Signal transduction by integrins: increased protein tyrosine phosphorylation caused by clustering of beta 1 integrins.

Abstract

The integrin family of cell adheson receptors mediates many of the interactions between cells and the extracellular matrix. Because the extracellular matrix has profound Influences on cell behavior, it seems llkely that t S transduce biochemical signals across the cell membrane. The nature ofthese putative signals has, thus far, rem elusive.Antibody-mediated clustering of integrin receptors was used to mimic the integrin clustering process that occurs during formation of adhesive contacts. Human epidermal carcinoma (KB) cells were incubated with an anti-lI integrin monocional antibody for 30 min on ice followed by incubation at 37C with anti-rat IgG. This treatment, which induced integrin clustering, stimulated the phosphorylation on tyrosine residues of a 115-to 130-kDa complex of proteins termed ppl3O. When integrins were clustered in the presence of the phosphatase inhibitor sodium orthovanadate, ppl3O showed a substantial increase in phosphorylation compared to the case in which integrins were clustered in the absence of vanadate. Maximal ppl3O phosphorylation was observed 10-20 min after initiation of integrin clustering in the absence of vanadate or after 5-10 min in its presence. These time courses roughly parallel the formation of integrin clusters on the cell surface as observed by fluorescence microscopy. ppl30 phosphorylation depended on the amount of anti-inte antibody present. Additionally, the tyrosine phosphorylation of ppl30 showed specificity since it was stmulated by antibodies to the integrin a3 and 3 subunits but not by antibodies to other integrin a subunits or to nonintgrin cell surface proteins. Immunoprecipitation experiments clearly demonstrated that ppl30 is not itself a PI integrin. It is postulated, therefore, that the integrinstimulated tyrosine phosphorylation of ppl30 may reflect part of an important signal transduction process between the extracellular matrix and the cell interior.Cell interactions with the extracellular matrix are important determinants of cellular morphology, growth, and differentiation (1-4). Contacts between cells and the extracellular matrix are mediated in part by members of the integrin superfamily of adhesive receptors (5-10). Integrins are heterodimeric cell surface glycoproteins consisting of noncovalently linked a and ( chains. The large extracellular amino-terminal domains of both chains associate to form an extracellular binding site for matrix proteins; each chain has a single a-helical transmembrane region and a short cytoplasmic domain (11,12). The abbreviated intracellular domains of integrins interact with a-actinin, talin, and probably other as yet to be discovered proteins to link integrins to the actin-containing cytoskeleton (9,13,14). Interference reflection microscopy in concert with fluorescence microscopy has shown that integrins can be clustered on the ventral surfaces of adherent cells in structures known as focal contacts (14-17). These structures provide a link (mediated through integrins) between extracellular matrix proteins...

Tec is involved in G protein-coupled receptor- and integrin-mediated signalings in human blood platelets

“…Platelet integrins have been shown to mediate tyrosine phosphorylation in multiple proteins following integrin engagement (Kornberg et al, 1991;Haimovich et al, 1993). As ®brinogen binding to GP IIb ± IIIa and subsequent platelet aggregation significantly augmented tyrosine phosphorylation in Tec, we examined whether direct stimulation of platelet integrins with immobilized ligands alone causes the phosphorylation in Tec.…”

“…Some of the signaling molecules in platelets have been reported to be tyrosine phosphorylated in a manner dependent on the engagement of platelet integrins such as GP IIb ± IIIa and GP Ia ± IIa Platelet aggregation was assayed concomitantly (Kornberg et al, 1991;Haimovich et al, 1993). Because ®brinogen binding to GP IIb ± IIIa and subsequent platelet aggregation signi®cantly augmented TRAPinduced tyrosine phosphorylation in Tec, we examined whether ligand binding to platelet integrins by itself causes tyrosine phosphorylation in Tec by assaying the state of the phosphorylation after platelet adhesion to immobilized ®brinogen or collagen ( Figure 3).…”

Scaffold mediated regulation of MAPK signaling and cytoskeletal dynamics: A perspective

“…The localization of tyrosine kinases to adhesion sites and increased phosphotyrosine content of focal adhesions [83,84] led to the proposal that focal adhesions serve as signaling organelles where environmental cues are translated into cytoskeletal changes for the required cellular response [85]. Gene ablation studies confirm this view.…”

Protein kinase Cα promotes apoptotic cell death in gastric cancer cells depending upon loss of anchorage

“…We next explored possible ability of integrin-mediated signals to suppress the e ect of TPA on apoptosis in the detached MKN45 cells. The anti-integrin b1 murine monoclonal antibody (Ab) K20 stimulates tyrosine phosphorylation of proteins of 115 to 130 kDa and mimics the attachment of the cells via b1 integrin to ®bronectin (Kornberg et al, 1991) when the antibodies were cross-linked on the surface of the cells by addition of anti-mouse immunoglobulin Ab (a-M). When MKN45 cells grew in suspension with TPA plus K20 for 24 h, loss of their viability was clearly suppressed (Figure 1d) and reached a level (cell survival was 81.5+1.8%) similar to those observed in the cells cultured without TPA (Figure 1a and b).…”