Affinity modulation of very late antigen-5 through phosphatidylinositol 3-kinase in mast cells

Adhesiveness of integrins is up-regulated rapidly by a number of molecules, including growth factors, cytokines, chemokines, and other cell surface re ceptors, through a mechanism termed inside-out signaling, The inside-out si gnaling pathways are thought to alter integrin affinity for ligand, or cell surface distribution of integrin by diffusion/clustering. However, it rema ins to be clarified whether any physiologically relevant agonists induce a rapid change in the affinity of beta(1) integrins and how ligand-binding af finity is modulated upon stimulation. In this study, we reported that affin ity of beta(1) integrin very late Ag-5 (VLA-5) for fibronectin was rapidly increased in bone marrow-derived mast cells by Ag cross-linking of Fc epsil on RI, Ligand-binding affinity of VLA-5 was also augmented by receptor tyro sine kinases when the phospholipase C gamma-1/protein kinase C pathway was inhibited, Wortmannin suppressed induction of the high affinity state VLA-5 in either case. Conversely, introduction of a constitutively active p110 s ubunit of phosphatidylinositol 3-kinase (PI 3-kinase) increased the binding affinity for fibronectin, Failure of a constitutively active Akt to stimul ate adhesion suggested that the affinity modulation mechanisms mediated by PI 3-kinase are distinct from the mechanisms to control growth and apoptosi s by PI 3-kinase, Taken together, our findings demonstrated that the increa se of affinity of VLA-5 was induced by physiologically relevant stimuli and PI 3-kinase was a critical affinity modulator of VLA-5.