biostudies-literatureKalesnikoff JNIAID NIH HHSNHLBI NIH HHSNCI NIH HHSNIGMS NIH HHS5308-17https://www.ebi.ac.uk/biostudies/studies/S-EPMC1890836biostudies-literatureUnknown109(12)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.BloodRoles of RabGEF1/Rabex-5 domains in regulating Fc epsilon RI surface expression and Fc epsilon RI-dependent responses in mast cells.PMC1890836AI070813P50 HL067674R01 CA072074S06 GM008205HL67674R01 AI023990R37 AI023990T32 GM007365GM08205R01 AI070813AI23990P01 HL067674CA72074Alejandro Barbieri MGalli SJRios EJTam SYChen CCKalesnikoff JTsai MfalseRoles of RabGEF1/Rabex-5 domains in regulating Fc epsilon RI surface expression and Fc epsilon RI-dependent responses in mast cells.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.2007-01-01T00:00:00Z2007 Jun2024-11-05T19:53:03.294Z2019-03-27T02:04:06ZS-EPMC18908361734166310.1182/blood-2007-01-067363