Ho-1 Gene Activation Research Articles

Cytotoxicity and Pro-inflammatory Properties of Aliphatic Alpha, Beta-unsaturated Acid and Ester Monomers in RAW264.7 Cells and Their Chemical Reactivity

α,β-Unsaturated ester monomers such as methyl methacrylates (MMA), 2-hydroxyethyl methacrylates (2-HEMA), ethyleneglycol dimethacrylate (EGDMA) and triethyleneglycol dimetacrylate (TEGDMA) have been widely used in dentistry as dental materials. The present study was designed to clarify the proinflammatory activity of monomers. The cytotoxicity of the monomers and their effects on the expression of cyclooxygenase-2 (Cox2), nitric oxide synthase 2 (Nos2) and heme oxygenase 1 (Ho-1) mRNAs in RAW264.7 cells were determined using a cell counting kit and real-time reverse transcriptase-polymerase chain reaction, respectively. The cytotoxicity declined in the order n-butyl acrylate (nBA) > acrylic acid > TEGDMA > EGDMA > methacrylic acid ≈ 2-HEMA > lauryl methacrylate > nBMA > MMA. nBA and EGDMA at 1 mM up-regulated the expression of Cox2 mRNA. In contrast, 1 mM nBA and 10 mM 2-HEMA up-regulated the expression of Nos2 mRNA. Up-regulation of Ho-1 mRNA expression was found for 0.1 mM nBA, 1 mM EGDMA and 2 mM TEGDMA. The electrophilicity, ω was calculated on the basis of the density function theory BLYP/6-31G*. nBA and EGDMA with high ω values exerted potent pro-inflammatory activities. nBA, EGDMA and TEGDMA upregulated Ho-1 gene expression. Ho-1 gene activation of monomers may promote resistance of chemical carcinogenesis in biological systems.

Bruton’s Tyrosine Kinase Is Required for TLR-Dependent Heme Oxygenase-1 Gene Activation via Nrf2 in Macrophages

Heme oxygenase (HO)-1 is the inducible isoform of the rate-limiting enzyme of heme degradation and provides cytoprotection against oxidative stress by its products carbon monoxide and biliverdin. More recently, HO-1 has also been shown to exert immunomodulatory functions via cell type-specific anti-inflammatory effects in myeloid/macrophage cells. In the current study, it is demonstrated that Bruton's tyrosine kinase (Btk), the gene of which is mutated in the human immunodeficiency X-linked agammaglobulinemia, is involved in the upregulation of HO-1 gene expression via TLR signaling in macrophages. The specific Btk inhibitor LFM-A13 blocked HO-1 induction by the classical TLR4 ligand LPS in cell cultures of RAW264.7 monocytic cells and primary mouse alveolar macrophages. Moreover, upregulation of HO-1 gene expression was abrogated in LPS-stimulated alveolar macrophages from Btk(-/-) mice. Transfection studies with luciferase reporter gene constructs demonstrated that LPS-dependent induction of HO-1 promoter activity was attenuated by pharmacological Btk inhibition and by an overexpressed dominant-negative mutant of Btk. This induction was mediated by the transcription factor Nrf2, which is a master regulator of the antioxidant cellular defense. Accordingly, nuclear translocation of Nrf2 in LPS-treated macrophages was reduced by Btk inhibition. The generation of reactive oxygen species, but not that of NO, was involved in this regulatory pathway. Btk-dependent induction of HO-1 gene expression was also observed upon macrophage stimulation with ligands of TLR2, TLR6, TLR7, and TLR9, suggesting that Btk is required for HO-1 gene activation by major TLR pathways.

Bruton's Tyrosine Kinase and Nrf2 mediate TLR-induced activation of Heme oxygenase-1 gene expression in macrophages (116.16)

