TNF-α induces TGF-β₁expression in lung fibroblasts at the transcriptional level<i>via</i>AP-1 activation

Abstract

Tumour necrosis factor-α (TNF-α) and transforming growth factor-β1 (TGF-β1) are peptides with multiple biological activities that influence neoplastic, immunologic and fibroproliferative diseases. There are clear interrelationships and overlap between the actions of TNF-α and TGF-β1 in lung fibrosis; therefore, we postulated that TNF-α may play a significant role in regulating TGF-β1 expression in lungs. We recently reported that TNF-α activates the extracellular regulated kinase (ERK)-specific pathway in fibroblasts resulting in stabilization of TGF-β1 mRNA and increased expression of TGF-β1. In the current study, we further investigated the molecular mechanisms involved in TNF-α regulation of TGF-β1 expression. Nuclear run-on assays showed that treatment of Swiss 3T3 fibroblasts with TNF-α increased transcription of the TGF-β1 gene in an ERK independent manner. Pre-treatment with the activator protein-1 (AP-1) inhibitor curcumin attenuated TNF-α induced transcription of the TGF-β1 gene. TNF-α induced increased levels of c-Jun and C-Fos in the nucleus accompanied by phosphorylation of c-Jun. In electrophoretic mobility shift assays, AP-1 binding to an AP-1 binding site found within the TGF-β1 promoter was increased in nuclear extracts from Swiss 3T3 fibroblasts treated with TNF-α. Together, these results suggest that TNF-α induces expression and DNA binding of AP-1 resulting in increased transcription of the TGF-β1 gene. It is essential to know which transcription pathways are activated because of the wide distribution of TNF-α and TGF-β1, the general lack of effective treatments for fibroproliferative disease and the possibility that targeting the correct transcription factors could be palliative.