title: Roles of RabGEF1/Rabex-5 domains in regulating Fc epsilon RI surface expression and Fc epsilon RI-dependent responses in mast cells.
abstract: RabGEF1/Rabex-5, a guanine nucleotide exchange factor (GEF) for the endocytic pathway regulator, Rab5, contains a Vps9 domain, an A20-like zinc finger (ZnF) domain, and a coiled coil domain. To investigate the importance of these domains in regulating receptor internalization and cell activation, we lentivirally delivered RabGEF1 mutants into RabGEF1-deficient (-/-) mast cells and examined Fc epsilon RI-dependent responses. Wild-type RabGEF1 expression corrected phenotypic abnormalities in -/- mast cells, including decreased basal Fc epsilon RI expression, slowed Fc epsilon RI internalization, elevated IgE + Ag-induced degranulation and IL-6 production, and the decreased ability of -/- cytosol to support endosome fusion. We showed that RabGEF1's ZnF domain has ubiquitin ligase activity. Moreover, the coiled coil domain of RabGEF1 is required for Rabaptin-5 binding and for maintaining basal levels of Rabaptin-5 and surface Fc epsilon RI. However, mutants lacking either of these domains normalized phenotypic abnormalities in IgE + antigen-activated -/- mast cells. By contrast, correction of these -/- phenotypes required a functional Vps9 domain. Thus, Fc epsilon RI-mediated mast cell functional activation is dependent on RabGEF1's GEF activity.
authors.affiliation: Department of Pathology, Stanford University School of Medicine, Stanford, CA 94305-5324, USA.
authors.forename: Janet
authors.initials: J
authors.lastname: Kalesnikoff
authors.forename: Eon J
authors.initials: EJ
authors.lastname: Rios
authors.forename: Ching-Cheng
authors.initials: CC
authors.lastname: Chen
authors.forename: M
authors.initials: M
authors.lastname: Alejandro Barbieri
authors.forename: Mindy
authors.initials: M
authors.lastname: Tsai
authors.forename: See-Ying
authors.initials: SY
authors.lastname: Tam
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Galli
mesh_terms: D001854:Bone Marrow Cells; D015550:Cell Degranulation; D002478:Cells, Cultured; D004705:Endocytosis; D005786:Gene Expression Regulation; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry / Q000502:physiology*; D006801:Humans; D015850:Interleukin-6 / Q000096:biosynthesis; D008407:Mast Cells / Q000166:cytology / Q000502:physiology*; D017455:Receptors, IgE / Q000172:deficiency / Q000235:genetics*
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D015850:Interleukin-6; C108382:RABGEF1 protein, human; D017455:Receptors, IgE