Transforming growth factor‐β1 regulation of ATF‐3 and identification of ATF‐3 target genes in breast cancer cells

Abstract

Abstract Transforming growth factor‐β1 (TGF‐β1) is a crucial molecule for stimulation of breast cancer invasion and formation of bone metastases. The molecular mechanisms of how TGF‐β1 mediates these effects have yet to be completely determined. We have found that activating transcription factor‐3 (ATF‐3) is strongly stimulated and its level is sustained by TGF‐β1 in highly invasive and metastatic human breast cancer (MDA‐MB231) and in mouse mammary pad tumor cells (r3T). ATF‐3 is also overexpressed in human primary breast cancer tissue. Overexpression of ATF‐3 increased normal human mammary epithelial cell number and DNA synthesis suggesting a role for ATF‐3 in cell proliferation. The functional role of ATF‐3 in breast cancer progression was determined by the RNA interference technique. Knockdown of ATF‐3 by ATF‐3 shRNA in MDA‐MB231 cells decreased expression of cell cycle gene, cyclin A1 in MDA‐MB231 cells. ATF‐3 shRNA also decreased expression of an invasive and metastatic gene, matrix metalloproteinase‐13 (MMP‐13; collagenase‐3) in these cells. Chromatin immunoprecipitation experiments identified the direct physical interaction of ATF‐3 protein on the human MMP‐13 promoter. Thus, the dysregulation of ATF‐3 by TGF‐β1 is likely to activate cyclin A1 and MMP‐13 genes in breast cancer cells and that would be key to the subsequent cancer cell invasion and metastasis. J. Cell. Biochem. 108: 408–414, 2009. © 2009 Wiley‐Liss, Inc.