Suberanilohydroxamic acid prevents TGF-β1-induced COX-2 repression in human lung fibroblasts post-transcriptionally by TIA-1 downregulation

Abstract Cyclooxygenase-2 ( COX - 2 ), with its main antifibrotic metabolite PGE 2 , is regarded as an antifibrotic gene. Repressed COX - 2 expression and deficient PGE 2 have been shown to contribute to the activation of lung fibroblasts and excessive deposition of collagen in pulmonary fibrosis. We have previously demonstrated that COX - 2 expression in lung fibroblasts from patients with idiopathic pulmonary fibrosis (IPF) is epigenetically silenced and can be restored by epigenetic inhibitors. This study aimed to investigate whether COX-2 downregulation induced by the profibrotic cytokine transforming growth factor-β1 (TGF-β1) in normal lung fibroblasts could be prevented by epigenetic inhibitors. We found that COX-2 protein expression and PGE 2 production were markedly reduced by TGF-β1 and this was prevented by the pan-histone deacetylase inhibitor suberanilohydroxamic acid (SAHA) and to a lesser extent by the DNA demethylating agent Decitabine (DAC), but not by the G9a histone methyltransferase (HMT) inhibitor BIX01294 or the EZH2 HMT inhibitor 3-deazaneplanocin A (DZNep). However, chromatin immunoprecipitation assay revealed that the effect of SAHA was unlikely mediated by histone modifications. Instead 3′-untranslated region (3′-UTR) luciferase reporter assay indicated the involvement of post-transcriptional mechanisms. This was supported by the downregulation by SAHA of the 3′-UTR mRNA binding protein TIA-1 (T-cell intracellular antigen-1), a negative regulator of COX-2 translation. Furthermore, TIA-1 knockdown by siRNA mimicked the effect of SAHA on COX-2 expression. These findings suggest SAHA can prevent TGF-β1-induced COX-2 repression in lung fibroblasts post-transcriptionally through a novel TIA-1-dependent mechanism and provide new insights into the mechanisms underlying its potential antifibrotic activity. Abbreviations SAHA suberanilohydroxamic acid TGF-β1 transforming growth factor-β1 COX-2 cyclooxygenase-2 TIA-1 T-cell intracellular antigen-1 PGE 2 prostaglandin E 2 IPF idiopathic pulmonary fibrosis DAC Decitabine HMT histone methyltransferase EZH2 enhancer of zeste homolog 2 DZNep 3-deazaneplanocin A 3′-UTR 3′-untranslated region α-SMA α-smooth muscle actin ECM extracellular matrix COL1 collagen 1 DNMT DNA methyltransferase HAT histone acetyltransferase HDAC histone deacetylase H3K9me3 histone H3 lysine 9 trimethylation ARE AUUUA-rich element HuR human antigen R ELAV1 ELAV-like RNA binding protein 1 TTP Tristetraprolin CUGBP2 CUG triplet repeat, RNA binding protein 2 F-NL fibroblast from non-fibrotic lung FCS fetal calf serum