title: Ras guanine nucleotide releasing factor 1 (RasGrf1) enhancement of Trk receptor-mediated neurite outgrowth requires activation of both H-Ras and Rac.
abstract: We previously demonstrated that the guanine nucleotide exchange factor, RasGrf1, binds nerve growth factor (NGF)-activated TrkA and facilitates neurotrophin-induced neurite outgrowth in PC12 cells. RasGrf1 can activate both Ras and Rac, via intrinsic Cdc25 and DH domains, respectively, suggesting that the activation of both could contribute to this process. Previous studies have assayed constitutive neurite outgrowth following RasGrf1 over-expression in PC12 cells, in either the absence or presence of ectopic H-Ras, and have suggested an essential role for either Ras or Rac depending on the presence of H-Ras over-expression. In contrast, in this study, we have addressed the mechanism of how RasGrf1 facilitates neurite outgrowth in response to the neurotrophins, NGF and BDNF. Using Ras/Rac activation assays and site-directed RasGrf1 mutants, we find that both Ras and Rac are essential to neurotrophin-induced neurite outgrowth. Moreover, we find that H-Ras over-expression rescues the loss of neurite outgrowth observed with a Rac minus mutant and that RasGrf1 differentially stimulates NGF-dependent activation of Rac or Ras, depending on cell type. Collectively, these studies clarify the mechanism of how RasGrf1 expression facilitates neurotrophin-induced neurite outgrowth. Moreover, they suggest that H-Ras over-expression should be used with caution to measure phenotypic responses.
authors: Molecular Brain Research Group, Laboratory of Neural Signaling, Robarts Research Institute, University of Western Ontario, 100 Perth Drive, London, ON, Canada N6A 5K8.
authors: Asghar
authors: A
authors: Talebian
authors: Kim
authors: K
authors: Robinson-Brookes
authors: James I S
authors: JI
authors: MacDonald
authors: Susan O
authors: SO
authors: Meakin
mesh_terms: D000818:Animals; D019208:Brain-Derived Neurotrophic Factor / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D020932:Nerve Growth Factor / Q000378:metabolism; D016501:Neurites / Q000378:metabolism / Q000502:physiology*; D016716:PC12 Cells; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D020917:Receptor, trkA / Q000378:metabolism; D020813:Receptor, trkB / Q000378:metabolism; D017475:Receptors, Nerve Growth Factor / Q000378:metabolism*; D015854:Up-Regulation; D020744:rac GTP-Binding Proteins / Q000378:metabolism*; D020666:ras-GRF1 / Q000235:genetics / Q000378:metabolism*
chemical_list: D019208:Brain-Derived Neurotrophic Factor; C513037:Rasgrf1 protein, mouse; D017475:Receptors, Nerve Growth Factor; D020666:ras-GRF1; D020932:Nerve Growth Factor; D020917:Receptor, trkA; D020813:Receptor, trkB; D016283:Proto-Oncogene Proteins p21(ras); D020744:rac GTP-Binding Proteins