Abstract
Bam32 (B cell adaptor molecule of 32 kDa) functions in the immune responses of various leukocytes. However, the role of neutrophil Bam32 in inflammation is entirely unknown. Here, we determined the role of Bam32 in chemokine CXCL2-induced neutrophil chemotaxis in three mouse models of neutrophil recruitment. By using intravital microscopy in the mouse cremaster muscle, we found that transmigrated neutrophil number, neutrophil chemotaxis velocity, and total neutrophil chemotaxis distance were increased in Bam32−/− mice when compared with wild-type (WT) mice. In CXCL2-induced mouse peritonitis, the total emigrated neutrophils were increased in Bam32−/− mice at 2 but not 4 h. The CXCL2-induced chemotaxis distance and migration velocity of isolated Bam32−/− neutrophils in vitro were increased. We examined the activation of small GTPases Rac1, Rac2, and Rap1; the levels of phospho-Akt2 and total Akt2; and their crosstalk with Bam32 in neutrophils. The deficiency of Bam32 suppressed Rap1 activation without changing the activation of Rac1 and Rac2. The pharmacological inhibition of Rap1 by geranylgeranyltransferase I inhibitor (GGTI298) increased WT neutrophil chemotaxis. In addition, the deficiency of Bam32, as well as the inhibition of Rap1 activation, increased the levels of CXCL2-induced Akt1/2 phosphorylation at Thr308/309 in neutrophils. The inhibition of Akt by SH-5 attenuated CXCL2-induced adhesion and emigration in Bam32−/− mice. Together, our results reveal that Bam32 has a suppressive role in chemokine-induced neutrophil chemotaxis by regulating Rap1 activation and that this role of Bam32 in chemokine-induced neutrophil recruitment relies on the activation of PI3K effector Akt.
Highlights
Neutrophil recruitment is a dynamic multi-step process that is regulated by a variety of molecules and signaling cascades elicited by the activation of Gi-coupled chemoattractant and chemokine receptors during acute inflammation [1]
We explored the role of B cell adaptor molecule of 32 kDa (Bam32) in CXCL2-induced neutrophil recruitment in mouse cremasteric post-capillary venules by using intravital microscopy
Because the activation of Rap1 was revealed to suppress the phosphorylation of Akt, which is the key modulator downstream of PI3K to regulate chemoattractant-induced recruitment in mouse neutrophils [22], we explored whether the Bam32 deficiency that impaired Rap1 activation changed CXCL2-induced phosphorylation of Akt
Summary
Neutrophil recruitment is a dynamic multi-step process that is regulated by a variety of molecules and signaling cascades elicited by the activation of Gi-coupled chemoattractant and chemokine receptors during acute inflammation [1]. Upon stimulation by various chemoattractants, PI3Kγ increases the localized accumulation of membranecaptive phospholipid PI(3,4,5)P3, which directs neutrophil movement and remodeling through binding recruited PI3K adaptors and effectors at the leading edge underneath the cell membrane [4]. The affinity of this interaction may vary: some signaling proteins such as Grp and Btk preferentially bind PI(3,4,5)P3 [5,6], some signaling proteins such as TAPP1/2 preferentially bind PI(3,4)P2 [7], and some others such as Akt bind both [8].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
