Heat shock induction of heme oxygenase mRNA in human Hep 3B hepatoma cells

Morpho-functional effects of heat stress on the gills of Antarctic T. bernacchii and C. hamatus

The effect of increasing ocean water temperature on morpho-functional traits of Antarctic marine species is under intense attention. In this work, we evaluated the effects of acute heat stress on the gills of the Antarctic haemoglobinless Chionodraco hamatus and the red blooded Trematomus bernacchii in terms of morphology, heat shock response, antioxidant defense and NOS/NO system. We showed in both species that the exposure to high temperature (4 °C) induced structural alterations, such as epithelial lifting and oedema of secondary lamellae. By immunolocalization we also observed that HSP-90, HSP-70, Xantine Oxidase, Heme Oxigenase and NOS are expressed in both species under control conditions. After heat stress the signals increase in C. hamatus being absent/or reduced in T. bernacchii. Our preliminary results suggest a specie-specific morpho-functional response of the gills of the two Antarctic teleosts to heat stress.

HMOX1 gene promoter alleles and high HO-1 levels are associated with severe malaria in Gambian children

Heme oxygenase 1 (HO-1) is an essential enzyme induced by heme and multiple stimuli associated with critical illness. In humans, polymorphisms in the HMOX1 gene promoter may influence the magnitude of HO-1 expression. In many diseases including murine malaria, HO-1 induction produces protective anti-inflammatory effects, but observations from patients suggest these may be limited to a narrow range of HO-1 induction, prompting us to investigate the role of HO-1 in malaria infection. In 307 Gambian children with either severe or uncomplicated P. falciparum malaria, we characterized the associations of HMOX1 promoter polymorphisms, HMOX1 mRNA inducibility, HO-1 protein levels in leucocytes (flow cytometry), and plasma (ELISA) with disease severity. The (GT)(n) repeat polymorphism in the HMOX1 promoter was associated with HMOX1 mRNA expression in white blood cells in vitro, and with severe disease and death, while high HO-1 levels were associated with severe disease. Neutrophils were the main HO-1-expressing cells in peripheral blood, and HMOX1 mRNA expression was upregulated by heme-moieties of lysed erythrocytes. We provide mechanistic evidence that induction of HMOX1 expression in neutrophils potentiates the respiratory burst, and propose this may be part of the causal pathway explaining the association between short (GT)(n) repeats and increased disease severity in malaria and other critical illnesses. Our findings suggest a genetic predisposition to higher levels of HO-1 is associated with severe illness, and enhances the neutrophil burst leading to oxidative damage of endothelial cells. These add important information to the discussion about possible therapeutic manipulation of HO-1 in critically ill patients.

HO-1 polymorphism as a genetic determinant behind the malaria resistance afforded by haemolytic disorders

Malaria affects thousands of people around the world representing a critical issue regarding health policies in tropical countries. Similarly, also haemolytic diseases such as sickle cell disease and thalassemias are a concern in different parts of the globe. It is well established that haemolytic diseases, such as sickle cell disease (SCD) and thalassemias, represent a resistance factor to malaria, which explains the high frequencies of such genetic variants in malaria endemic areas. In this context, it has been shown that the rate limiting enzyme heme oxygenase I (HO-1), responsible for the catabolism of the free heme in the body, is an important resistance factor in malaria and is also important in the physiopathology of haemolytic diseases. Here, we suggest that allelic variants of HO-1, which display significant differences in terms of protein expression, have been selected in endemic malaria areas since the HO-1 enzyme can enhance the protection against malaria conferred by haemolytic diseases This protection apply mainly in what concerns protection against severe malaria forms. Therefore, HO-1 genotyping would be fundamental to determine resistance of a given individual to lethal forms of malaria as well as to common clinical complications typical to haemolytic diseases and would be helpful in the establishment of public health politics.

Regulation of haeme oxygenase-1 for treatment of neuroinflammation and brain disorders

Injury to the CNS elicits a host defense reaction that utilizes astrocytes, microglia, neurons and oligodendrocytes. Neuroinflammation is a major host defense mechanism designed to restore normal structure and function after CNS insult, but like other forms of inflammation, chronic neuroinflammation may contribute to pathogenesis. The inducible haeme oxygenase isoform, haeme oxygenase-1 (HO-1), is a phase 2 enzyme upregulated in response to electrophilic xenobiotics, oxidative stress, cellular injury and disease. There is emerging evidence that HO-1 expression helps mediate the resolution of inflammation, including neuroinflammation. Whether this is solely because of the catabolism of haeme or includes additional mechanisms is unclear. This review provides a brief background on the molecular biology and biochemistry of haeme oxygenases and the actions of haeme, bilirubin, iron and carbon monoxide in the CNS. It then presents our current state of knowledge regarding HO-1 expression in the CNS, regulation of HO-1 induction in neural cells and discusses the prospect of pharmacological manipulation of HO-1 as therapy for CNS disorders. Because of recognized species and cellular differences in HO-1 regulation, a major objective of this review is to draw attention to areas where gaps exist in the experimental record regarding regulation of HO-1 in neural cells. The results indicate the HO-1 system to be an important therapeutic target in CNS disorders, but our understanding of HO-1 expression in human neural cells is severely lacking.

Pharmacological and clinical aspects of heme oxygenase

This review is intended to stimulate interest in the effect of increased expression of heme oxygenase-1 (HO-1) protein and increased levels of HO activity on normal and pathological states. The HO system includes the heme catabolic pathway, comprising HO and biliverdin reductase, and the products of heme degradation, carbon monoxide (CO), iron, and biliverdin/bilirubin. The role of the HO system in diabetes, inflammation, heart disease, hypertension, neurological disorders, transplantation, endotoxemia and other pathologies is a burgeoning area of research. This review focuses on the clinical potential of increased levels of HO-1 protein and HO activity to ameliorate tissue injury. The use of pharmacological and genetic probes to manipulate HO, leading to new insights into the complex relationship of the HO system with biological and pathological phenomena under investigation, is reviewed. This information is critical in both drug development and the implementation of clinical approaches to moderate and to alleviate the numerous chronic disorders in humans affected by perturbations in the HO system.

How many transcription factors does it take to turn on the heme oxygenase-1 gene?

