Journal
MOLECULAR CANCER THERAPEUTICS
Volume 15, Issue 7, Pages 1656-1668Publisher
AMER ASSOC CANCER RESEARCH
DOI: 10.1158/1535-7163.MCT-15-0857
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Funding
- CPRIT grant [RP120256]
- SPORE grant [P50 CA127001]
- Cancer Center Support Grant [CA016672]
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Glioblastoma (GBM) represents a compelling disease for kinase inhibitor therapy because most of these tumors harbor genetic alterations that result in aberrant activation of growth factor-signaling pathways. The PI3K/mammalian target of the rapamycin (mTOR) pathway is dysregulated in over 50% of human GBM but remains a challenging clinical target. Inhibitors against PI3K/mTOR mediators have limited clinical efficacy as single agents. We investigated potential bypass mechanisms to PI3K/mTOR inhibition using gene expression profiling before and after PI3K inhibitor treatment by Affymetrix microarrays. Mitogen-and stress-activated protein kinase 1 (MSK1) was markedly induced after PI3K/mTOR inhibitor treatment and disruption of MSK1 by specific shRNAs attenuated resistance to PI3K/mTOR inhibitors in glioma-initiating cells (GIC). Further investigation showed that MSK1 phosphorylates beta-catenin and regulates its nuclear translocation and transcriptional activity. The depletion of beta-catenin potentiated PI3K/mTOR inhibitor-induced cytotoxicity and the inhibition of MSK1 synergized with PI3K/mTOR inhibitors to extend survival in an intracranial animal model and decreased phosphorylation of beta-catenin at Ser552. These observations suggest that MSK1/beta-catenin signaling serves as an escape survival signal upon PI3K/mTOR inhibition and provides a strong rationale for the combined use of PI3K/mTOR and MSK1/beta-catenin inhibition to induce lethal growth inhibition in human GBM. (C) 2016 AACR.
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