CUDC-907 attenuates pulmonary fibrosis by reversing HDAC1-mediated SMAD4 deacetylation at lysine 45.

Pulmonary fibrosis is characterized by the persistent activation of fibroblasts into myofibroblasts, a process largely driven by TGF-β/SMAD signaling. Acetylation has emerged as a fundamental regulatory mechanism in cellular homeostasis and tissue fibrosis, yet whether and how the acetylation of core SMAD transcription factors at specific residues orchestrates this process remains entirely unknown. Here, through a screen of FDA-approved epigenetic modulators, we identify CUDC-907, a dual HDAC and PI3K inhibitor, as a potent suppressor of fibroblast activation and lung fibrosis. CUDC-907 attenuates TGF-β1-induced myofibroblast differentiation, contractile activity, and extracellular matrix deposition in human lung fibroblasts. Mechanistically, we demonstrate that TGF-β1 triggers the recruitment of HDAC1 to deacetylate SMAD4 at lysine 45 (K45), a modification that is essential for SMAD complex assembly and nuclear translocation. CUDC-907 targets this pathway by inhibiting HDAC1, thereby restoring SMAD4 K45 acetylation and sterically hindering the formation of the heteromeric SMAD signaling complex. Notably, mutation of K45 (K45R) or HDAC1 inactivation renders fibroblasts refractory to the anti-fibrotic effects of CUDC-907, establishing the HDAC1-SMAD4 K45 axis as the primary therapeutic target. Furthermore, therapeutic administration of CUDC-907 significantly ameliorates lung injury and collagen deposition in a bleomycin-induced mouse model. Collectively, our findings identify SMAD4 K45 acetylation as a critical molecular switch in fibrogenesis and position CUDC-907 as a promising epigenetic strategy for the treatment of fibrotic lung diseases.