The ability to communicate with the environment and respond to changes--particularly those of an adverse nature--within that environment is critical for cell function and survival. A key component of the overall cellular stress response includes adjustments in the gene expression program in favor of proteins that manifest activities capable of frustrating and eventually eliminating the molecular constituents of the stress condition. One protein providing such cytoprotective activity is heme oxygenase-1 (HO-1), an enzyme that catalyzes the rate-limiting reaction in heme catabolism (i.e., the oxidative cleavage of b-type heme molecules to yield equimolar quantities of biliverdin IXalpha, carbon monoxide, and iron). Because of the potent antioxidant, anti-inflammatory, and signaling properties of the reaction products, the HO-1 gene (hmox1) is frequently activated under a variety of cellular stress conditions. Cells use multiple signaling pathways and transcription factors to fine-tune their response to a specific circumstance. Among these factors, members of the heat-shock factor, nuclear factor-kappaB, nuclear factor-erythroid 2, and activator protein-1 families are arguably the most important regulators of the cellular stress response in vertebrates. Although there is functional overlap between individual families, each broadly regulates different aspects of the cellular stress response and thus, with some exceptions, modulates the expression of different sets of targets genes. To the best of our knowledge, hmox1 is unique in that it is proposed to be directly regulated by all four of these stress-responsive transcription factors. In this article we provide a review and analysis of the data supporting this proposition.

Up-regulation of the 31 kDa dehydroascorbate reductase in the modified skeletal muscle cell (nurse cell) during Trichinella spp. infection

Ascorbic acid (AA) is an important factor of defence against oxidative stress. AA is maintained in the reduced functional form by glutathione (GSH)-dependent dehydroascorbate (DHA) reducing enzymes, including the cytosolic glutaredoxin, the microsomal protein disulphide isomerase, and a DHA reductase of 31 kDa, hereafter referred to as DHAR, purified from rat liver cytosol and human red cells. As these mechanisms have rarely been studied in parasites, we looked for the possible presence of this 31 kDa protein in Trichinella spiralis L(1) larvae. Biochemical data, immunoblot analysis and immunohistochemical studies suggested the absence of this protein within parasites at this stage. However, they possess a low DHA reducing ability, which is probably due to the presence of glutaredoxin. On the other hand, immunohistochemical studies performed in histological sections of muscle tissue from Trichinella-infected animals showed an increase in DHAR in the nurse cell (NC) of T. spiralis- and Trichinella britovi-infected animals, compared with the surrounding muscle fibres. This result was confirmed by immunoblot analysis, whereas no such increase was observed in Trichinella pseudospiralis-infected animals. In the modified skeletal muscle cell also haeme oxygenase 1 increased, as well as lipoperoxidised proteins. Both findings suggest an oxidative stress of the NC, which might be related to the intense inflammatory reaction which surrounds the NC-parasite complex. Another possibility to explain the increase in DHAR could be that the NC needs to recycle a substantial amount of AA to synthesise the collagen capsule.

Acute lead exposure induces renal haeme oxygenase-1 and decreases urinary Na+ excretion

The effects of acute lead exposure on renal function, lipid peroxidation and the expression of haeme oxygenase (HO) in rat kidney were determined. A single injection of lead acetate (50 mg Pb/kg) was given to rats. Changes in renal function, characterized by a significant reduction in the Na+ excretion was observed six hours after Pb exposure; this effect persisted for 24 hours. TBARS levels increased in kidney cortex 24 hours after Pb administration. In kidney cortex, Pb exposure affected the expression of HO-1, a renal protein associated with oxidative stress. HO-1 mRNA increased 2.3-fold, three hours after Pb administration and remained increased for six, 12 and 24 hours. HO enzymatic activity and HO-1 protein increased six and three hours after Pb administration, respectively, and remained increased at 24 hours. HO inhibition by tin-protoporphyrin, potentiated Pb-induced increase in TBARS and prevented the Pb-induced reduction in Na+ excretion. Our data suggest that Pb may be acting through the generation of oxidant products and induction of HO.

Modulation of cGMP by human HO-1 retrovirus gene transfer in pulmonary microvessel endothelial cells

Carbon monoxide (CO) stimulates guanylate cyclase (GC) and increases guanosine 3',5'-cyclic monophosphate (cGMP) levels. We transfected rat-lung pulmonary endothelial cells with a retrovirus-mediated human heme oxygenase (hHO)-1 gene. Pulmonary cells that expressed hHO-1 exhibited a fourfold increase in HO activity associated with decreases in the steady-state levels of heme and cGMP without changes in soluble GC (sGC) and endothelial nitric oxide synthase (NOS) proteins or basal nitrite production. Heme elicited significant increases in CO production and intracellular cGMP levels in both pulmonary endothelial and pulmonary hHO-1-expressing cells. N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of NOS, significantly decreased cGMP levels in heme-treated pulmonary endothelial cells but not heme-treated hHO-1-expressing cells. In the presence of exogenous heme, CO and cGMP levels in hHO-1-expressing cells exceeded the corresponding levels in pulmonary endothelial cells. Acute exposure of endothelial cells to SnCl2, which is an inducer of HO-1, increased cGMP levels, whereas chronic exposure decreased heme and cGMP levels. These results indicate that prolonged overexpression of HO-1 ultimately decreases sGC activity by limiting the availability of cellular heme. Heme activates sGC and enhances cGMP levels via a mechanism that is largely insensitive to NOS inhibition.

Heme degradation and human disease: diversity is the soul of life

We all depend on molecular oxygen and heme for our life, as evident from the pigments in blood and daily wastes. About 80% of serum bilirubin is derived from hemoglobin of senescent erythrocytes, which have finished their mission of 120 days and have been phagocytized by macrophages in the reticuloendothelial system. Here we present an overview of the heme degradation processes and relevant disorders by focusing on heme oxygenase-1 (HO-1), a key enzyme in heme catabolism. HO-1 cleaves the porphyrin macrocycle of heme at the expense of molecular oxygen to release a linear tetrapyrrole biliverdin, carbon monoxide, and ferrous iron; biliverdin is rapidly reduced to bilirubin. Bilirubin is transported to the liver (hepatocytes), conjugated with glucuronic acid by bilirubin UDP-glucuronosyltransferase, and excreted into bile. Genetic diversity, a strategy in the host defense, is seen in the human ho-1 and UDP-glucuronosyltransferase genes. Moreover, striking interspecies variations are noted in the regulation of HO-1 expression by hypoxia, heat shock, or interferon-gamma, each of which mainly represses HO-1 expression in human cells. Implications of such a variety are discussed in relevance to the pathogenesis of severe malaria caused by Plasmodium falciparum, the most ancient foe of humans.

