title: Integrin-independent role of CalDAG-GEFI in neutrophil chemotaxis.
abstract: Chemotaxis and integrin activation are essential processes for neutrophil transmigration in response to injury. CalDAG-GEFI plays a key role in the activation of beta1, beta2, and beta3 integrins in platelets and neutrophils by exchanging a GDP for a GTP on Rap1. Here, we explored the role of CalDAG-GEFI and Rap1b in integrin-independent neutrophil chemotaxis. In a transwell assay, CalDAG-GEFI-/- neutrophils had a 46% reduction in transmigration compared with WT in response to a low concentration of LTB4. Visualization of migrating neutrophils in the presence of 10 mM EDTA revealed that CalDAG-GEFI-/- neutrophils had abnormal chemotactic behavior compared with WT neutrophils, including reduced speed and directionality. Interestingly, Rap1b-/- neutrophils had a similar phenotype in this assay, suggesting that CalDAG-GEFI may be acting through Rap1b. We investigated whether the deficit in integrin-independent chemotaxis in CalDAG-GEFI-/- neutrophils could be explained by defective cytoskeleton rearrangement. Indeed, we found that CalDAG-GEFI-/- neutrophils had reduced formation of F-actin pseudopodia after LTB4 stimulation, suggesting that they have a defect in polarization. Overall, our studies show that CalDAG-GEFI helps regulate neutrophil chemotaxis, independent of its established role in integrin activation, through a mechanism that involves actin cytoskeleton and cellular polarization.
authors.affiliation: Immune Disease Institute, Program in Cellular and Molecular Medicine, Department of Laboratory Medicine, Children's Hospital, and Department of Pathology, Harvard Medical School, 3 Blackfan Circle, Boston, MA 02115, USA.
authors.forename: Carla
authors.initials: C
authors.lastname: Carbo
authors.forename: Daniel
authors.initials: D
authors.lastname: Duerschmied
authors.forename: Tobias
authors.initials: T
authors.lastname: Goerge
authors.forename: Hidenori
authors.initials: H
authors.lastname: Hattori
authors.forename: Jiro
authors.initials: J
authors.lastname: Sakai
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Cifuni
authors.forename: Gilbert C
authors.initials: GC
authors.lastname: White
authors.forename: Magdalena
authors.initials: M
authors.lastname: Chrzanowska-Wodnicka
authors.forename: Hongbo R
authors.initials: HR
authors.lastname: Luo
authors.forename: Denisa D
authors.initials: DD
authors.lastname: Wagner
mesh_terms: D000199:Actins; D000818:Animals; D016764:Cell Polarity; D002634:Chemotaxis, Leukocyte; D003599:Cytoskeleton / Q000473:pathology; D020662:Guanine Nucleotide Exchange Factors / Q000502:physiology*; D016023:Integrins / Q000378:metabolism*; D007975:Leukotriene B4 / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D009504:Neutrophils / Q000502:physiology*; D020827:rap1 GTP-Binding Proteins / Q000502:physiology
chemical_list: D000199:Actins; D020662:Guanine Nucleotide Exchange Factors; D016023:Integrins; C485927:Rasgrp2 protein, mouse; D007975:Leukotriene B4; D020827:rap1 GTP-Binding Proteins