Spatiotemporal regulation of DNA repair proteins between Golgi and nucleus maintains genome stability

The Golgi complex serves as a critical hub for cellular homeostasis, yet its communication with the nucleus remains largely unexplored. By analyzing and siRNA-validating localization data from the Human Protein Atlas, we uncovered substantial proteome interconnectivity between the Golgi and nucleus, including an unexpected enrichment for DNA repair factors. We identify a cluster of DNA damage response (DDR) proteins occupying distinct sub-Golgi compartments that redistribute dynamically between the Golgi and nucleus in response to genotoxic stress, with the type of DNA lesion shaping the direction of redistribution. Focusing on the homologous recombination (HR) regulator RAD51C, we show that DNA damage triggers ataxia telangiectasia mutated (ATM)-dependent release of a giantin-tethered Golgi RAD51C pool, with subsequent importin-β-dependent nuclear import, where repair-associated foci form. Giantin depletion prematurely releases RAD51C, producing aberrant nuclear foci lacking key DDR markers, reducing ATM activation and HR efficiency, elevating genome instability, and accelerating proliferation. The Golgi thus acts as a spatiotemporal coordination node for DDR factors safeguarding genomic stability.