Abstract LB-151: Spred1 and neurofibromin interact to negatively regulate Ras/Raf/MEK/ERK signaling

Abstract The Ras/Mitogen Activated Protein Kinase (MAPK) plays a critical role in cell signaling downstream of receptor tyrosine kinases. The conserved Sprouty family proteins function as feedback regulators of Ras/MAPK signaling. Loss of function mutations in one family member, SPRED1, cause Legius syndrome, an autosomal dominant human disorder that resembles neurofibromatosis type 1 (NF1). Spred1 functions as a negative regulator of the Ras/MAPK pathway, however, the underlying molecular mechanism is poorly understood. We found Spred1 functioned by reducing Ras-GTP levels; SPRED1 loss-of function mutations identified in Legius syndrome patients were unable to regulate Ras activity levels. The N-terminal EVH1 domain of Spred1 was found to be crucial for its inhibitory function. Thus, we utilized tandem affinity purification of wild-type Spred1 and EVH1 domain mutants found in Legius syndrome to identify novel binding partners of the N-terminus. Analysis of protein complexes by mass spectrometry revealed neurofibromin, the NF1 gene product, as a novel Spred1 interacting protein. We show that neurofibromin is a Spred1 binding partner that is necessary for Spred1's inhibitory function. Spred1 requires neurofibromin to down-regulate Ras-GTP levels, and the interaction with Spred1 is required for neurofibromin localization to the plasma membrane. This novel mechanism leads to a better understanding of the regulation of the neurofibromin tumor suppressor protein. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-151. doi:1538-7445.AM2012-LB-151