization. Overall, we show that STAT5A–α-actinin-1 links cytoskeleton integrity to mitochondrial immune regulation.