p300/CBP-Driven Acetylation Stabilizes PARP7 to Reinforce Negative Feedback on IFN-I Signaling

Immune suppression within the tumor microenvironment (TME) remains a major barrier to effective immunotherapy, yet the molecular mechanisms that constrain type I interferon (IFN-I) signaling in tumor cells are incompletely understood. PARP7 (also known as TIPARP), a mono-ADP-ribosyltransferase, has been reported to suppress IFN-I signaling by modifying TBK1. Here, we identify PARP7 as a previously unrecognized acetylation substrate of the histone acetyltransferases p300 and CBP. We show that p300/CBP-mediated acetylation of PARP7 at lysine 32 markedly enhances its stability, thereby reinforcing repression of the TBK1-IRF3-STAT1 axis and suppressing IFN-{beta}-induced expression of interferon-stimulated genes, including CXCL10. Beyond their established function as transcriptional co-activators that support tumor cell proliferation, our findings uncover a direct role for p300/CBP in shaping innate antitumor immunity. Pharmacological inhibition of p300/CBP catalytic activity by A-485 abolishes PARP7 acetylation, accelerates its proteasomal turnover, and restores IFN-I signaling. In immunocompetent tumor models, this is accompanied by enhanced CD8+ T-cell infiltration and effector function. Together, these findings define a p300/CBP-PARP7 regulatory axis, uncover a non-canonical role for p300/CBP in innate immune suppression, and nominate this pathway as a tractable target for restoring antitumor immunity.