P-Rex1 and Vav1 Cooperate in the Regulation of Formyl-Methionyl-Leucyl-Phenylalanine–Dependent Neutrophil Responses

Abstract

G protein-coupled receptor (GPCR) activation elicits neutrophil responses such as chemotaxis and reactive oxygen species (ROS) formation, which depend on the small G protein Rac and are essential for host defense. P-Rex and Vav are two families of guanine-nucleotide exchange factors (GEFs) for Rac, which are activated through distinct mechanisms but can both control GPCR-dependent neutrophil responses. It is currently unknown whether they play specific roles or whether they can compensate for each other in controlling these responses. In this study, we have assessed the function of neutrophils from mice deficient in P-Rex and/or Vav family GEFs. We found that both the P-Rex and the Vav family are important for LPS priming of ROS formation, whereas particle-induced ROS responses and cell spreading are controlled by the Vav family alone. Surprisingly, fMLF-stimulated ROS formation, adhesion, and chemotaxis were synergistically controlled by P-Rex1 and Vav1. These responses were more severely impaired in neutrophils lacking both P-Rex1 and Vav1 than those lacking the entire P-Rex family, the entire Vav family, or both P-Rex1 and Vav3. P-Rex1/Vav1 (P1V1) double-deficient cells also showed the strongest reduction in fMLF-stimulated activation of Rac1 and Rac2. This reduction in Rac activity may be sufficient to cause the defects observed in fMLF-stimulated P1V1 neutrophil responses. Additionally, Mac-1 surface expression was reduced in P1V1 cells, which might contribute further to defects in responses involving integrins, such as GPCR-stimulated adhesion and chemotaxis. We conclude that P-Rex1 and Vav1 together are the major fMLFR -dependent Dbl family Rac-GEFs in neutrophils and cooperate in the control of fMLF-stimulated neutrophil responses.

Rac GTPase Activating Protein ARHGAP25 Regulates Leukocyte Transendothelial Migration in Mice

“…6). Deficiency in various RacGEFs was reported to result in decreased amount of GTP-bound Rac and a decrease in phagocyte migration (16,37,38) (i.e., changes opposite to our findings in animals lacking ARHGAP25). We thus ascribe the alteration of leukocyte trafficking in ARHGAP25-deficient animals to cytoskeletal reorganization due to elevation of RacGTP concentration.…”

“…The majority of these GEFs and GAPs are large proteins composed of several effector, interactive, and regulatory domains that suggest multiple functions (13,14). In neutrophils, a specific involvement of certain GEFs has been investigated for different neutrophil effector functions including chemotaxis and adhesion (15)(16)(17). In contrast, similar data on potentially interacting GAPs are still scarce (18)(19)(20).…”

The 3BP2 Adapter Protein Is Required for Chemoattractant-Mediated Neutrophil Activation

“…Neutrophils lacking both P-Rex1 and Vav1 have severe defects in fMLF-dependent ROS formation, chemotaxis, and adhesion, whereas these responses are normal or near normal in cells lacking the entire P-Rex family or the entire Vav family (93). These observations further confirmed the role of 3BP2 in the activation of different GEFs downstream of the fMLF receptor.…”

“…More recently, P-Rex1 and Vav1 have been shown to cooperate in the regulation of fMLF-dependent neutrophil response (93). Neutrophils lacking both P-Rex1 and Vav1 have severe defects in fMLF-dependent ROS formation, chemotaxis, and adhesion, whereas these responses are normal or near normal in cells lacking the entire P-Rex family or the entire Vav family (93).…”

Integrin Regulation during Leukocyte Recruitment

“…In neutrophils stimulated with leukotriene B 4 , Rap1 is activated by CalDAG-GEFI, which is activated by Ca 2+ and DAG, two products of PLC (39). In contrast, another study using fMLP stimulation revealed that the GEFs Vav1 and PRex1 redundantly mediate the activity of the GTPase Rac (40), suggesting that the different stimuli activate distinctly different pathways. A similar pathway was also demonstrated in human CD3 + T cells following the stimulation with CXCL12 leading to LFA-1, but not VLA-4, activation (32).…”