PMID: 18550856

Authors:

Takala H, Nurminen E, Nurmi SM, Aatonen M, Strandin T, Takatalo M, Kiema T, Gahmberg CG, Ylanne J, Fagerholm SC

Title:

Integrin {beta}2 phosphorylation on THR758 acts as a molecular switch to regulate 14-3-3 and filamin binding.

Journal:

Blood. 2008 Jun 12;.

Abstract:

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. Thr758 is contained in a Thr-triplet of beta2 that also mediates binding to filamin. Here, we investigated the binding of filamin, talin and 14-3-3 proteins to phosphorylated and unphosphorylated beta2 integrins by biochemical methods and X-ray crystallography. 14-3-3 proteins bound only to the phosphorylated integrin cytoplasmic peptide, with a high affinity (Kd 261 nM), whereas filamin bound only the unphosphorylated integrin cytoplasmic peptide (Kd 0.5 mM). Phosphorylation did not regulate talin binding to beta2 directly, but 14-3-3 was able to out-compete talin for the binding to phosphorylated beta2-integrin. X-ray crystallographic data clearly explained how phosphorylation eliminated filamin binding and induced 14-3-3 protein binding. Filamin knockdown in T cells led to an increase in stimulated cell adhesion to ICAM-1-coated surfaces. Our results suggest that the phosphorylation of beta2 integrins on Thr758 acts as a molecular switch to inhibit filamin binding and allow 14-3-3 protein binding to the integrin cytoplasmic domain, thereby modulating T cell adhesion.