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

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.

Tetraspanin CD9 stabilizes gp130 by preventing its ubiquitin-dependent lysosomal degradation to promote STAT3 activation in glioma stem cells

“…Disrupting CD9 potently suppressed GSC tumor growth, indicating that CD9 is an attractive therapeutic target to halt STAT3 signaling in GSCs to diminish their tumorigenic potential. Because CD9 is preferentially expressed in GSCs, but it is rarely expressed in neural stem cells or other normal brain cells, 15 targeting CD9 may specifically disrupt GSCdriven tumor progression with minimal impact on the physiological function of brain. As a cell surface protein, the Figure 8 A schematic diagram shows that CD9 binds to gp130 and stabilizes gp130 by blocking its ubiquitin-dependent lysosomal degradation to promote the BMX-mediated STAT3 activation in GSCs.…”

“…CD9 has a pro-tumorigenic role to promote cancer invasion and tumor growth in cervical cancer, gastric cancer and GBM. [13][14][15] In addition, CD9 expression has potential prognostic value to predict patient survival. 16 Moreover, CD9 is associated with the stem cell phenotype in embryonic stem cells (ES) and hematopoietic stem cells.…”

“…[17][18][19] Recently, CD9 has been shown to facilitate cell proliferation and tumorsphere formation of GSCs. 15 However, the molecular mechanisms underlying the CD9 function in GSC maintenance have not been elucidated.…”

TSPAN31 is a critical regulator on transduction of survival and apoptotic signals in hepatocellular carcinoma cells

“…This is largely because their short cytoplasmic tails are generally < 20 amino acids in length and lack canonical signaling motifs . However, several tetraspanins were recently shown to interact with intracellular signaling proteins such as phosphatidylinositol 3‐kinases (PI3K) and PKC . Tetraspanins can associate with a variety of transmembrane and cytosolic proteins to form tetraspanin‐enriched microdomains (TEMs), and influence cellular signaling pathways including cell proliferation, survival, adhesion, and motility .…”

“…However, several tetraspanins were recently shown to interact with intracellular signaling proteins such as Abbreviations 2D, two-dimensional; CDK4, cyclin dependent kinase 4; Co-IP, Coimmunoprecipitation; DMSO, dimethyl sulphoxide; EGF, Epidermal growth factor; HCC, hepatocellular carcinoma; IP, immunoprecipitation; NATsDB, Natural Antisense Transcripts Database; p-Akt, phosphorylated Akt; PI3K, phosphatidylinositol 3-kinases; p-GSK3b, phosphorylated GSK3b; PKB, protein kinase B; qRT-PCR, quantitative real-time PCR; Rb, retinoblastoma; TEMs, tetraspanin-enriched microdomains; TSPAN31¸tetraspanin 31; 3 0 UTR 3 0 untranslated regions. phosphatidylinositol 3-kinases (PI3K) and PKC [9][10][11]. Tetraspanins can associate with a variety of transmembrane and cytosolic proteins to form tetraspaninenriched microdomains (TEMs), and influence cellular signaling pathways including cell proliferation, survival, adhesion, and motility [12,13].…”