title: RabGEF1, a negative regulator of Ras signalling, mast cell activation and skin inflammation.
abstract: Mast cell activation induced by the aggregation of FcepsilonRI with IgE and antigen is mediated through the activation of multiple protein kinase cascades. This process induces mast cells to undergo degranulation, to synthesize and release lipid mediators, and to secrete multiple cytokines, chemokines and growth factors. We found that RabGEF1 (Rabex-5) binds to Ras and negatively regulates Ras activation and downstream effector pathways during FcepsilonRI-dependent mouse mast cell activation. Mast cells derived from RabGEF1-deficient mice exhibit significantly enhanced levels of degranulation, release of lipid mediators and secretion of cytokines in response to FcepsilonRI aggregation. RabGEF1 knockout mice have increased perinatal mortality and the mice that do survive develop severe skin inflammation and increased numbers of mast cells in the dermis, some of which exhibit morphological evidence of degranulation. These mice also show elevated concentrations of serum histamine and IgE. Thus, RabGEF1 is a negative regulator of Ras signalling and FcepsilonRI-dependent mast cell activation in vitro, and a lack of RabGEF1 results in the development of elevated numbers of mast cells in the skin and severe skin inflammation in vivo.
authors.affiliation: Departments of Pathology, Stanford University School of Medicine, 300 Pasteur Drive, Stanford, CA 94305-5324, USA.
authors.forename: See-Ying
authors.initials: SY
authors.lastname: Tam
authors.forename: Janet
authors.initials: J
authors.lastname: Kalesnikoff
authors.forename: Susumu
authors.initials: S
authors.lastname: Nakae
authors.forename: Mindy
authors.initials: M
authors.lastname: Tsai
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Galli
mesh_terms: D000818:Animals; D015550:Cell Degranulation; D016207:Cytokines / Q000276:immunology; D003872:Dermatitis / Q000276:immunology* / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D007073:Immunoglobulin E / Q000276:immunology; D008407:Mast Cells / Q000276:immunology*; D051379:Mice; D018345:Mice, Knockout; D017455:Receptors, IgE / Q000276:immunology; D015398:Signal Transduction / Q000502:physiology*; D012867:Skin / Q000033:anatomy & histology / Q000276:immunology*; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D016207:Cytokines; D020662:Guanine Nucleotide Exchange Factors; C510870:RabGEF1 protein, mouse; D017455:Receptors, IgE; D007073:Immunoglobulin E; D018631:ras Proteins