Crosstalk Between the PI3K/mTOR and MEK/ERK Pathways Involved in the Maintenance of Self-Renewal and Tumorigenicity of Glioblastoma Stem-Like Cells

Author:

Sunayama Jun123,Matsuda Ken-Ichiro14,Sato Atsushi14,Tachibana Ken1,Suzuki Kaori5,Narita Yoshitaka5,Shibui Soichiro5,Sakurada Kaori4,Kayama Takamasa4,Tomiyama Arata1,Kitanaka Chifumi123

Affiliation:

1. Departments of Molecular Cancer Science Yamagata University School of Medicine, Yamagata, Japan

2. Oncology Research Center, Research Institute for Advanced Molecular Epidemiology, Yamagata University, Yamagata, Japan

3. Global COE program for Medical Sciences, Japan Society for Promotion of Science, Tokyo, Japan

4. Departments of Neurosurgery, Yamagata University School of Medicine, Yamagata, Japan

5. Department of Neurosurgery, National Cancer Center Hospital, Tokyo, Japan

Abstract

Abstract The molecular signaling pathways orchestrating the biology of cancer stem-like cells (CSLCs), including glioblastoma, remain to be elucidated. We investigated in this study the role of the MEK/extracellular signal-regulated kinase (ERK) pathway in the control of self-renewal and tumorigenicity of glioblastoma CSLCs, particularly in relation to the PI3K/mTOR (mammalian target of rapamycin) pathway. Targeted inactivation of MEK alone using pharmacological inhibitors or siRNAs resulted in reduced sphere formation of both cell line- and patient-derived glioblastoma CSLCs, accompanied by their differentiation into neuronal and glial lineages. Interestingly, this effect of MEK inactivation was apparently augmented in the presence of NVP-BEZ235, a dual inhibitor of PI3K and mTOR. As a potential explanation for this observed synergy, we found that inactivation of either the MEK/ERK or PI3K/mTOR pathway triggered activation of the other, suggesting that there may be mutually inhibitory crosstalk between these two pathways. Significantly, inactivation of either pathway led to the reduced activation of p70S6K, and siRNA-mediated knockdown of p70S6K resulted in the activation of both pathways, which no longer maintained the cross-inhibitory relationship. Finally, combinational blockade of both pathways in glioblastoma CSLCs suppressed their tumorigenicity, whether transplanted subcutaneously or intracranially, more efficiently than blockade of either alone. Our findings suggest that there is p70S6K-mediated, cross-inhibitory regulation between the MEK/ERK and PI3K/mTOR pathways, in which each contribute to the maintenance of the self-renewal and tumorigenic capacity of glioblastoma CSLCs. Thus, combinational disruption of these pathways would be a rational and effective strategy in the treatment of glioblastoma.

Publisher

Oxford University Press (OUP)

Subject

Cell Biology,Developmental Biology,Molecular Medicine

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