The role of sphingosine 1-phosphate in the TNF-alpha induction of IL-8 gene expression in lung epithelial cells.
Tumor necrosis factor-alpha (TNF-alpha) is an important cytokine involved in the pathogenesis of inflammatory diseases of the lung. Interleukin-8 (IL-8), a C-X-C chemokine, is induced by TNF-alpha and initiates injury by acting as a chemoattractant for neutrophils and other immune cells. Although sphingolipids such as ceramide and sphingosine 1-phosphate (S1-P) have been shown to serve as signaling molecules in the TNF-alpha inflammatory response, their role in the TNF-alpha induction of IL-8 gene expression in lung epithelial cells is not known. We investigated the role of sphingolipids in the TNF-alpha induction of IL-8 gene expression in H441 lung epithelial cells. We found that TNF-alpha induced IL-8 mRNA levels by increasing gene transcription, and the stability of IL-8 mRNA was not affected. Exogenous S1-P but not ceramide or sphingosine increased IL-8 mRNA levels and IL-8 secretion. Dimethylsphingosine, an inhibitor of sphingosine kinase, partially inhibited TNF-alpha induction of IL-8 mRNA levels indicating the importance of intracellular increases in S1-P in the IL-8 induction. S1-P induction of IL-8 mRNA was due to an increase in gene transcription, and the stability of IL-8 mRNA was not affected. S1-P induction of IL-8 mRNA was associated with an increase in the binding activity of AP-1 but the activities of NF-kappaB and NF IL-6 were unchanged. S1-P induced the phosphorylation of ERK, p38 and JNK MAPKs. Pharmacological inhibitors of ERK and p38 but not JNK partly inhibited S1-P induction of IL-8 mRNA levels. These data show that increases in the intracellular S1-P partly mediate TNF-alpha induction of IL-8 gene expression in H441 lung epithelial cells via ERK and p38 MAPK signaling pathways and increased AP-1 DNA binding.
Chandru
Hemakumar
H
Department of Molecular Biology, University of Texas Health Center at Tyler, 11937 US Highway 271 Tyler, TX 75708-3154, USA.
Boggaram
Vijayakumar
V
D015152:Blotting, Northern; D045744:Cell Line, Tumor; D002518:Ceramides / Q000494:pharmacology; D024202:Electrophoretic Mobility Shift Assay; D004847:Epithelial Cells / Q000378:metabolism / Q000473:pathology; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D015151:Immunoblotting; D016209:Interleukin-8 / Q000235:genetics*; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D008168:Lung / Q000378:metabolism / Q000473:pathology; D008246:Lysophospholipids / Q000494:pharmacology*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D009841:Oligonucleotides / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D013997:Time Factors; D018808:Transcription Factor AP-1 / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D002518:Ceramides; D016209:Interleukin-8; D008246:Lysophospholipids; D016328:NF-kappa B; D009841:Oligonucleotides; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D018808:Transcription Factor AP-1; D014409:Tumor Necrosis Factor-alpha; C060506:sphingosine 1-phosphate; D008156:Luciferases; D020928:Mitogen-Activated Protein Kinases; C061800:N,N-dimethylsphingosine; D013110:Sphingosine