Long non-coding RNA NEAT1 is a transcriptional target of p53 and modulates p53-induced transactivation and tumor-suppressor function.

p53 is one of the most important tumor suppressor genes, and the direct transcriptional targets of p53 must be explored to elucidate its functional mechanisms. Thus far, the p53 targets that have been primarily studied are protein-coding genes. Our previous study revealed that several long non-coding RNAs (lncRNAs) are direct transcriptional targets of p53, and knockdown of specific lncRNAs modulates p53-induced apoptosis. In this study, analysis of next-generation chromatin immunoprecipitation-sequencing (ChIP-seq) data for p53 revealed that the lncRNA NEAT1 is a direct transcriptional target of p53. The suppression of NEAT1 induction by p53 attenuates the inhibitory effect of p53 on cancer cell growth and also modulates gene transactivation, including that of many lncRNAs. Furthermore, low expression of NEAT1 is related to poor prognosis in several cancers. These results indicate that the induction of NEAT1 expression contributes to the tumor-suppressor function of p53 and suggest that p53 and NEAT1 constitute a transcriptional network contributing to various biological functions and tumor suppression.

Identification and characterization of a metastatic suppressor BRMS1L as a target gene of p53.

The tumor suppressor p53 and its family members, p63 and p73, play a pivotal role in the cell fate determination in response to diverse upstream signals. As transcription factors, p53 family proteins regulate a number of genes that are involved in cell cycle arrest, apoptosis, senescence, and maintenance of genomic stability. Recent studies revealed that p53 family proteins are important for the regulation of cell invasion and migration. Microarray analysis showed that breast cancer metastasis suppressor 1-like (BRMS1L) is upregulated by p53 family proteins, specifically p53, TAp63γ, and TAp73ß. We identified two responsive elements of p53 family proteins in the first intron and upstream of BRMS1L. These response elements are well conserved among mammals. Functional analysis showed that ectopic expression of BRMS1L inhibited cancer cell invasion and migration; knockdown of BRMS1L by siRNA induced the opposite effect. Importantly, clinical databases revealed that reduced BRMS1L expression correlated with poor prognosis in patients with breast and brain cancer. Together, these results strongly indicate that BRMS1L is one of the mediators downstream of the p53 pathway, and that it inhibits cancer cell invasion and migration, which are essential steps in cancer metastasis. Collectively, our results indicate that BRMS1L is involved in cancer cell invasion and migration, and could be a therapeutic target for cancer.

Identification and analysis of large intergenic non-coding RNAs regulated by p53 family members through a genome-wide analysis of p53-binding sites.

p53 is one of the most important known tumor suppressor genes, and it is inactivated in approximately half of human cancers. p53 family members execute various functions, such as apoptosis induction and cell cycle arrest, by modulating transcriptional regulation. Therefore, the direct transcriptional targets of the p53 family must be explored to elucidate the functional mechanisms of family members. To identify the direct transcriptional targets of p53 family members, we performed chromatin immunoprecipitation together with next-generation sequencing (ChIP-seq) and searched for p53-binding motifs across the entire human genome. Among the identified ChIP-seq peaks, approximately half were located in an intergenic region. Therefore, we assumed large intergenic non-coding RNAs (lincRNAs) to be major targets of the p53 family. Recent reports have revealed that lincRNAs play an important role in various biological and pathological processes, such as development, differentiation, stemness and carcinogenesis. Through a combination of ChIP-seq and in silico analyses, we found 23 lincRNAs that are upregulated by the p53 family. Additionally, knockdown of specific lincRNAs modulated p53-induced apoptosis and promoted the transcription of a gene cluster. Our results suggest that p53 family members, and lincRNAs constitute a complex transcriptional network involved in various biological functions and tumor suppression.

p53-induced ARVCF modulates the splicing landscape and supports the tumor suppressive function of p53.

p53 is one of the most important tumor suppressor genes, and the exploration of p53-target genes is important for elucidation of its functional mechanisms. In this study, we identified Armadillo Repeat gene deleted in Velo-Cardio-Facial syndrome (ARVCF) as a direct target of p53 through ChIP-sequencing analysis. Activated p53 protein was found to bind to two distinct sites in the ARVCF gene, resulting in induction of ARVCF expression at both the mRNA and protein levels. We revealed that the knockdown of ARVCF inhibited p53-induced apoptosis. Interestingly, ARVCF interacted with hnRNPH2, which is involved in pre-mRNA splicing, and ARVCF knockdown induced dynamic changes in alternative splicing patterns. These results suggest that p53-induced ARVCF indirectly, but not directly, regulates p53 target selectivity through splicing alterations of specific genes. Thus, we demonstrated that the induction of ARVCF expression contributed to the tumor suppressive function of p53. Recently, it has been reported that many tumors have thousands of alternative splicing events that are not detectable in normal samples. ARVCF may play a role in alternative splicing events in cancer and may provide clues to explore novel approaches for cancer diagnosis and therapy.

