Akt- and MAPK-mediated activation and secretion of MMP-9 into stroma in breast cancer cells upon heregulin treatment

Several peptides, such as epidermal growth factor (EGF), heregulin (HRG) and transforming growth factor alpha (TGFα), are ligands for EGFR family. Heregulin beta 1 (HRG-β1) binds to ErbB-3 and -4 and plays important roles in the proliferation and tumorigenesis of breast cancer cells. We investigated proteins through which HRG treatment affects matrix metalloproteinase (MMP)-9 activity. Breast cancer cell lines, including SK-Br3, MCF-7 and MDA-MB-231, were treated with HRG-β1. After 24 h, the activity and expression levels of MMP-9 were increased, but MMP-2 activity was not changed. The increasing rates of MMP-9 activity and expression were most prominent in the SK-Br3 cell line. Upon treatment of SK-Br3 cells with HRG-β1, phosphorylation of Akt was increased showing a peak at 30 min after treatment, and the level decreased after 6 h. The expression levels of Akt were not changed upon HRG-β1 treatment. Phosphorylation of extracellular signal-regulated kinase 1/2 (ERK-1/2), downstream molecules of Akt, was also increased by HRG-β1 treatment. Pretreatment of LY294002, PI3K inhibitor, or PD98059, MAPK inhibitor, partially blocked the heregulin-induced MMP-9 activity. Furthermore, MMP-9 was found to be secreted in human breast cancer tissues. The present results suggest that Akt and MAPK mediate HRG-β1 signaling to MMP-9.