Abstract

Cell death, DNA damage, and inflammation are closely interconnected processes implicated in ageing, cancer, and inflammatory disorders, yet the endogenous mechanisms linking them remain unclear. We previously identified cell-free chromatin particles (cfChPs), released from dying cells, as biologically active entities that enter neighboring cells and induce DNA damage and inflammation. Here, we show that serum-derived circulating cfChPs are rapidly internalized by human peripheral blood mononuclear cells and trigger a previously unrecognized biphasic STING signaling response. An early phase involves rapid STING trafficking to the perinuclear region and nucleus, with activation of IRF3 and NF-{kappa}B preceding detectable DNA damage. This is followed by a later phase characterized by STING phosphorylation, puncta formation, persistent DNA damage, and robust inflammatory cytokine production. Pharmacological inhibition or genetic deletion of STING markedly attenuated these responses. These findings identify extracellular cfChPs as endogenous DNA-damaging agents and reveal biphasic STING signaling as a mechanistic link between cell death, DNA damage, and sterile inflammation.