Recombinant human soluble thrombomodulin ameliorates acetaminophen-induced liver toxicity in mice.

Recombinant human soluble thrombomodulin alpha (rhTM) has been developed as an anticoagulant with anti-inflammatory activity. Notably, acetaminophen (APAP) -induced liver disease (AILI) is caused by direct metabolite-induced hepatotoxicity as well as hepatic hyper-coagulation. To evaluate the utility of anticoagulant for the treatment of AILI, rhTM was administered in a mouse AILI model and liver damage was analyzed. AILI was induced in 8-week-old mice by intraperitoneal injection of APAP. rhTM (20 mg/kg) or placebo was injected at the same time as APAP administration. Serum alanine aminotransferase, fibrin degradation products and high-mobility group box 1 levels were significantly decreased in the rhTM-treated group compared with the control group. Furthermore, rhTM reduced the necrotic area and fibrin deposition in liver sections. rhTM suppressed the mRNA expression of heme oxygenase-1, plasminogen activator inhibitor type-1, tissue factors, and inflammatory cytokines compared with the control group. rhTM did not change the hepatic GSH content at 2 h after APAP injection, but restored them at 4 h after the insult. rhTM ameliorated liver damage in mice with AILI, probably via the improvement in liver perfusion induced by it's anticoagulant acitivity, which can lead to the suppression of secondary liver damage.

Hepatitis B caused by a hepatitis B surface antigen escape mutant.

Amino acid substitutions within the S gene involving the major antigenic a determinant of the hepatitis B virus (HBV) surface antigen (HBsAg) have been detected in cases of failure of immunization against the virus. Our report showed development of clinical hepatitis in presence of antibody to HBsAg in a healthy individual. A single amino acid substitution (G145R) within the a determinant of the HBsAg was determined by sequencing of the isolated HBV strain. Lamivudine treatment efficiently cleared the peripheral HBV DNA, HBsAg, and hepatitis B e antigen. In conclusion, the immune escape mutant in the S gene can cause hepatitis despite pre-existing naturally acquired immunity.

Effects of high fructose intake on liver injury progression in high fat diet induced fatty liver disease in ovariectomized female mice.

Epidemiology shows that the morbidity of nonalcoholic fatty liver disease (NAFLD) is increased in postmenopausal women and chronic high fructose intake induces NAFLD progression. To analyze the effects of high fructose intake on estrogen deficiency, we evaluated liver disease progression using ovariectomized mice fed with a high fat diet (HFD) for 12 weeks. Hepatic steatosis developed in all HFD groups. Fructose intake significantly increased the liver weight and serum alanine aminotransferase, which was not exacerbated by ovariectomy alone. Ovariectomy enhanced the hepatic inflammatory activity shown by tumor necrosis factor α upregulation in the groups with or without fructose intake. Both fructose intake and ovariectomy increased the hepatocytes with ballooning degeneration and hepatic macrophage infiltration and activated hepatic stellate cells. Coexistence of fructose intake and ovariectomy markedly enhanced liver cell destruction, macrophage accumulation, and progression of fibrosis. Liver damage was ameliorated by 17ß-estradiol supplementation. These findings suggest that high fructose intake enhanced the progression of NAFLD in ovariectomized female mice.

[Visualization and evaluation of the promoter activities of genes for stress-inducible proteins in response to environmental pollutants].

We examined the systematic assay of the reporter gene for the assessment of heavy metals and organic chemical pollutants using the reporter plasmids carrying stress-responsive elements fused to the green fluorescence protein (GFP) gene as follows: metallothionein (MTIIA), heme oxigenase-1 (HO-1), quinone reductase (ARE), and c-fos genes. The treatment of COS7 cells in which the c-fos gene promoter-, ARE-, or HO-1 enhancer-fused GFP with a low concentration of NaAsO(2) was introduced led to the detection of the fluorescent cells, and an agrichemical paraquat enhanced the fluorescence of ARE or HO-1 enhancer-transfected cells. The cells in which the plasmid carrying the MT-IIA gene promoter (the -765 bp upstream from the transcription initiation site) was introduced highly expressed GFP on treatment with CdCl(2), ZnSO(4), or CuCl(2). The plasmid carrying seven metal-responsive elements of the MT-IIA gene increased the response of the fluorescence intensity to these heavy metals. These results indicated that the use of the gene promoters and enhancers of the stress-responsive genes fused to GFP contributes to the visualization of pollutant-responsive mammalian cells and can be applied to biomonitoring of environmental pollution.

p53 mediates the suppression of cancer cell invasion by inducing LIMA1/EPLIN.

