The Study On The Function Of The C-Abl Kinase In β2 Integrin Signaling

Recruitment of leukocytes from blood into tissues plays an important role in host defense and inflammation, including tethering, rolling, adhesion and transmigration. This process is controlled by a variety of adhesion molecules, and members ofβ2 integrin subfamily are critical for the regulation of cellular adhesive activity in this event.β2 integrins are noncovalently associated heterodimers composed of a commonβ-chain and one of four uniqueα-chains.β2 integrins are in low affinity and nonadhesive state in resting leukocytes, and are rapidly activated to bind ligands in response to local inflammatory stimuli, such as cytokines or chemoattractants, a process known as"inside-out"activation. Once activated, integrins can deliver"outside-in"signals to regulate the cytoskeleton and signaling complex. Integrin signaling is critical for neutrophil firm adhesion and spreading, and oxidative burst, degranulation and protein tyrosine phosphorylation are all dependent on the cell adhesion mediated byβ2 integrin. However, the molecular mechanisms by which integrins regulate adhesive events in neutrophils are largely undefined. In neutrophils, adhesion-induced ligation ofβ2 integrin activates various non-receptor tyrosine kinases, which have been demonstrated critical in integrin signaling and leads to cytoskeleton rearrangements, cell growth, survival, and motility. c-Abl kinase as a non-receptor protein tyrosine kinase plays an essential role in signaling transduction from various receptors and in F-actin reassembly. Thus, we speculate that c-Abl kinase plays a role in neutrophilβ2 integrin signaling. In this paper, we focus on the function and mechnism of c-Abl kinase in neutrophils induced byβ2 integrin engagement.c-Abl kinase is activated byβ2 integrin engagement. The expression ofβ2 integrin on neutrophils induced by TNF-αis not affected by c-Abl kinase inhibitor STI571, suggesting that c-Abl kinase is not involved in TNF-αinduced integrin inside-out activation. Inhibiton of c-Abl kinase impaires neutrophil sustained adhesion and spreading, which is similar with c-Abl kinase knock-out cells. Thus, we conclude that c-Abl kinase is mainly involved inβ2 integrin outside-in signaling.In resting neutrophils, c-Abl kinase is approximatively uniform in the cytosol. After neutrophil adhesion mediated byβ2 integrin, c-Abl kinase is redistributed and colocalized withβ2 integrin. We have shown that c-Abl kinase interacts with the cytoplasmic domain ofβ2 integrin afterβ2 integrin engagement by immunoprecipitation and GST pull-down assay, but this interaction is not direct. Talin is a major cytoskeletal protein and constitutively and directly binds to integrinβ2 cytoplasmic domains with its head domain. The recruitment of c-Abl kinase toβ2 integrin is dependent on the interaction between c-Abl kinase SH3 domain and talin head domain.The Vav family proteins are cytoplasmic guanine nucleotide exchange factors, and involved in the regulation of neutrophil adhesion mediated byβ2 integrin. Our results show that c-Abl kinase constitutively and directly associates with Vav, and the activity of Vav is regulated by c-Abl kinase inβ2 integrin signaling transduction. c-Abl kinase SH3 domain and Vav SH2 domain are involved in this association, and Tyr134 in c-Abl kinase SH3 domain is critical.Our results have defined that c-Abl kinase can be activated byβ2 integrin engagemnet in neutrophils. Talin head domain, as aβ2 integrin cytoplasmic binding protein, is critical for the recruitment of c-Abl kinase toβ2 integrin. After activated, c-Abl kinase can regulate neutrophil adhesion and spreading via Vav. The c-Abl kinase has a novel role in innate immunity.