Abstract The inducible isoform of heme oxygenase (HO)-1, is involved in heme degradation producing CO and biliverdin, mediating cytoprotection against oxidative stress. Recently, HO-1 has been shown to evoke potent anti-inflammatory and immunomodulatory effects in macrophages. Here we demonstrate that Bruton's tyrosine kinase (Btk), the gene of which is mutated in human immunodeficiency X-linked agammaglobulinemia, is involved in toll-like receptor (TLR)-induced gene expression of HO-1 in macrophages. The Btk inhibitor LFM-A13 blocked the induction of HO-1 by LPS (TLR4 ligand) in RAW264.7 macrophages and primary mouse alveolar macrophages. Furthermore, LPS-stimulated up-regulation of HO-1 gene expression was abrogated in alveolar macrophages from Btk-/- mice. In addition, inhibition of Btk with LFM-A13 attenuated the LPS-induced luciferase activity of the HO-1 promoter in transfection studies in RAW264.7 cells. This effect was mediated by the transcription factor Nrf2, which is a master regulator of the cellular antioxidant defense. Immunofluorescence studies revealed that the nuclear translocation of Nrf2 in LPS-treated macrophages was reduced by Btk inhibition. Moreover, the generation of reactive oxygen species (ROS), but not that of NO, was involved in this regulatory pathway. Btk-dependent induction of HO-1 gene expression via Nrf2 was also observed upon stimulation by TLR7 and TLR9 ligands, suggesting Btk to be generally involved in TLR-mediated HO-1 gene activation.

Simvastatin-dependent up-regulation of heme oxygenase-1 via mRNA stabilization in human endothelial cells

Heme oxygenase (HO)-1, which is the inducible isoform of the rate-limiting enzyme of heme degradation, has potent antioxidant and anti-inflammatory effects and is an emerging therapeutic target for the treatment of cardiovascular disease. 3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, also termed statins, induce HO-1 gene expression in endothelial cells, but the underlying regulatory mechanisms are not well studied. To further investigate the statin-specific HO-1 regulation, we examined HO-1 gene expression by simvastatin in cell cultures of human endothelial cells. Simvastatin-dependent HO-1 gene activation was significantly reduced by pharmacological inhibition of the p38 MAPK and phosphotidylinositol-3-kinase (PI3K)/Akt pathways. Although HO-1 is considered to be primarily regulated at the transcriptional level, simvastatin induced activity of a human HO-1 promoter gene construct only to a minor extent. By contrast, studies with actinomycin D indicated that the half-life of HO-1 mRNA was significantly prolonged in the presence of simvastatin suggesting a post-transcriptional mode of HO-1 regulation. The increased HO-1 mRNA stability by this compound was blocked by inhibition of PI3K/Akt, but not by that of p38 MAPK. In conclusion, statin-dependent up-regulation of endothelial HO-1 is mainly regulated by stabilization of HO-1 mRNA via a PI3K/Akt-dependent signaling pathway.

An atypical NF-kappa B-regulated pathway mediates phorbol ester-dependent Heme oxygenase-1 gene activation in monocytes

Heme oxygenase (HO)-1 is the rate-limiting enzyme of heme degradation. More recently, HO-1 has been shown to have anti-inflammatory and antioxidant functions, which have been demonstrated in HO-1 knockout mice models and a human case of HO-1 genetic deficiency. Moreover, targeted induction of HO-1 has been shown to have therapeutic effects in various disease models. Here, it is reported that the HO-1 gene is transcriptionally induced by the phorbol ester phorbol myristate acetate (PMA), which is a prototypical activator of PKC, in various monocytic cells. The PMA-dependent induction of HO-1 has a different time-dependent pattern of induction from that of lipopolysaccharide-dependent HO-1 induction in these cells. Activation of HO-1 by PMA was mediated via a newly identified kB element of the proximal rat HO-1 gene promoter region (-284 to -275). This HO-kB element was a nuclear target for the NF-kB subunit p65/RelA as determined by nuclear binding assays and transfection experiments with luciferase reporter gene constructs in RAW264.7 monocytes. Moreover, PMA-dependent induction of endogenous HO-1 gene expression and promoter activity was abrogated in embryonic fibroblasts from p65-/- mice. PMA-dependent HO-1 gene activation was reduced by an overexpressed dominant negative mutant of IkB, but not by dominant negative IkB kinase-2 (IKK2) suggesting that the classical NF-kB pathway was not involved in this regulation. The antioxidant N-acetylcysteine and inhibitors of p38 MAPK or serine/threonine kinase CK2 blocked PMA-dependent HO-1 gene activation. Finally, it is demonstrated by luciferase assays with a Gal4-CHOP fusion protein that activation of p38 MAPK by PMA was independent of CK2. Taken together, induction of HO-1 gene expression by PMA is regulated via an IKK-independent atypical NF-kB pathway that is mediated via activation of p38 MAPK and CK2.