Lead, chemical porphyria, and heme as a biological mediator

One of the most well-characterized symptoms of lead poisoning is porphyria. The biochemical signs of lead intoxication related to porphyria are delta-aminolevulinic aciduria, coproporphyrinuria, and accumulation of free and zinc protoporphyrin in erythrocytes. From the 1970s to the early 80s, almost all of the enzymes in the heme pathway had been purified and characterized, and it was demonstrated that delta-aminolevulinic aciduria is due to inhibition of delta-aminolevulinate dehydratase by lead. Lead also inhibits purified ferrochelatase; however, the magnitude of inhibition was essentially nil even under pathological conditions. Further study proved the disturbance of iron-reducing activity by moderate lead exposure. Far different from these two enzymes, lead failed to inhibit purified coproporphyrinogen oxidase, i.e., the mechanism of coproporphyrinuria has not yet been understood. During the 80s to the 90s, the effects of environmental hazards including lead were elucidated through stress proteins, indicating the induction of some heme pathway enzymes as stress proteins. At that time, gene environment interaction was another focus of toxicology, since gene carriers of porphyrias are considered to be a high-risk group to chemical pollutants. Toxicological studies from the 70s to the 90s focused on the direct effect of hazards on biological molecules, such as the heme pathway enzymes, and many environmental pollutants were proved to affect cytosolic heme. Recently, we demonstrated the mechanism of the heme-controlled transcription system, which suggests that the indirect effects of environmental hazards are also important for elucidating toxicity, i.e., the hazards can affect cell functions through such biological mediators as regulatory heme. It is, therefore, probable that toxicology in the future will focus on biological systems such as gene regulation and signal transduction systems.

Regulation of cyclooxygenase by the heme-heme oxygenase system in microvessel endothelial cells

Heme oxygenase (HO) is a microsomal enzyme that oxidatively cleaves heme to form biliverdin, with the release of iron and carbon monoxide (CO). HO not only controls the availability of heme for the synthesis of heme proteins but also is responsible for the generation of CO, which binds to the heme moiety of heme proteins thus affecting their enzymatic activity. Cyclooxygenase (COX) is a heme protein that catalyzes the conversion of arachidonic acid to prostaglandin H(2), the precursor of prostanoids that participate in the regulation of vascular function. The goal of the present study was to determine whether the heme-HO system regulates COX enzyme expression and activity in vascular endothelial cells. Endothelial cells stably transfected with the human HO-1 gene exhibited a severalfold increase in human HO-1 mRNA levels, which was accompanied by an increase in HO activity and a marked decrease in prostaglandin (PG) E(2) and 6-keto-PGF(1alpha) levels. Exposure of cells to CoCl(2), an inducer of HO-1 gene expression, resulted in increases in HO-1 protein levels and HO activity. The increase in HO activity was associated with a subsequent decrease in COX activity, which returned to normal levels following normalization of HO activity. The addition of heme resulted in an increase in COX activity with an increase in PGE(2) and 6-keto-PGF(1alpha) levels. The degree of HO-1 expression and, consequently, the level of cellular heme, were directly related to COX activity. These results demonstrate that the heme-HO system can function as a cellular regulator of the expression of vascular COX, thus influencing the generation of prostanoids, PGE(2) and PGI(2), known to play a role in vascular homeostasis.

Regulation of human heme oxygenase in endothelial cells by using sense and antisense retroviral constructs

Our objective was to determine whether overexpression and underexpression of human heme oxygenase (HHO)-1 could be controlled on a long-term basis by introduction of the HO-1 gene in sense (S) and antisense (AS) orientation with an appropriate vector into endothelial cells. Retroviral vector (LXSN) containing viral long terminal repeat promoter-driven human HO-1 S (LSN-HHO-1) and LXSN vectors containing HHO-1 promoter (HOP)-controlled HHO-1 S and AS (LSN-HOP-HHO-1 and LSN-HOP-HHO-1-AS) sequences were constructed and used to transfect rat lung microvessel endothelial cells (RLMV cells) and human dermal microvessel endothelial cells (HMEC-1 cells). RLMV cells transduced with HHO-1 S expressed human HO-1 mRNA and HO-1 protein associated with elevation in total HO activity compared with nontransduced cells. Vector-mediated expression of HHO-1 S or AS under control of HOP resulted in effective production of HO-1 or blocked induction of endogenous human HO-1 in HMEC-1 cells, respectively. Overexpression of HO-1 AS was associated with a long-term decrease (45%) of endogenous HO-1 protein and an increase (167%) in unmetabolized exogenous heme in HMEC-1 cells. Carbon monoxide (CO) production in HO-1 S- or AS-transduced HMEC-1 cells after heme treatment was increased (159%) or decreased (50%), respectively, compared with nontransduced cells. HO-2 protein levels did not change. These findings demonstrate that HHO-1 S and AS retroviral constructs are functional in enhancing and reducing HO activity, respectively, and thus can be used to regulate cellular heme levels, the activity of heme-dependent enzymes, and the rate of heme catabolism to CO and bilirubin.

Heme oxygenase-1 expression in oral squamous cell carcinoma as involved in lymph node metastasis

Thirty-eight oral squamous cell carcinomas (SCCs) were semi-quantitatively analyzed by immunohistochemical staining, and the relation between heme oxygenase-1 (HO-1) expression and the clinical status were correlated. High immunostaining of HO-1 was detected in lymph node metastasis negative groups (P = 0.0018) and in well-differentiated SCCs (P = 0.0016). There were no significant correlations between heme oxygenase-1 expression and other factors, such as size of the tumor, staging, age and sex. These findings further support the proposition that high heme oxygenase-1 expression in oral SCCs can be useful in identifying patients at low risk of lymph node metastasis.

Nitrosative and oxidative stress induced heme oxygenase-1 accumulation in rat mesangial cells

The formation of nitric oxide (NO.) and superoxide (O2-) promotes rat mesangial cell death. Apoptotic death is characterized by DNA fragmentation, caspase-3 activation and concomitant poly(ADPribose) polymerase cleavage, as well as accumulation of the tumor suppressor protein p53. In close association with apoptotic parameters we noticed upregulation of heme oxygenase by the NO donor S-nitrosoglutathione (GSNO) and the redox cycler 2,3-dimethoxy-1,4-naphthoquinone (DMNQ) in a time- and concentration-dependent manner. In response to the NO. donor, heme oxygenase-1 expression was more easily obtained than initiation of apoptosis. Radical (NO./O2-) cogeneration abrogated DNA fragmentation, suppressed caspase activation and lowered p53 accumulation, thereby promoting cell survival of mesangial cells. In contrast, heme oxygenase-1 expression remained elevated under conditions of GSNO/DMNQ coadministration. Conclusively, heme oxygenase-1 is a stress marker for both nitrosative and oxidative stress. Accumulation of heme oxygenase-1 is found under conditions of both, apoptotic cell death and cell survival, thereby questioning a specific cytoprotective role of heme oxygenase-1 under conditions of NO. and/or O2- formation in rat mesangial cells.

