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

Neža Podergajs,Heidi Espedal,Miloš Vittori,Rolf Bjerkvig,Christel Herold-Mende,Tamara Lah Turnšek,Marjan Koršič,Helena Motaln,Urška Verbovšek,Nina Obad,Uroš Rajčević,Hrvoje Miletic

doi:10.18632/oncotarget.5477

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.

Highlights

Glioblastoma (GBM) is the most common primary brain tumor, as well as the most aggressive of primary gliomas
Among the de-regulated genes, the literature and the Biomine Search Engine were searched for any up-regulated genes that encode plasma membrane proteins, and that are putatively associated with receptor tyrosine kinases (RTKs), such as epidermal growth factor receptor (EGFR) or fibroblast growth factor receptor (FGFR), which are often overexpressed in GBM
Since CD9 is a novel protein and belongs to a family www.impactjournals.com/oncotarget of tetraspanins which are involved in EGFR and FGFR signaling pathways [23, 32], we chose this protein for further validation and functional studies in GBM stem cells (GSCs) lines

Summary

Introduction

Glioblastoma (GBM) is the most common primary brain tumor, as well as the most aggressive of primary gliomas. Despite modern treatments, following diagnosis, the overall median survival remains only about 15 months [1]. GBM stem cells (GSCs) show characteristics of normal neural stem cells (NSCs), such as self-renewal and expression of the stem cell markers CD133, www.impactjournals.com/oncotarget nestin and SOX2 [8, 9]. New approaches for GBM treatment are aimed at selective targeting of GSCs [11]. As most of the known stem cell markers are common to both GSCs and NSCs [12], novel selective GSC markers need to be identified to provide better targets for GBM therapies

Objectives

Methods

Results

Conclusion