Cytotoxic effects of flavonoids against a human colon cancer derived cell line, COLO 201: A potential natural anti-cancer substance

The proliferation of a human colon carcinoma cell line, COLO 201, was effectively suppressed through apoptosis in the presence of flavonoids, an ethanol extract from Vitex agnus-castus fruits. The induction of apoptosis was not inhibited by the presence of an anti-oxidant, N-acetyl- l-cysteine, whereas only HO-1 gene expression levels increased among other typical oxidative stress-associated genes examined after Vitex treatment. These results suggest that Vitex treatment activates a pathway associated with HO-1 gene activation, resulting in the induction of apoptosis in COLO 201. Results also implicate a potential clinical chemotherapeutic application of Vitex for the treatment of colon cancer patients.

An Atypical NF-κB-Regulated Pathway Mediates Phorbol Ester-Dependent Heme Oxygenase-1 Gene Activation in Monocytes

Heme oxygenase (HO)-1 catalyzes the rate-limiting step of heme degradation and plays an important anti-inflammatory role via its enzymatic products carbon monoxide and biliverdin. In this study it is reported that the HO-1 gene is transcriptionally induced by the phorbol ester PMA in cell cultures of monocytic cells with a regulatory pattern that is different from that of LPS-dependent HO-1 induction in these cells. Activation of HO-1 by PMA was mediated via a newly identified kappaB element of the proximal rat HO-1 gene promoter region (-284 to -275). This HO-kappaB element was a nuclear target for the NF-kappaB subunit p65/RelA as determined by nuclear binding assays and transfection experiments with luciferase reporter gene constructs in RAW264.7 monocytes. Moreover, PMA-dependent induction of endogenous HO-1 gene expression and promoter activity was abrogated in embryonic fibroblasts from p65(-/-) mice. PMA-dependent HO-1 gene activation was reduced by an overexpressed dominant negative mutant of IkappaBalpha, but not by dominant negative IkappaB kinase-2, suggesting that the classical NF-kappaB pathway was not involved in this regulation. The antioxidant N-acetylcysteine and inhibitors of p38 MAPK or serine/threonine kinase CK2 blocked PMA-dependent HO-1 gene activation. Finally, it is demonstrated by luciferase assays with a Gal4-CHOP fusion protein that the activation of p38 MAPK by PMA was independent of CK2. Taken together, induction of HO-1 gene expression by PMA is regulated via an IkappaB kinase-independent, atypical NF-kappaB pathway that is mediated via the activation of p38 MAPK and CK2.

Differential roles for Nrf2 and AP-1 in upregulation of HO-1 expression by arsenite in murine embryonic fibroblasts

Heme oxygenase-1 (HO-1) is markedly upregulated by sodium arsenite and previous studies implicated the transcriptional enhancers Nrf2 and AP-1 in arsenite-induced ho-1 gene expression in murine cells. To further evaluate the role of Nrf2 and its signalling pathway in the induction of HO-1 in response to low levels of arsenite, this paper studied wild-type and Nrf2-deficient murine embryonic fibroblasts. It was found that Nrf2 plays a crucial role in the early activation of ho-1 transcription and that increased Nrf2 levels returned to basal levels within 24 h. In Nrf2−/− cells, ho-1 gene activation increased gradually and HO-1 protein levels were approximately half of those attained in Nrf2+/+ cells. The tyrosine kinase inhibitor genistein and JNK inhibitor SP600125 significantly attenuated arsenite induced increases in ho-1 mRNA levels in Nrf2 deficient cells but had negligible effects on Nrf2 activation, suggesting tyrosine kinase/JNK/c-Jun plays a key role in the HO-1 upregulation via AP-1.

Diallyl sulfide induces heme oxygenase-1 through MAPK pathway

Diallyl sulfide (DAS), is protective against chemically induced heptotoxicity, mutagenesis, and carcinogenesis. The mechanism of its protective effects is not fully understood. In this study, we found that DAS can induce the expression of heme oxygenase-1 (HO-1), which plays a critical role in the cell defense system against oxidative stress. DAS causes a dose- and time-dependent increase of HO-1 protein and mRNA level without toxicity in HepG2 cells. DAS-induced HO-1 protein expression is dependent on newly synthesized mRNA and newly synthesized protein. DAS increases Nrf2 protein expression, nuclear translocation, and DNA-binding activity. The MAP kinase ERK is activated by DAS. Both ERK and p38 pathways play an important role in DAS-induced Nrf2 nuclear translocation and ho-1 gene activation. DAS stimulates a transient increase of reactive oxygen species (ROS). N-Acetyl-cysteine blocked this increase of ROS production as well as DAS-induced ERK activation, Nrf2 protein expression and nuclear translocation, and ho-1 gene activation. The increase in HO-1 produced by DAS protected the HepG2 cells against toxicity by hydrogen peroxide or arachidonic acid. These results suggest that DAS induces ho-1 through production of ROS, and Nrf2 and MAPK (ERK and p38) mediate this induction. Induction of ho-1 may play a role in the protective effects of DAS.

