Constitutional heterozygous loss-of-function mutations in the SPRED1 gene cause a phenotype known as Legius syndrome, which consists of symptoms of multiple café-au-lait macules, axillary freckling, learning disabilities, and macrocephaly. Legius syndrome resembles a mild neurofibromatosis type 1 (NF1) phenotype. It has been demonstrated that SPRED1 functions as a negative regulator of the Ras-ERK pathway and interacts with neurofibromin, the NF1 gene product. However, the molecular details of this interaction and the effects of the mutations identified in Legius syndrome and NF1 on this interaction have not yet been investigated. In this study, using a yeast two-hybrid system and an immunoprecipitation assay in HEK293 cells, we found that the SPRED1 EVH1 domain interacts with the N-terminal 16 amino acids and the C-terminal 20 amino acids of the GTPase-activating protein (GAP)-related domain (GRD) of neurofibromin, which form two crossing ␣-helix coils outside the GAP domain. These regions have been shown to be dispensable for GAP activity and are not present in p120 GAP . Several mutations in these N-and C-terminal regions of the GRD in NF1 patients and pathogenic missense mutations in the EVH1 domain of SPRED1 in Legius syndrome reduced the binding affinity between the EVH1 domain and the GRD. EVH1 domain mutations with reduced binding to the GRD also disrupted the ERK suppression activity of SPRED1. These data clearly demonstrate that SPRED1 inhibits the Ras-ERK pathway by recruiting neurofibromin to Ras through the EVH1-GRD interaction, and this study also provides molecular basis for the pathogenic mutations of NF1 and Legius syndrome.Spred (Sprouty-related protein with an EVH1 domain) family proteins, initially discovered as c-Kit-and c-Fms-binding proteins, have been shown to suppress the Ras-ERK pathway. Spreds form a subfamily of the Sprouty/Spred family, which is characterized by the Sprouty-related C-terminal cysteine-rich (SPR) 3 domain. In mammals, four Sprouty homologues and three members of the Spred family of proteins, Spred1, Spred2, and Spred3, have been discovered. Mammalian Spreds can negatively regulate the Ras-Raf-ERK pathway (1, 2); however, compared with Spred1 and Spred2, Spred3 has much weaker ERK suppression activity (3). The SPR domain has been shown to be palmitoylated, causing Sprouty and Spred to localize in the membrane fraction (4, 5). Spred1 and Spred2 are composed of an N-terminal enabled/vasodilator-stimulated protein homology 1 (EVH1) domain, a central c-Kit-binding domain, and a cysteine-rich C-terminal SPR domain, whereas Spred3 lacks a functional c-Kit-binding domain.

Mitogen-activated protein kinase (MAPK) cascades are involved in a variety of cellular responses including proliferation, differentiation, and apoptosis. We have developed an expression screening method to detect in vivo substrates of MAPKs in mammalian cells, and identified a membrane protein, linker for activation of T cells (LAT), as an MAPK target. LAT, an adapter protein essential for Tcell signaling, is phosphorylated at its Thr 155 by ERK in response to T-cell receptor stimulation. Thr 155 phosphorylation reduces the ability of LAT to recruit PLCc1 and SLP76, leading to attenuation of subsequent downstream events such as [Ca 2 þ ] i mobilization and activation of the ERK pathway. Our data reveal a new role for MAPKs in a negative feedback loop in T-cell activation via threonine phosphorylation of LAT.

Cytokines from group 2 innate lymphoid cells (ILC2s) have been implicated in acute allergic responses, such as papain-induced lung inflammation. However, the means of homeostatic regulation of ILC2s have not been established. In this study, we demonstrated that Spred1, a negative regulator of the Ras–ERK pathway, plays an important role in the proliferation and apoptosis of ILC2s and in cytokine secretion from ILC2s. Intranasal administration of papain stimulated IL-5 and IL-13 production in the lung, which was enhanced when Spred1 was deleted. In vitro, Spred1−/− ILC2s proliferated faster than wild type ILC2s did and produced higher levels of cytokines in response to IL-33. On the contrary, a MEK inhibitor suppressed ILC2 proliferation and cytokine production. Spred1 deficiency resulted in stabilization of GATA3, which has been shown to play essential roles in the maintenance and cytokine production of ILC2. These data suggest that Spred1 negatively regulates ILC2 development and functions through the suppression of the Ras–ERK pathway.