The tumor suppressor gene p53 is frequently mutated in human cancer. p53 executes various functions, such as apoptosis induction and cell cycle arrest, by modulating transcriptional regulation. In this study, LIM domain and Actin-binding protein 1 (LIMA1) was identified as a target of the p53 family using a cDNA microarray. We also evaluated genome-wide occupancy of the p53 protein by performing chromatin immunoprecipitation-sequencing (ChIP-seq) and identified two p53 response elements in the LIMA1 gene. LIMA1 protein levels were increased by treatment with nutlin-3a, a small molecule that activates endogenous p53. In addition, LIMA1 expression was significantly downregulated in cancers compared with normal tissues. Knockdown of LIMA1 significantly enhanced cancer cell invasion and partially inhibited p53-induced suppression of cell invasion. Furthermore, low expression of LIMA1 in cancer patients correlated with decreased survival and poor prognosis. Thus, p53-induced LIMA1 inhibits cell invasion, and the downregulation of LIMA1 caused by p53 mutation results in decreased survival in cancer patients. Collectively, this study reveals the molecular mechanism of LIMA1 downregulation in various cancers and suggests that LIMA1 may be a novel prognostic predictor and a therapeutic target for cancer.

Profiling cancer-related gene mutations in oral squamous cell carcinoma from Japanese patients by targeted amplicon sequencing.

Somatic mutation analysis is a standard practice in the study of human cancers to identify mutations that cause therapeutic sensitization and resistance. We performed comprehensive genomic analyses that used PCR target enrichment and next-generation sequencing on Ion Proton semiconductor sequencers. Forty-seven oral squamous cell carcinoma (OSCC) samples and their corresponding noncancerous tissues were used for multiplex PCR amplification to obtain targeted coverage of the entire coding regions of 409 cancer-related genes (covered regions: 95.4% of total, 1.69 megabases of target sequence). The number of somatic mutations in 47 patients with OSCC ranged from 1 to 20 with a mean of 7.60. The most frequent mutations were in TP53 (61.7%), NOTCH1 (25.5%), CDKN2A (19.1%), SYNE1 (14.9%), PIK3CA (10.6%), ROS1 (10.6%), and TAF1L (10.6%). We also detected copy number variations (CNVs) in the segments of the genome that could be duplicated or deleted from deep sequencing data. Pathway assessment showed that the somatic aberrations within OSCC genomes are mainly involved in several important pathways, including cell cycle regulation and RTK-MAPK-PI3K. This study may enable better selection of therapies and deliver improved outcomes for OSCC patients when combined with clinical diagnostics.

The antioxidant role of a reagent, 2',7'-dichlorodihydrofluorescin diacetate, detecting reactive-oxygen species and blocking the induction of heme oxygenase-1 and preventing cytotoxicity.

Heme oxygenase-1 (HO-1) degrades heme into biliverdin, iron and CO. The enzyme participates in adaptive and protective responses to oxidative stress and various inflammatory stimuli, and is induced in response to reactive oxygen species (ROS). 2',7'-Dichlorodihydrofluorescin diacetate (DCFH-DA) is a common reagent used to detect ROS by the oxidation of 2',7'-dichlorodihydrofluorescin (DCFH) to fluorescent dichlorodihydrofluorescein. We previously found that rapid oxidation of DCFH occurred with heme-compounds as well as ROS [Ohashi, T. et al. (2002) FEBS Lett. 511, 21-27], and then examined the effect of DCFH-DA on the induction of HO-1 expression by arsenite, cadmium and hemin, which induce oxidative stress and cytotoxicity. We found suppression of the arsenite-, cadmium- and hemin-dependent induction of HO-1 with DCFH-DA. The suppression occurred at the transcriptional level since the promoter activity of the Maf-recognition site of the HO-1 gene decreased with the DCFH-DA treatment. DCFH abolished the phosphorylation of extracellular signal-regulated kinase, the nuclear translocation of a transcriptional activator Nrf2, and cell death. An antioxidant, N-acetylcysteine (NAC), also suppressed the induction by arsenite and cadmium, but not that by hemin, indicating that DCFH blocked a different site in the stress signal pathway from NAC. Considering that the oxidation of DCFH diminishes ROS generated by various stressors, our findings provide a potential strategy for protection of cells from toxic insults using DCFH-like molecules.