Transcriptional activation of HO-1 gene in mouse monocyte-macrophage cell line, RAW 264.7, by caffeic acid derivatives and ferulic acid derivatives.

Transcriptional activation of HO-1 gene in mouse monocyte-macrophage cell line, RAW 264.7, by caffeic acid derivatives and ferulic acid derivatives.

Degradation of Transcription Factor Nrf2 via the Ubiquitin-Proteasome Pathway and Stabilization by Cadmium

Nrf2 mediates inducer-dependent activation of the heme oxygenase-1 (HO-1) gene (Alam, J., Stewart, D., Touchard, C., Boinapally, S., Choi, A. M., and Cook, J. L. (1999) J. Biol. Chem. 274, 26071-26078), but the mechanism by which HO-1 inducers regulate Nrf2 function is not known. Treatment of mouse hepatoma (Hepa) cells with 50 microm CdCl(2) increased the amount of Nrf2 protein in a time-dependent manner; induction was observed within 30 min, prior to the accumulation of HO-1 mRNA. Cadmium did not significantly affect the steady-state level of Nrf2 mRNA or the initial rate of Nrf2 protein synthesis but increased the half-life of Nrf2 from approximately 13 to 100 min. Proteasome inhibitors, but not other protease inhibitors, enhanced the expression of Nrf2, and ubiquitinylated Nrf2 was detected after proteasome inhibition. Cycloheximide inhibited cadmium-stimulated Nrf2 expression and DNA binding activity and attenuated HO-1 mRNA accumulation. Conversely, proteasome inhibitors enhanced HO-1 mRNA and protein accumulation by a Nrf2-dependent mechanism. Together, these results indicate that Nrf2 is targeted for rapid degradation by the ubiquitin-proteasome pathway and that cadmium delays the rate of Nrf2 degradation leading to ho-1 gene activation.

TLR4 mediates LPS-induced HO-1 expression in mouse liver: role of TNF-alpha and IL-1beta.

Heme oxygenase (HO)-1 catalyzes the conversion of heme to biliverdin, iron and carbon monoxide. HO-1 is induced by many stimuli including heme, Hb, heat stress,lipopolysaccharide (LPS) and cytokines. Previous studies demonstrated that LPS induced HO-1 gene activation and HO-1 expression in liver. However, the mechanisms of LPS-induced HO-1 expression in liver remain unknown. The effect of toll-like receptor-4 (TLR4) on LPS-induced liver HO-1 expression and the role of TNF-alpha and IL-1beta in this condition were determined. HO-1 expression was determined by immunofluorescent staining and immunoblotting. Double immunofluorescent staining was performed to determine the cell type of HO-1 expression in liver. A low dose of LPS significantly increased HO-1 expression in the liver which was localized in Kupffer cells only. Furthermore, HO-1 expression was enhanced by three doses of LPS. HO-1 expression was significantly inhibited in the liver of TLR4 mutant mice. While the liver HO-1 expression in TNF KO mice was much lower than that in C57 mice following the same LPS treatment, IL-1beta KO had a slight influence on liver HO-1 expression following LPS treatment. The present results confirm that macrophages are the major source of HO-1 in the liver induced by LPS. This study demonstrates that TLR4 plays a dominant role in mediating HO-1 expression following LPS. LPS-induced HO-1 expression is mainly mediated by endogenous TNF-alpha, but only partially by endogenous IL-1beta.

TGF-beta1 stimulates HO-1 via the p38 mitogen-activated protein kinase in A549 pulmonary epithelial cells.