Regulation of expression of the human heme oxygenase-1 gene in transfected chick embryo liver cell cultures

Induction of heme oxygenase (HO) has been proposed as a protective cellular mechanism against oxidative damage. In previous work (Tyrrell et al., Carcinogenesis [1993] 14, 761-765), portions of the 5' promoter region of the human HO-1 gene linked to the reporter gene chloramphenicol acetyl transferase (CAT), had been transiently expressed in HeLa cells. To extend the study of human HO gene expression into primary liver cells, these reporter gene fusion constructs, containing 121 or 1416 base pairs of the untranscribed 5'-upstream sequences of the human HO-1 gene, were used along with pSV beta-Gal plasmid to dually transfect primary cultures of chick embryo liver cells (CELC). The transfected cells were treated with selected metals, heme, phorbol ester, and chemical agents that produce oxidative stress (H2O2 or sodium arsenite). Reporter gene activities were measured 18-20 h later. Our major findings are: (1) these HO-CAT constructs were expressed in CELC; (2) unlike HeLa cells, the expression of CAT was detected in CELC without the need for the SV40 enhancer; (3) sodium arsenite and cobalt chloride induced the expression of the HO-CAT constructs whereas heme had no effect on or decreased CAT expression for all of the transfected constructs; (4) study of endogenous chick HO-1 gene expression in CELC showed that HO-1 responded to sodium arsenite treatment in a dose-dependent fashion, and the response was rapid and transient. We conclude that, in chick liver cell cultures, induction of the HO-1 gene by heme is fundamentally different from that produced by transition metals or sodium arsenite. Furthermore, the results suggest that expression of the HO-1 gene is highly conserved across species.

Heme oxygenase induction with attenuation of experimentally induced corneal inflammation

Heme oxygenase (HO), by catabolizing heme to bile pigments, down-regulates cellular levels of heme and hemeproteins; certain of the latter, i.e. cytochrome P450s, generate pro-inflammatory products from endogenous substrates. Two HO isozymes, the products of distinct genes, have been described; HO-1 is the inducible one, whereas HO-2 is believed to be constitutively expressed. We studied the inducing effects of several metal compounds [CoCl2, SnCl2, ZnCl2, heme, and cobalt protoporphyrin (CoPP)] on HO-1 mRNA content and enzyme activity in cultures of rabbit corneal epithelial (RCE) cells; these metal compounds are known to induce HO in other tissues. Additionally, we studied HO-1 expression in an experimental model of ocular inflammation produced in rabbit corneas by extended contact lens wear, and the relation of HO expression to the induced inflammatory process. SnCl2 added to RCE cells in vitro produced marked time- and concentration-dependent increases in HO-1 mRNA and HO-1 enzyme activity; CoCl2, ZnCl2, and CoPP were inducers of HO as well, though to a lesser degree than SnCl2. Corneas treated for 6 days with contact lenses impregnated with SnCl2 displayed substantially less corneal inflammation, swelling, and new vessel invasion than did controls; attenuation of ocular inflammation was paralleled by SnCl2-induced increases in HO mRNA and HO activity in corneal epithelial cells from treated eyes. It is suggested that amelioration of the inflammatory response produced by extended contact lens wear is due, in part, to the induction of high levels of HO-1 activity by SnCl2, which results in diminished production of pro-inflammatory mediators generated through heme-dependent metabolic processes. Regulation of HO activity in this manner may have clinical applications.

Mechanism of induction of heme oxygenase by metalloporphyrins in primary chick embryo liver cells: evidence against a stress-mediated response

Heme oxygenase catalyzes the first and rate-controlling step in heme catabolism. One of the two forms of heme oxygenase (heme oxygenase-1) has been shown to be increased by heme, metals, and in some systems, by certain environmental stresses. However, it remains uncertain whether heme induces hepatic heme oxygenase-1 by a general stress response, or a specific heme-dependent cellular response. The work communicated here explores this issue by examining possible mechanisms whereby heme and other metalloporphyrins induce heme oxygenase-1 in normal liver cells. Primary cultures of chick embryo liver cells were tested for their ability to increase heme oxygenase mRNA after exposure to selected metalloporphyrins (heme, chromium mesoporphyrin, cobalt protoporphyrin and manganese protoporphyrin). The ability of antioxidants to decrease metalloporphyrin-mediated induction of heme oxygenase-1 mRNA was also tested. Our results indicate that: 1) the increase in heme oxygenase-1 mRNA mediated by heme or other metalloporphyrins may involve a short-lived protein(s) since the increase was prevented by several inhibitors of protein synthesis; and 2) in normal liver cells, heme-dependent oxidative stress does not play a key role in the heme-mediated induction of heme oxygenase-1. We conclude that heme and other non-heme metalloporphyrins induce heme oxygenase-1 through a mechanism requiring protein synthesis, not because metalloporphyrins increase cellular oxidative or other stress.

Diminished heme oxygenase-1 mRNA expression in RPE cells from diabetic donors as quantitated by competitive RT/PCR

PURPOSE

The RPE is essential in the maintenance of retinal vasculature homeostasis, since increased cellular expression of heme oxygenase-1 (HO-1) has been implicated as a defense mechanism against oxidative stress. This study was done in an effort to determine the levels of the stress protein (32 kD), HO-1, in retinal pigment epithelium (RPE) cells obtained from diabetic and normal eyes.

METHODS

We measured the levels of HO-1 in the RPE from eight normal and six diabetic donor eyes. For comparison, HO-1 levels were assayed in RPE cells from four donor eyes with long-standing hypertension. Heme oxygenase-1 mRNA copy number was determined by competitive RT/PCR on various ex vivo samples and on RPE cultured from the same donors. Total RNA (1-200 ng) was reverse-transcribed and then amplified by PCR in the same tube as an internal standard obtained by deleting a 50 bp restriction site from the native HO-1 gene.

RESULTS

Relative to the RPE obtained from control donor eyes, RPE from diabetic donors exhibited significantly decreased levels of HO-1 mRNA. In contrast, no significant difference in the levels of HO-1 mRNA was observed in RPE samples derived from hypertensive donor eyes. The diabetic group showed a range of 340-450 HO-1 mRNA copies/ng of total RNA, as compared to 425-8,000 HO-1 mRNA copies/ng of total RNA in RPE from normal donors and 460-7605 copies/ ng in hypertensive donor eyes.

CONCLUSIONS

This study represents initial studies exploring the quantitative expression of heme oxygenase in the RPE human eyes. The decreased expression of HO-1, a stress/heat shock protein, may in the RPE contribute to the vulnerability of the neuroretina to significant metabolic alterations encountered in the diabetic state. This was a limited study; additional screening from different donor eyes will be done in order to establish the relationship between RPE, HO-1 expression and eye diseases in which oxidative stress is believed to be a determinant in the pathophysiology.

