Protein kinase C regulates macrophage tumor necrosis factor secretion: direct protein kinase C activation restores tumor necrosis factor production in endotoxin tolerance.
BACKGROUND
Macrophages pretreated in vitro with endotoxin (LPSp) secrete less tumor necrosis factor (TNF) in response to a second LPS activating (LPSa) stimulus. Protein kinase C (PKC) is required for TNF secretion in a macrophage stimulated with LPSa. In these experiments we examined the role of PKC in TNF signal transduction in naive and tolerant macrophages.


METHODS
Murine macrophages were cultured +/- LPSp for 24 hours. Cultures were washed and treated for 1 hour with PKC inhibitors or phorbol myristate acetate (PMA), a direct PKC activator. Cells were then stimulated with a range of LPSa for 6 hours, and TNF was determined by bioassay.


RESULTS
LPSa-stimulated TNF secretion by nontolerant macrophages was inhibited by LPSp in the absence of PMA. PKC inhibitors decreased TNF by naive macrophages and exaggerated inhibition in tolerant cells. Depletion of PKC by 24 hours of PMA decreased TNF production by both naive and tolerant macrophages. PKC activation with PMA 1 hour before LPSa augmented TNF secretion in naive cells and reversed TNF inhibition of tolerant cells.


CONCLUSIONS
Direct PKC activation with PMA restored TNF secretion in LPS-tolerant macrophages. Endotoxin tolerance may alter the LPSa signal transduction pathway between the LPS receptor and PKC activation.
West
M A
MA
Department of Surgery, Hennepin County Medical Center, University of Minnesota, Minneapolis, USA.
LeMieur
T
T
Clair
L
L
Bellingham
J
J
Rodriguez
J L
JL
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D002478:Cells, Cultured; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D004361:Drug Tolerance; D004731:Endotoxins / Q000633:toxicity; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004926:Escherichia coli; D007700:Kinetics; D008070:Lipopolysaccharides / Q000633:toxicity*; D017737:Macrophages, Peritoneal / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis* / Q000378:metabolism
D004731:Endotoxins; D004791:Enzyme Inhibitors; D008070:Lipopolysaccharides; D014409:Tumor Necrosis Factor-alpha; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate