Bacterial lipopolysaccharide induces HIF-1 activation in human monocytes via p44/42 MAPK and NF-kappaB.
Inflammatory mediators activate the transcriptional complex HIF-1 (hypoxia-inducible factor-1), the key regulator of hypoxia-induced gene expression. Here we report that bacterial LPS (lipopolysaccharide) induces HIF-1alpha mRNA expression and HIF-1alpha protein accumulation in human monocytes as well as in non-differentiated and differentiated cells of the human monocytic cell line THP-1 under normoxic conditions. LPS and hypoxia synergistically activated HIF-1. Whereas LPS increased HIF-1alpha mRNA expression through activation of a NF-kappaB (nuclear factor kappaB) site in the promoter of the HIF-1alpha gene, hypoxia post-translationally stabilized HIF-1alpha protein. HIF-1alpha activation was followed by increased expression of the HIF-1 target gene encoding ADM (adrenomedullin). Knocking down HIF-1alpha by RNA interference significantly decreased ADM expression, which underlines the importance of HIF-1 for the LPS-induced ADM expression in normoxia. Simultaneously with HIF-1 activation, an increase in p44/42 MAPK (mitogen-activated protein kinase) phosphorylation was observed after incubation with LPS. In cells pretreated with the p44/42 MAPK inhibitor PD 98059 or with RNAi (interfering RNA) directed against p44/42 MAPK, LPS-induced HIF-1alpha accumulation and ADM expression were significantly decreased. From these results we conclude that LPS critically involves the p44/42 MAPK and NF-kappaB pathway in the activation of HIF-1, which is an important transcription factor for LPS-induced ADM expression.
Frede
Stilla
S
Institut für Physiologie, Universität Duisburg-Essen Hufelandstrasse 55, D-45122 Essen, Federal Republic of Germany.
Stockmann
Christian
C
Freitag
Patricia
P
Fandrey
Joachim
J
D053607:Adrenomedullin; D002460:Cell Line; D024202:Electrophoretic Mobility Shift Assay; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology; D051793:Hypoxia-Inducible Factor 1 / Q000378:metabolism*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000096:biosynthesis*; D018950:Lipopolysaccharide Receptors / Q000096:biosynthesis; D008070:Lipopolysaccharides / Q000494:pharmacology*; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009000:Monocytes / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism*; D010455:Peptides / Q000378:metabolism; D034622:RNA Interference
D005419:Flavonoids; C497442:HIF1A protein, human; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; D016328:NF-kappa B; D010455:Peptides; D053607:Adrenomedullin; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one