Adhesion-activating phorbol ester increases the mobility of leukocyte integrin LFA-1 in cultured lymphocytes.

Abstract

Lymphocytes activate adhesion to intracellular adhesion molecule 1 (ICAM-1) via leukocyte function-associated antigen 1 (LFA-1), their major ␤ 2 integrin, in response to PMA (phorbol 12-myristate 13-acetate) without an increase in the number of receptors expressed. The molecular details of the mechanism are unknown. To determine the effect of PMA activation on LFA-1 movement within the plasma membrane, we used the single particle tracking technique to measure the diffusion rate of LFA-1 molecules on EBVtransformed B cells before and after PMA activation. Diffusion of LFA-1 on unactivated cells was restricted compared to CR1 (CD35), another transmembrane protein of equivalent size. PMA caused a 10-fold increase in the diffusion rate of LFA-1 without any effect on CD35. The increased LFA-1 motion induced by PMA was random, not directed, indicating that it was due to a release of constraints rather than the application of forces. The diffusion rates of LFA-1 are consistent with cytoskeletal attachment before and free diffusion after PMA. Cytochalasin D led to an equivalent increase in mobility and, at low doses, stimulated adhesion. We propose that the release of LFA-1 from cytoskeletal constraints is an important early step in activation of adhesion, implying that the nonadhesive state of LFA-1 is actively maintained by the lymphocyte cytoskeleton. ( J. Clin. Invest. 1996. 97:2139 -2144 .)

Requirement of Integrin β3 Tyrosine 747 for β3 Tyrosine Phosphorylation and Regulation of αvβ3 Avidity

“…The fact that tyrosine phosphorylation is required for K562 adhesion, where ␤ 3 function is regulated, but not CS-1 adhesion, where ␤ 3 function is constitutive, suggests that the hematopoietic ␤ 3 integrin activation cascade rather than adhesion itself requires tyrosine phosphorylation. A requirement for ␤ 3 tyrosine phosphorylation in the response to activation signals but not for the process of adhesion and spreading supports a model in which integrin activation is actively suppressed in unstimulated hematopoietic cells (26).…”

Vav1 transduces TCR signals required for LFA‐1 function and cell polarization at the immunological synapse

“…Some agonists such as Mg 2+ ions or chemokines induce an affinity change, switching LFA-1 from a low to a high affinity state and we show here that this route to adhesion is Vav1-independent [25,26]. In contrast, TCR signaling induces an avidity change by allowing LFA-1 clustering [27,28]. In the resting lymphocyte, LFA-1 is held uniformly dispersed around the cell by interactions with the actin cytoskeleton.…”

“…In the resting lymphocyte, LFA-1 is held uniformly dispersed around the cell by interactions with the actin cytoskeleton. Inside-out signaling leads to release of LFA-1 from the cytoskeletal anchor, translocation to the IS, clustering and reallocation with the actin cytoskeleton [27][28][29][30].…”

Endosomal clathrin drives actin accumulation at the immunological synapse

“…These data, together with the quantification of polymerized actin at the IS, show that actin polymerization occurs at low levels in clathrin and Hrs KD cells, in contrast to the extraordinary levels observed in control T cells expressing normal amounts of clathrin at MVBs. Partial inhibition of actin polymerization (using low doses of cytochalasin D) have long been known to enhance integrin function (Kucik et al, 1996), which, together with the slight increase of CD3 expression observed on the surface of clathrin KD cells, could partially explain the increase of IL-2 secretion. This increased IL-2 secretion, as well as the increased TCR-dependent signalling that occurs in clathrin KD T cells, could also be explained by recent data suggesting that the actin cytoskeleton somehow destabilizes TCR-MHC interactions, as shown by treatment with cytochalasin D and latrunculin A, which greatly prolonged TCR-MHC interactions at the IS (Huppa et al, 2010).…”