Non-canonical activation of VEGFA through TIMM44-dependent mitochondrial remodelling.

Coordination of mitochondrial functional states with nuclear transcriptional programs remain critical for cellular adaptation. Here, we identify mitochondrial protein import capacity as a regulator of redox-dependent signalling in tumour cells. We show that the mitochondrial import motor component TIMM44, which is upregulated in angiogenesis-driven tumours, drives respiratory remodelling without increasing mitochondrial abundance. This mitochondrial reprogramming establishes a redox-competent state that activates ASK1-p38MAPK, resulting in SP1-dependent upregulation of VEGFA independently of HIF stabilization. Importantly, induction of mitochondrial biogenesis via PGC-1α fails to recapitulate this response despite increased active mitochondrial content, demonstrating that abundance of active mitochondria or generic metabolic activation is insufficient to drive this HIF-independent transcription. Collectively, our findings identify mitochondrial protein import process as an active signalling regulator rather than a passive housekeeping role, which links mitochondrial proteostasis to redox-sensitive kinase activation and transcriptional control. This work highlights a non-canonical mitochondrial signalling mechanism through which cells couple organelle remodelling to gene expression programs.