Abstract 3173: The role of the Src/Stat3 axis in autocrine HGF signalling in invasive human breast cancer

Recent studies have shown that the proto-oncogene Met is frequently over-expressed in breast cancers, particularly the highly aggressive basal-like subtype. The Elliott lab has previously shown co-expression of HGF and Met in invasive human breast cancers, but not in normal breast epithelium (CJPP 80:91-102, 2002), and a novel activating role of Src and Stat3 on HGF transcription and transformation of breast epithelial cells (Oncogene 25:2773-84, 2006). Together, these findings suggest that the Src/Stat3 axis promotes autocrine HGF/Met signalling, and thereby contributes to invasion and metastasis in breast cancer. To assess the role of Src/Stat3 activation and autocrine HGF/Met signaling in breast metastasis, we have used the human breast carcinoma cell line MDA-MB-231, which exhibits basal-like characteristics. To directly assess the role of Src, we have expressed an activated Src mutant in MDA-MB-231 cells (MDA-Src). Using western blotting analysis, we observed increased levels of active Stat3 (pY705) and Met (pY1234/1235), as well as increased total Stat3, HGF and Met proteins in MDA-Src cells, compared to MDA-MB-231 cells. This finding supports a role of Src in activation of Stat3 and HGF/Met signalling in MDA-MB-231 cells. Treatment of the above cell lines with Dasatinib, an ATP-competitive inhibitor of Src family kinases, resulted in a decrease in the activity of Src and Met, while the levels of activated Stat3 (pY705) and HGF protein were unchanged. In contrast, treatment with CPA7, an inhibitor of Stat3-mediated gene transcription, produced a marked decrease in total HGF protein in addition to decreased Src and Met activity. These results suggest that Src inhibition alone is not sufficient to inhibit the Stat3-dependent expression of HGF in MDA-MB-231 cells, and that inhibition of Stat3 gene transcription rather than its activation is key to the inhibition of the HGF/Met autocrine loop. We are currently performing immunohistochemical analyses of Src/Stat3 and HGF/Met expression on a cohort of human breast cancer tissues (n=59). Preliminary results have shown increased expression and nuclear localization of active Stat3 in breast tumours compared to normal mammoplasty tissues, which is concurrent with HGF expression. These findings implicate a role of the Src/Stat3 axis in regulating autocrine HGF/Met signaling in a human breast cancer cell line model, and may lead to a predictive marker for targeting of breast cancer subtypes which may exploit this pathway. (Supported by CBCRA and CIHR). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3173.