Introduction: Understanding the mechanism of metastatic program is essential to reducing the mortality of cancer patients. It is well known that epithelial-mesenchymal transition (EMT) contributes to cancer metastasis. Recently, numerous studies have documented the role of erbB3-mediated oncogenic signaling in breast cancer progression. In this study, we have focused on investigating the effect of Stat3 activation on EMT-induced by erbB3 receptor in erbB2-positive (erbB2+) breast cancer cells.

Methods: Immunofluorescence analyses were performed to study the localization and expression of EMT markers in erbB2+ breast cancer cells. Lentiviral vector containing shRNA was used to specifically knockdown erbB3. Western blot analyses were performed to assess the expression and activation of proteins. Cell growth (MTS) assays were used to determine cell viability. Wound healing and transwell assays were used to examine the motility and migration of cells.

Results: We discovered that ectopic expression of erbB3 facilitated EMT, as evidenced by change of cell morphology, induction of mesenchymal markers Vimentin, Snail, Slug, ZEB1 and repression of the epithelial marker E-cadherin in erbB2+ breast cancer cells. Wound healing and transwell assays indicated that the capability of cell motility and migration was enhanced. In contrast, specific knockdown of erbB3 abrogated the observations described above. Moreover, elevated expression of erbB3 potently stimulated activation of Stat3, which has been validated to act as a promoter of tumor invasion and metastasis in many type cancers. Suppression of Stat3 signaling via its inhibitor, S3I-201, significantly alleviated EMT and cell motility/migration that were triggered by activation of erbB3. To further assess the clinical relevance of erbB3 signaling in cancer metastasis, we took advantage of a publicly accessible portal that allows analysis of the effect of genes on survival using 4,142 breast cancer samples (http://kmplot.com/analysis/). Kaplan-Meier survival curves showed that the erbB2+ breast cancer patients with erbB3-high expression tended to have a shorter Distance Metastasis-free Survival (DMFS).

Conclusion: Activation of Stat3 signaling by erbB3 promotes EMT and shifts the cellular phenotype toward a mesenchymal state that is advantageous for cancer metastasis. Our data shed a new sight on erbB3's role in erbB2+ breast cancer metastasis and may facilitate the development of novel strategy for treatment of tumor progression.

Keywords: ErbB3, Stat3, EMT, Metastasis, Breast Cancer

Citation Format: Hui Lyu, Ying Wu, Yan Zhou, Bolin Liu. Stat3 signaling in erbB3-mediated epithelial-mesenchymal transition in erbB2-positive breast cancer cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1593.