TGF-beta induces fibronectin synthesis through a c-Jun N-terminal kinase-dependent, Smad4-independent pathway

Transforming growth factor-beta (TGF-beta) exerts its effects on cell proli feration, differentiation and migration in part through its modulation of e xtracellular matrix components, such as fibronectin and plasminogen activat or inhibitor-1 (PAI-1), Although the SMAD family of proteins recently has b een shown to be a key participant in TGF-beta signaling, other signaling pa thways have also been shown to be activated by TGF-beta, We report here tha t c-Jun N-terminal kinase (JNK), a member of the MAP kinase family, is acti vated in response to TGF-beta in the human fibrosarcoma HT1080-derived cell line BAHgpt, Stable expression of dominant-negative forms of JNK1 and MKK4 , an upstream activator of JNK, results in loss of TGF-beta-stimulated fibr onectin mRNA and protein induction, while having little effect on TGF-beta- induced levels of PAI-1. The human fibronectin promoter contains three CRE elements, one of which has been shown to bind a c-Jun-ATF-2 heterodimer, Ut ilizing a GAL4 fusion trans-reporting system, me demonstrate a decrease in transactivating potential of GAL4-c-Jun and GAL4-ATF-2 in dominant-negative JNK1- and MKK4-expressing cells. Finally, we show that TGF-beta-induced fi bronectin synthesis is independent of Smad4, These results demonstrate that TGF-beta-mediated fibronectin induction requires activation of JNK which i n turn modulates the activity of c-Jun and ATF-2 in a Smad4-independent man ner.