Abstract
Abstract INTRODUCTION Glioblastomas (GBMs) are resistant to traditional therapies, and new treatment is urgently needed. NOTCH signaling is highly activated in glioma and activated NOTCH signaling is associated with increased tumor growth and therapeutic resistance. Effect of oncolytic virus therapy on NOTCH signaling activation has not been reported to our knowledge. METHODS Western blotting, real time Q-PCR, reporter assay, and bioluminescence mice imaging were used to evaluate oHSV-mediated activation of NOTCH signaling. High throughput analysis of HSV-1-encoded microRNAs and genes were performed to identify the activator of NOTCH signaling, and in silico analysis, 3’ untranslated region (3’UTR) assay, and immunoprecipitation were used to uncover the down-stream signaling. Anti-tumor efficacy of NOTCH inhibitor, gamma-secretase inhibitor (GSI) combined with oHSV was evaluated using intracranial glioma-bearing mouse xenografts. RESULTS oHSV infection induced NOTCH activity in glioma PDX cells. High throughput analysis uncovered this to be due to HSV-1-encoded miR-H16 (miR-H16). 3’UTR analysis of Factor Inhibiting HIF-1 (FIH-1) indicated miR-H16 directly target FIH-1 and repress its protein expression. Immunoprecipitation analysis also uncovered that FIH-1 reduction liberated Mild bomb 1 (Mib1) from FIH-1 mediated sequestration, permitting it to activate NOTCH signaling by ubiquitination of NOTCH ligands. Forced expression of either antago-miR-H16 or FIH-1 attenuated the oHSV-induced NOTCH activation. Furthermore, oHSV therapy-induced activation of NOTCH signaling sensitized tumors to GSI, resulting in significantly improved therapeutic response to oHSV therapy and prolonged the survival in several intracranial GBM xenografts. CONCLUSION In this study, we identified the mechanism of oHSV therapy-mediated activation of NOTCH signaling, and showed the therapeutic benefit of combining oHSV with GSI.
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