TNF‐α induces TGF‐β 1 expression in lung fibroblasts at the transcriptional level via AP‐1 activation

Tumour necrosis factor‐α (TNF‐α) and transforming growth factor‐β 1 (TGF‐β 1 ) 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‐β 1 in lung fibrosis; therefore, we postulated that TNF‐α may play a significant role in regulating TGF‐β 1 expression in lungs. We recently reported that TNF‐α activates the extracellular regulated kinase (ERK)‐specific pathway in fibroblasts resulting in stabilization of TGF‐β 1 mRNA and increased expression of TGF‐β 1 . In the current study, we further investigated the molecular mechanisms involved in TNF‐α regulation of TGF‐β 1 expression. Nuclear run‐on assays showed that treatment of Swiss 3T3 fibroblasts with TNF‐α increased transcription of the TGF‐β 1 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‐β 1 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‐β 1 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‐β 1 gene. It is essential to know which transcription pathways are activated because of the wide distribution of TNF‐α and TGF‐β 1 , the general lack of effective treatments for fibroproliferative disease and the possibility that targeting the correct transcription factors could be palliative.