title: The lipocalin alpha1-microglobulin protects erythroid K562 cells against oxidative damage induced by heme and reactive oxygen species.
abstract: Alpha(1)-microglobulin is a 26 kDa plasma and tissue glycoprotein that belongs to the lipocalin protein superfamily. Recent reports show that it is a reductase and radical scavenger and that it binds heme and has heme-degrading properties. This study has investigated the protective effects of alpha(1)-microglobulin against oxidation by heme and reactive oxygen species in the human erythroid cell line, K562. The results show that alpha(1)-microglobulin prevents intracellular oxidation and up-regulation of heme oxygenase-1 induced by heme, hydrogen peroxide and Fenton reaction-generated hydroxyl radicals in the culture medium. It also reduces the cytosol of non-oxidized cells. Endogeneous expression of alpha(1)-microglobulin was up-regulated by these oxidants and silencing of the alpha(1)-microglobulin expression increased the cytosol oxidation. alpha(1)-microglobulin also inhibited cell death caused by heme and cleared cells from bound heme. Binding of heme to alpha(1)-microglobulin increased the radical reductase activity of the protein as compared to the apo-protein. Finally, alpha(1)-microglobulin was localized mainly at the cell surface both when administered exogeneously and in non-treated cells. The results suggest that alpha(1)-microglobulin is involved in the defence against oxidative cellular injury caused by haemoglobin and heme and that the protein may employ both heme-scavenging and one-electron reduction of radicals to achieve this.
authors: Division of Infection Medicine, Lund University, Lund, Sweden.
authors: Magnus G
authors: MG
authors: Olsson
authors: Tor
authors: T
authors: Olofsson
authors: Hans
authors: H
authors: Tapper
authors: Bo
authors: B
authors: Akerstrom
mesh_terms: D000510:Alpha-Globulins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D002470:Cell Survival / Q000187:drug effects; D006418:Heme / Q000494:pharmacology*; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D020014:K562 Cells; D008856:Microscopy, Fluorescence; D016877:Oxidants / Q000494:pharmacology; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000187:drug effects* / Q000502:physiology*; D010100:Oxygen / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000494:pharmacology*; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D000510:Alpha-Globulins; D016877:Oxidants; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D017382:Reactive Oxygen Species; C016001:alpha-1-microglobulin; D006418:Heme; D006861:Hydrogen Peroxide; D010100:Oxygen