Analysis of renal function during telaprevir-based triple therapy for chronic hepatitis C.

Telaprevir (TVR) is used for the treatment of chronic hepatitis C in a combination therapy with pegylated-interferon and ribavirin. Although renal dysfunction is one of the critical adverse outcomes of this treatment, little is known regarding the mechanism of its onset. The present study assessed the association of renal function with TVR dose and viral response. Hematological, biochemical, urinary and virological parameters of renal function were examined during the TVR-based triple therapy of patients infected with hepatitis C virus (HCV) genotype 1b. Serum creatinine levels were increased and the estimated glomerular filtration rate (eGFR) was decreased in every patient during TVR administration, but these values recovered to normal levels following cessation of TVR. Fractional excretion of sodium was <1% at days 3 and 7, appearing similar regardless of baseline renal function. Urinary ß2-microglobulin levels were elevated and were significantly higher in patients with renal dysfunction, as compared with those not exhibiting renal dysfunction (P<0.05). The reduction in renal function was milder in patients treated with a reduced TVR dose, and these patients had a significantly lower risk of developing renal dysfunction (P<0.05). Using a multivariate analysis, TVR dose and eGFR at the initiation of treatment were identified as significant contributory factors in the development of renal dysfunction. Reduction in TVR dose did not lead to a significant increase in the viral kinetics of HCV or detrimental effects on the sustained viral response (SVR) rate. It is hypothesized that renal dysfunction during TVR treatment is caused by damage of the renal tubule, in addition to pre-renal dysfunction, and that reduction in TVR dose reduces the rate of renal dysfunction without causing a significant decrease in the SVR rate.

Rapid oxidation of dichlorodihydrofluorescin with heme and hemoproteins: formation of the fluorescein is independent of the generation of reactive oxygen species.

Oxidative stress and the generation of reactive oxygen species (ROS) have been implicated in the pathogenesis of cellular damage. These events have usually been reported in terms of oxidation of a reporter molecule such as 2',7'-dichlorodihydrofluorescin diacetate (DCFH-DA). Treatment of HeLa cells with hemin or metalloporphyrins resulted in a rapid oxidation of DCFH in a time- and dose-dependent manner. This oxidation was inhibited by treatment of the cells with a large amount of superoxide dismutase and catalase, which is different from observations that these enzymes had no effect on the induction of heme oxygenase-1, a stress-induced protein, in hemin-treated cells. To examine the possibility that the oxidation of DCFH is independent of the generation of ROS, the oxidation was measured using hemoglobin-synthesizing erythroleukemia K562 cells. When K562 cells were treated with delta-aminolevulinic acid, a precursor of heme, oxidation of DCFH increased depending on the heme content in cells. Then DCFH-DA was oxidized directly with heme, hemoglobin, myoglobin and cytochrome c. These results suggest that oxidation of DCFH is not always related to the generation of ROS but may be related to heme content in cells.

Influence of canine cumulus oophorus on homologous sperm motility.

Sperm ejaculated by 8 beagle dogs and the cumuli oophori collected from 3 estrous beagle bitches were co-incubated, and penetration of the sperm into cumuli was observed to investigate the influence of cumuli on homologous sperm. The percentages of hyperactivated sperm and acrosome-reacted sperm were calculated after incubation with homogenized cumuli. The hyaluronic acid content of the incubated cumuli was measured, and hyperactivation and the acrosome reaction of the sperm were evaluated in medium containing hyaluronic acid. The mean percentage of hyperactivated sperm (33.0%) and number (3.0) of sperm that had penetrated a cumulus among sperm incubated for 7 hr were significantly higher than the values for sperm incubated for 0.5 hr (P<0.01). Almost all sperm that had penetrated the cumuli had intact acrosome, as though they were hyperactivated. The percentages of motile sperm (77.3%) and hyperactivated sperm (23.6%) after 2 hr incubation in the medium containing homogenized cumuli were significantly higher than in control medium (P<0.01), but there was no difference between cumulus and control media in the percentages of acrosome-reacted sperm. The hyaluronic acid content of a cumulus increased after 24 hr incubation. After 2 and 4 hr of incubation the percentages of hyperactivated sperm in the medium containing hyaluronic acid were significantly higher than in the control medium (P<0.01). These results suggest that canine hyperactivated sperm with intact acrosome can penetrate homologous cumuli and that the sperm are able to pass through the cumulus because the hyperactivated movement is maintained by hyaluronic acid secreted by the cumulus cells.

