Abstract
2081 Background: Thymosin β4 (TB4) is a pleiotropic actin-sequestering polypeptide that is involved in wound healing and developmental processes. TB4 gene silencing promotes differentiation of neural progenitor cells whereas TB4 overexpression initiates cortical folding of developing brain hemispheres. However, a role of TB4 in malignant gliomas has not yet been investigated. Methods: We first analyzed TB4 expression on tissue microarrays and performed REMBRANDT and TCGA database interrogations. We analyzed TB4 expression in a panel of 8 long-term glioma cell lines and 7 glioma-initiating cell lines. Using lentiviral transduction, we modulated TB4 expression in LNT-229, U87MG and the glioma-initiating cell line GS-2. We studied clonogenic survival, migration, invasion, self-renewal, differentiation capacity of TB4-depleted or TB4-overexpressing glioma cells in vitro and tumorigenicity upon orthotopic implantation in vivo. Finally, we performed an Affymetrix gene chip analysis to unravel the molecular network of TB4 signaling effects. Results: TB4 expression increased with the grade of malignancy in gliomas and correlated with patient survival. In vitro, TB4 gene silencing by lentiviral transduction decreased migration, invasion, growth and self-renewal, and promoted differentiation and the susceptibility to undergo apoptotic cell death upon nutrient depletion in LNT-229, U87MG and the glioma stem-cell line GS2, respectively. In vivo, survival of nude mice bearing tumors derived from TB4-depleted glioma cells was improved and the tumorigenicity of the GS2 glioma stem-cell line was decreased. The gene expression pattern was shifted from the mesenchymal towards the pro-neural gene signature upon TB4 gene silencing. The clustering of differentially regulated genes involved TGF-β and p53 signaling networks. Conclusions: TB4 may be a key regulator of malignancy in glioblastoma and therefore a novel candidate molecular target for anti-glioma therapies.
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