Role of TTK/Mps-1 upregulation by Ral GTPase activation in pancreatic oncogenesis

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DESCRIPTION (provided by applicant): Pancreatic cancer is a deadly disease with few therapeutic options available. While success has been made in signal transduction-targeted therapies for some cancers, no significant targeted therapies have been identified for pancreatic cancer. The oncogene KRAS is activated by mutation in ~100% of pancreatic cancer ductal adenocarcinomas (PDAC). However, efforts to develop direct inhibitors of K-Ras have been disappointing. Therefore, focus has shifted to inhibiting the effector signaling cascades activated downstream of K-Ras. The canonical K-Ras effector pathways, Raf-MEK-ERK and PI3K-AKT-mTOR have received the most attention with >40 inhibitors of these two pathways currently under evaluation in clinical trials. However, recent studies investigating KRAS dependency and synthetic lethality argue that other effectors are key to K-Ras regulated transformation. The Ral guanine-nucleotide exchange factor (RalGEF)-Ral pathway is a non-canonical K-Ras effector pathway that have recently been validated for its importance in K-Ras-mediated oncogenesis. RalGEF activates the RalA and RalB Ras-like small GTPases. RalA regulates PDAC anchorage-independent growth in vitro and tumorigenesis in vivo, whereas RalB regulates invasion in vitro and metastasis in vivo. Transcription factor activation is a key consequence of Ral effector signaling. Therefore, we hypothesize that gene array profiling will identify key gene targets of Ral signaling, providing therapeutically useful avenues for drug discovery. Recently I performed gene array analyses and identified the gene encoding the dual specificity protein kinase TTK (also called Mps-1) as a transcript regulated by both RalA and RalB in PDAC. I also identified TTK mRNA overexpression in PDAC primary tumors and metastatic lesions compared to normal pancreas tissue. Furthermore, my preliminary studies have validated the requirement for TTK expression in PDAC anchorage-independent growth and Matrigel invasion in vitro. Thus, TTK may be an attractive and tractable target for anti-Ral and Ras drug discovery. In Aim 1, I will further validate the role of TTK in PDAC oncogenesis by using orthotopic tumor mouse models that better model the invasive and metastatic disease of the patient. In Aim 2, I will establish the importance of specific Ral effector signaling pathways for TTK expression and PDAC growth. RalBP1/RLIP76 and the Sec5 and Exo84 exocyst components are the best- characterized Ral effectors and I will determine if Ral mutants that differentially uncouple Ral from these effectors can rescue impaired TTK expression due to endogenous Ral silencing. Finally, Aim 3 studies will utilize missense and truncation mutants of TTK to investigate the requirement for kinase and non-kinase sequences in TTK function in PDAC anchorage-independent growth and invasion through Matrigel. Taken together, these studies will require me to master an array of experimental techniques, while preparing me to do both basic and translational research. PUBLIC HEALTH RELEVANCE: Pancreatic cancer is a deadly disease with few therapeutic options. Ral GTPases have a validated role in pancreatic cancer oncogenesis downstream of the oncogene KRAS. TTK/Mps1 is a protein kinase regulated by Ral signaling and represents a novel anti-Ral therapeutic target for blocking Ras signaling in pancreatic cancer drug discovery.