KLC1-ROS1 Fusion Exerts Oncogenic Properties of Glioma Cells via Specific Activation of JAK-STAT Pathway

Simple Summary By examining the detailed molecular oncogenic mechanisms of KLC1-ROS1 fusion, the function of a novel RTK fusion was investigated to discover novel therapeutic targets for glioma. When wild-type ROS1 and KLC1-ROS1 fusions were expressed in human glioma cell lines, immunoblotting revealed that KLC1-ROS1 fusion specifically activated the JAK2-STAT3 axis compared with wild-type ROS1. Immunoprecipitation revealed a more efficient association of KLC1-ROS1 fusion with JAK2 compared with wild-type ROS1. A mutagenesis study of KLC1-ROS1 fusion demonstrated the essential roles of both the KLC1 and ROS1 domains in the serum factor-independent constitutive activation of the fusion. In addition, KLC1-ROS1 fusion induced the upregulation of cell proliferation and invasion compared to wild-type ROS1 in a JAK-STAT-dependent manner under serum deprivation. Overall, our results suggested that molecules other than RTKs may serve as novel therapeutic targets for gliomas with RTK fusions.Abstract Here, we investigated the detailed molecular oncogenic mechanisms of a novel receptor tyrosine kinase (RTK) fusion, KLC1-ROS1, with an adapter molecule, KLC1, and an RTK, ROS1, discovered in pediatric glioma, and we explored a novel therapeutic target for glioma that possesses oncogenic RTK fusion. When wild-type ROS1 and KLC1-ROS1 fusions were stably expressed in the human glioma cell lines A172 and U343MG, immunoblotting revealed that KLC1-ROS1 fusion specifically activated the JAK2-STAT3 pathway, a major RTK downstream signaling pathway, when compared with wild-type ROS1. Immunoprecipitation of the fractionated cell lysates revealed a more abundant association of the KLC1-ROS1 fusion with JAK2 than that observed for wild-type ROS1 in the cytosolic fraction. A mutagenesis study of the KLC1-ROS1 fusion protein demonstrated the fundamental roles of both the KLC1 and ROS1 domains in the constitutive activation of KLC1-ROS1 fusion. Additionally, in vitro assays demonstrated that KLC1-ROS1 fusion upregulated cell proliferation, invasion, and chemoresistance when compared to wild-type ROS1. Combination treatment with the chemotherapeutic agent temozolomide and an inhibitor of ROS1, JAK2, or a downstream target of STAT3, demonstrated antitumor effects against KLC1-ROS1 fusion-expressing glioma cells. Our results demonstrate that KLC1-ROS1 fusion exerts oncogenic activity through serum-independent constitutive activation, resulting in specific activation of the JAK-STAT pathway. Our data suggested that molecules other than RTKs may serve as novel therapeutic targets for RTK fusion in gliomas.