Abstract 1002: Role of Mixed Lineage Kinase-3 in modulating ß-catenin signaling in cancer cells

Introduction: s-catenin is a multifunctional protein that can regulate different cellular functions depending on its sub-cellular localization, and interacting partners. In the membrane, it interacts with E-cadherin and regulates cell adhesion and migration. In the cytoplasm, it interacts with TCF/LEF family of transcription factors and induces transcription of downstream targets (example: Cyclin D1, c-myc), which in turn mediate different cellular events. s-catenin is a well established human oncogene, with numerous reports describing its over-expression and associated enhanced s-catenin/TCF transcriptional activity in different tumors. Signaling pathways regulating s-catenin/TCF axis are thus important targets for developing anticancer therapies particularly to control those with abnormal TCF activation. Paradoxically, s-catenin can also induce cell death under certain conditions, the detailed mechanism of which is still obscure. It is conceivable that various upstream signaling pathways can modulate s-catenin-dependent downstream events via post-translational modification. To understand the role of novel signaling pathways in regulating s-catenin function, we focused on Mixed Lineage Kinase-3 (MLK-3), due to its close involvement with pro-migratory and apoptotic events. MLK3 is a MAP Kinase Kinase Kinase (MAP3K) member that primarily functions via activation of c-Jun-N-terminal Kinase (JNK) pathway. Aims: The present study was designed to determine whether MLK3 can regulate s-catenin expression and functional activities in cancer cells. Experimental procedures: Cell lines originating from human embryonic kidney (HEK293), cervical carcinoma (HeLa), and prostate cancer (LNCaP) were utilized to determine the effect of MLK3 on s-catenin expression and downstream events. These studies were performed utilizing Western Blot analysis, Immunoprecipitation, and luciferase assays. Results: Ectopic overexpression of MLK3-wild type (WT) resulted in a significant increase in s-catenin protein expression in all the cell types tested. This effect requires the kinase activity of MLK3 since the kinase dead mutant MLK3-K/A was unable to induce s-catenin expression. Immunoprecipitation studies also indicated that MLK3 can interact with s-catenin in vivo in a kinase-independent manner. Surprisingly, MLK3-mediated increase in s-catenin protein expression was associated with a reduction in s-catenin/TCF transcriptional activity, although TCF4-s-catenin interaction was not reduced under these conditions. Conclusion: The present study reveals that MLK3 can increase s-catenin protein expression but lead to an inhibition of s-catenin/TCF transcriptional activity, possibly via recruiting a transcriptional repressor. This pathway can be exploited further for developing MLK3/s-catenin-based therapeutic strategies to target particularly those with aberrant s-catenin/TCF signaling. 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 1002.