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Loss of Collapsin Response Mediator Protein1, as Detected by iTRAQ Analysis, Promotes Invasion of Human Gliomas Expressing Mutant EGFRvIII

¹ Arthur and Sonia Labatts Brain Tumor Research Center, Hospital for Sick Children's Research Institute, University of Toronto, ² Department of Chemistry and Centre for Research in Mass Spectrometry, York University, ³ Division of Neuropathology, Department of Pathology, Toronto Western Hospital, University of Toronto, and ⁴ Division of Neurosurgery, Department of Surgery, Toronto Western Hospital, University of Toronto, Toronto, Canada

Requests for reprints: Abhijit Guha, Hospital for Sick Children's University Health Network, 4W-446 West Wing, 399 Bathurst Street, Toronto, Ontario, M5T 2S8, Canada. Phone: 416-603-5740; Fax: 416-603-5298; E-mail: Abhijit.Guha{at}uhn.on.ca.

Glioblastoma multiforme (GBM) is the most common and lethal primary human brain tumor. GBMs are characterized by a variety of genetic alterations, among which oncogenic mutations of epidermal growth factor receptor (EGFRvIII) is most common. GBMs harboring EGFRvIII have increased proliferation and invasive characteristics versus those expressing wild-type (wt) EGFR. To identify the molecular basis of this increased tumorgenic phenotype, we used iTRAQ-labeling differential proteomic analysis. Among several differentially expressed proteins, we selected CRMP1, a protein implicated in cellular invasion that was markedly decreased in GBMs expressing EGFRvIII, for further study. The differential expression of CRMP1 was confirmed in a panel of human GBM cell lines and operative specimens that express wtEGFR or mutant EGFRvIII by quantitative real-time PCR, Western blot, and immunohistochemical analysis. In human GBM samples, decreased expression of CRMP1 correlated with EGFRvIII positivity. Knockdown of CRMP1 by siRNA resulted in increased invasion of wtEGFR expressing human GBM cells (U87 and U373) to those found in isogenic GBM cells. Exogenous expression of EGFRvIII in these wtEGFR-expressing GBM cells promoted their ability to invade and was accompanied by decreased expression of CRMP1. Rescuing CRMP1 expression decreased invasion of the EGFRvIII-expressing GBM cells by tilting the balance between Rac and Rho. Collectively, these results show that the loss of CRMP1 contribute to the increased invasive phenotype of human GBMs expressing mutant EGFRvIII. [Cancer Res 2009;69(22):8545–54]

Key Words: GBM • EGFR • EGFRvIII • iTRAQ • CRMP1 • Cell Invasion