Background: The CD133(+) stem cell population in recurrent gliomas is associated with clinical features such as therapy resistance, blood-brain barrier disruption and, hence, tumor infiltration. Screening of a large panel of glioma samples increasing histological grade demonstrated frequencies of CD133(+) cells which correlated with high expression of cyclooxygenase (COX)-2 and of membrane type-1 matrix metalloproteinase (MT1-MMP).

The lectin from Canavalia ensiformis (Concanavalin-A, ConA), one of the most abundant lectins known, enables one to mimic biological lectin/carbohydrate interactions that regulate extracellular matrix protein recognition. As such, ConA is known to induce membrane type-1 matrix metalloproteinase (MT1-MMP) which expression is increased in brain cancer. Given that MT1-MMP correlated to high expression of cyclooxygenase (COX)-2 in gliomas with increasing histological grade, we specifically assessed the early proinflammatory cellular signaling processes triggered by ConA in the regulation of COX-2. We found that treatment with ConA or direct overexpression of a recombinant MT1-MMP resulted in the induction of COX-2 expression. This increase in COX-2 was correlated with a concomitant decrease in phosphorylated AKT suggestive of cell death induction, and was independent of MT1-MMP’s catalytic function. ConA- and MT1-MMP-mediated intracellular signaling of COX-2 was also confirmed in wild-type and in Nuclear Factor-kappaB (NF-κB) p65−/− mutant mouse embryonic fibroblasts (MEF), but was abrogated in NF-κB1 (p50)−/− and in I kappaB kinase (IKK) γ−/− mutant MEF cells. Collectively, our results highlight an IKK/NF-κB-dependent pathway linking MT1-MMP-mediated intracellular signaling to the induction of COX-2. That signaling pathway could account for the inflammatory balance responsible for the therapy resistance phenotype of glioblastoma cells, and prompts for the design of new therapeutic strategies that target cell surface carbohydrate structures and MT1-MMP-mediated signaling. Concise summary Concanavalin-A (ConA) mimics biological lectin/carbohydrate interactions that regulate the proinflammatory phenotype of cancer cells through yet undefined signaling. Here we highlight an IKK/NF-κB-dependent pathway linking MT1-MMP-mediated intracellular signaling to the induction of cyclooxygenase-2, and that could be responsible for the therapy resistance phenotype of glioblastoma cells.

Recent advances in the understanding of stem cell mobilization, cell-matrix interaction, and biodistribution have enabled the development of new therapeutic strategies (1, 2). Although locally transplanted bone marrow-derived stromal cells (BMSC) 2 have already been used clinically (3-5), less invasive routes of BMSC transplantation have become the focus of recent attention (6 -8). In fact, several clinical applications now use intravenous administration of genetically engineered BMSC either as an ideal vehicle for gene transfer or as a platform for the systemic delivery of therapeutic recombinant proteins in vivo (6,9,10). This implies that these circulating, systemically infused cells must respond to serum-derived cues that direct their ultimate biodistribution. The molecular players regulating cellular mobilization, chemotaxis, and cell survival of BMSC have received little attention.Among the mediators known to exert potent cellular chemotactic effects, sphingosine 1-phosphate (S1P) is one of the most important bioactive lysophospholipids secreted in blood plasma either upon platelet activation (11) or from brain tumor-derived glioma cells (12). In fact, we have demonstrated that BMSC chemotaxis was very strong in response to S1P (13) and required reorganization of the actin cytoskeleton and remodeling of the extracellular matrix (ECM) through a complex, cooperative signal transduction network involving cell surface matrix metalloproteinase (MMP) activity (14). Currently, the molecular characterization and the nature of that MMP, regulating both BMSC chemotaxis and interaction with the ECM protein microenvironment, remain poorly understood. Recently, we highlighted functional cross-talk between the membrane type-1 MMP (MT1-MMP) and the S1P receptor EDG-1-mediated signaling in BMSC chemotaxis (13). Interestingly, aside from its classical role in ECM proteolysis, MT1-MMP is also involved in transducing crucial intracellular signaling that may control several processes related to BMSC mobilization and cell survival (13)(14)(15)(16).Given that impaired chemotaxis was recently observed in bone marrow cells isolated from a microsomal glucose 6-phos-* This work was supported by a grant of the Natural Sciences and EngineeringResearch Council of Canada (NSERC) (to B. A.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 2 The abbreviations used are: BMSC, bone marrow-derived stromal cell(s); ConA, concanavalin A; ECM, extracellular matrix; G6P, glucose 6-phosphate; G6Pase, glucose-6-phosphatase; G6PT, G6P transporter; MMP, matrix metalloproteinase; MT1-MMP, membrane type-1 MMP; PI, propidium iodine; siRNA, small interfering RNA; S1P, sphingosine 1-phosphate; PBS, phosphate-buffered saline; Wt, wild type; GFP, green fluorescent protein.

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The contributions of membrane type-1 matrix metalloproteinase (MT1-MMP) and of the glucose-6-phosphate transporter (G6PT) in sphingosine-1-phosphate (S1P)-mediated Ca 2+ mobilization were assessed in glioblastoma cells. We show that gene silencing of MT1-MMP or G6PT decreased the extent of S1P-induced Ca 2+ mobilization, chemotaxis, and extracellular signal-related kinase phosphorylation. Chlorogenic acid and (À)-epigallocatechin-3-gallate, two diet-derived inhibitors of G6PT and of MT1-MMP, respectively, reduced S1P-mediated Ca 2+ mobilization. An intact MT1-MMP/G6PT signaling axis is thus required for efficient Ca 2+ mobilization in response to bioactive lipids such as S1P. Targeted inhibition of either MT1-MMP or G6PT may lead to reduced infiltrative and invasive properties of brain tumor cells.