Glioblastoma is the most common and aggressive malignant brain tumor in adults, and glioblastoma stem cells (GSCs) contribute to treatment resistance and recurrence. Inhibition of Stat5b in GSCs suppresses cell proliferation and induces apoptosis. Herein, we investigated the mechanisms of growth inhibition by Stat5b knockdown (KD) in GSCs.
GSCs were established from a murine glioblastoma model in which shRNA-p53 and EGFR/Ras mutants were induced in vivo using a Sleeping Beauty transposon system. Microarray analyses were performed on Stat5b-KD GSCs to identify genes that are differentially expressed downstream of Stat5b. RT-qPCR and western blot analyses were used to determine Myb levels in GSCs. Myb-overexpressing GSCs were induced by electroporation. Proliferation and apoptosis were evaluated by a trypan blue dye exclusion test and annexin-V staining, respectively.
MYB, which is involved in the Wnt pathway, was identified as a novel gene whose expression was down-regulated by Stat5b-KD in GSCs. Both MYB mRNA and protein levels were down-regulated by Stat5b-KD. Overexpression of Myb rescued cell proliferation that was suppressed by Stat5b-KD. Furthermore, Stat5b-KD-induced apoptosis in GSCs was significantly inhibited by Myb overexpression.
Down-regulation of Myb mediates Stat5b-KD-induced inhibition of proliferation and induction of apoptosis in GSCs. This may represent a promising novel therapeutic strategy against glioblastoma.

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