Quantitative measurement of heme oxygenase-1 in the human renal adenocarcinoma

Heme oxygenase (HO-1) is the rate-limiting enzyme in heme catabolism. HO-1, a stress protein, has been suggested to be involved in defense mechanisms against agents that may induce oxidative stress. It has been proposed that renal HO gene expression regulates important hemoprotein(s) such as cytochrome P450 and may be essential to maintain homeostasis in the kidney. Because accurate assessment of HO-1 mRNA in normal and disease states in kidney were not available due to the limited number of cells, we developed a system to quantitate human HO-1 mRNA in samples limited in cell number and/or mRNA copies. Total RNA from human kidney was used to establish this technique; it was reverse-transcribed and then amplified by polymerase chain reaction (PCR) in a tube also containing an internal standard obtained by deleting 50 bp from the original human HO-1 gene. This allowed us to use the same primers for both the sample and internal standard. After amplification, templates were resolved by acrylamide gel electrophoresis and quantitated either by densitometry or radioactivity counted from the bands excised from the gel. When the internal standard is present in the reaction mixture, the ratio of amplified sample vs. the standard template is proportional to the amount of sample RNA, and it is therefore possible to calculate the number of specific mRNA molecules. We have used this approach to quantitate the number of HO-1 mRNA molecules in adenocarcinoma cells. Results show that reverse transcription (RT)/PCR methods were able to determine the number of HO-1 mRNA copies in biopsy samples of human adenocarcinoma cells.

Dual role of heme oxygenase in epithelial cell injury: contrasting effects of short-term and long-term exposure to oxidant stress

This study examined the role of heme oxygenase (HO) in the acquisition of resistance to hydrogen peroxide (H2O2) and hemin toxicity by renal epithelial cells (BSC-1). BSC-1 cells adapted by long-term exposure to H2O2 exhibited a twofold increase in basal HO activity and expression of HO-1 mRNA as compared with their wild-type counterparts. Exposure of both adapted and wild-type BSC-1 cells to H2O2 induced HO-1 mRNA. When cells were exposed to H202 for 24 hours, cell viability was reduced; however, an inhibitor of HO activity, Zn 2,4-bis-glycol protoporphyrin IX, improved cell viability. In a similar manner, ZnDBG completely overcame the reduction in cell viability brought about by 1 hour of hemin treatment. In addition, cells preexposed to hemin for 24 hours maintained a high level of HO mRNA and acquired resistance to further challenge with H2O2. Hemin treatment per se was associated with a detectable reduction in BSC-1 cell viability; however, the effect of hemin was not additive to the cytotoxicity of hydrogen peroxide, suggesting a common pathway of cell injury. In conclusion, two interrelated stressors, H2O2 and hemin, produced a stimulation of HO-1, and this was associated with a reduction in the viability of BSC-1 cells. Long-term exposure (24 hours) to both stressors resulted in the acquisition of some resistance to a further acute challenge of oxidant stress in BSC-1 cells.

Transient induction of heme oxygenase after cortical stab wound injury

Heme oxygenase (HO) exists as two isoenzymes designated heme oxygenase-1 (HO-1) and heme oxygenase-2 (HO-2). HO-1 has been identified as a heat shock or stress protein and is inducible whereas HO-2 is largely refractory to induction. HO-2 is the predominant isoenzyme in normal brain and appears to have a predominantly neuronal distribution in cerebral cortex. Cortical stab wound injury resulted in HO-1 induction as determined by Western blot analysis. Immunohistochemical analysis suggested that induced HO-1 was largely restricted to reactive astrocytes and macrophage-like cells. Enhanced HO-1 immunoreactivity was observed in hypertrophied, GFAP+ reactive astrocytes near the wound margin as early as 12 h after injury. Very rarely were HO-1+ neurons observed and then only up to 6 h after stabbing. Maximal numbers of HO-1+ astrocytes were found 3 days after stabbing. Their numbers declined thereafter. By 5 days after stab injury few HO-1+ reactive astrocytes were observed although GFAP+ reactive astrocytes were still prominent near the wound margin. HO-1+ macrophage-like cells were initially observed between 1 and 3 days after injury and they persisted in the margin of the wound for at least 14 days. The proximity of HO-1+ cells to the wound margin suggests that factors associated with injury contribute to the regulation of HO-1 in injured cortex.

Localization of heme oxygenase in rat retina: effect of light adaptation

Heme oxygenase-2 isozyme is the predominant form of heme oxygenase in rat brain by western blot analysis. Heme oxygenase-1 isozyme is not induced by light adaptation in rat retina by western blot analysis. Immunocytochemistry localizes heme oxygenase-2 in three areas of the retina: the retinal pigment epithelium, inner segment and external nuclear layers of the rat retina. Ganglion cells and cell bodies of the internal nuclear layer of the retina and Müller cells were largely unstained for heme oxygenase-2. The localization of heme oxygenase-2 in the retina implies that its function is not associated with phototransduction. Also, light adaptation does not appear to induce heme oxygenase-1, a measure of oxidative injury.

Transfection of the human heme oxygenase gene into rabbit coronary microvessel endothelial cells: protective effect against heme and hemoglobin toxicity

Heme oxygenase (HO) is a stress protein and has been suggested to participate in defense mechanisms against agents that may induce oxidative injury such as metals, endotoxin, heme/hemoglobin, and various cytokines. Overexpression of HO in cells might therefore protect against oxidative stress produced by certain of these agents, specifically heme and hemoglobin, by catalyzing their degradation to bilirubin, which itself has antioxidant properties. We report here the successful in vitro transfection of rabbit coronary microvessel endothelial cells with a functioning gene encoding the human HO enzyme. A plasmid containing the cytomegalovirus promoter and the human HO cDNA complexed to cationic liposomes (Lipofectin) was used to transfect rabbit endothelial cells. Cells transfected with human HO exhibited an approximately 3.0-fold increase in enzyme activity and expressed a severalfold induction of human HO mRNA as compared with endogenous rabbit HO mRNA. Transfected and nontransfected cells expressed factor VIII antigen and exhibited similar acetylated low-density lipoprotein uptake (two important features that characterize endothelial cells) with > 85% of cells staining positive for each marker. Moreover, cells transfected with the human HO gene acquired substantial resistance to toxicity produced by exposure to recombinant hemoglobin and heme as compared with nontransfected cells. The protective effect of HO overexpression against heme/hemoglobin toxicity in endothelial cells shown in these studies provides direct evidence that the inductive response of human HO to such injurious stimuli represents an important tissue adaptive mechanism for moderating the severity of cell damage produced by these blood components.

Heat shock of human synovial and dermal fibroblasts induces delayed up-regulation of collagenase-gene expression

We investigated the effect of heat shock on the expression of the collagenase gene in normal human synovial and dermal fibroblasts. Heat shock (42-44 degrees C for 1 h) caused a marked increase in heat-shock protein 70 (HSP-70) mRNA levels, followed by a delayed increase in collagenase mRNA levels, in both cell types. Pretreatment with cycloheximide had no effect on the heat-shock-induced increase in HSP-70 mRNA expression, but abrogated the induction of collagenase mRNA during the recovery. To study the mechanisms of collagenase-gene induction by heat shock, the transcriptional activity of a collagenase-promoter-driven chloramphenicol acetyltransferase (CAT) reporter gene was examined in transient transfection experiments. Heat shock was followed by a > 2-fold increase in CAT activity driven by a 3.8 kb fragment of the collagenase promoter, or by a construct containing an AP-1 binding site. A mutation in the AP-1 binding site abolished the effect of heat shock. Electrophoretic-mobility-shift assays revealed a marked increase in DNA-binding activity specific for the AP-1 binding site in nuclear extracts prepared from synovial fibroblasts recovering from heat shock. These results indicate that heat shock causes a delayed increase in collagenase-gene expression in human fibroblasts, and suggests that this stimulation involves, at least in part, transcriptional activation through an AP-1 binding site. Heat shock appears to initiate a programme of cellular events resulting in collagenase-gene expression, and therefore may contribute to connective-tissue degradation in disease states.

