Fig 2: Active EP300 inactivates HDAC1 in IPF. a WB using the indicated antibodies and whole-cell protein extracts from Ctrl and IPF lung fibroblasts (hLF) derived from three different donors each. ActEP300, active EP300. See Supplementary Fig. 6a–c. b Top: HDAC1-specific activity assay using nuclear or cytosolic protein extracts from Ctrl or IPF hLF treated with placebo (vehicle solution) or 10 µM EP300 inhibitor (EP300ihn, CBP30). Bottom: WB monitoring the quality of the fractions used in the HDAC1 activity assay. LMNB1, nuclear marker. GAPDH, cytosolic marker. See Supplementary Figs. 6d and 7a. c Sequential ChIP (ChIP–reChIP) analysis of representative MIRLET7D target promoters using HDAC1- or HDAC2-specific antibodies, followed by AcK- or PhS-specific antibodies, respectively, and chromatin isolated from Ctrl or IPF hLF after treatment with EP300inh or transfection of a dominant-negative EP300 (dnEP300) construct. IgG, immunoglobulin G (negative control). See Supplementary Fig. 7. d WB using the indicated antibodies after Co-IP assay using immunoglobulin G (IgG; negative control) or HDAC1-specific antibodies to immunoprecipitate endogenous HDAC1 from nuclear protein extracts of Ctrl hLF. Input, 5% of IP starting material. e WB after Co-IP assay as in d using C1D-specific antibodies to immunoprecipitate endogenous C1D from nuclear protein extracts of Ctrl hLF that were transfected with full-length (fl) or deletion mutant 3 (del3, lacking C1D interaction domain on amino acids 1–285) HA-tagged EXOSC10 constructs25. f WB after Co-IP assay as in d using C1D-specific antibodies to immunoprecipitate endogenous C1D from nuclear protein extracts of IPF hLF that were either transfected with empty plasmid or with dnEP300 expression construct or treated with EP300inh as indicated. In all plots, data are shown as mean (SD) (n = 3 biologically independent experiments in b; n = 2 biologically independent experiments in c); asterisks, P-values after unpaired t-test, two tailed, ***P < 0.001; **P < 0.01; *P < 0.05. Source data are provided as a Source Data file

Fig 3: Schematic representation of epidermal growth factor (EGF)‐mediated high‐mobility group protein A2 (HMGA2) transcription in hepatocellular carcinoma (HCC) cells. EGF can induce p300 phosphorylation at the Ser1834 site through activation of the PI3K/AKT signaling pathway in HCC; p300 subsequently catalyzes histone H3 acetylation at K9 residues, leading to HMGA2 transcription in HCC. EGFR, epidermal growth factor receptor

Fig 4: EP300 inhibition counteracts fibrosis hallmarks in bleomycin mouse model. a Scheme shows experimental setup. Three group of mice (control group n = 4, experimental groups n = 5, in each group biologically independent animals) were orotracheally instilled with saline or bleomycin (1.25 mU per g body weight) at day 0 and subsequently orotracheally instilled with placebo (vehicle solution) or EP300 inhibitor (EP300inh, CBP30, 550 pmol per g body weight) on days 9, 12, 15, and 18. Mice were collected for analysis at day 21. b Top: representative histological analysis using hematoxylin and eosin (H&E) stain on left lung sections from mice treated as in a. Squares are shown below at higher magnification. Bottom, representative light microscopy after Sirius red staining monitoring collagen deposition on left lung sections from mice treated as in a. Scale bar = 100 µm. See Supplementary Fig. 8. c Left: fibrotic (Ashcroft) score quantification from representative Sirius red staining on left lung sections from mice treated as in a. Right, collagen content quantification by Sircol assay using lung homogenates from mice treated as in a. Data are shown as mean (SD) (n = 10, 8, or 7 biologically independent samples); asterisks, P-values after unpaired t-test, two tailed, ***P < 0.001. Source data are provided as a Source Data file. d WB using the indicated antibodies and lung homogenates from three representative mice from each experimental group described in a. e Confocal microscopy after immunostaining using EP300, actP300, or inaEP300-specific antibodies in lung sections from representative mice from each experimental group described in a. ActEP300, active EP300; inaEP300, inactive EP300. DAPI, nuclear staining. Scale bar, 500 µm

Fig 5: Model. a In healthy lung fibroblasts, C1D-bound MIRLET7D-ncRNA duplexes attract active HDAC1/2 and the MiCEE complex to specific loci. Active HDAC1/2 deacetylate H3K27, whereas EZH2 mediates trimethylation of H3K27, thereby leading to heterochromatin formation and transcriptional silencing. b In IPF lung fibroblasts, reduced MIRLET7D and active EP300, which inactivates HDAC1/2 and interacts with C1D, disrupt the MiCEE complex interfering with heterochromatin formation and transcriptional silencing at specific loci