Interaction of matrix with integrin receptors is required for optimal LPS-induced MAP kinase activation

Abstract

Exposure of macrophages to endotoxin [lipopolysaccharide (LPS)] results in a cascade of events resulting in the release of multiple inflammatory and anti-inflammatory mediators. The Toll-like receptor (TLR) 4 complex is the major receptor that mediates LPS signaling. However, there is evidence that other surface molecules may play a complementary role in the TLR-induced events. Integrin receptors are one class of receptors that have been linked to LPS signaling. This study investigates the role of macrophage integrin receptors in the activation of mitogen-activated protein (MAP) kinases by LPS. In conditions where macrophages were not permitted to adhere to matrix or a tissue culture surface, we found a decrease in LPS signaling as documented by a marked reduction in tyrosine phosphorylation of whole cell proteins. This was accompanied by a significant decrease in extracellular signal-regulated kinase and c-Jun NH 2-terminal kinase MAP kinase activation. Inhibition of integrin signaling, with EDTA or RGD peptides, decreased LPS-induced MAP kinase activity. The functional consequence of blocking integrin signaling was demonstrated by decreased LPS-induced tumor necrosis factor-␣ production. These observations demonstrate that, in addition to the TLR receptor complex, optimal LPS signaling requires complementary signals from integrin receptors.Toll-like receptor; tumor necrosis factor; integrins; lipopolysaccharide; mitogen-activated protein LIPOPOLYSACCHARIDE (LPS) plays a pivotal role in the innate immune response to gram-negative bacteria (31, 42). LPS signaling is initiated by an interaction between LPS and LPS-binding protein, allowing binding to CD14 and association with another cell membrane receptor, which contains an intracellular signaling domain. This other receptor has recently been determined to be Toll-like receptor (TLR) 4, and significant work has been done to define this complex (for review see Refs. 1,17,22). In addition to the TLR complex, a number of other membrane receptors have been proposed to play a role in LPS signaling. These include ␤ 2 -integrins, a purinergic receptor (P2X 7 ), moesin, triggering receptor expressed on myeloid cells-1, a recently described complex that includes heat shock proteins 90 and 70, complement receptor 4, and bone morphogenic protein (20,23,28,40,41). Several previous studies have suggested a role for the integrin receptors in LPS signaling (12,23,29,36). Recently, Perera et al. (29) showed a decreased LPS response [some cytokines, e.g., cyclooxygenase-2 and interleukin (IL)-12 p35, and a slight decrease in p38 activation] in peritoneal macrophages from CD11b (a major integrin chain in macrophages)-knockout mice (29). This study evaluates the link between adherence and LPS-induced mitogen-activated protein (MAP) kinase activation and tumor necrosis factor (TNF)-␣ production in a murine macrophage line.Integrins are a family of cell surface glycoproteins (for review see Refs. 2,3,18). Each integrin is a heterodimer that contains an ␣-and a ␤-subunit. Each subuni...

Cross Talk between MyD88 and Focal Adhesion Kinase Pathways

“…Furthermore, FAK-expressing cells transfected with the FAK inhibitor FRNK produced significantly lower amounts of IL-6 upon LPS challenge. This is in line with previous results showing that LPS induced FAK phosphorylation in a murine monocytic cell line (18). We further demonstrated that other TLR ligands may also induce FAK phosphorylation at Tyr 397 and require FAK for cytokine release because comparable results have been obtained with the TLR2 ligand Pam 3 CSK 4 (data not shown).…”

Src Tyrosine Kinases Mediate Activations of NF-κB and Integrin Signal during Lipopolysaccharide-Induced Acute Lung Injury

“…These findings suggest that LPS activates integrins, increasing integrin ligation and clustering, and thus triggering an "outside-in" signaling that amplifies the action of LPS. Consistent with our in vivo data, Monick et al (14) proposed the hypothesis that in vitro treatment of macrophages with LPS results in "insideout" integrin activation, and increased cellular adherence, providing integrin "outside-in" signaling to MAP kinases. Indeed, signals from integrin receptors seem to be required for optimal LPS signaling in macrophages.…”

“…Moreover, the Arg-GlyAsp (RGD) motif of ECM entities that associate with integrin ␣ v ␤ 3 signaling appears to be involved in NF-B activation (12). Furthermore, in macrophages, integrins play a complementary role in LPS signaling, i.e., in the activations of MAP kinases (such as ERK and JNK), and in TNF-␣ production (13,14). These relations suggest that integrin signaling in macrophages mediates or amplifies inflammation.…”

Hyperoxia Induces Macrophage Cell Cycle Arrest by Adhesion-dependent Induction of p21Cip1 and Activation of the Retinoblastoma Protein

“…Previously, we reported that cell adhesion (integrin signaling) was required for lipopolysaccharide-induced activation of the mitogen-activated kinase (MAPK), extracellular regulated kinase (ERK), and optimal tumor necrosis factor-␣ production (31). In this study, we evaluated the role of adhesion (tissue culture plates and extracellular matrix-coated plates with collagen type I, collagen type IV, or fibronectin) on hyperoxia-induced growth arrest in macrophages.…”