In lung injury and progressive lung diseases, the multifunctional cytokine transforming growth factor-beta1 (TGF-beta1) modulates inflammatory responses and wound repair. Heme oxygenase-1 (HO-1) is a stress-inducible protein that has been demonstrated to confer cytoprotection against oxidative injury and provide a vital function in maintaining tissue homeostasis. Here we report that TGF-beta1 is a potent inducer of HO-1 and examined the signaling pathway by which TGF-beta1 regulates HO-1 expression in human lung epithelial cells (A549). TGF-beta1 (1-5 ng/ml) treatment resulted in a marked time-dependent induction of HO-1 mRNA in A549 cells, followed by corresponding increases in HO-1 protein and HO enzymatic activity. Actinomycin D and cycloheximide inhibited TGF-beta1-responsive HO-1 mRNA expression, indicating a requirement for transcription and de novo protein synthesis. Furthermore, TGF-beta1 rapidly activated the p38 mitogen-activated protein kinase (p38 MAPK) pathway in A549 cells. A chemical inhibitor of p38 MAPK (SB-203580) abolished TGF-beta1-inducible HO-1 mRNA expression. Both SB-203580 and expression of a dominant-negative mutant of p38 MAPK inhibited TGF-beta1-induced ho-1 gene activation, as assayed by luciferase activity of an ho-1 enhancer/luciferase fusion construct (pMHO1luc-33+SX2). These studies demonstrate the critical intermediacy of the p38 MAPK pathway in the regulation of HO-1 expression by TGF-beta1.

Multiple basic-leucine zipper proteins regulate induction of the mouse heme oxygenase-1 gene by arsenite

The mechanism of heme oxygenase-1 ( ho-1) gene activation by arsenite was examined. Arsenite-stimulated expression of a ho-1 promoter/luciferase chimera in a dose-dependent manner in mouse hepatoma (Hepa) cells. Mutation analyses identified the arsenite-responsive sequence as the stress-response element (StRE), which resembles the binding sites for the AP-1 superfamily of basic-leucine zipper factors. In electrophoretic mobility shift assays, up to seven specific StRE–protein complexes were routinely detected using extracts from untreated Hepa cells whereas a single complex was typically observed after treatment with arsenite. Antibody “supershift” experiments identified Nrf2, JunD, and ATF3 in control complexes and the amount of these factors increased significantly in the arsenite-induced complex. MafG, ATF2, FosB, and JunB were also detected in the arsenite complex. Activation of a StRE-dependent luciferase gene by arsenite was inhibited to varying degrees by dominant-negative mutants of Nrf2, MafK, c-Fos, and CREB but most strongly with the latter. Together, these results implicate multiple basic-leucine zipper transcription factors in ho-1 gene activation by arsenite.

Activation of the mouse heme oxygenase-1 gene by 15-deoxy-Delta(12,14)-prostaglandin J(2) is mediated by the stress response elements and transcription factor Nrf2.

The mechanism of heme oxygenase-1 (ho-1) gene activation by 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) was examined. 15d-PGJ(2) stimulated expression of HO-1 mRNA and protein and of a mouse ho-1 gene promoter/luciferase fusion construct (HO15luc) in a dose-dependent manner in mouse hepatoma (Hepa) cells. HO15luc expression was not effected by troglitazone, a peroxisome proliferator-activated receptor-gamma (PPAR-gamma) ligand, but induction by 15d-PGJ(2) was abrogated by the antioxidant N-acetylcysteine. The primary 15d-PGJ(2) responsive sequences were localized to a 5' distal enhancer (E1) and identified as the stress-response element, previously shown to mediate ho-1 activation by several agents, including heme and heavy metals. Treatment of Hepa cells with 15d-PGJ(2) stimulated stress-response element-binding activity as judged by electrophoretic mobility shift assays. Antibody "supershift" experiments identified NF-E2 related factor 2 (Nrf2), but not Fos, Jun, or activating transcription factor/cyclic AMP response element binding protein transcription factors, within the 15d-PGJ(2)-induced complexes. Similarly, a dominant-negative mutant of Nrf2, but not of c-Jun or c-Fos, abrogated 15d-PGJ(2)-stimulated E1 transcription activity. Finally, prior induction of HO-1 in RAW264.7 mouse macrophages by 15d-PGJ(2) attenuated cell death caused by diesel exhaust particle extracts. These results demonstrate that induction of mouse HO-1 expression by 15d-PGJ(2) is independent of PPAR-gamma but dependent on oxidative stress, is regulated by the oxidative stress-activated transcription factor Nrf2, and provides cytoprotective activity.

