Rap1a and PI3Kγ each promote integrin α4β1-dependent myeloid cell adhesion.

<p>(A) Schematic of circulating, unstimulated myeloid cells, indicating inactive receptor tyrosine kinases, chemokine receptors and Toll-like Receptor/IL-1 Receptor family members (TIR family) and inactive downstream PI3Kγ and integrin α4β1. (B) Schematic of stimulated myeloid cells showing all three receptor types that activate PI3Kγ, thereby promoting integrin α4β1 conformational changes, leading to integrin activation. Co-factors that may play roles in activating integrin α4β1 include PKC, Rap1, RIAM, talin and paxillin. (C) Representative immunoblot of GTP-Rap and total Rap in myeloid cells that were stimulated with or without the chemoattractants IL-1β, IL6 or SDF1α and treated with the PI3Kγ inhibitor, TG100-115 (+) or the chemically similar, inert control (-). (D) Adhesion to the integrin α4β1 ligand VCAM-1 (expressed as fluorescence units, F.U.) of chemoattractant-stimulated WT and Rap1a−/− CD11b+ cells and Rap1a or non-silencing siRNA-transfected CD11b+ cells (n = 3), *P<0.01, Rap1a−/− vs WT and Rap1a vs nonsilencing siRNA. (E) Adhesion to VCAM-1 of CD11bGr1lo monocytes sorted from WT, p110γ−/− and Rap1a−/− animals (n = 3), *P<0.01, p110γ−/− and Rap1a−/− vs WT. (F) Adhesion to VCAM-1 of CD11bGr1hi granulocytes sorted from WT, p110γ−/− and Rap1a−/− animals (n = 3), *P<0.01, p110γ−/− and Rap1a−/− vs WT.