Identification of a novel mechanism for endotoxin-mediated down-modulation of CC chemokine receptor expression.
In the present study, we explored the molecular mechanisms by which bacterial endotoxin (LPS) mediates the down-regulation of CCR2 receptors on human monocytes. We found that LPS induced a marked reduction in CCR2 cell surface protein levels which was blocked by pretreatment with the tyrosine kinase inhibitors genistein and herbimycin A. The effector mechanism underlying LPS-induced CCR2 down-modulation appears to involve the enzymatic activity of proteinases since Western blot analysis of LPS-stimulated monocytes revealed the degradation of a 38-kDa species corresponding to the CCR2B monomer. In RBL cells expressing the CCR2B-green fluorescent protein (GFP) fusion chemokine receptor, LPS stimulated the internalization and degradation of CCR2. The serine proteinase inhibitor N-alpha-p-tosyl-L-lysine chloromethyl ketone blocked LPS-induced down-modulation of CCR2 in monocytes and CCR2B-GFP in RBL cells. This work describes a previously uncharacterized mechanism for CC chemokine receptor down-modulation that is dependent upon tyrosine kinase activation and serine proteinase-mediated receptor degradation and may provide further insight into the mechanisms of leukocyte regulation during immunological and inflammatory responses.
Xu
L
L
Laboratory of Molecular Immunology and Inflammation, John P. Robarts Research Institute, London, Canada.
Khandaker
M H
MH
Barlic
J
J
Ran
L
L
Borja
M L
ML
Madrenas
J
J
Rahimpour
R
R
Chen
K
K
Mitchell
G
G
Tan
C M
CM
DeVries
M
M
Feldman
R D
RD
Kelvin
D J
DJ
D018932:Chemokine CCL2 / Q000494:pharmacology; D015536:Down-Regulation; D019833:Genistein / Q000494:pharmacology; D006801:Humans; D008070:Lipopolysaccharides / Q000494:pharmacology*; D009000:Monocytes / Q000737:chemistry / Q000187:drug effects; D054390:Receptors, CCR2; D019707:Receptors, Chemokine; D018121:Receptors, Cytokine / Q000032:analysis / Q000187:drug effects*; D012697:Serine Endopeptidases / Q000502:physiology; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology; D014107:Tosyllysine Chloromethyl Ketone / Q000494:pharmacology
C515334:CCR2 protein, human; D018932:Chemokine CCL2; D008070:Lipopolysaccharides; D054390:Receptors, CCR2; D019707:Receptors, Chemokine; D018121:Receptors, Cytokine; D015842:Serine Proteinase Inhibitors; D014107:Tosyllysine Chloromethyl Ketone; D019833:Genistein; D012697:Serine Endopeptidases