Transforming growth factor-β1 regulation of ATF-3, c-Jun and JunB proteins for activation of matrix metalloproteinase-13 gene in human breast cancer cells.

Transforming growth factor-beta1 (TGF-β1) plays a significant role in breast cancer mediated bone metastasis, and it stimulated expression of matrix metalloproteinase-13 (MMP-13; an invasive and metastasis gene) via activating transcription factor-3 (ATF-3) in human breast cancer cells (MDA-MB231). We further dissected the role of ATF-3 and its interacting proteins (activator protein-1; AP-1) for TGF-β1-stimulation of MMP-13 expression in these cells. Chromatin immunoprecipitation (ChIP) experiment identified the TGF-β1-stimulation of ATF-3 interaction at the AP-1 site of the MMP-13 promoter in a sustained and prolonged manner in MDA-MB231 cells. In silico protein-protein interaction, co-immunoprecipitation and western blot experiments identified the ATF-3 interaction and regulation of c-Jun and JunB proteins in these cells. The sequential ChIP assay confirmed the presence of c-Jun/ATF-3 complex at the AP-1 site of the MMP-13 promoter in MDA-MB231 cells upon TGF-β1-treatment. Hence, our results suggested that TGF-β1-treatment stimulated a sustained and prolonged expression of ATF-3, and its interaction and regulation of c-Jun protein and their assembly as a protein complex at the AP-1 site of the MMP-13 promoter could be responsible for MMP-13 gene activation in MDA-MB231 cells.