A Ca2+-dependent autoregulation of lipopolysaccharide-induced IL-8 receptor expression in human polymorphonuclear neutrophils.
IL-8, a potent neutrophil chemotactic agent, is known to be a key mediator in several inflammatory diseases. We found that 10 ng/ml of serum-activated LPS (Escherichia coli) efficiently up-regulated IL-8R on the surface of neutrophils within 30 min of LPS stimulation by 115 to 120% through de novo protein synthesis. After 30 min of LPS stimulation, reduction of IL-8R level was initiated and the normal level was restored within 2 h of LPS interaction. EDTA or EGTA and bestatin separately inhibited the receptor down-regulation by 98%, indicating the involvement of metalloprotease(s), more specifically an aminopeptidase in the process. Induction and subsequent reduction of IL-8 binding in serum-activated LPS-stimulated cells have been demonstrated in autoradiography. Intracellular Ca2+ level in these stimulated neutrophils was increased and decreased with alteration of IL-8R level. Although IL-8 binding was drastically reduced, the total IL-8R level, as detected by anti-IL-8R Ab measured by 125I-labeled anti-rabbit IgG, remained almost unaltered, indicating that minimal proteolysis occurred in IL-8R. Anti-IL-8R Ab and IL-8 itself could prevent this down-regulation significantly, suggesting that the susceptible epitope(s) might be in the IL-8 binding domain of the receptor. Under Ca2+-depleted conditions, the proteolysis was inhibited, which was accelerated upon addition of 1 mM of CaCl2. The study demonstrates that LPS-induced up-regulation of IL-8R leads to amplified IL-8-mediated biologic responses of neutrophils that are restored to normal level by activation of a Ca2+-dependent aminopeptidase. This may be useful for understanding the regulation of LPS-mediated inflammatory responses of neutrophils during bacterial infection.
Bhattacharya
C
C
Division of Immunobiology, Indian Institute of Chemical Biology, Calcutta.
Samanta
S
S
Gupta
S
S
Samanta
A K
AK
D000626:Aminopeptidases / Q000378:metabolism; D015703:Antigens, CD / Q000378:metabolism*; D001667:Binding, Competitive; D002118:Calcium / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D015536:Down-Regulation; D006801:Humans; D016209:Interleukin-8 / Q000378:metabolism*; D008024:Ligands; D008070:Lipopolysaccharides / Q000494:pharmacology; D009504:Neutrophils / Q000378:metabolism*; D018123:Receptors, Interleukin / Q000378:metabolism*; D023062:Receptors, Interleukin-8A; D015398:Signal Transduction; D013997:Time Factors; D015854:Up-Regulation
D015703:Antigens, CD; D016209:Interleukin-8; D008024:Ligands; D008070:Lipopolysaccharides; D018123:Receptors, Interleukin; D023062:Receptors, Interleukin-8A; D000626:Aminopeptidases; D002118:Calcium