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Signaling and Regulation

Oligodendrocyte Lineage Transcription Factor 2 Inhibits the Motility of a Human Glial Tumor Cell Line by Activating RhoA

¹ Laboratory of Molecular and Cellular Pathology, ² Laboratory of Pathophysiology and Signal Transduction, Hokkaido University School of Medicine; ³ Department of Molecular Pathobiology and 21st Century Center of Excellence Program for Zoonosis Control, Hokkaido University Research Center for Zoonosis Control, Sapporo, Japan; and ⁴ Department of Neurosurgery, National Cancer Center, Tokyo, Japan

Requests for reprints: Hirofumi Sawa, Department of Molecular Pathobiology, Hokkaido University Research Center for Zoonosis Control, N18, W9, Kita-ku, Sapporo 060-0818, Japan. Phone: 81-11706-5185; Fax: 81-11706-5185. E-mail: h-sawa{at}czc.hokudai.ac.jp

The basic helix-loop-helix transcription factor, oligodendrocyte lineage transcription factor 2 (OLIG2), is specifically expressed in the developing and mature central nervous system and plays an important role in oligodendrogenesis from neural progenitors. It is also expressed in various types of glial tumors, but rarely in glioblastoma. Although we previously showed that OLIG2 expression inhibits glioma cell growth, its role in tumorigenesis remains incompletely understood. Here, we investigated the effect of OLIG2 expression on the migration of the human glioblastoma cell line U12-1. In these cells, OLIG2 expression is controlled by the Tet-off system. Induction of OLIG2 expression inhibited both the migration and invasiveness of U12-1 cells. OLIG2 expression also increased the activity of the GTPase RhoA as well as inducing the cells to form stress fibers and focal adhesions. Experiments using short interfering RNA against p27^Kip1 revealed that up-regulation of the p27^Kip1 protein was not essential for RhoA activation, rather it contributed independently to the decreased motility of OLIG2-expressing U12-1 cells. Alternatively, semiquantitative reverse transcription-PCR analysis revealed that mRNA expression of RhoGAP8, which regulates cell migration, was decreased by OLIG2 expression. Furthermore, expression of C3 transferase, which inhibits Rho via ADP ribosylation, attenuated the OLIG2-induced inhibition of cell motility. Imaging by fluorescence resonance energy transfer revealed that in U12-1 cells lacking OLIG2, the active form of RhoA was localized to protrusions of the cell membrane. In contrast, in OLIG2-expressing cells, it lined almost the entire plasma membrane. Thus, OLIG2 suppresses the motile phenotype of glioblastoma cells by activating RhoA. (Mol Cancer Res 2007;5(10):1099–109)