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Lipopolysaccharide induces expression of fibronectin ₅₁-integrin receptors in human monocytic cells in a protein kinase C-dependent fashion

Division of Pulmonary, Allergy, and Critical Care Medicine, Department of Medicine, Emory University School of Medicine, and The Atlanta Veterans Affairs Medical Center, Atlanta, Georgia 30322

Submitted 22 July 2003 ; accepted in final form 24 March 2004

LPS is an outer-membrane glycolipid component of gram-negative bacteria known for its fervent ability to activate monocytic cells and for its potent proinflammatory capabilities. In addition, LPS triggers the release of cytokines and chemokines as well as cell-cell adhesion molecules. We postulate that LPS may also affect the expression of matrix-binding integrin receptors, thereby modulating cell-adhesive functions in monocytic cells. To test this hypothesis, we investigated the effects of LPS on the expression of the integrin ₅₁, a fibronectin receptor, in a human monocytic cell line (U937) as well as in isolated human peripheral blood mononuclear cells (PBMCs). We found that LPS increased the expression of ₅₁ receptors and enhanced the adherence of U937 cells and PBMCs to fibronectin-coated surfaces; this was blocked by anti-₅₁ antibodies. LPS increased ₅-subunit mRNA accumulation in a dose- and time-dependent manner. The induction by LPS occurred, at least in part, at the level of gene transcription as indicated by experiments using ₅ intact and deletion promoter constructs. LPS-induced ₅ gene transcription was associated with rapid induction of conventional PKC- protein and activity, was blocked by PKC inhibitors, and was mimicked by lipid A. Finally, we found that an anti-CD14 antibody was able to inhibit the LPS response. Overall, the data suggest that LPS stimulates ₅ gene transcription via CD14 and PKC-dependent signals to enhance the expression of functional ₅₁ receptors in monocytic cells. This process may help stimulate monocytic cell activation and facilitate their migration into fibronectin-containing tissues during infection.

integrins; sepsis; endotoxin; signal transduction

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