Coenzyme A homeostasis regulates hypoxic signalling via UBFD1 in triple-negative breast cancer

Hypoxia-inducible factors (HIFs) orchestrate cellular responses to oxygen deprivation and are frequently activated in triple-negative breast cancer (TNBC), driving metastasis and poor prognosis ^1,2 . However, the full mechanisms of how HIFs are activated are not completely understood. It has been long noted that certain tumours have decreased levels of coenzyme A compared to surrounding tissues ^3,4 , but the functional consequences of this remain unknown. Here, we identify Coenzyme A Synthase (CoAsy) as a novel regulator of HIF signalling. We demonstrate that CoAsy loss stabilises HIF-1α and HIF-2α independently of the canonical oxygen sensing pathway. Proximity-labelling proteomics revealed that CoAsy deficiency disrupts the association between HIF-1α and the proteasome through UBFD1, a novel CoA-binding protein that scaffolds HIFα for degradation. UBFD1’s CoA-dependent interaction with HIF-α is mediated by its PH domain, which undergoes CoAlation, an understudied post-translational modification. COASY loss of heterozygosity occurs in ∼1/3 of breast cancer patients and correlates with increased HIF activity, lack of hormone receptor expression and poor patient outcome. In vivo studies confirm that restoring CoAsy expression in tumours suppresses metastasis to the lung. These findings uncover a critical metabolic checkpoint regulating hypoxic signalling and identify CoAsy as a potential biomarker and therapeutic target in aggressive breast cancers.