A Kinome-Wide RNAi Screen in Drosophila Glia Reveals That the RIO Kinases Mediate Cell Proliferation and Survival through TORC2-Akt Signaling in Glioblastoma

Abstract

Glioblastoma, the most common primary malignant brain tumor, is incurable with current therapies. Genetic and molecular analyses demonstrate that glioblastomas frequently display mutations that activate receptor tyrosine kinase (RTK) and Pi-3 kinase (PI3K) signaling pathways. In Drosophila melanogaster, activation of RTK and PI3K pathways in glial progenitor cells creates malignant neoplastic glial tumors that display many features of human glioblastoma. In both human and Drosophila, activation of the RTK and PI3K pathways stimulates Akt signaling along with other as-yet-unknown changes that drive oncogenesis. We used this Drosophila glioblastoma model to perform a kinome-wide genetic screen for new genes required for RTK- and PI3K-dependent neoplastic transformation. Human orthologs of novel kinases uncovered by these screens were functionally assessed in mammalian glioblastoma models and human tumors. Our results revealed that the atypical kinases RIOK1 and RIOK2 are overexpressed in glioblastoma cells in an Akt-dependent manner. Moreover, we found that overexpressed RIOK2 formed a complex with RIOK1, mTor, and mTor-complex-2 components, and that overexpressed RIOK2 upregulated Akt signaling and promoted tumorigenesis in murine astrocytes. Conversely, reduced expression of RIOK1 or RIOK2 disrupted Akt signaling and caused cell cycle exit, apoptosis, and chemosensitivity in glioblastoma cells by inducing p53 activity through the RpL11-dependent ribosomal stress checkpoint. These results imply that, in glioblastoma cells, constitutive Akt signaling drives RIO kinase overexpression, which creates a feedforward loop that promotes and maintains oncogenic Akt activity through stimulation of mTor signaling. Further study of the RIO kinases as well as other kinases identified in our Drosophila screen may reveal new insights into defects underlying glioblastoma and related cancers and may reveal new therapeutic opportunities for these cancers.

Amitriptyline Improves Motor Function via Enhanced Neurotrophin Signaling and Mitochondrial Functions in the Murine N171-82Q Huntington Disease Model

“…Both Riok1 and Rps3a were both significantly altered by AMI in all three studied tissues. AMI treatment up-regulated Riok1 in all tissues studied, and pertinent to the remedial activities of AMI, it has been recently demonstrated that this kinase is a critical controller of AKTmediated cell survival (78). The consistent AMI-mediated reduction of Rps3a may also indicate that this is linked to potential cell protection mechanisms (79) and anti-inflammatory behavior (80).…”

CLK2 Is an Oncogenic Kinase and Splicing Regulator in Breast Cancer

“…NUAK2 is an AMPK-related kinase and a putative oncogene in melanoma (52,53). RIOK2 regulates glioblastoma growth and survival via regulating AKT (54). In this study, we focused on the more detailed characterization of CLK2, a dual specificity kinase implicated in the regulation of splicing due to its ability to phosphorylate SR proteins (55)(56)(57).…”

Identification of a Small Molecule That Selectively Inhibits ERG-Positive Cancer Cell Growth

“…Thus the affinity of RIOK2 for ERGi-USU is distinctively higher than all other kinases. RIOK2 is an atypical serine/threonine kinase required for the normal maturation of the 40S subunit of the eukaryotic ribosome in ribosomal biogenesis (39 ERGi-USU. These results showed that dose dependent decreases in RIOK2 protein levels in response to ERGi-USU closely mirrored the selective cell growth inhibitory effect of ERGi-USU (Fig 4B-E and inset).…”