Abstract
The integrin leukocyte function-associated antigen-1 (LFA-1) plays a pivotal role in leukocyte adhesion and migration, but the mechanism(s) by which this integrin is regulated has remained incompletely understood. LFA-1 integrin activity requires phosphorylation of its β2-chain and interactions of its cytoplasmic tail with various cellular proteins. The α-chain is constitutively phosphorylated and necessary for cellular adhesion, but how the α-chain regulates adhesion has remained enigmatic. We now show that substitution of the α-chain phosphorylation site (S1140A) in T cells inhibits the phosphorylation of the functionally important Thr-758 in the β2-chain, binding of α-actinin and 14-3-3 protein, and expression of an integrin-activating epitope after treatment with the stromal cell-derived factor-1α. The presence of this substitution resulted in a loss of cell adhesion and directional cell migration. Moreover, LFA-1 activation through the T-cell receptor in cells expressing the S1140A LFA-1 variant resulted in less Thr-758 phosphorylation, α-actinin and talin binding, and cell adhesion. The finding that the LFA-1 α-chain regulates adhesion through the β-chain via specific phosphorylation at Ser-1140 in the α-chain has not been previously reported and emphasizes that both chains are involved in the regulation of LFA-1 integrin activity.
Highlights
The integrin leukocyte function–associated antigen-1 (LFA-1) plays a pivotal role in leukocyte adhesion and migration, but the mechanism(s) by which this integrin is regulated has remained incompletely understood
The results indicate an important role for integrin ␣-chains in the modulation of leukocyte functions by regulating -chain phosphorylation, which results in altered cytoplasmic protein interactions, followed by changes in adhesion and migration
When the phosphorylation site serine was substituted by alanine, phosphorylation could not be recognized by a Ser(P)-1140 –specific antibody (Fig. 1C)
Summary
The integrin leukocyte function–associated antigen-1 (LFA-1) plays a pivotal role in leukocyte adhesion and migration, but the mechanism(s) by which this integrin is regulated has remained incompletely understood. We show that substitution of the ␣-chain phosphorylation site (S1140A) in T cells inhibits the phosphorylation of the functionally important Thr-758 in the 2-chain, binding of ␣-actinin and 14-3-3 protein, and expression of an integrin-activating epitope after treatment with the stromal cell–derived factor-1␣. The presence of this substitution resulted in a loss of cell adhesion and directional cell migration. When cells expressed the LFA-1 S1140A mutation, there was no phosphorylation of the 2-chain on Thr-758, but there was a loss of both ␣-actinin and 14-3-3 binding and the presence of the integrin activation-reporter epitope L16 upon treatment with the chemokine stromal cell– derived factor-1␣ (SDF-1␣). The results indicate an important role for integrin ␣-chains in the modulation of leukocyte functions by regulating -chain phosphorylation, which results in altered cytoplasmic protein interactions, followed by changes in adhesion and migration
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