Array-based genome-wide RNAi screening to identify shRNAs that enhance p53-related apoptosis in human cancer cells.

p53 transduction is a potentially effective cancer therapy but does not result in a good therapeutic response in all human cancers due to resistance to apoptosis. To discover factors that overcome resistance to p53-induced apoptosis, we attempted to identify RNAi sequences that enhance p53-induced apoptosis. We screened a genome-wide lentiviral shRNA library in liver cancer Huh-7 and pancreatic cancer Panc-1 cells, both of which resist p53-induced apoptosis. After the infection of adenovirus expressing p53 or LacZ as a control, shRNA-treated populations were analyzed by microarray. We identified shRNAs that were significantly decreased in p53-infected cells compared with control cells. Among these shRNAs, shRNA-58335 was markedly decreased in both cancer cell lines tested. shRNA-58335 enhanced p53-related apoptosis in vitro and augmented the inhibitory effect of adenoviral p53 transduction on tumor growth in vivo. Furthermore, the enhanced apoptotic response by shRNA-58335 was also confirmed by treatment with PRIMA-1, which reactivates mutant p53, instead of adenoviral p53 transduction. We found that shRNA-58335 evokes the apoptotic response following p53 transduction or functional restoration of p53 with a small molecule drug in cancer cells resistant to p53-induced apoptosis. The combination of p53 restoration and RNAi-based drugs is expected to be a promising novel cancer therapy.

AKR1B10, a transcriptional target of p53, is downregulated in colorectal cancers associated with poor prognosis.

UNLABELLED: p53 is one of the most important tumor suppressor genes, and it is frequently inactivated in various cancers. p53 modulates various cellular functions, such as apoptosis and cell-cycle arrest via transcriptional regulation. Recently, p53 has been reported to be involved in a wide range of cellular metabolic pathways, including glycolysis, oxidative phosphorylation, glutaminolysis, and the antioxidant response. To understand the functional mechanism of p53, it is important to find out the direct transcriptional targets of p53. In this study, aldo-keto reductase family 1, member B10 (AKR1B10) was identified as a direct target of the p53 family by cDNA microarray analysis after comparing the mRNA expression of control and H1299 cells that overexpressed with p53 family members. In addition, we found that the expression of AKR1B10 was significantly decreased in colorectal cancers and adenomas as compared with normal colon tissues. Knockdown of AKR1B10 significantly inhibited p53-induced apoptosis in colorectal cancer cells, whereas the overexpression of AKR1B10 enhanced p53-induced apoptosis and inhibited tumor proliferation in vivo. Furthermore, low expression of AKR1B10 in colon cancer patients was correlated with decreased survival and poor prognosis. These results suggest that decreased expression of AKR1B10 could disrupt the tumor suppressive function of p53, which result in decreased survival in colorectal cancer patients. In summary, AKR1B10 may be a novel prognostic predictor and a novel therapeutic target for colorectal cancer. IMPLICATIONS: AKR1B10, a transcriptional target of p53, is also a novel prognostic and therapeutic molecule in colorectal cancer.

A case of fatal intrahepatic cholestasis with primary AL amyloidosis: is early diagnosis possible?

Immunoglobulin light chain-associated (AL) amyloidosis is a multisystemic disorder characterized by extracellular deposition of immunoglobulin light chain produced by a proliferative plasma cell clone. Although the liver is the major organ involved in AL amyloidosis, hepatic involvement is often clinically asymptomatic and severe intrahepatic cholestasis as the primary manifestation of the disease is rare. A 60-year-old man with severe jaundice, massive ascites and highly elevated alkaline phosphatase was diagnosed with AL amyloidosis by a transjugular liver biopsy. He had undergone a yearly medical check that showed no abnormalities except for mild elevation of serum γ-glutamyltransferase at 1 year before admission. Owing to his poor condition and rapidly progressive liver and renal dysfunction, neither stem cell transplantation nor a combination of chemotherapeutic agents could be applied, and he died 1.5 months after admission. An autopsy revealed amyloid deposition in the systemic organs, and there was no evidence of multiple myeloma. Continuous elevation of γ-glutamyltransferase may be a useful marker for early diagnosis of fatal hepatic amyloidosis.

