Function of aberrant EGFR in malignant gliomas.

The most common alteration of the epidermal growth factor receptor (EGFR) gene in human malignant gliomas is an in-frame deletion of exon 2-7 from the extra-cellular domain. To study the relationship between the expression of this aberrant EGFR and cell proliferation, as well as apoptosis in malignant gliomas, we have developed U-87MG cell transfectants that express the aberrant (mutant-type) or normal (wild-type) EGFR. We analyzed cell number, tumor volume, and MIB-1 positive rate as proliferation markers, and found that in tissue culture, tumors derived from U-87 MG cells (mutant-type) have the same proliferative activity as those derived from U-87 MG cells (wild-type). However, when cells expressing mutant EGFR were implanted into nude mice subcutaneously, the tumorigenic capacity was much enhanced. We also found that the apototic index of tumors derived from U-87 MG cells (mutant-type) was less than 0.1%, whereas that of wild-type tumor was 1%. These results suggest that aberrant EGFR affects the malignancy of glioma by stimulating proliferation and inhibiting apoptosis.