title: Continuous de novo biosynthesis of haem and its rapid turnover to bilirubin are necessary for cytoprotection against cell damage.
abstract: It is well known that haem serves as the prosthetic group of various haemoproteins that function in oxygen transport, respiratory chain, and drug metabolism. However, much less is known about the functions of the catabolites of haem in mammalian cells. Haem is enzymatically degraded to iron, carbon monoxide (CO), and biliverdin, which is then converted to bilirubin. Owing to difficulties in measuring bilirubin, however, the generation and transport of this end product remain unclear despite its clinical importance. Here, we used UnaG, the recently identified bilirubin-binding fluorescent protein, to analyse bilirubin production in a variety of human cell lines. We detected a significant amount of bilirubin with many non-blood cell types, which was sensitive to inhibitors of haem metabolism. These results suggest that there is a basal level of haem synthesis and its conversion into bilirubin. Remarkably, substantial changes were observed in the bilirubin generation when cells were exposed to stress insults. Since the stress-induced cell damage was exacerbated by the pharmacological blockade of haem metabolism but was ameliorated by the addition of biliverdin and bilirubin, it is likely that the de novo synthesis of haem and subsequent conversion to bilirubin play indispensable cytoprotective roles against cell damage.
authors.affiliation: Department of Biotechnology, Kyoto Institute of Technology, Kyoto 606-8585, Japan.
authors.forename: Taka-aki
authors.initials: TA
authors.lastname: Takeda
authors.affiliation: Department of Biotechnology, Kyoto Institute of Technology, Kyoto 606-8585, Japan.
authors.forename: Anfeng
authors.initials: A
authors.lastname: Mu
authors.affiliation: Department of Biotechnology, Kyoto Institute of Technology, Kyoto 606-8585, Japan.
authors.forename: Tran Tien
authors.initials: TT
authors.lastname: Tai
authors.affiliation: Department of Biotechnology, Kyoto Institute of Technology, Kyoto 606-8585, Japan.
authors.forename: Sakihito
authors.initials: S
authors.lastname: Kitajima
authors.affiliation: Department of Biotechnology, Kyoto Institute of Technology, Kyoto 606-8585, Japan.
authors.forename: Shigeru
authors.initials: S
authors.lastname: Taketani
mesh_terms: D018053:Arsenites / Q000494:pharmacology; D001663:Bilirubin / Q000378:metabolism*; D019256:Cadmium Chloride / Q000494:pharmacology; D045744:Cell Line, Tumor; D019610:Cytoprotection / Q000502:physiology*; D005294:Ferrochelatase / Q000037:antagonists & inhibitors / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism; D057809:HEK293 Cells; D006367:HeLa Cells; D006418:Heme / Q000096:biosynthesis / Q000378:metabolism*; D051547:Heme Oxygenase-1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D056945:Hep G2 Cells; D006801:Humans; D061986:MCF-7 Cells; D008293:Malates / Q000494:pharmacology; D008928:Mitochondria / Q000378:metabolism; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000378:metabolism; D011485:Protein Binding; D017670:Sodium Compounds / Q000494:pharmacology
chemical_list: D018053:Arsenites; D005456:Fluorescent Dyes; D008293:Malates; D017670:Sodium Compounds; D006418:Heme; C017947:sodium arsenite; C058705:diethyl malate; D051547:Heme Oxygenase-1; D044925:Oxidoreductases Acting on CH-CH Group Donors; C019789:biliverdin reductase; D005294:Ferrochelatase; D019256:Cadmium Chloride; D001663:Bilirubin