Overexpression of deletion-mutant epidermal growth factor receptor is associated with altered genotoxic stress-provoked p53 mRNA induction in a human glioblastoma cell line

A distinct 801-bp deletion mutation of the epidermal growth factor receptor (EGFR) gene is frequently present in primary glioblastoma multiforme (GBM), confers enhanced tumorigenicity in vivo and is prognostic of a shorter interval to clinical relapse. This study sought to investigate whether overexpression of deletion-mutant (Δ) EGFR affects genotoxic stress-provoked mRNA inductions of p53 and murine double minute 2 (MDM2), two other genes strongly involved in the pathogenesis of GBM. In a set of human wild-type (wt) p53 GBM cell lines (U-87MG and U-87MG.ΔEGFR) that exclusively differ in EGFR expression (endogenous wt EGFR expression and exogenous ΔEGFR overexpression, respectively), ultraviolet (UV) light irradiation-mediated EGFR, p53 and MDM2 genotoxic stress-provoked mRNA inductions were assessed by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) and densitometry of electrophoretically separated and stained RT-PCR products. Although baseline (at 0 J/m²) p53 mRNA expression in U-87MG.ΔEGFR was 42-fold reduced, maximum p53 induction (at 8 J/m²) amounted to 130% compared to U-87MG. Thus, ultimate UV light-mediated p53 mRNA induction was 131.5-fold in U-87MG.ΔEGFR and 2.8-fold in U-87MG. In contrast, neither wt/ΔEGFR nor MDM2 mRNA expressions were significantly inducible, and MDM2 mRNA profiles were essentially the same among U-87MG and U-87MG.ΔEGFR. These data suggest that in human GBM overexpression of ΔEGFR is associated with differential genotoxic stress-provoked p53 mRNA induction whereas MDM2 mRNA expression is apparently not directly affected by EGFR status.