Tài liệu Báo cáo khoa học: Hypoxia reduces the expression of heme oxygenase-2 in various types of

Hypoxia reduces the expression of heme oxygenase-2 in

various types of human cell lines

A possible strategy for the maintenance of intracellular heme level

Yongzhao Zhang1

, Kazumichi Furuyama1

, Kiriko Kaneko1

, Yuanying Ding1

, Kazuhiro Ogawa2,*,

Miki Yoshizawa1

, Masaki Kawamura1

, Kazuhisa Takeda1

, Tadashi Yoshida3 and Shigeki Shibahara1

1 Department of Molecular Biology and Applied Physiology, Tohoku University School of Medicine, Sendai, Japan

2 Department of Molecular Pharmacology, Tohoku University School of Medicine, Sendai, Japan

3 Department of Biochemistry, Yamagata University School of Medicine, Yamagata, Japan

Heme oxygenase (HO) is the rate-limiting enzyme in

heme catabolism and cleaves heme to release iron, car￾bon monoxide and biliverdin at the expense of molecu￾lar oxygen and NADPH [1,2]. HO consists of two

structurally related isozymes, HO-1 and HO-2 [3–5].

Characteristically, human HO-1 contains no cysteine

residue [6], whereas HO-2 contains at least two copies of

a potential heme-binding site, consisting of the cysteine

and proline (CP motif) [7,8]. Importantly, these CP

motifs are not involved in heme breakdown reactions

[8], suggesting that HO-2 may sequester heme to main￾tain the intracellular heme level. In addition, expression

of HO-1 mRNA is induced by various stimuli, such as

hemin and nitric oxide donors, in which expression of

Keywords

erythroid cells; heme oxygenase-1; heme

oxygenase-2; hemoglobin; hypoxia

Correspondence

S. Shibahara, Department of Molecular

Biology and Applied Physiology, Tohoku

University School of Medicine, 2-1 Seiryo￾machi, Aoba-ku, Sendai, Miyagi 980-8575,

Japan

Fax: +81 22 717 8118

Tel: +81 22 717 8117

E-mail: [email protected]

*Present address

Department of Molecular Pharmacology,

Kanazawa University Graduate School of

Medical Science, Kanazawa, Japan

(Received 26 January 2006, revised 5 May

2006, accepted 15 May 2006)

doi:10.1111/j.1742-4658.2006.05319.x

Heme oxygenase consists of two structurally related isozymes, heme oxyge￾nase-1 and and heme oxygenase-2, each of which cleaves heme to form bili￾verdin, iron and carbon monoxide. Expression of heme oxygenase-1 is

increased or decreased depending on cellular microenvironments, whereas lit￾tle is known about the regulation of heme oxygenase-2 expression. Here we

show that hypoxia (1% oxygen) reduces the expression levels of heme oxyge￾nase-2 mRNA and protein after 48 h of incubation in human cell lines, inclu￾ding Jurkat T-lymphocytes, YN-1 and K562 erythroleukemia, HeLa cervical

cancer, and HepG2 hepatoma, as judged by northern blot and western blot

analyses. In contrast, the expression level of heme oxygenase-1 mRNA varies

under hypoxia, depending on the cell line; it was increased in YN-1 cells,

decreased in HeLa and HepG2 cells, and remained undetectable in Jurkat

and K562 cells. Moreover, heme oxygenase-1 protein was decreased in YN-1

cells under the conditions used, despite the induction of heme oxygenase-1

mRNA under hypoxia. The heme oxygenase activity was significantly

decreased in YN-1, K562 and HepG2 cells after 48 h of hypoxia. To explore

the mechanism for the hypoxia-mediated reduction of heme oxygenase-2

expression, we showed that hypoxia shortened the half-life of heme oxyge￾nase-2 mRNA (from 12 h to 6 h) in YN-1 cells, without affecting the half-life

of heme oxygenase-1 mRNA (9.5 h). Importantly, the heme contents were

increased in YN-1, HepG2 and HeLa cells after 48 h of incubation under

hypoxia. Thus, the reduced expression of heme oxygenase-2 may represent

an important adaptation to hypoxia in certain cell types, which may contrib￾ute to the maintenance of the intracellular heme level.

Abbreviations

HO, heme oxygenase; HRE, hypoxia response element; MARE, Maf recognition element.

3136 FEBS Journal 273 (2006) 3136–3147 ª 2006 The Authors Journal compilation ª 2006 FEBS