Objective: Heregulin beta 1 (HRG-β1) acts in breast cancer cell proliferation and tumorigenesis and it acts through the activation of ErbB-2. MMP-9 plays important roles in metastasis and it shows extensive staining patterns in immunohistochemistry. In this study, we examined the signal pathway through which heregulin induces MMP-9 activation and massive secretion of MMP-9 into stroma. Methods: Expression levels of MMP-9, Akt and MAPK upon heregulin were examined in breast cancer cell lines, SK-Br3, MCF-7 and MDA-MB-231. HRG-β1-induced secretion of MMP-9 was examined by gelatin zymography assay. Direct relationships between activation of Akt and MAPK and MMP-9 secretion upon HRG-β1 treatment were confirmed by inhibitor assay. In addition, secretion of MMP-9 in breast cancer was confirmed by immunohistochemistry. Results: Upon heregulin treatment, MMP-9 activity was increased but MMP-2 activity was not changed. The increasing rates of MMP-9 activity and expression were highest in SK-Br3 cell line. Upon HRG-β1 treatment, phosphorylation of Akt was also increased. The increase of MMP-9 activity was observed in cell culture media but not in cell lysates. In SK-Br3 cells, Akt phosphorylation showed peak in 30 min after treatment and after 6 hrs, the level was decreased. In MCF-7 cells, Akt phosphorylation showed highest level in 30 min after treatment and on 6 hrs, the level was decreased to 20% compared to the peak. But in MDA-MB-231 cells, Akt phosphorylation was merely increased. The expression levels of Akt were not changed upon HRG treatment. Phosphorylation of extracellular signal-regulated kinase 1/2 (ERK-1/2), down-stream molecules of Akt, was also increased by HRG treatment. Pretreatment of LY294002, PI3K inhibitor, or PD98059, MAPK inhibitor, partially blocked the MMP-9 activity. Conclusions: Heregulin induces the activation and secretion of MMP-9 but not of MMP-2 in Sk-Br3 cells. Akt and MAPK are responsible for these regulations.
98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA