Role of Protein Methylation in Cell Mitosis and Glioblastoma

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Methylation on histone and non-histone proteins is a common and important post-translational modification (PTM) that controls protein functions and activities in modulating cancer tumorigenicity and responses to therapies. In this project, we will investigate the mechanism for protein arginine (R) methylation regulation of GBM tumorigenicity by elucidating the role of protein arginine methyltransferase 6 (PRMT6) on cell mitosis through specific arginine methylation of regulator of chromosome condensation 1 (RCC1), thereby regulating GBM phenotype and responses to therapies. We provide novel evidence that PRMT6 regulates RCC1 activity through methylation of RCC1 at R214, the arginine residue required for RCC1 activation of Ran GTPase through association with histones in chromosome, thereby affecting cell mitotic process, GBM tumorigenicity and responses to therapies. We demonstrate that casein kinase 2 (CK2), a ubiquitously expressed and constitutively active serine/threonine kinase that is important in cancers stimulates PRMT6 methyltransferase activity by phosphorylating threonine 21 of PRMT6 protein. Additionally, genetic depletions or small molecule targeting of PRMT6, RCC1 or CK2 inhibited GBM tumorigenicity in vitro and in vivo, and enhanced anti-tumor effects by radiation therapy (RT). These strong scientific premises provide the basis for the overarching hypothesis of this proposal: CK2-activated PRMT6 induces asymmetric dimethylation (aDMA) of RCC1, thereby regulating cell mitosis, GBM tumorigenicity as well as GBM responses to RT. We will address this hypothesis in the context of three specific aims: 1) Determine how PRMT6-induced R214 aDMA of RCC1 affects cell mitotic process as well as GBM tumor biologic properties in vitro and in vivo; 2) Define mechanisms by which CK2 regulates PRMT6 activity, and the relationships between CK2-associated phosphorylation of PRMT6, RCC1 function, cell mitosis, GBM tumor phenotypes, and association with GBM patient outcome; and 3) Determine whether PRMT6 and CK2 directed combination therapy is more effective than corresponding monotherapies, and whether such combination therapy enhances the anti-tumor activity of RT and temozolomide (TMZ) treatment. At the completion of this project, we will learn how PRMT6-catayzed aDMA of RCC1 shapes of cell mitosis, GBM phenotype and response to therapy. Our proposed studies will be the first to address the role of PRMT activity on non-histone aDMA of RCC1 in cell mitosis, GBM tumor biology and responses to therapies. This knowledge, in turn, will provide clear indication of the potential benefit of including combination of inhibition of PRMT6 and CK2 with RT and TMZ as part of treatment strategy for patient with GBM.