Intermediate-affinity LFA-1 binds α-actinin-1 to control migration at the leading edge of the T cell

Abstract

T lymphocytes use LFA-1 to migrate into lymph nodes and inflammatory sites. To investigate the mechanisms regulating this migration, we utilize mAbs selective for conformational epitopes as probes for active LFA-1. Expression of the KIM127 epitope, but not the 24 epitope, defines the extended conformation of LFA-1, which has intermediate affinity for ligand ICAM-1. A key finding is that KIM127-positive LFA-1 forms new adhesions at the T lymphocyte leading edge. This LFA-1 links to the cytoskeleton through α-actinin-1 and disruption at the level of integrin or actin results in loss of cell spreading and migratory speed due to a failure of attachment at the leading edge. The KIM127 pattern contrasts with high-affinity LFA-1 that expresses both 24 and KIM127 epitopes, is restricted to the mid-cell focal zone and controls ICAM-1 attachment. Identification of distinctive roles for intermediate- and high-affinity LFA-1 in T lymphocyte migration provides a biological function for two active conformations of this integrin for the first time.

Requirement of open headpiece conformation for activation of leukocyte integrin αXβ2

“…Our data suggest that the intermediate affinity state observed in the literature for the related β 2 integrin LFA-1 (16)(17)(18)(19)(20) does not have to come from an individual conformational state, but could instead result from a mixture of conformational states. Previous studies showed that LFA-1 binding to ICAM-3, compared with ICAM-1, required more activation as defined by the number of activation agents needed (19)(20)(21).…”

“…MEM148 did not bind to bent α X β 2 , in agreement with studies that show the presence of the closed headpiece in the bent conformation of α X β 2 (4). m24 also is a reporter of β 2 integrin activation and is widely used to detect high affinity LFA-1 on intact cells (16,32,33). m24 binds to residues near the MIDAS and in the βI domain, including Arg-122 and Glu-175 (Fig.…”

“…Furthermore, there has been much speculation about an intermediate affinity state between the bent, low affinity and the activated, high affinity states. At the leading edge of migrating T lymphocytes, a distinct population of LFA-1 was defined as in an intermediate affinity state by the exposure of different monoclonal antibody epitopes (16). Lateral mobility measurements of LFA-1 on T cell surfaces suggested an intermediate conformational state with distinct diffusion profile (17).…”

Coordinated RhoA signaling at the leading edge and uropod is required for T cell transendothelial migration

“…2 a and Fig. 3 f; Smith et al, 2005;Stanley et al, 2008), and thus, could represent regions of T cell adhesion to ICAM-1 on the apical plasma membrane of EC and on the basal membrane after TEM (Millán et al, 2006). FRET efficiency was not dependent on the probe concentration (Fig.…”

Multiple roles for RhoA during T cell transendothelial migration

“…Similar clusters of active LFA-1 have been observed in the lamellipodia of T cells migrating on a rigid substrate coated with ICAM-1. 40,41 It has been hypothesized that RhoA and ROCK are involved in switching LFA-1 from a high to low affinity for ICAM-1, thereby disengaging LFA-1 from ICAM-1 and allowing migration forwards. 41 Inhibition of Rho or ROCK promoted integrin clustering in T cells 42 supporting a role for RhoA in disassembly of integrin clusters.…”