Cobalt Induces Heme Oxygenase-1 Expression by a Hypoxia-inducible Factor-independent Mechanism in Chinese Hamster Ovary Cells: REGULATION BY Nrf2 AND MafG TRANSCRIPTION FACTORS

We have shown previously that activation of the heme oxygenase-1 (ho-1) gene by hypoxia in aortic smooth muscle cells is mediated by hypoxia-inducible factor-1 (HIF-1). In mutant (Ka13) Chinese hamster ovary cells lacking HIF activity, accumulation of ho-1 mRNA in response to hypoxia and the hypoxia-mimetic CoCl(2) was similar to that observed in wild type (K1) cells. These results support the existence of HIF-dependent and HIF-independent mechanisms for ho-1 gene activation by hypoxia and CoCl(2). In Ka13 cells, CoCl(2) stimulated expression of a luciferase reporter gene under the control of a 15-kilobase pair mouse ho-1 promoter (pHO15luc). Mutation analyses identified the cobalt-responsive sequences as the stress-response elements (StREs). In electrophoretic mobility shift assays, two specific StRE-protein complexes were observed using extracts from Ka13 cells. In response to cobalt, the level of the slower migrating complex X increased, whereas that of complex Y decreased, in a time-dependent manner. Members of the AP-1 superfamily of basic-leucine zipper factors bind to the StRE. Antibody supershift electrophoretic mobility shift assays did not detect Jun, Fos, or ATF/CREB proteins but identified Nrf2 and the small Maf protein, MafG, as components of complex X. Furthermore, dominant-negative mutants of Nrf2 and small Maf, but not of other bZIP factors, attenuated cobalt-mediated gene activation. Additional experiments demonstrated that induction by cobalt does not result from increased expression of MafG or regulated nuclear translocation of Nrf2 but is dependent on cellular oxidative stress. Unlike cobalt, hypoxia did not stimulate pHO15luc expression and did not increase StRE binding activity, indicating distinct mechanisms for ho-1 gene activation by cobalt and hypoxia in Chinese hamster ovary cells.

Mechanism of Heme Oxygenase-1 Gene Activation by Cadmium in MCF-7 Mammary Epithelial Cells: ROLE OF p38 KINASE AND Nrf2 TRANSCRIPTION FACTOR

The mouse heme oxygenase-1 (HO-1) gene, ho-1, contains two inducible enhancers, E1 and E2. Of several cell lines tested, induction of an E1/luciferase fusion construct, pE1-luc, by CdCl(2) is most pronounced in MCF-7 cells. In these cells, E1, but not E2, is necessary and sufficient for ho-1 gene activation. Exposure of MCF-7 cells to 10 micrometer CdCl(2) stimulates phosphorylation of ERK, JNK, and p38 mitogen-activated protein kinases, implicating one or more of these signaling pathways in ho-1 gene induction. SB203580, an inhibitor of p38, diminishes cadmium-stimulated pE1-luc expression and HO-1 mRNA levels by up to 70-80%. PD098059, an ERK pathway inhibitor, does not affect HO-1 mRNA induction at the highest concentration (40 micrometer) tested. Similarly, co-expression of a dominant-negative mutant of p38alpha, but not of ERK1, ERK2, JNK1, or JNK2, reduces basal and cadmium-induced pE1-luc activity. E1 contains binding sites for the activator protein-1 (Fos/Jun), Cap'n'Collar/basic leucine zipper (CNC-bZIP), and CCAAT/enhancer-binding protein (C/EBP) families of transcription factors. A dominant-negative mutant of Nrf2 (a CNC-bZIP member), but not of c-Jun or C/EBPbeta, inhibits pE1-luc activation by cadmium. Induction of the endogenous ho-1 gene is also inhibited by the Nrf2 mutant. Mutations of E1 that inhibit cadmium inducibility also suppress the trans-activation and DNA binding activities of Nrf2, and SB203580, but not PD098059, attenuates Nrf2-mediated trans-activation of pE1-luc. Taken together, these results indicate that cadmium induces ho-1 gene expression via sequential activation of the p38 kinase pathway and Nrf2.

Heme Oxygenase as a Shock Protein.

Heme oxygenase (HO : EC 1.14.99.3) is a key enzyme for heme catabolism and catalyzes the oxidative degradation of heme to form biliverdin IXa, an immediate precursor of bilirubin. The HO activity can be induced by treatment with hemin, the substrate itself, as well as with various other non-heme stress inducers. Recently, it has been shown that HO is a major 32 kDa stress protein inducible by treatments with heavy metals, heat shock, or acute phase inducers. The induction of HO is considered to be a member of the defense system against environmental hazards, because bilirubin is one of the antioxidants. Among two isozymes of HO, i.e., HO-1 and HO-2, only HO-1 is inducible. In the present article, therefore, we described the molecular mechanisms of HO-1 gene activation by environmental hazards. We also discussed the HO-1 gene regulation during differentiation of erythrocytes and monocytes.