Induction by prostaglandin A1 of haem oxygenase in myoblastic cells: an effect independent of expression of the 70 kDa heat shock protein

Prostaglandins of the A type (PGA) induce the synthesis of 70 kDa heat shock proteins (hsp70) in a large variety of mammalian cells. Induction of hsp70 has been associated with a cytoprotective effect of PGA1 after virus infection or thermal injury. In the present report we provide evidence that, in murine myoblasts, PGA1 is not able to induce hsp70 expression, whereas it increases the synthesis of the constitutive protein, hsc70, and dramatically induces the synthesis of a 32 kDa protein (p32). The p32 protein has been identified as haem oxygenase. PGA1 acts at the transcriptional level by inducing haem oxygenase mRNA synthesis, and the signal for induction appears to be associated with decreased intracellular GSH levels. Haem oxygenase, a low-molecular-mass stress protein induced in mammalian cells by oxidant stress, is known to be part of a general inducible antioxidant defence pathway. The fact that prostaglandin synthesis is stimulated in muscle during contraction and in the heart in response to ischaemia raises the possibility that induction of haem oxygenase by PGA in myoblasts could be part of a protective mechanisms in operation during stress and hypoxia.

Differential expression of heme oxygenase-1 in cultured cortical neurons and astrocytes determined by the aid of a new heme oxygenase antibody. Response to oxidative stress

Heme oxygenase exists as two isoenzymes designated heme oxygenase-1 (HO-1) and heme oxygenase-2 (HO-2). HO-2 is made constitutively in many cell types whereas HO-1 is a stress protein inducible by heat, heavy metals, ultraviolet irradiation, and oxidative stress. Recombinant rat HO-1 was expressed in bacteria and antiserum designated HO-1713 was raised against the purified protein. HO-1713 detected recombinant rat HO-1 and recombinant rat HO-2. In rat tissues it detected HO-1 and a second, unidentified band designated HO-L (heme oxygenase-like immunoreactivity) which was not HO-2. Cultured rat cortical neurons and forebrain astrocytes were exposed to hydrogen peroxide (0.14-0.7 micromolar for 30 or 60 min). Neurons which contained little detectable HO-1 and which were sensitive to hydrogen peroxide at the high end of the dose curve failed to induce HO-1 by Western blot analysis. In contrast, cultured rat forebrain astrocytes which contained HO-1 under normal culture conditions and which were resistant to injury by hydrogen peroxide, increased their content of immunoreactive HO-1 by 7-fold within 3 h after exposure. Our results support a protective role for HO-1 in oxidative injury and suggest that the relative inability of neurons to increase HO-1 after oxidative stress may contribute to their selective vulnerability vis-a-vis astrocytes. They also suggest that differential expression of heme oxygenase in studies utilizing CNS cultures may alter normal cell physiology and cell survival.

Nitric oxide and intracellular heme

Figure 2 depicts a working hypothesis for these results. Activation of .NO synthesis results in nitrogen oxide-induced loss of protein-bound heme from CYP proteins, which remain relatively intact. This heme liberation results in a decrease in heme synthesis (decreased ALAS) and an increase in heme degradation (increased HO). In addition, .NO synthesis results in direct inhibition of ferrochelatase, which further contributes to inhibition of heme synthesis. There also appears to be a mechanism to repair or resynthesize CYP after .NO synthesis is inhibited. Finally, a result of this effect may be protection against cellular injury, since increased HO is an important response against cellular injury from a variety of insults.

Identification of binding sites for transcription factors NF-kappa B and AP-2 in the promoter region of the human heme oxygenase 1 gene

Heme oxygenase (HO) is the rate-limiting enzyme in heme catabolism and its activity is induced by many agents, including its substrate heme, heavy metals, UV radiation, and other injurious oxidant conditions. We examined the presence of several regulatory elements in the promoter region of the human HO-1 gene which could possibly account for its induction in response to diverse agents or influences. Heme treatment increased both HO activity and HO-1 mRNA in the human erythroleukemic cell line K562. Electrophoretic mobility-shift assays of nuclear protein extracts from heme-treated and control cells with specific oligonucleotide probes containing binding sites for known transcription factors, including AP-1, AP-2, Sp1, NF-kappa B, CTF/NF1, TFIID, OKT1, and CREB, and oligonucleotides containing serum-, metal-, and glucocorticoid-responsive elements demonstrated a specific and marked increase in the NF-kappa B and AP-2 transcription factors and, to a lesser extent, an increase in AP-1. No significant increase in other transcription factors over the control, untreated cells was observed. DNase I footprint assays using purified transcription factors revealed the presence of NF-kappa B and AP-2 binding sites in the proximal part of the promoter region of the human HO-1 gene. Moreover, nucleotide sequence analysis of the HO-1 promoter region showed that the protected regions encompassed NF-kappa B and AP-2 consensus binding sites. The presence of regulatory sequences for the binding of transcription factors such as NF-kappa B and AP-2, whose activation is associated with the immediate response of the cell to an injury, may be an indication of the important role which HO-1 may play in defense mechanisms against tissue injury.

3,5,5-Trimethylhexanoylferrocene induction of heme oxygenase activity in normal hepatocytes

Recent work showed that the combination of 50 microM glutethimide plus 50 microM ferric nitrilotriacetate (FeNTA) synergistically induces heme oxygenase (HO) activity in cultured chick embryo liver cells (Cable et al., Biochem Biophys Res Commun 168: 176-181, 1990). This synergistic induction is due to increased heme synthesis, which then acts to increase HO gene transcription. The aim of the current studies was to characterize the effects on hepatic heme metabolism of (3,5,5-trimethylhexanoyl)ferrocene (TMH-ferrocene), which causes hepatic iron-loading in rats. Unlike FeNTA, TMH-ferrocene alone maximally induced HO activity at 5-10 microM TMH-ferrocene. At higher concentrations, HO activities declined, as did total cellular protein synthesis. Induction of HO was maximal after a 12-hr exposure to TMH-ferrocene, similar to induction by glutethimide plus FeNTA. The effect of TMH-ferrocene on HO could not be ascribed to greater cellular uptake of iron, since cell-associated iron levels were higher after FeNTA than after TMH-ferrocene treatment. TMH-ferrocene (up to 20 microM) did not induce delta-aminolevulinic acid synthase activity. Uroporphyrin accumulation in cells treated with TMH-ferrocene was minimal, but the combination of TMH-ferrocene and glutethimide caused a synergistic increase in uroporphyrin accumulation, similar to treatment with glutethimide plus FeNTA. 4,6-Dioxoheptanoic acid, an inhibitor of heme synthesis, blocked the induction of HO caused by glutethimide and FeNTA, but did not decrease the induction of HO by TMH-ferrocene. TMH-ferrocene-mediated induction of HO does not appear to be due to lipid peroxidation, since malondialdehyde formation was greater for ferrocene (a structural analog of TMH-ferrocene that does not induce HO) than for TMH-ferrocene. Furthermore, the anti-oxidant, butylated hydroxyanisole, which prevented lipid peroxidation, decreased HO induced by glutethimide plus FeNTA, but butylated hydroxyanisole did not affect HO induced by TMH-ferrocene. We conclude that, unlike the combination of glutethimide plus FeNTA, TMH-ferrocene induces HO activity by a mechanism that is independent of cellular heme synthesis.

