Abstract A181: Dissecting the crosstalk between wt and mutant EGFR in glioblastoma multiforme

Abstract

Abstract Glioblastoma Multiforme (GBM) exhibits intratumoral heterogeneity on the morphological and molecular levels, a hallmark feature which may contribute to its poor response to targeted therapy. A powerful oncogenic event in GBM is amplification and rearrangement of the epidermal growth factor receptor (EGFRvIII variant, deleted for exons 2–7, hereafter EGFR), yet notably, only a minority of primary tumor cells possess this signature lesion while the remainder maintain expression of the wildtype EGFR (wtEGFR). We observed that tumorigenicy of wtEGFR expressing cells can be significantly enhanced by the presence of EGFR-expressing cells within the tumor, suggesting that soluble factors produced by the latter cells might mediate this potent tumor enhancement. Here we show that in vitro treatment of U87 cells overexpressing wtEGFR (U87wt) with conditioned media from U87 cells overexpressing EGFR (U87) resulted in the activation of wtEGFR, STAT3, Akt, and Erk1/2. Surprisingly, U87 failed to demonstrate any increase in EGFR ligand production that could explain the enhanced wtEGFR phosphorylation. To identify the molecular mediators of this transactivation we analyzed the expression in U87 of cytokines of the IL-6 family, which are known potent activators of STAT3. We found a robust enhancement of the expression of IL-6 and LIF in U87 , compared to the parental cell line. Use of neutralizing antibodies allowed us to demonstrate that these candidate cytokines are responsible not only for the activation of STAT3, but also of the EGFR; results of which were confirmed by antibodies that block accessibility of their common gp130 receptor subunit. The analysis of other similar cellular systems suggested that, although not necessarily through the same cytokine(s), the more tumorigenic cells overexpressing EGFR generate signals to neighboring cells by engaging gp130, which is responsible for the activation of EGFR and STAT3. The importance of this circuitry in vivo was further demonstrated when, by knocking down gp130 expression in U87wt, we completely prevented the tumor growth enhancement usually observed in mixed composition tumors. These observations suggest gp130 as a potential new target for the treatment of gliomas. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A181.