Cross-talk between Insulin Receptor and Integrin α5β1 Signaling Pathways

Abstract

The ligation and clustering of cell surface ␣␤ heterodimeric integrins enhances cell adhesion and initiates signaling pathways that regulate such processes as cell spreading, migration, differentiation, proliferation and apoptosis. Here we show that insulin treatment of Chinese hamster ovary cells expressing insulin receptors (CHO-T) markedly promotes cell adhesion onto a fibronectin matrix, but not onto bovine serum albumin or poly-lysine. Incubation of cells with a GRGDSP peptide that specifically binds integrins (but not the nonspecific GRADSP peptide) abolishes this insulin effect, as does the potent phosphoinositide 3-kinase (PI 3-kinase) inhibitor wortmannin. Moreover, a specific blocking monoclonal anti-␣ 5 ␤ 1 integrin antibody, PB-1, blocks insulin-stimulated cell adhesion onto fibronectin. Conversely, activating ␣ 5 ␤ 1 integrins on CHO-T cells by adherence onto fibronectin markedly potentiates the action of insulin to enhance insulin receptor and insulin receptor substrate (IRS)-1 tyrosine phosphorylation. Activation of ␣ 5 ␤ 1 integrin also markedly potentiates the recruitment of p85-associated PI 3-kinase activity to IRS-1 in response to submaximal levels of insulin in CHO-T cells. These data indicate that insulin potently activates integrin ␣ 5 ␤ 1 mediated CHO-T cell adhesion, while integrin ␣ 5 ␤ 1 signaling in turn enhances insulin receptor kinase activity and formation of complexes containing IRS-1 and PI 3-kinase. These findings raise the hypothesis that insulin receptor and ␣ 5 ␤ 1 integrin signaling act synergistically to enhance cell adhesion.The tyrosine kinase activity of the cell surface insulin receptor is required to mediate its many biological actions. Insulin receptor activation promotes the rapid autophosphorylation of its ␤ subunit, as well as tyrosine phosphorylation of proteins involved in insulin signaling, such as insulin receptor substrate (IRS) 1 and Shc proteins (1-4). Insulin-mediated phosphorylation of these proteins is thought to provide tyrosine phosphate docking sites for the recruitment of signaling proteins containing Src homology 2 domains (SH2) (1, 5, 6). One SH2 domaincontaining family of proteins which associates with IRS proteins in response to insulin are isoforms of the p85 regulatory subunit of the p110-type PI 3-kinases (1-4, 7). PI 3-kinase activity in such signaling complexes appears to be required for insulin action on many cellular processes, including glucose transport (8, 9), glycogen synthesis (9, 10), stress fiber breakdown (11), and membrane ruffling (12). Thus, inhibition of PI 3-kinase activity by wortmannin or disruption of PI 3-kinase recruitment to IRS proteins by dominant inhibitory constructs of p85 subunits ablate the actions of insulin on these processes (11-13). Our understanding of the downstream elements that mediate the action of the 3Ј-phosphoinositide products of the PI 3-kinases is incomplete, but appear to include protein kinases such as PDK1 and Akt/protein kinase B (PKB) (14), a family of proteins containing Sec7 homology domains (...

TNF-α Potentiates C5a-Stimulated Eosinophil Adhesion to Human Bronchial Epithelial Cells: A Role for α5β1 Integrin

“…In our study, it is unlikely that activation of ␣ M ␤ 2 integrin occurs first, leading to ␣ 5 ␤ 1 integrin activation, because this would increase adhesion following priming alone, and this was not observed. Cooperative effects, similar to those of TNF-␣ and ␣ 5 ␤ 1 integrin, have been described for ␣ 5 ␤ 1 integrin with insulin on adhesion to fibronectin of Chinese hamster ovary cells and with IL-11 for CD34 ϩ hemopoietic stem/progenitor cell adhesion (51,52). Requirement for a soluble (TNF-␣) and an adhesion-dependent (␣ 5 ␤ 1 integrin) signal for eosinophil priming may prevent inappropriate activation of eosinophils in the circulation while enhancing adhesion in the airways.…”

Integrin α1-null Mice Exhibit Improved Fatty Liver When Fed a High Fat Diet Despite Severe Hepatic Insulin Resistance

“…In contrast, we found that activation of this pathway was down-regulated in HF-fed itga1 Ϫ/Ϫ mice compared with HF-fed itga1 ϩ/ϩ mice, indicating that the absence of integrin ␣1 dampens MAPK signaling despite hepatic insulin resistance, and JNK activation is not responsible for the observed decrease in IRS1 Tyr phosphorylation in HF-fed itga1 Ϫ/Ϫ mice. There is considerable cross-talk between the insulin and integrin signaling cascades (9,(11)(12)(13). A potential mediator of this cross-talk is the integrin-specific signaling molecule FAK.…”

“…Several studies have suggested a role for integrins in the promotion of insulin action (9,(11)(12)(13)(14). Integrin ␣5␤1 binding to its ligand fibronectin enhances insulin-stimulated tyrosine phosphorylation of both the insulin receptor and IRS1 (13). Integrin ␤1 activation through its engagement with an anti-integrin ␤1 antibody or fibronectin leads to IRS1, PI3K, and subsequent Akt activation in isolated rat adipocytes (11).…”

“…Upon ligand binding, integrins transduce signals across the plasma membrane to facilitate outside-in cell signaling (10). Several studies have suggested a role for integrins in the promotion of insulin action (9,(11)(12)(13)(14). Integrin ␣5␤1 binding to its ligand fibronectin enhances insulin-stimulated tyrosine phosphorylation of both the insulin receptor and IRS1 (13).…”

Focal adhesion kinase regulates insulin resistance in skeletal muscle

“…A regulatory role of FAK in IRS-1 levels [11,12] and hepatic insulin action [13,14] has also been reported. Genetic studies have provided evidence for interaction between integrin and insulin signalling [15,16]. The available literature also focuses on the role of FAK in insulin-mediated effects on the cytoskeleton [10,17].…”