Abstract A46: KLF4 overcomes tamoxifen resistance by suppressing MAPK signaling pathway in breast cancer

Kruppel-like factor 4 (KLF4) has critical roles in breast cancer development and progression and several solid tumors. Tamoxifen (TAM) resistance represents a daunting challenge to the successful treatment of breast cancer. KLF4 expression, function, and regulation in the efficacy of TAM therapy in breast cancer have yet to be demonstrated. Here, we investigated the clinical significance and biologic effects of KLF4 in breast cancer. Firstly, higher expression of KLF4 was correlated with increased TAM sensitivity in breast cells, and analysis of GEO datasets indicated that KLF4 expression was positively correlated with ERa and enhanced expression of KLF4 sensitized breast cancer patients to endocrine therapy. Knockdown of KLF4 in MCF-7 and BCAP37 cells led to increased TAM resistance, while ectopic KLF4 expression promoted the responsiveness of MCF-7/TAM and T47D cells to TAM. Secondly, ectopic KLF4 overexpression suppressed MCF-7/TAM cell growth, invasion, and migration ability. Besides, KLF4 expression was downregulated in breast cancer tumor tissues and high expression of KLF4 linked to favorable outcome. Mechanistically, KLF4 may enhance the responsiveness of breast cancer cells to TAM through suppressing mitogen-activated protein kinase (MAPK) signaling pathway. We found that ERK and P38 were relatively activated in MCF-7/TAM compared with MCF-7, and treatment with MAPK-specific inhibitors can significantly suppress cell viability. Knockdown of KLF4 activated ERK and P38 and drove MCF-7 cells to become resistant to TAM. Conversely, overexpression of KLF4 in MCF-7/TAM cells suppressed ERK and P38 signaling and resulted in enhanced sensitivity to TAM. Therefore, our findings suggest that KLF4 contributes to TAM efficiency in breast cancer via phosphorylation modification of ERK and P38 signaling. Collectively, this study highlighted the significance of KLF4/MAPK signal interaction in regulating TAM resistance of breast cancer, and suggested that targeting the KLF4/MAPK signaling may be a potential therapeutic strategy for breast cancer treatment, especially for TAM-resistant patients. Note: This abstract was not presented at the conference. Citation Format: Yunlu Jia, Wang Linbo. KLF4 overcomes tamoxifen resistance by suppressing MAPK signaling pathway in breast cancer [abstract]. In: Proceedings of the AACR Special Conference: Advances in Breast Cancer Research; 2017 Oct 7-10; Hollywood, CA. Philadelphia (PA): AACR; Mol Cancer Res 2018;16(8_Suppl):Abstract nr A46.