Glioblastoma (GBM) is a particularly lethal brain neoplasm that accounts for half of malignant and fifteen percent of all primary brain tumors diagnosed in adults. These statistics elevate GBM to a priority in neuro-oncology research, but the tumors remain incurable with an exceptionally poor median survival of fifteen months after diagnosis. In order to promote targeted therapy development, there are ongoing efforts to understand GBM at a molecular level, which involve characterization of these tumors via their transcriptional and mutational profile. Recent studies indicate aberrations in receptor tyrosine kinase (RTKs), including EGFR and PDGFRA, and the Pi-3 kinase (PI3K) signaling pathways are major drivers of tumorigenesis in GBM. Using a Drosophila melanogasterGBM model to locate downstream targets of these pathways, our laboratory has identified right open reading frame 2 (RIOK2) serine-threonine kinase as a downstream effector of aberrant RTK-PI3K signaling in glial tumorigenesis. Subsequent follow-up studies indicate that RIOK2, which is overexpressed in RTK mutant human GBMs, drives survival and proliferation of RTK-PI3K-dependent human GBM cells. In order to understand how RIOK2 functions to promote tumorigenesis through RTK-PI3K signaling, we used a chemical genetics approach in both Drosophilaand cultured human GBM cells to test the effects of catalytic inhibition of RIOK2 in tumorous glia as well as normal glia to find that RIOK2 catalytic activity is essential for the growth of tumor cells, but dispensable for the growth of normal glia. However, the substrates of RIOK2 are unknown. Therefore, through a combination of proteomic and genetic approaches, we are currently seeking to identify potential targets of RIOK2 catalytic activity. Together, our data indicate a role for RIOK2 in promoting GBM tumorigenesis and our ongoing studies reveal an important tumor-specific target signaling pathway for consideration in experimental therapeutics.
