Hypoxia-mimicked mitochondrial stress triggers APOBEC3A-mediated DNA damage via non-canonical innate immune activation.

Hypoxia is a hallmark of the tumour microenvironment, driving metabolic reprogramming, immune activation, and genome instability. Here, we showed that cobalt chloride (CoCl2), a hypoxia-mimicking agent, potently induces the expression of the DNA cytidine deaminase APOBEC3A (A3A) in THP-1, a human monocytic cell line. A3A upregulation occurred in a dose-dependent manner, independently of type I interferon signalling, and was accompanied by increased double-strand DNA breaks. Transcriptomic profiling revealed broad hypoxia-driven reprogramming, characterized by activation of the stress response and downregulation of mitochondrial signalling pathways. Mechanistically, cobalt chloride induced mitochondrial dysfunction, metabolic reprogramming, and cytosolic release of mitochondrial DNA (mtDNA). Cytosolic mtDNA was transcribed by RNA polymerase III into immunostimulatory RNA, which activated the RIG-I/TRAF6/NF-κB signalling cascade to drive A3A expression. Inhibition or knockdown of RNA polymerase III markedly reduced both A3A levels and DNA damage, highlighting the central role of this pathway. All together, our findings reveal a novel interferon-independent signalling route through which hypoxia-induced mitochondrial stress activates A3A, directly linking metabolic dysfunction to genome instability. This mechanism involves mitochondrial perturbation as a key driver of APOBEC3-mediated mutagenesis in hypoxic tumours and other diseases associated with mitochondrial stress.