Abstract LB-023: STK17A, a novel serine threonine kinase, promotes cancer stemness phenotypes by phosphorylating β-catenin

Cancer stem cells (CSCs) are considered to play an important role in cancer therapy resistance, metastasis, and recurrence. Wnt/β-catenin is one of key signaling pathways that confer cancer stemness properties to a portion of the heterogeneous cancer cell population. Dysregulation of the Wnt/β-catenin pathway may lead to accumulation of β-catenin and aberrant activation of its target gene transcription. However, it has been proven difficult to design a therapeutic targeting β-catenin. Identification of a drugguble target for the β-catenin pathway is highly desirable given the importance of β-catenin in promoting cancer stemness. Here, we demonstrate that Serine Threonine Kinase 17A (STK17A), a novel member of the death-associated protein family of serine/threonine kinases, promotes cancer stemness phenotypes via β-catenin. Over-expression of STK17A resulted in increased anchorage-independent spherogenesis and invasive phenotype of cancer cells, whereas STK17A gene silencing reduced these malignant phenotypes. Overexpression of STK17A led to increased transcriptional activity of β-catenin and upregulation of its target genes. These changes were accompanied by increased phosphorylation of β-catenin at ser675. Cell-free in vitro kinase assay revealed that STK17A directly phosphorylates β-catenin at ser675 in an ATP-dependent manner. Moreover, BBI-503 (Amcasertib), a first-in-class cancer stemness kinase inhibitor, was found to potently inhibit STK17A, leading to inhibition of β-catenin phosphorylation at ser675. These results suggest that inhibition of STK17A is a promising approach for targeting cancer stemness. Citation Format: Taiki Kida, Harry A. Rogoff, Chiang J. Li. STK17A, a novel serine threonine kinase, promotes cancer stemness phenotypes by phosphorylating β-catenin [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-023. doi:10.1158/1538-7445.AM2017-LB-023