== Coupling of EGFR and ErbB2 in NF1 MPNST cell lines. proliferation of tissues derived from the neural crest.1,2The overall incidence of approximately 1 in 3,000 includes about 50% of cases that arise due to new mutations in Palifosfamide the NF1 gene,3which encodes a tumor suppressor protein called neurofibromin. Patients with NF1 present numerous clinical manifestations and are at an increased risk of developing certain tumors, most commonly neurofibromas.2The majority of cells in neurofibromas are derived from Schwann cells, and these tumors can affect any peripheral nerve. In approximately 10% of cases, plexiform neurofibromas progress to malignant peripheral nerve sheath tumors (MPNSTs).4There is currently no pharmacological treatment for MPNSTs. Prognosis for NF1 patients with MPNSTs is poor, with only 21% of patients surviving 5 years from time of diagnosis.5 While haploinsufficiency for functional neurofibromin protein drives some aspects of the disease, and provides a favorable microenvironment for tumor development,68loss of heterozygosity is found in the transformed Schwann cell component of MPNSTs.9Neurofibromin downregulates the activity of the small GTPase Ras.10Ras has pivotal roles in cell survival, proliferation, and differentiation by transducing responses initiated at the cell surface to several intracellular signaling molecules, including those that constitute the Raf-MEK-ERK and PI3K-Akt axes.11,12We have previously demonstrated that basal N- and K-Ras and ERK1/2 activities are higher in NF1 MPNST cells, and that activation of the ERK1/2 signaling pathway is critical for their proliferation.13A rational approach to NF1 MPNST therapy may derive from such characterization of the critical signal transduction pathways that drive MPNST proliferation.14,15 In addition to loss of functional neurofibromin, neurofibromas and MPNSTs show significant alterations in the expression of one CAB39L or more of the epidermal growth factor receptor (ErbB) family of receptor tyrosine kinases.16,17These changes significantly affect the responsiveness of Schwann cells to ErbB ligands.16While quiescent Schwann cells Palifosfamide do not express the EGFR, loss of neurofibromin has been shown to correlate with aberrant expression of this receptor in Schwann cells.16,18Increased EGFR abundance and activity are associated with the development and progression of multiple human solid tumors,19,20and play important roles in NF1-associated malignancy. For example, transgenic murine Schwann cells that have targeted overexpression of the EGFR exhibit features of neurofibromas, such as hyperplasia, collagen deposition, mast cell infiltration, and dissociation from axons.21The EGFR confers a mechanism by which Schwann cells respond to mitogenic factors and activate Ras-mediated proliferative and pro-survival signaling pathways, which are greatly potentiated in the context of neurofibromin deficiency.22 Another ErbB family member that has been connected to NF1 tumor pathologies is the ErbB2 tyrosine kinase. ErbB2 is expressed in normal Schwann cells, and heterodimerization of ErbB2 with ErbB3 is believed to direct neuregulin-mediated signaling in Schwann cells.23While there is no known ligand for ErbB2, this protein readily heterodimerizes with the other ErbB family members and greatly enhances their signaling.24Overexpressed ErbB2 can also homodimerize, resulting in ligand-independent signaling and contributing to tumorigenesis.25,26Previous reports have found an inverse relationship between neurofibromin expression and ErbB2 levels,27and constitutive activation of ErbB2 in Schwann cells results in formation of invasive Schwann cell tumors.27,28 In this study, we found that two independent NF1 MPNST lines indicated higher levels of EGFR and have a prolonged and more potent ERK activation in Palifosfamide response to EGF. We also found strong coupling between EGFR.