DISTINCT FUNCTIONAL ROLES OF WILD-TYPE EGFR AND ITS MUTANT EGFRVIII IN GLIOBLASTOMA DEVELOPMENT

The epidermal growth factor receptor (EGFR) is a well-known mediator of invasion, proliferation and survival of tumor cells. Amplification and associated overexpression of wild-type (wt) EGFR is the most common genetic alteration in primary glioblastoma (GBM), with a frequency of about 40-50%. Of the GBMs that have an amplification of EGFR, 50-60% also express the mutated EGFRvIII, which lacks the ligand-binding domain resulting in a constitutive activation of the receptor. It has been widely accepted that both wtEGFR and EGFRvIII substantially contribute to GBM pathogenesis, however, their specific in vivo functions are still a matter of debate. In this work we determined distinct functional roles of wtEGFR and the mutant EGFRvIII within human GBM cells in vivo. We genetically modified stem cell cultures of two different human GBM biopsies with low or absent wtEGFR expression to overexpress either wtEGFR or EGFRvIII. By orthotopic transplantation of the different cell-populations into the brains of immune-deficient rats, we were able to distinguish two different phenotypes based on MRI, histology/ immunohistochemistry and molecular analyses. Tumors with overexpression of wtEGFR showed an increased invasive growth pattern, while angiogenesis was either not observed or decreased compared to the original tumor cells. In contrast, EGFRviii overexpressing tumors were more angiogenic and less invasive compared to the control tumors and wtEGFR expressing tumors. Up-regulation of HIF1A as well as a panel of angiogenic factors confirmed angiogenesis in EGFRvIII overexpressing tumors. Integrated bioinformatics of microarray and proteomics data point to differences in signaling pathway activation between wtEGFR and EGFRvIII. In conclusion, our results demonstrate contrasting roles of wtEGFR and its mutant EGFRvIII in invasion and angiogenesis and suggest a concerted action of both receptors to promote the aggressive phenotype of human GBM in vivo.