Suppression of cytochrome P450IA1 by interleukin-6 in human HepG2 hepatoma cells

The effects of interleukin-6 (IL-6), the major inducer of the acute-phase reaction, on the expression of cytochrome P450IA1 (CYPIA1) were examined using human HepG2 hepatoma cells. Treatment of cells with IL-6 decreased the level of 3-methylcholanthrene-induced CYPIA1 protein and its mRNA. Nuclear runoff analysis revealed that the effect of IL-6 was largely transcriptional. IL-6 treatment of HepG2 cells increased mRNA for microsomal heme oxygenase, the rate-limiting enzyme in heme catabolism, suggesting that the suppressive effect of IL-6 on CYPIA1 mRNA may be due to a loss of heme. Consistent with this hypothesis, simultaneous treatment of cells with Sn-mesoporphyrin, an inhibitor of heme oxygenase, prevented the IL-6-mediated suppression of CYPIA1. These findings suggest that the suppression of P450IA1 mRNA by IL-6 appears to occur, at least in part, from the decline in free heme content as a result of the induction of heme oxygenase. Our results raise the possibility that other physiological as well as environmental stimuli which affect cellular heme concentrations may also modulate the expression of P450s.

Molecular basis for heme-dependent induction of heme oxygenase in primary cultures of chick embryo hepatocytes. Demonstration of acquired refractoriness to heme

The effects of heme on the induction of mRNA and protein synthesis for heme oxygenase-1 have been studied in primary cultures of chick embryo liver cells. Heme increased the amount of mRNA and the rate of heme oxygenase-1-gene transcription in a dose-dependent fashion, with a maximal 20-fold increase occurring at 20 microM heme. The largest increase in the rate of transcription, measured by nuclear run-on assays, occurred at 5 h, 2 h earlier than the maximum increase in the amount of mRNA, measured by densitometry of Northern blots. 7-15 h after heme addition, the half-life of heme-oxygenase-1 mRNA was 3.5 h in the presence or absence of actinomycin D. In contrast, addition of cycloheximide markedly increased the stability of the message (half-life = 18 h), suggesting that a short-lived protein plays a key role in modulating heme oxygenase-1 mRNA levels. The half-life of heme-induced heme-oxygenase-1 protein, measured by [35S]methionine labelling and immunoprecipitation, was 15 h. This long half-life of the protein can largely account for the additional finding that, following addition of heme, the amount of enzyme protein in the cells increased for 10 h, after which it remained essentially constant for 15 h. A striking finding was that, after an initial burst of heme-stimulated gene transcription, the cells became refractory to further heme-mediated induction. This acquired resistance could not be attributed to the following: a longer duration of culture time; cellular toxicity caused by heme; a lack of heme in the medium or the cells; secretion of heme-binding proteins into the medium, preventing further heme uptake; the induction of cellular heme catabolism sufficient to deplete cellular heme. Instead, the results suggest a down-regulation of the intracellular machinery required for heme-dependent induction of heme oxygenase-1.

The role of inorganic metals and metalloporphyrins in the induction of haem oxygenase and heat-shock protein 70 in human hepatoma cells

The role of inorganic metals and metalloporphyrins in the induction of mRNAs for haem oxygenase and heat-shock protein 70 (hsp70), the two heat-shock proteins, was examined in human HepG2 and Hep3B hepatoma cells. SnCl2, but not Sn-protoporphyrin, was found to be a potent inducer of both haem oxygenase and hsp70 mRNAs. In contrast, CoCl2, ZnCl2 and FeCl2 caused little induction of haem oxygenase and hsp70 mRNAs, whereas the porphyrin complexes of these metals strongly induced haem oxygenase mRNA, without influencing the level of hsp70 mRNA. The induction process was largely transcriptional, as judged by the inhibition of induction by actinomycin D, but not by cycloheximide, and by increased transcription demonstrated by nuclear run-off analysis. Since CoCl2 is a potent inducer of haem oxygenase in vivo in animals, the possibility of the biosynthesis of Co-protoporphyrin was examined in human hepatoma cells by incubating them with CoCl2 and protoporphyrin, or delta-aminolaevulinate (ALA), the precursor of protoporphyrin. Both types of treatment led to a potent induction of haem oxygenase mRNA. Co-protoporphyrin formation was also spectrally demonstrated in cells incubated with the metal and ALA. The results of this study indicate that certain metals, e.g. SnCl2, may directly induce haem oxygenase mRNA, whereas with other elements, incorporation of the metal into the porphyrin macrocycle is necessary for induction. Therefore CoCl2, like haemin, may activate the haem oxygenase gene via a haem-responsive transcription factor, whereas SnCl2 may exert its effect via a metal-responsive transcription factor.

Cytokine induction of haem oxygenase mRNA in mouse liver. Interleukin 1 transcriptionally activates the haem oxygenase gene

Accumulation of the mRNA coding for haem oxygenase (HO, EC 1.14.99.3) was stimulated by treating mice with endotoxin (lipopolysaccharide, LPS; 20 micrograms/mouse intraperitoneally), suggesting that haem catabolism is a target of infection and inflammation in vivo. Therefore various cytokines, possible mediators for the biological responses to LPS, were administered intraperitoneally to mice, and the levels of HO mRNA were measured by Northern-blotting analysis using the rat HO cDNA as a probe [Shibahara, Müller, Taguchi and Yoshida (1985) Proc. Natl. Acad. Sci. U.S.A. 82, 7865-7869]. Marked induction of HO mRNA was observed 2 h after administration of interleukin 1 (IL-1) (34-fold) and tumour necrosis factor (19.5-fold) (5 micrograms/mouse), whereas interleukin 6 (6.2 micrograms/mouse) was much less active (3.5-fold) and interleukin 2 (25 micrograms/mouse) and interferon-gamma (3 micrograms/mouse) were ineffective. HO mRNA induced by the cytokines of LPS accumulated rapidly (maximum at 1-2 h after administration), preceding the elevation of HO enzymic activity. Treatment of mice with IL-1 stimulated the transcription of the HO gene by 4-fold, as assessed by in vitro nuclear-run-on assay. These results indicate that enzymic haem catabolism in the liver is a process inducible in vivo by inflammatory cytokines, which up-regulate HO synthesis at the transcriptional level. Increased removal of haem might be part of the protective mechanisms elicited by the acute-phase response, possibly to reduce the pro-oxidant state of the cell.

