Cbl and Akt regulate CXCL8-induced and CXCR1- and CXCR2-mediated chemotaxis

CXCL8 (IL-8) plays an important role in the pathogenesis of a variety of inflammatory diseases. However, little is known about the signaling pathways that regulate CXCL8-induced chemotaxis. Here, we found that CXCL8 treatment of CXCR1- and CXCR2-over-expressing L1.2 cells (CXCR1-L1.2 and CXCR2-L1.2, respectively) induced the phosphorylation of Cbl and Akt. The tyrosine kinase inhibitor Tyrphostin A9, phosphatidylinositol-3 kinase (PI3K) inhibitor LY294002 as well as proteasome inhibitors significantly blocked the CXCL8-induced chemotaxis of L1.2 cells and human neutrophils. We further found that stimulation with CXCL8 enhanced the association of the PI3K subunit p85 with Cbl. Additionally, over-expression of wild-type Cbl and G306E-Cbl (mutation in the tyrosine kinase-binding domain) inhibited chemotaxis by approximately 50% as compared with the vector control, whereas the 70Z mutant (deletion in the RING finger domain) did not reduce migration. However, wild-type Cbl or its mutants had no effect on the CXCL8-induced activation of MAPK, indicating that Cbl specifically modulated CXCL8-induced chemotaxis. Furthermore, over-expression of the kinase-dead Akt mutant decreased CXCL8-induced chemotaxis by 60% and diminished Cbl phosphorylation as compared with the vector control. The CXCL8-induced phosphorylation of Cbl was also reduced when cells were pre-treated with the PI3K inhibitor LY294002. Lastly, we have shown that pre-treatment of L1.2 cells with the proteasome inhibitor Lactacystin blocks CXCL8-induced internalization of the CXCR1 and CXCR2 receptors. These studies provide new information regarding CXCL8-induced signaling pathways that may regulate chemotaxis and receptor internalization.