Heme oxygenase 1 (HO-1) catalyzes heme breakdown, eventually releasing iron, carbon monoxide, and bilirubin IXalpha. HO-1 is induced by its substrate heme and various environmental factors, which represents a protective response against oxidative stresses. Here we show that hypoxia represses HO-1 expression in three human cell types but induces it in rat, bovine, and monkey cells, indicating the inter-species difference in the hypoxic regulation of HO-1 expression. The hypoxia-mediated ...

DESIGN: It has recently been shown that deficiency of adrenomedullin (AM), a potent vasodilator peptide, leads to insulin resistance. We studied expression of AM in NIH 3T3-L1 adipocytes and compared it with expression of resistin, an adipocyte-derived peptide hormone that is proposed to cause insulin resistance. Moreover, we studied the effects of tumor necrosis factor-alpha (TNF-alpha), a known mediator of insulin resistance, on the expression of AM and resistin in 3T3-L1 ...

Heme oxygenase consists of two structurally related isozymes, heme oxygenase-1 and and heme oxygenase-2, each of which cleaves heme to form biliverdin, iron and carbon monoxide. Expression of heme oxygenase-1 is increased or decreased depending on cellular microenvironments, whereas little is known about the regulation of heme oxygenase-2 expression. Here we show that hypoxia (1% oxygen) reduces the expression levels of heme oxygenase-2 mRNA and protein after 48 h of incubation in human ...

The retinal pigment epithelium (RPE) is essential for maintenance of photoreceptors and normally functions under conditions enriched with reactive oxygen species. RPE therefore expresses various defense enzymes against oxidative stress, including heme oxygenase-1 (HO-1). HO-1 catalyzes heme breakdown to release iron, carbon monoxide, and biliverdin, which is reduced to bilirubin, a potent radical scavenger. HO-1 expression is induced by various environmental factors, which has been ...

Erythroid-specific 5-aminolevulinate synthase (ALAS2) is the rate-limiting enzyme for heme biosynthesis in erythroid cells, and a missense mutation of the ALAS2 gene is associated with congenital sideroblastic anemia. However, the gene responsible for this form of anemia remains unclear in about 40% of patients. Here, we identify a novel erythroid-specific enhancer of 130 base pairs in the first intron of the ALAS2 gene. The newly identified enhancer contains a cis-acting element that is ...

δ-Aminolevulinic acid (ALA)-induced porphyrin accumulation is widely used in the treatment of cancer, as photodynamic therapy. To clarify the mechanisms of the tumor-preferential accumulation of protoporphyrin, we examined the effect of the expression of heme-biosynthetic and -degradative enzymes on the ALA-induced accumulation of protoporphyrin as well as photodamage. The transient expression of heme-biosynthetic enzymes in HeLa cells caused variations of the ALA-induced accumulation of ...

In eukaryotic cells, heme production is tightly controlled by heme itself through negative feedback-mediated regulation of nonspecific 5-aminolevulinate synthase (ALAS1), which is a rate-limiting enzyme for heme biosynthesis. However, the mechanism driving the heme-dependent degradation of the ALAS1 protein in mitochondria is largely unknown. In the current study, we provide evidence that the mitochondrial ATP-dependent protease ClpXP, which is a heteromultimer of CLPX and CLPP, is ...

Coproporphyrinogen oxidase (CPOX), the sixth enzyme in the heme-biosynthetic pathway, catalyzes oxidative decarboxylation of coproporphyrinogen to protoporphyrinogen and is located in the intermembrane space of mitochondria. To clarify the importance of CPOX in the regulation of heme biosynthesis in erythroid cells, we established human erythroleukemia K562 cells stably expressing mouse CPOX. The CPOX cDNA-transfected cells had sevenfold higher CPOX activity than cells transfected with ...

Sideroblastic anemia is characterized by anemia with the emergence of ring sideroblasts in the bone marrow. There are two forms of sideroblastic anemia, i.e., congenital sideroblastic anemia (CSA) and acquired sideroblastic anemia. In order to clarify the pathophysiology of sideroblastic anemia, a nationwide survey consisting of clinical and molecular genetic analysis was performed in Japan. As of January 31, 2012, data of 137 cases of sideroblastic anemia, including 72 cases of ...

Intracellular heme concentrations are maintained in part by heme degradation, which is catalyzed by heme oxygenase. Heme oxygenase consists of two structurally related isozymes, HO-1 and HO-2. Recent studies have identified HO-2 as a potential oxygen sensor. To gain further insights into the regulatory role of HO-2 in heme homeostasis, we analyzed the expression profiles of HO-2 and the biochemical consequences of HO-2 knockdown with specific short interfering RNA (siRNA) in human cells. ...

Hypoxia induces expansion of erythroid precursor cells through erythropoietin production. However, it has also been suggested that hypoxia could enhance hemoglobin production in erythroid cells directly. To identify the molecules that are involved in hemoglobin production under hypoxia, we examined the expression profile of mRNAs in YN-1 human erythroleukemia cells under hypoxia. DNA array analysis revealed that the expression of transforming growth factor (TGF)-beta1 and mitoferrin, ...

The erythroid transcription factor NF-E2 is an obligate heterodimer composed of two different subunits (p45 and p18), each containing a basic region-leucine zipper DNA binding domain, and it plays a critical role in erythroid differentiation as an enhancer-binding protein for expression of the beta-globin gene. We show here that dimethyl sulfoxide treatment of wild-type murine erythroleukemia cells, but not a mutant clone of dimethyl sulfoxide-resistant cells, increases NF-E2 activity ...

GATA-1 is a transcription factor essential for erythroid cell development, and knockdown of GATA-1 gene results in maturation arrest and transformation of erythroblasts. To clarify the mechanism that gives rise to this abnormal phenotype, genes that are aberrantly expressed in the spleen of heterozygous GATA-1 knockdown mutant mouse (referred to as GATA-1 mutant mouse) were identified by using cDNA array. One of these genes, YB-1, was found to be highly expressed in the spleen of GATA-1 ...

Sideroblastic anemia is characterized by anemia with the emergence of ring sideroblasts in the bone marrow. Ring sideroblasts are erythroblasts characterized by iron accumulation in perinuclear mitochondria due to impaired iron utilization. There are two forms of sideroblastic anemia, i.e., inherited and acquired sideroblastic anemia. Inherited sideroblastic anemia is a rare and heterogeneous disease caused by mutations of genes involved in heme biosynthesis, iron–sulfur (Fe–S) cluster ...

Heme plays an important biomodulating role in various cell functions. In this study, we examined the effects of hemin on cellular sensitivity to imatinib and other anti-leukemia reagents. Hemin treatment of human BCR/ABL-positive KCL22 leukemia cells increased IC(50) values of imatinib, that is, the drug resistance, in a dose-dependent manner without any change in the BCR/ABL kinase activity. Imatinib-induced apoptosis was also suppressed by hemin treatment in KCL22 cells. Hemin ...