Identification of a nuclear protein that constitutively recognizes the sequence containing a heat-shock element. Its binding properties and possible function modulating heat-shock induction of the rat heme oxygenase gene

Heme oxygenase is an essential enzyme in heme catabolism, and also known as a 32-kDa heat-shock protein in rat. The rat heme-oxygenase gene promoter contains a functional heat-shock element (HSE) designated as HSE1 (-290 to -276 from the transcriptional initiation site), which consists of three copies of a 5-bp unit (5'-NGAAN-3';-->) in alternating orientation. Here we identified a putative HSE (-221 to -212), designated as HSE2, consisting of an inverted repeat of this 5-bp unit (<==>). Using transient expression assays, we show that HSE1 is sufficient to confer the heat-inducibility (a three fold to fourfold increase) on the reporter gene located downstream from the rat heme-oxygenase gene promoter, but HSE2 alone is not, suggesting that HSE2, a HSE of a tail-to-tail configuration, is not functional in vivo. However, the presence of both HSE1 and HSE2 in the promoter region increased the heat-mediated induction of the reporter-gene expression by more than 15-fold. Gel mobility-shift assays indicate that both HSE1 and HSE2 are recognized by activated heat-shock factor present only in heat-shocked rat glioma cells. Interestingly, the sequence containing HSE2 is also bound by a protein that is present in nuclear extracts prepared from either heat-shocked or non-shocked glioma cells, but this nuclear protein is unable to bind to HSE1. We suggest that a protein binding to the sequence containing HSE2 may be involved in transcriptional regulation of the rat heme oxygenase gene under thermal stress.

Relationships between thermotolerance, oxidative stress responses and induction of stress proteins in human tumour cell lines

Thermotolerance, resistance to oxidative stress and induction of stress proteins were examined in a panel of 10 human tumour cell lines. An inverse relationship was indicated between intrinsic thermotolerance (cell survival after treatment at 43.5 degrees for 3 hr) and thermotolerance induced by pretreatment at 42.5 degrees for 30 min. Similar levels of induction of hsp 70 were found in cell lines with high or low levels of intrinsic thermotolerance; induction of other stress proteins could not be detected. Cell survival following treatment with H2O2 correlated with that following streptonigrin treatment (P < 0.05). Pretreatment with buthionine sulphoximine or diamide synergistically increased the toxicity of heat, H2O2 and streptonigrin whereas reduced glutathione had the reverse effect. No direct correlation was found, however, between tolerance to heat and to oxidative stress, and hsp 70 was not induced by the latter. The stress protein heme oxygenase, detected by immunoblotting with the monoclonal antibody HO, was induced by H2O2 in melanoma cell lines but not in HeLa. Cadmium and arsenite ions, however, readily induced heme oxygenase in HeLa, indicating that in these cells induction of heme oxygenase by oxidative stress involves a different mechanism. Overall, the results suggest that tolerance to heat or oxidative stress in these cell lines may not necessarily be associated with the induction of heat shock proteins or heme oxygenase but that cell survival after both types of stress depends to a certain extent on cellular sulphydryls.

Interleukin-6 down regulates the expression of transcripts encoding cytochrome P450 IA1, IA2 and IIIA3 in human hepatoma cells

Effects of human interleukin-6 (hIL-6), the major acute phase inducer, on the expression of transcripts encoding cytochrome P450s were examined in human hepatoma-derived cells. Using reverse-transcription polymerase chain reaction, it was demonstrated that three hepatoma cell lines, HepG2, HepG2f and Hep3B, express P450 mRNAs encoding IA1, IA2 and IIIA3, the major P450 isozymes involved in carcinogen metabolism, and that they also show induction responses to treatment with their specific inducers. When hepatoma cells were treated with hIL-6, the levels of IA1, IA2 and IIIA3 mRNAs were markedly suppressed. These findings suggest that significant down regulation of cytochrome P450s may occur during the acute phase reaction, which may result in alterations in drug biotransformation.

Heme oxygenase is a heat shock protein and PEST protein in rat astroglial cells

Cultured rat forebrain astrocytes contained significant amounts of immunostainable heme oxygenase-1 (HO-1) isozyme, whereas HO-1 was undetectable in spontaneously transformed rat astroglial cells (ATs). HO-1 was inducible in both cell types by heat shock and by submicromolar amounts of H2O2. Inhibition of RNA synthesis with actinomycin D or protein synthesis with cycloheximide resulted in the rapid loss of immunostainable heme oxygenase in astrocytes. Analysis of the primary structure of heme oxygenase suggests that it is a PEST protein, i.e., targeted for rapid turnover.

A heat-inducible nuclear factor that binds to the heat-shock element of the human haem oxygenase gene

Haem oxygenase is a heat-shock protein in several rat tissues, as well as in certain human cells such as Hep3B hepatoma cells. In common with other heat-shock-protein genes, both the human and the rat haem oxygenase genes contain a heat-shock element (HSE) in their promoter regions. In the present study we have identified a factor in nuclear extracts of human Hep3B cells which binds specifically to the HSE of the human haem oxygenase gene. The factor in Hep3B cells was significantly induced within 1 h after heat-shock treatment, and the induction was blocked by treatment of cells with actinomycin D or cycloheximide. The factor was not detected in human HepG2 hepatoma cells, which exhibit the heat-mediated induction of heat-shock protein 70 mRNA, but not that of haem oxygenase mRNA. These findings suggest that the heat-inducible nuclear factor is increased at the level of transcription and that it may activate the human haem oxygenase gene via the HSE after heat treatment.

Mechanism of synergistic induction of hepatic heme oxygenase by glutethimide and iron: studies in cultured chick embryo liver cells

Heme oxygenase, the rate controlling enzyme for heme catabolism, is inducible by a variety of treatments, some of which induce by a heme-dependent mechanism and others by a heme-independent mechanism. This work shows that, in cultured chick embryo liver cells, synergistic induction of heme oxygenase by iron, added with the phenobarbital-like drug, glutethimide was heme-dependent. Addition of an inhibitor of heme biosynthesis abolished the synergistic induction of heme oxygenase providing evidence for the heme-dependent mechanism of induction. Glutethimide and iron appeared to induce at the transcriptional level since both heme oxygenase mRNA and protein levels correlate with changes in heme oxygenase activity.