A transcriptomic, proteomic, and functional genetic atlas dissects neurofibromin function in the peripheral nervous system

The NF1 tumor suppressor gene is recurrently mutated in human cancers and is associated with the neurofibromatosis type 1 (NF-1) cancer predisposition syndrome. NF1 encodes neurofibromin, a Ras guanosine triphosphate (GTPase) activating protein that negatively regulates Ras signaling. NF1 mutation accordingly leads to Ras misactivation and downstream activation of RAF/MEK/ERK signaling, leading to the approval of the MEK inhibitor selumetinib for NF-1 associated peripheral nervous system (PNS) tumors. However, how NF1 loss modifies response to selumetinib and the utility of targeting additional upstream inputs or downstream outputs of Ras these tumors remain unclear. Here, we perform RNA-sequencing, phosphoproteomic, pharmacologic, and proximal proteomic analysis across a panel of CRISPR interference immortalized peripheral nerve (iPN) cells to systematically dissect the function of neurofibromin loss. Small guide NF1 (sgNF1) repression is sufficient to increase Ras GTP levels and alter gene expression to promote cell proliferation and dedifferentiation, with sgNF1 iPNs showing decreased sensitivity to selumetinib due to altered feedback regulation to Ras/RAF/ MEK/ERK. Upstream small guide PTPN11 (sgPTPN11) repression leads to the inverse gene expression signature, decreasing cell proliferation and promoting differentiation, and sgPTPN11 iPNs are more sensitive to selumetinib. However, upstream sonof sevenless 1 inhibition shows limited efficacy in iPNs due to compensation by SOS2. Finally, proximal proteomics reveals Kirsten rat sarcoma virus (KRAS), but not Harvey rat sarcoma virus (HRAS) or neuroblastoma Ras viral oncogene homolog (NRAS), associates with neurofibromin in iPN cells, and pan-KRAS inhibition is sufficient to block ERK activation and CDK1/2 activation in NF1 mutant cells, suggesting blocking KRAS may be a therapeutic approach for NF1 mutant PNS tumors.