Transmembrane protein CD9 is glioblastoma biomarker, relevant for maintenance of glioblastoma stem cells

Abstract

// Neža Podergajs 1 , Helena Motaln 1 , Uroš Rajčević 2 , Urška Verbovšek 1 , Marjan Koršič 3 , Nina Obad 4 , Heidi Espedal 4 , Miloš Vittori 1 , Christel Herold-Mende 5 , Hrvoje Miletic 4 , Rolf Bjerkvig 4, 6 , Tamara Lah Turnšek 1, 7 1 Department of Genetic Toxicology and Cancer Biology, National Institute of Biology, 1000 Ljubljana, Slovenia 2 Department of Biochemistry, Blood Transfusion Centre of Slovenia, 1000 Ljubljana, Slovenia 3 Department of Neurosurgery, University Medical Centre, University of Ljubljana, 1000 Ljubljana, Slovenia 4 Department of Biomedicine, University of Bergen, 5009 Bergen, Norway 5 Division of Neurosurgical Research, Department of Neurosurgery, University of Heidelberg, 69120 Heidelberg, Germany 6 NorLux Neuro-Oncology Laboratory, Centre de Recherche Public de la Santé, 1526 Luxembourg, Luxembourg 7 Department of Biochemistry, Faculty of Chemistry and Chemical Engineering, University of Ljubljana, 1000 Ljubljana, Slovenia Correspondence to: Tamara Lah Turnšek, e-mail: Tamara.Lah@nib.si Keywords: biomarker, CD9, glioblastoma stem cells, neural stem cells, tetraspanin Received: May 02, 2015      Accepted: October 31, 2015      Published: November 11, 2015 ABSTRACT The cancer stem cell model suggests that glioblastomas contain a subpopulation of stem-like tumor cells that reproduce themselves to sustain tumor growth. Targeting these cells thus represents a novel treatment strategy and therefore more specific markers that characterize glioblastoma stem cells need to be identified. In the present study, we performed transcriptomic analysis of glioblastoma tissues compared to normal brain tissues revealing sensible up-regulation of CD9 gene. CD9 encodes the transmembrane protein tetraspanin which is involved in tumor cell invasion, apoptosis and resistance to chemotherapy. Using the public REMBRANDT database for brain tumors, we confirmed the prognostic value of CD9, whereby a more than two fold up-regulation correlates with shorter patient survival. We validated CD9 gene and protein expression showing selective up-regulation in glioblastoma stem cells isolated from primary biopsies and in primary organotypic glioblastoma spheroids as well as in U87-MG and U373 glioblastoma cell lines. In contrast, no or low CD9 gene expression was observed in normal human astrocytes, normal brain tissue and neural stem cells. CD9 silencing in three CD133+ glioblastoma cell lines (NCH644, NCH421k and NCH660h) led to decreased cell proliferation, survival, invasion, and self-renewal ability, and altered expression of the stem-cell markers CD133, nestin and SOX2. Moreover, CD9 -silenced glioblastoma stem cells showed altered activation patterns of the Akt, MapK and Stat3 signaling transducers. Orthotopic xenotransplantation of CD9 -silenced glioblastoma stem cells into nude rats promoted prolonged survival. Therefore, CD9 should be further evaluated as a target for glioblastoma treatment.