Malignant Peripheral Nerve Sheath Tumor Invasion Requires Aberrantly Expressed EGF Receptors and Is Variably Enhanced by Multiple EGF Family Ligands

Aberrant epidermal growth factor receptor (EGFR) expression promotes the pathogenesis of malignant peripheral nerve sheath tumors (MPNSTs), the most common malignancy associated with neurofibromatosis type 1, but the mechanisms by which EGFR expression promotes MPNST pathogenesis are poorly understood. We hypothesized that inappropriately expressed EGFRs promote MPNST invasion and found that these kinases are concentrated in MPNST invadopodia in vitro. Epidermal growth factor receptor knockdown inhibited the migration of unstimulated MPNST cells in vitro, and exogenous EGF further enhanced MPNST migration in a substrate-specific manner, promoting migration on laminin and, to a lesser extent, collagen. In this setting, EGF acts as a chemotactic factor. We also found that the 7 known EGFR ligands (EGF, betacellulin, epiregulin, heparin-binding EGF, transforming growth factor-alpha [TGF-alpha], amphiregulin, and epigen) variably enhanced MPNST migration in a concentration-dependent manner, with TGF-alpha being particularly potent. With the exception of epigen, these factors similarly promoted the migration of nonneoplastic Schwann cells. Although transcripts encoding all 7 EGFR ligands were detected in human MPNST cells and tumor tissues, only TGF-alpha was consistently overexpressed and was found to colocalize with EGFR in situ. These data indicate that constitutive EGFR activation, potentially driven by autocrine or paracrine TGF-alpha signaling, promotes the aggressive invasive behavior characteristic of MPNSTs.