Threonine Phosphorylation Sites in the β2 and β7 Leukocyte Integrin Polypeptides

Abstract

The cytoplasmic domains of integrins play a key role in a variety of integrin-mediated events including adhesion, migration, and signaling. The molecular mechanisms that enhance integrin function are still incompletely understood. Because protein kinases are known to be involved in the signaling and the activation of integrins, the role of phosphorylation has been studied by several groups. The β2 leukocyte integrin subunit has previously been shown to become phosphorylated in leukocytes on cytoplasmic serine and functionally important threonine residues. We have now mapped the phosphorylated threonine residues in activated T cells. After phorbol ester stimulation, all three threonine residues (758–760) of the threonine triplet became phosphorylated but only two at a time. CD3 stimulation leads to a strong threonine phosphorylation of the β2 integrin, but differed from phorbol ester activation in that phosphorylation occurred only on threonine 758. The other leukocyte-specific integrin, β7, has also been shown to need the cytoplasmic domain and leukocyte-specific signal transduction elements for integrin activation. Cell activation with phorbol ester, and interestingly, through the TCR-CD3 complex, caused β7 integrin binding to VCAM-1. Additionally, cell activation led to increased phosphorylation of the β7 subunit, and phosphoamino acid analysis revealed that threonine residues became phosphorylated after cell activation. Sequence analysis by manual radiosequencing by Edman degradation established that threonine phosphorylation occurred in the same threonine triplet as in β2 phosphorylation.

β2 integrin phosphorylation on Thr758 acts as a molecular switch to regulate 14-3-3 and filamin binding

“…Of these, both ␤1 and ␤7 integrins are known to be phosphorylated in cells. 12,42 There is conflicting evidence about the involvement of 14-3-3 proteins in ␤1 integrin-mediated adhesion. 4,43,44 To our knowledge, however, the direct effects of ␤1 phosphorylation on 14-3-3 interactions have not been studied.…”

“…10 Thr758 is a physiologically important amino acid residue in the ␤2 cytoplasmic tail, and becomes phosphorylated after T-cell stimulation with T-cell receptor (TCR) antibodies or with phorbol esters. [11][12][13] After its phosphorylation, ␤2 binds to 14-3-3 proteins both in vitro and in cells. 4 Blocking of this interaction with a ␤2 Thr758 to Ala mutation, or by expression of constructs that bind to 14-3-3 proteins and block their interactions with target proteins, leads to abrogation of actin cytoskeleton rearrangements, cell spreading, and adhesion to ICAM ligands.…”

Forced expression of Nanog in hematopoietic stem cells results in a γδT-cell disorder

“…Integrin ␣4␤7 (LPAM-1) expressed in a subset of effector T cells or ␥␦T cells in the intestine 31,32 can mediate cell migration as a receptor for MAdCAM-1 and VCAM-1. [33][34][35] Therefore, the expression of integrin ␤7 in Nanog T cells BLOOD, 1 JULY 2007 ⅐ VOLUME 110, NUMBER 1 For personal use only. on May 12, 2018.…”

Phosphorylation of the LFA-1 Integrin β2-Chain on Thr-758 Leads to Adhesion, Rac-1/Cdc42 Activation, and Stimulation of CD69 Expression in Human T Cells

“…The phospho-specific antibody recognized the ␤2 polypeptide only from T cells that were stimulated with OKT3 (Fig. 1B), confirming specific phosphorylation of Thr-758 in T cells activated through the T cell receptor (20). Using the pThr-758-phospho-specific antibody, we investigated the distribution of Thr-758-phosphorylated integrins in detergent-soluble and -insoluble fractions from activated T cells.…”

“…1 To whom correspondence should be addressed. receptor stimulation (20), and this leads to recruitment of 14-3-3 proteins to the integrin (5, 11). 14-3-3 proteins are adaptor proteins that bind to phospho-serine-or phospho-threonine-containing sequences in proteins.…”