Mutations in the NF1 tumor suppressor gene cause neurofibromatosis type 1 (NF1), the most common genetic disorder in man with a predisposition to cancer. NF1 encodes a GTPase activating protein (GAP) for p21ras (Ras) called neurofibromin, and studies by us and others have shown that the Ras signaling pathways are hyperactive in cells from NF1 patients. Individuals with NF1 have a wide range of malignant and nonmalignant manifestations, including the debilitating plexiform neurofibromas that collectively affect 15-40% of NF1 patients and are a major source of life long morbidity and mortality. Neurofibromas are complex tumors composed of Schwann cells, endothelial cells, fibroblasts, and high concentrations of degranulating mast cells. Studies in cutaneous, mammary, and pancreatic cancers have emphasized the role of inflammatory cells, including mast cells, in altering the tumor microenvironment and facilitating malignant outgrowth. Our group provided the first genetic, cellular, and biochemical evidence that haploinsufficiency of Nf1 alters Ras activity and cell fates in mast cells1, 2. We recently found that Nf1-/- Schwann cells secrete excessive quantities of kit- ligand to recruit mast cells to the tumor microenvironment. 3. Further, using a genetically engineered murine model that closely recapitulates the development of plexiform neurofibromas in NF1 patients, we have now used bone marrow transplantation to demonstrate as a proof of concept that haploinsufficiency of Nf1 in the hematopoietic component of the tumor microenvironment and particularly mast cells is necessary for tumor progression. In this application, we propose to build on these observations and pursue a molecular target identified in the previous funding period. We have recently shown that p21 activated kinase 1 (Pak 1), a serine/threonine kinase, is hyperactivated in Nf1 mast cells2. We hypothesize that Pak1 functions as a key intracellular signaling pathway node that regulates multiple pathologic mast cell processes. Preliminary data from our lab using a Pak1-/- mouse support this hypothesis. Here, we propose to use a genetic intercross to test the role of Pak1 on pathological Nf1 mast cell functions and the biochemical effectors that mediate these functions in vitro. In addition, utilizing the genetically engineered murine model of plexiform neurofibromas and state-of the art experimental imaging developed by investigators on this application, studies to test the role of Pak1 in promoting hematopoietic cell mediated initiation of plexiform neurofibromas in vivo are proposed. Project Narrative: We have previously identified a role for inflammatory mast cells in the genesis of a common type of congenital tumor called plexiform neurofibromas. Studies in this application propose studies in genetically engineered mice to test the role of a protein called Pak1 that we hypothesize are integral to mast cell function and tumor progression. If the hypothesis is correct, we would predict that developing small molecules that inhibit Pak1 function could be useful as a molecular therapy for treatment of plexiform neurofibromas.

National Institute of Health (NIH)
National Cancer Institute (NCI)
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Hematopoiesis Study Section (HP)
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Mufson, R Allan
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Indiana University-Purdue University at Indianapolis
Schools of Medicine
United States
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Ferguson, Michael J; Rhodes, Steven D; Jiang, Li et al. (2016) Preclinical Evidence for the Use of Sunitinib Malate in the Treatment of Plexiform Neurofibromas. Pediatr Blood Cancer 63:206-13
Zeng, Yi; Broxmeyer, Hal E; Staser, Karl et al. (2015) Pak2 regulates hematopoietic progenitor cell proliferation, survival, and differentiation. Stem Cells 33:1630-41
Rhodes, Steven D; Zhang, Wei; Yang, Dalong et al. (2015) Dystrophic spinal deformities in a neurofibromatosis type 1 murine model. PLoS One 10:e0119093
Molosh, Andrei I; Johnson, Philip L; Spence, John P et al. (2014) Social learning and amygdala disruptions in Nf1 mice are rescued by blocking p21-activated kinase. Nat Neurosci 17:1583-90
Staser, Karl; Park, Su-Jung; Rhodes, Steven D et al. (2013) Normal hematopoiesis and neurofibromin-deficient myeloproliferative disease require Erk. J Clin Invest 123:329-34
Staser, Karl; Shew, Matthew A; Michels, Elizabeth G et al. (2013) A Pak1-PP2A-ERM signaling axis mediates F-actin rearrangement and degranulation in mast cells. Exp Hematol 41:56-66.e2
Nalepa, Grzegorz; Barnholtz-Sloan, Jill; Enzor, Rikki et al. (2013) The tumor suppressor CDKN3 controls mitosis. J Cell Biol 201:997-1012
Yang, Feng-Chun; Staser, Karl; Clapp, D Wade (2012) The plexiform neurofibroma microenvironment. Cancer Microenviron 5:307-10
Staser, Karl; Yang, Feng-Chun; Clapp, D Wade (2012) Pathogenesis of plexiform neurofibroma: tumor-stromal/hematopoietic interactions in tumor progression. Annu Rev Pathol 7:469-95
Robertson, Kent A; Nalepa, Grzegorz; Yang, Feng-Chun et al. (2012) Imatinib mesylate for plexiform neurofibromas in patients with neurofibromatosis type 1: a phase 2 trial. Lancet Oncol 13:1218-24

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