Background:The roles of ESRP1 and ESRP2 during carcinogenesis remain unknown. Results: ESRPs are up-regulated during carcinogenesis but down-regulated in invasive fronts. ESRP1 suppresses expression of the Rac1b isoform, whereas ESRP2 represses epithelial-mesenchymal transition-inducing transcription factors. Conclusion: ESRP1 and ESRP2 suppress cell motility through distinct transcriptional and/or post-transcriptional mechanisms. Significance: Our findings reveal a novel molecular network that regulates cancer cell motility.
Background: To date, the Smad cofactor involved in cell motility induced by transforming growth factor- (TGF-) has not been identified. Results: Knockdown of oligodendrocyte transcription factor-1 (Olig1), as well as inhibition of the Olig1-Smad interaction, resulted in attenuation of TGF--induced cell motility. Conclusion: Olig1 is involved in TGF--induced cell motility. Significance: This study enhances understanding of the regulation of TGF--induced cell motility.
Cytochrome P450 1A1 (CYP1A1) catalyzes the metabolic activation of polycyclic aromatic hydrocarbons (PAHs) such as benzo[a]pyrene (B[a]P) and is transcriptionally regulated by the aryl hydrocarbon receptor (AhR)/AhR nuclear translocator (ARNT) complex upon exposure to PAHs. Accordingly, inhibition of CYP1A1 expression reduces production of carcinogens from PAHs. Although transcription of the CYP1A1 gene is known to be repressed by transforming growth factor-β (TGF-β), how TGF-β signaling is involved in the suppression of CYP1A1 gene expression has yet to be clarified. In this study, using mammalian cell lines, along with shRNA-mediated gene silencing, CRISPR/Cas9-based genome editing, and reporter gene and quantitative RT-PCR assays, we found that TGF-β signaling dissociates the B[a]P-mediated AhR/ARNT heteromeric complex. Among the examined Smads, Smad family member 3 (Smad3) strongly interacted with both AhR and ARNT via its MH2 domain. Moreover, hypoxia-inducible factor 1α (HIF-1α), which is stabilized upon TGF-β stimulation, also inhibited AhR/ARNT complex formation in the presence of B[a]P. Thus, TGF-β signaling negatively regulated the transcription of the CYP1A1 gene in at least two different ways. Of note, TGF-β abrogated DNA damage in B[a]P-exposed cells. We therefore conclude that TGF-β may protect cells against carcinogenesis because it inhibits CYP1A1-mediated metabolic activation of PAHs as part of its anti-tumorigenic activities.
Smad proteins are transcriptional regulators activated by TGF-. They are known to bind to two distinct Smad-responsive motifs, namely the Smad-binding element (SBE) (5-GTCTAGAC-3) and CAGA motifs (5-AGCCAGACA-3 or 5-TGTCTGGCT-3). However, the mechanisms by which these motifs promote Smad activity are not fully elucidated. In this study, we performed DNA CASTing, binding assays, ChIP sequencing, and quantitative RT-PCR to dissect the details of Smad binding and function of the SBE and CAGA motifs. We observed a preference for Smad3 to bind CAGA motifs and Smad4 to bind SBE, and that either one SBE or a triple-CAGA motif forms a cis-acting functional half-unit for Smad-dependent transcription activation; combining two half-units allows efficient activation. Unexpectedly, the extent of Smad binding did not directly correlate with the abilities of Smad-binding sequences to induce gene expression. We found that Smad proteins are more tolerant of single bp mutations in the context of the CAGA motifs, with any mutation in the SBE disrupting function. CAGA and CAGA-like motifs but not SBE are widely distributed among stimulus-dependent Smad2/3-binding sites in normal murine mammary gland epithelial cells, and the number of CAGA and CAGA-like motifs correlates with fold-induction of target gene expression by TGF-. These data, demonstrating Smad responsiveness can be tuned by both sequence and number of repeats, provide a compelling explanation for why CAGA motifs are predominantly used for Smad-dependent transcription activation in vivo. This work was supported by Japan Society for the Promotion of Science (JSPS) KAKENHI Grants 16H05150 (to K. Miyazawa) and 18K06626 (to Y. I.), JSPS Core-to-Core Program "Cooperative International Framework in TGF- Family Signaling," the Fugaku Trust for Medicinal Research (to K. Miyazawa), the Mitsubishi Science Foundation (to K. Miyazawa), and the Terumo Foundation for Life Science and Arts (to K. Miyazawa). The authors declare that they have no conflicts of interest with the contents of this article. This article contains Tables S1-S7 and Figs. S1-S6. Raw data of CASTing analysis have been deposited in the DDBJ BioProject database under BioProject accession number DRA007794. The ChIP-seq data reported in this paper have been submitted to the Gene Expression Omnibus (GEO) database under GEO accession number GSE121254.
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