Identification of novel pathways causing NF1-driven Schwann cell tumors

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Abstract The NF1 gene product, neurofibromin, was identified in 1990, yet fundamental questions remain unanswered concerning its intracellular location(s), binding partners, and signaling properties. It is known that the large (>200kd) tumor suppressor protein contains a small domain that turns of RAS proteins, so that loss of NF1 function leads to RAS activation on cell stimulation. The remaining NF1 sequence can interact with a chaperone, SPRED1, and other proteins in vitro and/or in specific cell types. In Schwan cells, NF1 loss results in formation of neurofibromas, tumors in the peripheral nerves. It is still unknown which interaction partners and RAS proteins are relevant in Schwann cells. Here we propose to identify NF1 interaction partners, including relevant RAS proteins, that contribute to Schwann cell tumorigenesis. This is because in mammals there are six highly homologous NF1-related RAS paralogs, divided into two families. Our studies rely on interdisciplinary approaches, including cell/mouse genetics, and state of the art biochemical and molecular biology techniques, and our expertise in preclinical testing. Our preliminary data, enabled by new reagents and technologies, supports key roles for canonical RAS proteins in NF1 mutant Schwann cell proliferation. We will now assess the specific roles of RAS proteins in primary Schwann cells in vitro, and in neurofibroma in vivo, and test a potential targeted therapy in vivo. Importantly, whether neurofibromin has Schwann cell-specific interaction partners beyond RAS proteins is unknown. Using proximity biotinylation our preliminary studies identify novel potential NF1-interaction partners in Schwann cells. We will identify complexes containing neurofibromin and these proteins and specific RAS paralogs, and additional complexes that may form on cell stimulation, and test if blocking identified pathways is useful therapeutically.