Heme oxygenase-1 protein localizes to the nucleus and activates transcription factors important in oxidative stress.
Heme oxygenase-1 (HO-1), the rate-limiting enzyme in heme degradation, is an integral membrane protein of the smooth endoplasmic reticulum. However, we detected an HO-1 immunoreactive signal in the nucleus of cultured cells after exposure to hypoxia and heme or heme/hemopexin. Under these conditions, a faster migrating HO-1 immunoreactive band was enriched in nuclear extracts, suggesting that HO-1 was cleaved to allow nuclear entry. This was confirmed by the absence of immunoreactive signal with an antibody against the C terminus and the lack of a C-terminal sequence by gas chromatographymass spectrometry. Incubation with leptomycin B prior to hypoxia abolished nuclear HO-1 and the faster migrating band on Western analysis, suggesting that this process was facilitated by CRM1. Furthermore, preincubation with a cysteine protease inhibitor prevented nuclear entry of green fluorescent protein-labeled HO-1, demonstrating that protease-mediated C-terminal cleavage was also necessary for nuclear transport of HO-1. Nuclear localization was also associated with reduction of HO activity. HO-1 protein, whether it was enzymatically active or not, mediated activation of oxidant-responsive transcription factors, including activator protein-1. Nevertheless, nuclear HO-1 protected cells against hydrogen peroxide-mediated injury equally as well as cytoplasmic HO-1. We speculate that nuclear localization of HO-1 protein may serve to up-regulate genes that promote cytoprotection against oxidative stress.
Lin
Qing
Q
Children's Hospital of Philadelphia and Department of Pediatrics, University of Pennsylvania, Philadelphia, PA 19104, USA.
Weis
Sebastian
S
Yang
Guang
G
Weng
Yi-Hao
YH
Helston
Rachel
R
Rish
Kimberly
K
Smith
Ann
A
Bordner
Jessica
J
Polte
Tobias
T
Gaunitz
Frank
F
Dennery
Phyllis A
PA
D021581:Active Transport, Cell Nucleus / Q000187:drug effects / Q000502:physiology; D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D015687:Cell Hypoxia / Q000502:physiology; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000201:enzymology* / Q000235:genetics; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D006418:Heme / Q000494:pharmacology; D051547:Heme Oxygenase-1 / Q000235:genetics / Q000378:metabolism*; D006466:Hemopexin / Q000494:pharmacology; D006801:Humans; D006861:Hydrogen Peroxide; D028884:Karyopherins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D041681:NIH 3T3 Cells; D016877:Oxidants; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology*; D017434:Protein Structure, Tertiary / Q000502:physiology; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology; D000097606:Exportin 1 Protein
D000903:Antibiotics, Antineoplastic; D005231:Fatty Acids, Unsaturated; D006418:Heme; D051547:Heme Oxygenase-1; D006466:Hemopexin; D006861:Hydrogen Peroxide; D028884:Karyopherins; D016877:Oxidants; D018160:Receptors, Cytoplasmic and Nuclear; D018808:Transcription Factor AP-1; D000097606:Exportin 1 Protein; C038753:leptomycin B