Monocyte adherence induced by lipopolysaccharide involves CD14, LFA-1, and cytohesin-1. Regulation by Rho and phosphatidylinositol 3-kinase.
Mechanisms regulating lipopolysaccharide (LPS)-induced adherence to intercellular adhesion molecule (ICAM)-1 were examined using THP-1 cells transfected with CD14-cDNA (THP-1wt). THP-1wt adherence to ICAM-1 was LPS dose-related, time-dependent, and inhibited by antibodies to either CD14 or leukocyte function associated antigen (LFA)-1, but was independent of any change in the number of surface expressed LFA-1 molecules. A potential role for phosphatidylinositol (PI) 3-kinase (PI 3-kinase) in LPS-induced adherence was examined using the PI 3-kinase inhibitors LY294002 and Wortmannin. Both inhibitors selectively attenuated LPS-induced, but not phorbol 12-myristate 13-acetate-induced adherence. Inhibition by these agents was unrelated to any changes in either LPS binding to or LFA-1 expression by THP-1wt cells. LPS-induced adherence was also abrogated in U937 cells transfected with a dominant negative mutant of of PI 3-kinase. Toxin B from Clostridium difficile, an inhibitor of the Rho family of GTP-binding proteins, abrogated both PI-3 kinase activation and adherence induced by LPS. Cytohesin-1, a phosphatidylinositol 3,4,5-triphosphate-regulated adaptor molecule for LFA-1 activation, was found to be expressed in THP-1wt cells. In addition, treatment of THP-1wt with cytohesin-1 antisense attenuated LPS-induced adherence. These findings suggest a model in which LPS induces adherence through a process of "inside-out" signaling involving CD14, Rho, and PI 3-kinase. This converts low avidity LFA-1 into an active form capable of increased binding to ICAM-1. This change in LFA-1 appears to be cytohesin-1-dependent.
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Department of Medicine (Division of Infectious Diseases), The University of British Columbia, Faculties of Medicine and Science, The Research Institute of the Vancouver Hospital and Health Sciences Center, Vancouver, British Columbia V5Z 3J5, C.
Knutson
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Herrera-Velit
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Nandan
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Reiner
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D002448:Cell Adhesion / Q000187:drug effects*; D015815:Cell Adhesion Molecules / Q000378:metabolism*; D002460:Cell Line; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism; D018950:Lipopolysaccharide Receptors / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000494:pharmacology*; D016169:Lymphocyte Function-Associated Antigen-1 / Q000378:metabolism*; D009000:Monocytes / Q000166:cytology*; D010641:Phenotype; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism
D015815:Cell Adhesion Molecules; D020662:Guanine Nucleotide Exchange Factors; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; D016169:Lymphocyte Function-Associated Antigen-1; C100723:cytohesin-1; D018799:Intercellular Adhesion Molecule-1; D019869:Phosphatidylinositol 3-Kinases; D019204:GTP-Binding Proteins