Human tear lipocalin acts as an oxidative-stress-induced scavenger of potentially harmful lipid peroxidation products in a cell culture system.
Human tear lipocalin [lipocalin 1 (lcn-1); von Ebner's gland protein] is a member of the lipocalin superfamily that is known to bind an unusual variety of lipophilic ligands. Because of its properties and its tissue-specific expression it has been suggested that lcn-1 might act as a physiological protection factor of epithelia. Overexpression of lcn-1 under certain disease conditions supported such a function. However, experimental investigations into its exact biological role and its mode of expression were impeded because lcn-1 was previously found to be produced only in serous glands. To overcome this problem we therefore sought a cell line that produced lcn-1 endogenously. Using reverse-transcriptase-mediated PCR analysis we found expression of lcn-1 in the human teratocarcinoma-derived NT2 precursor cells. Under normal conditions the production of lcn-1 is low. However, treatment of the cells with H(2)O(2) or FeSO(4), which typically induce lipid peroxidation, significantly enhanced the expression of lcn-1. Binding studies revealed that arachidonic acid and several lipid peroxidation products including 7beta-hydroxycholesterol, 8-isoprostane and 13-hydroxy-9,11-octadecadienoic acid specifically bind to lcn-1. To investigate the physiological consequence of this observation we purified holo-(lcn-1) from culture medium and extracted the bound ligands. The presence of F(2)-isoprostanes in the extracts obtained from the fractions containing lcn-1 indicates that these typical lipid peroxidation products are indeed ligands of the protein in vivo. These results support the idea that lcn-1 acts as a physiological scavenger of potentially harmful lipophilic molecules; lcn-1 might therefore be a novel member of the cellular defence against the deleterious effects of oxidative stress.
Lechner
M
M
Institut für Mikrobiologie (Medizinische Fakultät), Universität Innsbruck, Fritz Pregl Strasse 3, A-6020 Innsbruck, Austria.
Wojnar
P
P
Redl
B
B
D016718:Arachidonic Acid / Q000378:metabolism; D001667:Binding, Competitive; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D003619:Dansyl Compounds / Q000378:metabolism; D015237:Dinoprost / Q000031:analogs & derivatives / Q000378:metabolism; D028441:F2-Isoprostanes; D005227:Fatty Acids / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism; D006801:Humans; D015227:Lipid Peroxidation / Q000502:physiology*; D008054:Lipid Peroxides / Q000378:metabolism*; D054835:Lipocalin 1; D018384:Oxidative Stress / Q000502:physiology*; D017382:Reactive Oxygen Species / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D013666:Tears / Q000502:physiology*; D018243:Teratocarcinoma; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; D003619:Dansyl Compounds; D028441:F2-Isoprostanes; D005227:Fatty Acids; D005456:Fluorescent Dyes; C518443:LCN1 protein, human; D008054:Lipid Peroxides; D054835:Lipocalin 1; D017382:Reactive Oxygen Species; D011994:Recombinant Proteins; D016718:Arachidonic Acid; C054400:11-(dansylamino)undecanoic acid; D015237:Dinoprost