Transendothelial migration of lymphocytes mediated by intraendothelial vesicle stores rather than by extracellular chemokine depots.

Chemokines presented by the endothelium are critical for integrin-dependent adhesion and transendothelial migration of naive and memory lymphocytes. Here we found that effector lymphocytes of the type 1 helper T cell (T(H)1 cell) and type 1 cytotoxic T cell (T(C)1 cell) subtypes expressed adhesive integrins that bypassed chemokine signals and established firm arrests on variably inflamed endothelial barriers. Nevertheless, the transendothelial migration of these lymphocytes strictly depended on signals from guanine nucleotide-binding proteins of the G(i) type and was promoted by multiple endothelium-derived inflammatory chemokines, even without outer endothelial surface exposure.

Regulation of integrin activity and signalling.

The ability of cells to attach to each other and to the extracellular matrix is of pivotal significance for the formation of functional organs and for the distribution of cells in the body. Several molecular families of proteins are involved in adhesion, and recent work has substantially improved our understanding of their structures and functions. Also, these molecules are now being targeted in the fight against disease.

Beta2 integrin phosphorylation on Thr758 acts as a molecular switch to regulate 14-3-3 and filamin binding.

Leukocyte integrins of the beta2 family are essential for immune cell-cell adhesion. In activated cells, beta2 integrins are phosphorylated on the cytoplasmic Thr758, leading to 14-3-3 protein recruitment to the beta2 integrin. The mutation of this phosphorylation site impairs cell adhesion, actin reorganization, and cell spreading.

Regulation of LFA-1-dependent inflammatory cell recruitment by Cbl-b and 14-3-3 proteins.

Inside-out signaling regulation of the beta2-integrin leukocyte function-associated antigen-1 (LFA-1) by different cytoplasmic proteins, including 14-3-3 proteins, is essential for adhesion and migration of immune cells. Here, we identify a new pathway for the regulation of LFA-1 activity by Cbl-b, an adapter molecule and ubiquitin ligase that modulates several signaling pathways. Cbl-b-/- mice displayed increased macrophage recruitment in thioglycollate-induced peritonitis, which was attributed to Cbl-b deficiency in macrophages, as assessed by bone marrow chimera experiments.

14-3-3 proteins bind both filamin and alphaLbeta2 integrin in activated T cells.

Engagement of the T cell receptor (TCR) initiates intracellular signaling cascades that result in T cell activation, differentiation, acquisition of effector functions, or apoptosis. The signals from the TCR are coupled to distal signaling pathways by adapter proteins leading to dramatic changes in the cytoskeleton, transcription, and activation of integrins, which mediate adhesion. LFA-1 (leukocyte function-associated antigen-1) integrin (alphaLbeta2 or CD11a/CD18) plays an important role in adhesion, for example, by linking extracellular ligands to the actin cytoskeleton.

Phosphorylation of the LFA-1 integrin beta2-chain on Thr-758 leads to adhesion, Rac-1/Cdc42 activation, and stimulation of CD69 expression in human T cells.

Phosphorylation of the leukocyte function-associated antigen-1 (LFA-1) integrin beta2-chain on Thr-758 occurs after T cell receptor stimulation and leads to 14-3-3 recruitment to the integrin, actin cytoskeleton reorganization, and increased adhesion. Here, we have investigated the signaling effects of beta2 integrin Thr-758 phosphorylation. A penetratin-coupled phospho-Thr-758-beta2 peptide (mimicking the part of the integrin beta-chain surrounding Thr-758) stimulated adhesion of human T cells to the LFA-1 ligand intercellular adhesion molecule-1 (ICAM-1).

Interfering with leukocyte integrin activation--a novel concept in the development of anti-inflammatory drugs.

Inflammation is a crucial response against invading pathogens, in which immune cells, including neutrophils and T cells, are recruited into tissue from the bloodstream to help clear infection. However, a prevailing inflammatory response where the immune cells attack healthy tissue is associated with many diseases, including asthma, rheumatoid arthritis, atherosclerosis and multiple sclerosis. Integrins are key players in the recruitment of immune cells from the bloodstream into tissues, and are thus therapeutic targets for intervention with inflammatory responses.

Specific integrin alpha and beta chain phosphorylations regulate LFA-1 activation through affinity-dependent and -independent mechanisms.

Integrins are adhesion receptors that are crucial to the functions of multicellular organisms. Integrin-mediated adhesion is a complex process that involves both affinity regulation and cytoskeletal coupling, but the molecular mechanisms behind this process have remained incompletely understood. In this study, we report that the phosphorylation of each cytoplasmic domain of the leukocyte function-associated antigen-1 integrin mediates different modes of integrin activation.