title: HIF-1alpha protein is an essential factor for protection of myeloid cells against LPS-induced depletion of ATP and apoptosis that supports Toll-like receptor 4-mediated production of IL-6.
abstract: Sepsis is the leading cause of death in intensive care units, which reflects detrimental host response to infection where lipopolysaccharide (LPS) shared by Gram-negative bacteria acts as a potent activator of immune cells via Toll-like receptor 4 (TLR4). Recently it was found that TLR4 downstream signalling leads to the accumulation of hypoxia-inducible factor 1 alpha (HIF-1alpha), which is important for TLR4-dependent expression of pro-inflammatory cytokines, however, basic biochemical mechanisms of involvement of this protein in TLR4 downstream signalling remains unclear. Here we found that knockdown of the expression of HIF-1alpha protein by siRNA led to the depletion of ATP, which corresponded to the constant increase in the activity of apoptosis signal-regulating kinase 1 (ASK1) and therefore apoptosis as estimated based on the increase in the activity of caspase 3. On the other hand, LPS-dependent production of IL-6 was attenuated. Treatment of HIF-1alpha knockdown cells with extracellular ATP in combination with LPS preserved the IL-6 expression but not the activity of ASK1 on the level observed in LPS-stimulated control cells. We therefore suggested that HIF-1alpha protein supports LPS-dependent expression of IL-6 by preventing depletion of ATP. On the other hand HIF-1alpha protein is selectively required for down-regulation of ASK1 activated during LPS-induced TLR4 downstream signalling.
authors.affiliation: Medway School of Pharmacy, University of Kent, United Kingdom.
authors.forename: Harjinder
authors.initials: H
authors.lastname: Lall
authors.forename: Karen
authors.initials: K
authors.lastname: Coughlan
authors.forename: Vadim V
authors.initials: VV
authors.lastname: Sumbayev
mesh_terms: D000255:Adenosine Triphosphate / Q000172:deficiency*; D017209:Apoptosis / Q000187:drug effects*; D045744:Cell Line, Tumor; D003035:Cobalt / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects; D005110:Extracellular Space / Q000187:drug effects; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D015850:Interleukin-6 / Q000096:biosynthesis*; D008070:Lipopolysaccharides / Q000494:pharmacology*; D048848:MAP Kinase Kinase Kinase 5 / Q000235:genetics; D022423:Myeloid Cells / Q000166:cytology* / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D051197:Toll-Like Receptor 4 / Q000276:immunology*
chemical_list: D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D015850:Interleukin-6; D008070:Lipopolysaccharides; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D003035:Cobalt; D000255:Adenosine Triphosphate; D048848:MAP Kinase Kinase Kinase 5; C482858:MAP3K5 protein, human; C018021:cobaltous chloride