IRF3-p300 axis controls global acetylation and mitotic progression

Accurate mitotic progression depends on precisely regulated post-translational modifications, including lysine acetylation, but the upstream mechanisms governing acetylation during mitosis remain unclear. Here, we identify the IRF3-p300 axis as a major regulator of global protein acetylation during mitosis. We show that p300 serves as the major lysine acetyltransferase active during mitosis, and its enzymatic activity is essential for proper cell division. Notably, p300 activation during mitosis requires phosphorylation and dimerization of IRF3, a transcription factor known for its role in innate immunity. IRF3 interacts with and activates p300, and depletion of either IRF3 or p300 reduces global mitotic protein acetylation and delays mitotic progression. These defects are rescued by wild-type IRF3 or p300, but not by phosphorylation- or dimerization-deficient IRF3 mutants or catalytically inactive p300. Mass spectrometry analysis reveals that the mitotic acetylome is substantially altered upon loss of IRF3 or p300, with widely overlapping subsets of non-histone proteins-many involved in RNA biogenesis and processing-being affected. These findings reveal a non-canonical role for IRF3 as an upstream activator of p300 and establish the IRF3-p300 axis as a key signaling pathway that ensures proper mitotic progression through global regulation of protein acetylation.