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Serum response factor (SRF) is a widely expressed transcription factor involved in immediate-early and tissue-specific gene expression, cell proliferation and differentiation. We defined a new role of SRF as a nuclear repressor of the tumor growth factor β1 (TGF-β1) growth-inhibitory signal during cell proliferation. We show that SRF significantly inhibits the TGF-β1/Smad-dependent transcription by associating with Smad3. SRF causes resistance to the TGF-β1 cytostatic response by directly repressing the Smad transcriptional activity and Smad binding to DNA. Furthermore, we demonstrated that overexpression of SRF markedly decreases the level of Smad3 complex binding to the promoters of Smad3 target genes, p15INK4b and p21Cip1. This leads to the inhibition of expression of TGF-β1-responsive genes. SRF therefore acts as a nuclear repressor of Smad3-mediated TGF-β1 signaling.Oncogene (2007) 26, 173–185. doi:10.1038/sj.onc.1209774; published online 3 July 2006 [ABSTRACT FROM AUTHOR]

FRA-1, a member of the FOS family of transcription factors, is overexpressed in a variety of human tumors, and contributes to tumor progression. In addition to mitogens, various toxicants and carcinogens persistently induce FRA-1 expression in vitro and in vivo. Although the mitogen induced expression of c-FOS is relatively well understood, it is poorly defined in the case of FRA-1. Our recent analysis of the FRA-1 promoter has shown a critical role for a TRE located at −318 in mediating the TPA-induced expression. The −379 to −283 bp promoter segment containing a critical TRE (−318), however, is insufficient for the induction of FRA-1 promoter. Here, we show that a 40-bp (−276/−237) segment, comprising a TCF binding site and the CArG box (collectively known as serum response element, SRE), and an ATF site, is also necessary for the FRA-1 induction by TPA and EGF. Interestingly, the −283 to +32 bp FRA-1 promoter fragment containing an SRE and an ATF site alone was also insufficient to confer TPA sensitivity to a reporter gene. However, in association with the −318 TRE, the SRE and ATF sites imparted a strong TPA-inducibility to the reporter. Similarly, EGF also required these motifs for the full induction of this gene. Using ChIP assays we show that, in contrast to c-Jun, SRF, Elk1, ATF1 and CREB proteins bind to SRE and ATF sites of the FRA-1 promoter, constitutively. RNAi-mediated knockdown of endogenous SRF, ELK1 and c-JUN protein expression significantly reduced TPA-stimulated FRA-1 promoter activity. Thus, a bipartite enhancer formed by an upstream TRE and the downstream SRE and ATF sites and the cognate factors is necessary and sufficient for the regulation of FRA-1 in response to mitogens.Oncogene (2005) 24, 4193–4205. doi:10.1038/sj.onc.1208583 Published online 4 April 2005 [ABSTRACT FROM AUTHOR]