Expression of cytoplasmic-domain substituted epidermal growth factor receptor inhibits tumorigenicity of EGFR-overexpressed human glioblastoma multiforme

The accumulated results of recent clinical studies have indicated that aberrant epidermal growth factor receptor (EGFR) activation due to gene amplification and/or rearrangement contributes to increased malignancy and poor prognosis in many human cancers, especially in human glioblastoma multiforme (GBM). The elevated EGFR signaling in GBM has been correlated with shorter interval to relapse and lower survival rates, even in patients treated with surgery, radiation therapy, and/or chemotherapy. Therefore, the blockade of EGFR signaling in GBM may provide an ideal alternative therapeutic strategy. In this study, two EGFR-overexpressing human GBM cell lines (i.e., DBTRG and GBM 8901) were used as a model system. We demonstrated that expression of a human EGFR (EGFR(t)-EGFP) chimera protein in which the cytoplasmic domain is substituted by EGFP significantly reduced the EGF-induced endogenous EGFR autophosphorylation, EGF-induced downstream extracellular signal-regulated kinase (ERK) and Akt signaling, and the proportion of internalized receptors in EGF stimulated cells. Furthermore, these cells' anchorage-independent growth in vitro was decreased and their tumorigenicity in vivo abrogated or strongly suppressed. Our data suggest that EGFR(t)-EGFP abrogates tumor growth by disrupting receptor activation via competing for EGF-like ligands, forming non-activated heterodimers with endogenous EGFR, and inhibiting the EGFR endosomal signaling by substantially diminishing receptor internalization. This treatment modality (termed 'dominant-negative EGFR therapy') and its efficacy for gliomas or other tumors are under scrutiny.