Abstract 2004: Identification of MLK4 as a novel regulator of cancer stem cells in triple-negative breast cancer

Abstract

Abstract Cancer stem cells (CSCs) are a small population of cancer cells that are capable of self-renewal and tumor initiation. As a result, targeting CSCs is a potential therapeutic strategy for preventing cancer relapse and metastasis. Mixed lineage kinase 4 (MLK4), a serine/threonine kinase, is known to regulate mesenchymal glioma stem cells and to drive tumorigenesis in colorectal cancer. We found that MLK4 was highly expressed in triple-negative breast cancer (TNBC) compared to other breast cancer subtypes according to the database from The Cancer Genome Atlas. Furthermore, multiple datasets indicated that higher expression of MLK4 was associated with poor prognosis in breast cancer. Despite the correlation of MLK4 and clinical outcome, the function of MLK4 in breast cancer is still not known. In this study, we found that knockdown of MLK4 significantly decreased secondary mammosphere formation, the CD44+/CD24- CSC population, invasion and migration in TNBC cell lines. In addition to suppressing CSC phenotypes in vitro, knockdown of MLK4 also inhibited tumor growth in NOD/SCID mice. Secondary transplantation of tumor cells demonstrated that silencing of MLK4 significantly decreased tumor-initiating cell frequency. As accessed by qPCR, knockdown of MLK4 led to decreased expression of mesenchymal genes (CD44 and VIM) and concomitant increased expression of epithelial genes (CDH1 and claudin genes). Immunohistochemical staining revealed that knockdown of MLK4 in xenografts resulted in increased expression of CK19, a luminal-epithelial marker. These studies indicate that MLK4 plays an important role in the function of mesenchymal-like CSCs in TNBC. Silencing of MLK4 in TNBC cell lines can transform CSC in these tumors to a more differentiated epithelial cell state. Together, these studies identify that MLK4 is a potential therapeutic target for CSCs in TNBC. Citation Format: Chang-Ching Lin, Miao-Chia Lo, Rebecca Moody, Nicholas Stevers, Samantha Tinsley, Mari Gasparyan, Max Wicha, Duxin Sun. Identification of MLK4 as a novel regulator of cancer stem cells in triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2004.