LIPT1 loss confers replication stress and PARP inhibitor sensitivity through PrimPol-mediated ssDNA gaps

Replication stress (RS) and altered metabolism are two hallmarks of cancer, yet how metabolic perturbations contribute to RS remains poorly understood. Lipotransferase 1 (LIPT1) catalyzes the covalent attachment of lipoic acid to mitochondrial 2-ketoacid dehydrogenases, sustaining flux through the tricarboxylic acid (TCA) cycle. Loss of LIPT1 causes accumulation of 2-hydroxyglutarate (2-HG), which is known to inhibit α-ketoglutarate (α-KG)–dependent histone demethylases and promotes heterochromatin formation. Here, we show that 2-HG–driven heterochromatin impedes replication fork progression, causing fork stalling and RS in LIPT1-deficient cancer cells. To bypass stalled forks, PrimPol-mediated repriming resumes DNA synthesis but leaves behind single-stranded DNA (ssDNA), which requires poly (ADP-ribose) polymerase 1 (PARP1) for repair. Furthermore, nascent DNA at reprimed forks undergoes MRE11-dependent degradation, further destabilizing replication fork integrity. Consequently, LIPT1 deficiency promotes replication and genome instability, and therapeutic vulnerability to PARP inhibitor. Together, these findings reveal a mechanistic link between mitochondrial lipoylation and replication fork stability, uncovering a metabolic basis for genome instability in cancer.