Lipopolysaccharide-induced c-Jun NH2-terminal kinase activation in human neutrophils: role of phosphatidylinositol 3-Kinase and Syk-mediated pathways.
Polymorphonuclear leukocytes (neutrophils) respond to lipopolysaccharide (LPS) through the up-regulation of several pro-inflammatory mediators. We have recently shown that LPS-stimulated neutrophils express monocyte chemoattractant protein 1 (MCP-1), an AP-1-dependent gene, suggesting that LPS activates the c-Jun N-terminal kinase (JNK) pathway in neutrophils. Previously, we have shown the activation of p38 MAPK, but not JNK, in suspended neutrophils stimulated with LPS but have recently shown activation of JNK by TNF-alpha in an adherent neutrophil system. We show here that exposure to LPS activates JNK in non-suspended neutrophils and that LPS-induced MCP-1 expression, but not tumor necrosis factor-alpha (TNF-alpha) or interleukin-8 (IL-8), is dependent on JNK activation. In addition, LPS stimulation of non-suspended neutrophils activates Syk and phosphatidylinositol 3-kinase (PI3K). Inhibition of Syk with piceatannol or PI3K with wortmannin inhibited LPS-induced JNK activation and decreased MCP-1 expression after exposure to LPS, suggesting that both Syk and PI3K reside in a signaling pathway leading to LPS-induced JNK activation in neutrophils. This Syk- and PI3K-dependent pathway leading to JNK activation after LPS exposure in non-suspended neutrophils is specific for JNK, because inhibition of neither Syk nor PI3K decreased p38 activation after LPS stimulation. Furthermore we show that PI3K inhibition decreased LPS-induced Syk activation suggesting that PI3K resides upstream of Syk in this pathway. Finally, we show that Syk associates with Toll-like receptor 4 (TLR4) upon LPS stimulation further implicating Syk in the LPS-induced signaling pathway in neutrophils. Overall our data suggests that LPS induces JNK activation only in non-suspended neutrophils, which proceeds through Syk- and PI3K-dependent pathways, and that JNK activation is important for LPS-induced MCP-1 expression but not for TNF-alpha or IL-8 expression.
Arndt
Patrick G
PG
Department of Medicine and Division of Cell Biology, National Jewish Medical and Research Center, Denver, Colorado, USA. Patrick.Arndt@UCHSC.edu
Suzuki
Naohito
N
Avdi
Natalie J
NJ
Malcolm
Kenneth C
KC
Worthen
G Scott
GS
D000873:Anthracenes / Q000494:pharmacology; D001483:Base Sequence; D018932:Chemokine CCL2 / Q000378:metabolism; D017931:DNA Primers; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D048031:JNK Mitogen-Activated Protein Kinases; D008070:Lipopolysaccharides / Q000494:pharmacology*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009504:Neutrophils / Q000187:drug effects* / Q000201:enzymology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000072377:Syk Kinase
D000873:Anthracenes; D018932:Chemokine CCL2; D017931:DNA Primers; D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D048031:JNK Mitogen-Activated Protein Kinases; D008070:Lipopolysaccharides; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011505:Protein-Tyrosine Kinases; D000072377:Syk Kinase; C432165:pyrazolanthrone; C000606896:SYK protein, human