Abstract

Signal transducers and activators of transcription (STAT) are central regulators of cytokine-mediated immunity in metazoans, yet their ancestral functions prior to the emergence of interferon signalling remain poorly understood. Dictyostelium discoideum expresses four STAT-like factors that impact the intracellular fate of Mycobacterium marinum (Mm). Using dst knockout strains, we identify DstA and DstB as susceptibility factors, whereas DstC acts as a resistance factor, revealing a regulatory axis controlling the integrity of the Mm-containing vacuole (MCV). Despite the absence of canonical cytokine receptors and JAK kinases, DstA rapidly translocates to the nucleus in a damage-dependent manner, whereas DstB and DstC exhibit delayed cytosolic redistribution. DstA associates with VacA, a membrane microdomain component, regulates its transcription and accumulation at the MCV, while VacA acts as a cytoplasmic anchor that limits DstA nuclear translocation. Our findings establish STAT-like proteins as evolutionarily ancient regulators of vacuole integrity and host defence, providing new insights into the origins of STAT-mediated immune responses during mycobacterial infection.