Abstract
Transforming growth factor beta (TGF-β) is the main cytokine responsible for the induction of the epithelial-mesenchymal transition of breast cancer cells, which is a hallmark of tumor transformation to the metastatic phenotype. Recently, research demonstrated that the chemokine CCL2 gene expression level directly correlates with the TGF-β activity in breast cancer patients. CCL2 attracts tumor-associated macrophages and is, therefore, considered as an important inductor of breast cancer progression; however, the precise mechanisms underlying its regulation by TGF-β are unknown. Here, we studied the behavior of the CCL2 gene in MDA-MB-231 and HCC1937 breast cancer cells representing mesenchymal-like phenotype activated by TGF-β. Using bioinformatics, deletion screening and point mutagenesis, we identified binding sites in the CCL2 promoter and candidate transcription factors responsible for its regulation by TGF-β. Among these factors, only the knock-down of EGR1 and RXRA made CCL2 promoter activity independent of TGF-β. These factors also demonstrated binding to the CCL2 promoter in a TGF-β-dependent manner in a chromatin immunoprecipitation assay, and point mutations in the EGR1 and RXRA binding sites totally abolished the effect of TGF-β. Our results highlight the key role of EGR1 and RXRA transcription factors in the regulation of CCL2 gene in response to TGF-β pathway.
Highlights
Transforming growth factor beta (TGF-β) is the main cytokine responsible for the induction of the epithelial-mesenchymal transition of breast cancer cells, which is a hallmark of tumor transformation to the metastatic phenotype
These data are supported by the fact that, in the 4T1-BALB/c breast cancer (BC) allograft mouse model, the inhibition of TGF-β causes a significant reduction in the levels of CCL2 expression in the primary tumor site, which correlates with lower levels of lung m etastases[14]
We identified the region spanning from − 1196 to + 488 bp from the CCL2 transcription start site (TSS) as the potential promoter (Fig. 1)
Summary
Transforming growth factor beta (TGF-β) is the main cytokine responsible for the induction of the epithelial-mesenchymal transition of breast cancer cells, which is a hallmark of tumor transformation to the metastatic phenotype. Research demonstrated that the chemokine CCL2 gene expression level directly correlates with the TGF-β activity in breast cancer patients. Deletion screening and point mutagenesis, we identified binding sites in the CCL2 promoter and candidate transcription factors responsible for its regulation by TGF-β Among these factors, only the knock-down of EGR1 and RXRA made CCL2 promoter activity independent of TGF-β. One of the key pathogenic functions of TGF-β is the induction of the epithelial-mesenchymal transition that results in the loss of the epithelial phenotype of the tumor and its transition to the aggressive metastatic s tage[4] This process is accompanied by activation of the range of genes responsible for the invasion and migration of cancer cells. We aimed to identify the mechanism underlying regulation of CCL2 gene expression by TGF-β in advanced-stage triple-negative BC cells with mesenchymal-like phenotype
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