A 5-bp insertion in Mip causes recessive congenital cataract in KFRS4/Kyo rats.

We discovered a new cataract mutation, kfrs4, in the Kyoto Fancy Rat Stock (KFRS) background. Within 1 month of birth, all kfrs4/kfrs4 homozygotes developed cataracts, with severe opacity in the nuclei of the lens. In contrast, no opacity was observed in the kfrs4/+ heterozygotes. We continued to observe these rats until they reached 1 year of age and found that cataractogenesis did not occur in kfrs4/+ rats. To define the histological defects in the lenses of kfrs4 rats, sections of the eyes of these rats were prepared. Although the lenses of kfrs4/kfrs4 homozygotes showed severely disorganised fibres and vacuolation, the lenses of kfrs4/+ heterozygotes appeared normal and similar to those of wild-type rats. We used positional cloning to identify the kfrs4 mutation. The mutation was mapped to an approximately 9.7-Mb region on chromosome 7, which contains the Mip gene. This gene is responsible for a dominant form of cataract in humans and mice. Sequence analysis of the mutant-derived Mip gene identified a 5-bp insertion. This insertion is predicted to inactivate the MIP protein, as it produces a frameshift that results in the synthesis of 6 novel amino acid residues and a truncated protein that lacks 136 amino acids in the C-terminal region, and no MIP immunoreactivity was observed in the lens fibre cells of kfrs4/kfrs4 homozygous rats using an antibody that recognises the C- and N-terminus of MIP. In addition, the kfrs4/+ heterozygotes showed reduced expression of Mip mRNA and MIP protein and the kfrs4/kfrs4 homozygotes showed no expression in the lens. These results indicate that the kfrs4 mutation conveys a loss-of-function, which leads to functional inactivation though the degradation of Mip mRNA by an mRNA decay mechanism. Therefore, the kfrs4 rat represents the first characterised rat model with a recessive mutation in the Mip gene.

Haplotype analysis excludes the functional protoporphyrinogen oxidase promoter polymorphism -1081G>A as a modifying factor in the clinical expression of variegate porphyria.

Variegate porphyria (VP) is caused by the founder-type protoporphyrinogen oxidase (PPOX) gene mutation R59W in the majority of South African patients. VP is inherited as an autosomal dominant disease with incomplete penetrance and no genotype-phenotype association has been established to date. In an attempt to determine whether a relatively common mutation in the promoter region of the gene (-1081G>A) represents a low-expression allele that may influence clinical manifestation of the disease when inherited from the non-carrier (R59W-negative) parent, we have studied the effect of the mutated allele using an in vitro luciferase assay. Haplotype analysis was furthermore used to evaluate the added information obtained by considering the possible influence of this mutation in combination with a polymorphism in intron 2 (206G>C) of the gene in a genotype-phenotype correlation study. Although the mutation at nucleotide -1081 resulted in a significant reduction in transcriptional activity relative to the reference wild type, no evidence could be obtained that a specific haplotype inherited from the normal parent affects clinical expression of the disease. We thus conclude that other factors such as modifier loci unrelated to the PPOX gene may determine clinical manifestation of VP.

Low- and high-level expressions of heme oxygenase-1 in cultured cells under uninduced conditions.

Heme oxygenase-1 (HO-1) degrades heme into biliverdin, iron, and CO. The enzyme participates in adaptive and protective responses to oxidative stress and various inflammatory stimuli. We examined the regulation of HO-1 expression in culture cells under uninduced conditions. Observations by in situ hybridization and immunostaining showed that in cultured mouse fibroblast Balb/3T3 cells not subjected to treatment, 10-15% of cells highly expressed HO-1. The similar pattern of the expression of HO-1 was observed with mouse embryo liver BNL-CL2 cells and Chinese hamster ovary cells. The marked expression of HO-1 was related to the activation of stress-activated protein kinase and to the expression of cyclooxygenase (Cox)-2. When the cells were treated with arachidonic acid, a precursor of prostaglandin, induction of HO-1 in the HO-1-expressing cells but not in the low-expressing cells occurred. This increase was abrogated by the treatment with the Cox inhibitors, indomethacin, and dexamethasone. Neither prostaglandin H2, E2 nor F2a induced HO-1 expression. These results suggest that some cells respond to the cellular stress and intermediates of prostaglandin biosynthesis may act as endogenous stressors to induce HO-1.