Enhanced tumorigenic behavior of glioblastoma cells expressing a truncated epidermal growth factor receptor is mediated through the Ras-Shc-Grb2 pathway

A mutant epidermal growth factor receptor (Delta EGFR) containing a deletion of 267 amino acids from the extracellular domain is common in human glioblastomas. We have previously shown that the mutant receptor fails to bind EGF, is constitutively phosphorylated, and confers upon U87MG glioblastoma cells expressing it (U87MG.Delta EGFR), an increased ability to form tumors in mice. Here we demonstrate that the constitutively phosphorylated Delta EGFR enhances growth of glioblastoma cells through increased activity of Ras: 1) there was an increase in the proportion of Ras present in the GTP-bound form, and 2) introduction of neutralizing anti-has 259 antibodies into U87MG and U87MG.Delta EGFR cells by microinjection inhibited DNA synthesis to the same low level in both cell populations, We also show that the truncated EGF receptor constitutively associates with the adapter proteins Shc and Grb2 which are involved in the recruitment of Ras to activated receptors, Several derivatives of Delta EGFR containing single, or multiple mutations at critical autophosphorylation sites were constructed and used to demonstrate that the major She binding site is Tyr-1148, and that Grb2 association occurs primarily through Tyr-1068, We conclude that the increased tumorigenic potential of glioblastoma cells expressing the truncated EGF receptor is due at least in part to has activation presumably involving the Shc and Grb2 adapter proteins.