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// Helena Costa 1, * , Xinling Xu 1, * , Gitta Overbeek 1, * , Suhas Vasaikar 2 , C. Pawan K. Patro 3 , Ourania N. Kostopoulou 1 , Masany Jung 1 , Gowhar Shafi 4 , Sharan Ananthaseshan 1 , Giorgos Tsipras 2 , Belghis Davoudi 1 , Abdul-Aleem Mohammad 1 , Hoyin Lam 1, 7 , Klas Straat 1, 5 , Vanessa Wilhelmi 1 , Mingmei Shang 2 , Jesper Tegner 2 , Joo Chuan Tong 3 , Kum Thong Wong 6 , Cecilia Soderberg-Naucler 1, ** , Koon-Chu Yaiw 1, ** 1 Cell and Molecular Immunology, Department of Medicine, Center for Molecular Medicine, Unit for Experimental Cardiovascular Research and Department of Neurology, Karolinska Institutet, Stockholm, Sweden 2 Unit of Computational Medicine, Department of Medicine, Center for Molecular Medicine, Karolinska Institutet, Stockholm, Sweden 3 Social & Cognitive Computing Department, Institute of High Performance Computing, Agency for Science, Technology and Research, Singapore 4 Department of Genomics and Bioinformatics, Positive Bioscience, Mumbai, India 5 Division of Gene Technology, School of Biotechnology, Science for Life Laboratory, Royal Institute of Technology (KTH), Solna, Sweden 6 Department of Pathology, Faculty of Medicine, University of Malaya, Malaysia 7 Present affiliation: Division of Cancer Studies, King’s College London, London, UK * These authors have contributed equally to this work ** Shared senior authorship Correspondence to: Koon-Chu Yaiw, email: koon.yaiw@ki.se Cecilia Soderberg-Naucler, email: cecilia.naucler@ki.se Keywords: cytomegalovirus, glioblastoma, arginase, treatment Received: September 16, 2015 Accepted: May 14, 2016 Published: May 30, 2016 ABSTRACT Background: Both arginase (ARG2) and human cytomegalovirus (HCMV) have been implicated in tumorigenesis. However, the role of ARG2 in the pathogenesis of glioblastoma (GBM) and the HCMV effects on ARG2 are unknown. We hypothesize that HCMV may contribute to tumorigenesis by increasing ARG2 expression. Results: ARG2 promotes tumorigenesis by increasing cellular proliferation, migration, invasion and vasculogenic mimicry in GBM cells, at least in part due to overexpression of MMP2/9. The nor-NOHA significantly reduced migration and tube formation of ARG2-overexpressing cells. HCMV immediate-early proteins (IE1/2) or its downstream pathways upregulated the expression of ARG2 in U-251 MG cells. Immunostaining of GBM tissue sections confirmed the overexpression of ARG2, consistent with data from subsets of Gene Expression Omnibus. Moreover, higher levels of ARG2 expression tended to be associated with poorer survival in GBM patient by analyzing data from TCGA. Methods: The role of ARG2 in tumorigenesis was examined by proliferation-, migration-, invasion-, wound healing- and tube formation assays using an ARG2-overexpressing cell line and ARG inhibitor, N (omega)-hydroxy-nor-L-arginine (nor-NOHA) and siRNA against ARG2 coupled with functional assays measuring MMP2/9 activity, VEGF levels and nitric oxide synthase activity. Association between HCMV and ARG2 were examined in vitro with 3 different GBM cell lines, and ex vivo with immunostaining on GBM tissue sections. The viral mechanism mediating ARG2 induction was examined by siRNA approach. Correlation between ARG2 expression and patient survival was extrapolated from bioinformatics analysis on data from The Cancer Genome Atlas (TCGA). Conclusions: ARG2 promotes tumorigenesis, and HCMV may contribute to GBM pathogenesis by upregulating ARG2.