AbstractIdiopathic pulmonary fibrosis (IPF) causes progressive fibrosis and worsening pulmonary function. Prognosis is poor and no effective therapies exist. We show that programmed cell death 5 (PDCD5) expression is increased in the lungs of patients with IPF and in mouse models of lung fibrosis. Lung fibrosis is significantly diminished by club cell-specific deletion of Pdcd5 gene. PDCD5 mediates β-catenin/Smad3 complex formation, promoting TGF-β-induced transcriptional activation of matricellular genes. Club cell Pdcd5 knockdown reduces matricellular protein secretion, inhibiting fibroblast proliferation and collagen synthesis. Here, we demonstrate the club cell-specific role of PDCD5 as a mediator of lung fibrosis and potential therapeutic target for IPF.