Granulocyte-Macrophage Colony Stimulating Factor Receptor Contributes to Plexiform Neurofibroma Initiation

Plexiform neurofibroma (PNF) is an immune cell-rich peripheral nerve sheath tumor that develops primarily in individuals with Neurofibromatosis Type 1 (NF1). Granulocyte-macrophage colony stimulating factor receptor-β (GM-CSFR-β^c) is a shared component of receptors for the cytokines GM-CSF, IL-3, and IL-5, ligands with immunomodulatory and tumor promoting roles. In the present study, we use genetically engineered mouse model of neurofibroma. We identified the expression of GM-CSFR-β^c and GM-CSFR-α on PNF cells and on macrophages and dendritic cells in the PNF, using the Nf1^f/f; DhhCre mouse model of neurofibroma formation. Genetic deletion of GM-CSFR-β^c in this model reduced the number of PNFs, which was associated with decreased numbers of tumor-associated Iba1+ macrophages and CD11c+ dendritic cells (DC), while loss of GM-CSFR-α had no effect. Deletion of GM-CSFR-α or GM-CSFR-β^c did not improve mouse survival or the structure of Remak bundles in peripheral nerves. Proteome analysis of tumor lysates showed altered levels of numerous cytokines after receptor loss, suggesting that the compensatory effects of other cyto/chemokines maintain a proinflammatory environment promoting neurofibroma. Thus, GM-CSFR-β^c signaling contributes modestly to neurofibroma formation, apparently independently of its ligand GM-CSF.