Phenotypical Flexibility of the EGFRvIII-Positive Glioblastoma Cell Line and the Multidirectional Influence of TGFβ and EGF on These Cells-EGFRvIII Appears as a Weak Oncogene.

BACKGROUND

The biological role of EGFRvIII (epidermal growth factor receptor variant three) remains unclear.

METHODS

Three glioblastoma DK-MG sublines were tested with EGF (epidermal growth factor) and TGFβ (transforming growth factor β). Sublines were characterized by an increased percentage of EGFRvIII-positive cells and doubling time (DK-MG to DK-MG), number of amplicons, and EGFRvIII mRNA expression. The influence of the growth factors on primary EGFRvIII positive glioblastomas was assessed.

RESULTS

The overexpression of exoEGFRvIII in DK-MG did not convert them into DK-MG, and this overexpression did not change DK-MG to DK-MG; however, the overexpression of RAS increased the proliferation of DK-MG. Moreover, the highest EGFRvIII phosphorylation in DK-MG did not cause relevant AKT (known as protein kinase B) and ERK (extracellular signal-regulated kinase) activation. Further analyses indicate that TGFβ is able to induce apoptosis of DK-MG cells. This subline was able to convert to DK-MG, which appeared resistant to this proapoptotic effect. EGF acted as a pro-survival factor and stimulated proliferation; however, simultaneous senescence induction in DK-MG cells was ambiguous. Primary EGFRvIII positive (and SOX2 (SRY-Box Transcription Factor 2) positive or SOX2 negative) glioblastoma cells differentially responded to EGF and TGFβ.

CONCLUSIONS

The roles of TGFβ and EGF in the EGFRvIII context remain unclear. EGFRvIII appears as a weak oncogene and not a marker of GSC (glioma stem cells). Hence, it may not be a proper target for CAR-T (chimeric antigen receptor T cells).