CPSF6-mediated alternative polyadenylation of RUNX1 to regulate silica-induced pulmonary fibrosis progression

Pulmonary fibrosis occurs when myofibroblasts and the extracellular matrix (ECM) excessively accumulate in the lung interstitium. Detailed studies elucidating the role of cleavage and polyadenylation-specific factor 6 (CPSF6) during fibroblast-myofibroblast transition (FMT) remain limited. A silica-induced mouse pulmonary fibrosis model and a transforming growth factor-β1 (TGF-β1) induced fibroblast activation model were performed to investigate the role and mechanism of CPSF6. The expression of CPSF6 and profibrotic markers was determined by quantitative real-time polymerase chain reaction (qRT-PCR) analysis, Western blotting, and immunofluorescence assays. Dual-luciferase reporter gene assays and RNA immunoprecipitation (RIP) assays were performed to investigate the association between RUNX1 3' untraslated region (3′UTR) and miR-30a-5p. CPSF6 was downregulated in silica-induced murine fibrotic lung tissues and primary fibroblasts. Silencing CPSF6 via adeno-associated virus (AAV) in vivo exacerbated pulmonary fibrosis, while ectopic CPSF6 expression mitigated the condition. TGF-β1 effectively decreased CPSF6 expression in fibroblasts (MRC-5 and mouse primary lung fibroblast). CPSF6 overexpression blocked the profibrotic effect of TGF-β1, while inhibition of CPSF6 was found to trigger FMT. Notably, Runt-related transcription factor 1 (RUNX1), a crucial transcription factor implicated in fibrosis, was identified as a downstream effector of CPSF6. Mechanistically, CPSF6 loss favored the utilization of the proximal poly (A) site in the 3'UTR of RUNX1, leading to the production of a short 3'UTR RUNX1 transcript and more protein by avoiding being targeted for degradation by miR-30a-5p. CPSF6 is implicated in the pathogenesis of fibrosis through its function in fibroblast activation, thereby enhancing the mechanistic understanding of fibrotic progression.