title: Down-regulation of heme oxygenase-2 is associated with the increased expression of heme oxygenase-1 in human cell lines.
abstract: Intracellular heme concentrations are maintained in part by heme degradation, which is catalyzed by heme oxygenase. Heme oxygenase consists of two structurally related isozymes, HO-1 and HO-2. Recent studies have identified HO-2 as a potential oxygen sensor. To gain further insights into the regulatory role of HO-2 in heme homeostasis, we analyzed the expression profiles of HO-2 and the biochemical consequences of HO-2 knockdown with specific short interfering RNA (siRNA) in human cells. Both HO-2 mRNA and protein are expressed in the eight human cancer cell lines examined, and HO-1 expression is detectable in five of the cell lines, including HeLa cervical cancer and HepG2 hepatoma. Down-regulation of HO-2 expression with siRNA against HO-2 (siHO-2) caused induction of HO-1 expression at both mRNA and protein levels in HeLa and HepG2 cells. In contrast, knockdown of HO-1 expression did not noticeably influence HO-2 expression. HO-2 knockdown prolonged the half-life of HO-1 mRNA twofold in HeLa cells. Transient transfection assays in HeLa cells revealed that the 4.5-kb human HO-1 gene promoter was activated with selective knockdown of HO-2 in a sequence-dependent manner. Moreover, HO-2 knockdown caused heme accumulation in HeLa and HepG2 cells only when exposed to exogenous hemin. HO-2 knockdown may mimic a certain physiological change that is important in the maintenance of cellular heme homeostasis. These results suggest that HO-2 may down-regulate the expression of HO-1, thereby directing the co-ordinated expression of HO-1 and HO-2.
authors.affiliation: Department of Molecular Biology and Applied Physiology, Tohoku University School of Medicine, Sendai, Japan.
authors.forename: Yuanying
authors.initials: Y
authors.lastname: Ding
authors.forename: Yong Z
authors.initials: YZ
authors.lastname: Zhang
authors.forename: Kazumichi
authors.initials: K
authors.lastname: Furuyama
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Ogawa
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Igarashi
authors.forename: Shigeki
authors.initials: S
authors.lastname: Shibahara
mesh_terms: D015536:Down-Regulation; D006367:HeLa Cells; D006418:Heme / Q000378:metabolism; D006419:Heme Oxygenase (Decyclizing) / Q000235:genetics* / Q000378:metabolism; D051547:Heme Oxygenase-1 / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D019169:Jurkat Cells; D020014:K562 Cells; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering; D014407:Tumor Cells, Cultured
chemical_list: D012333:RNA, Messenger; D034741:RNA, Small Interfering; D006418:Heme; D006419:Heme Oxygenase (Decyclizing); D051547:Heme Oxygenase-1; C105245:heme oxygenase-2