CLPX regulates mitochondrial fatty acid β-oxidation in liver cells.

Mitochondrial fatty acid oxidation (β-oxidation) is an essential metabolic process for energy production in eukaryotic cells, but the regulatory mechanisms of this pathway are largely unknown. In the present study, we found that several enzymes involved in β-oxidation are associated with CLPX, the AAA+ unfoldase that is a component of the mitochondrial matrix protease ClpXP. The suppression of CLPX expression increased β-oxidation activity in the HepG2 cell line and in primary human hepatocytes without glucagon treatment.

Heme-dependent recognition of 5-aminolevulinate synthase by the human mitochondrial molecular chaperone ClpX.

The caseinolytic mitochondrial matrix peptidase chaperone subunit (ClpX) plays an important role in the heme-dependent regulation of 5-aminolevulinate synthase (ALAS1), a key enzyme in heme biosynthesis. However, the mechanisms underlying the role of ClpX in this process remain unclear. In this in vitro study, we confirmed the direct binding between ALAS1 and ClpX in a heme-dependent manner.

Establishment of a cell model of X-linked sideroblastic anemia using genome editing.

ALAS2 gene mutations cause X-linked sideroblastic anemia. The presence of ring sideroblasts in a patient's bone marrow is the hallmark of sideroblastic anemia, but the precise mechanisms underlying sideroblast formation are largely unknown. Using a genome-editing system, a mutation was introduced in the erythroid-specific enhancer of the ALAS2 gene in HUDEP2 cells, which were derived from human umbilical stem cells and can produce erythrocytes.

Iron metabolism in erythroid cells and patients with congenital sideroblastic anemia.

Sideroblastic anemias are anemic disorders characterized by the presence of ring sideroblasts in a patient's bone marrow. These disorders are typically divided into two types, congenital or acquired sideroblastic anemia. Recently, several genes were reported as responsible for congenital sideroblastic anemia; however, the relationship between the function of the gene products and ring sideroblasts is largely unclear.

Expression of (Pro)renin Receptor During Rapamycin-Induced Erythropoiesis in K562 Erythroleukemia Cells and Its Possible Dual Actions on Erythropoiesis.

(Pro)renin receptor ((P)RR), a specific receptor for renin and prorenin, is expressed in erythroblastic cells. (P)RR has multiple biological actions: prorenin activation, stimulation of the intracellular signaling including extracellular signal-regulated kinases, and functional complex formation with vacuolar H-ATPase (v-ATPase). However, the functional implication of (P)RR in erythroblast cells has not been clarified.

Novel Mechanisms for Heme-dependent Degradation of ALAS1 Protein as a Component of Negative Feedback Regulation of Heme Biosynthesis.

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 involved in the heme-dependent degradation of ALAS1 in mitochondria.

Enhancements of the production of bilirubin and the expression of β-globin by carbon monoxide during erythroid differentiation.

Heme is degraded by heme oxygenase to form iron, carbon monoxide (CO), and biliverdin. However, information about the catabolism of heme in erythroid cells is limited. In this study, we showed the production and export of bilirubin in murine erythroleukemia (MEL) cells.

Identification of a novel erythroid-specific enhancer for the ALAS2 gene and its loss-of-function mutation which is associated with congenital sideroblastic anemia.

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.

Clinical and genetic characteristics of congenital sideroblastic anemia: comparison with myelodysplastic syndrome with ring sideroblast (MDS-RS).

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.

Depletion of glutamine enhances sodium butyrate-induced erythroid differentiation of K562 cells.

Human erytholeukemia K562 cells are induced to differentiate along the erythroid lineage by a variety of chemical compounds, including hemin, sodium butyrate and 1-β-d-arabinofuranosylcytosine. We have investigated the induction of erythroid differentiation of K562 cells by glutamine depletion. When K562 cells were cultured in glutamine-minus medium, the induction of hemoglobin synthesis, accompanied by those of heme-biosynthetic enzymes and erythroid transcriptional factors, was observed.

Coordinated expression of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 4 and heme oxygenase 2: evidence for a regulatory link between glycolysis and heme catabolism.

Heme is an essential requirement for cell survival. Heme oxygenase (HO) is the rate-limiting enzyme in heme catabolism and consists of two isozymes, HO-1 and HO-2. To identify the protein that regulates the expression or function of HO-1 or HO-2, we searched for proteins that interact with both isozymes, using protein microarrays.

Expression of (pro)renin receptor in human erythroid cell lines and its increased protein accumulation by interferon-γ.

The renin-angiotensin system is known to enhance erythropoiesis. (Pro)renin receptor ((P)RR), a specific receptor for renin and prorenin, has recently been identified. However, expression of (P)RR in erythroid cells has not been studied.

The carboxyl-terminal region of erythroid-specific 5-aminolevulinate synthase acts as an intrinsic modifier for its catalytic activity and protein stability.

Erythroid-specific 5-aminolevulinate synthase (ALAS2) is essential for hemoglobin production, and a loss-of-function mutation of ALAS2 gene causes X-linked sideroblastic anemia. Human ALAS2 protein consists of 587 amino acids and its carboxyl(C)-terminal region of 33 amino acids is conserved in higher eukaryotes, but is not present in prokaryotic ALAS. We explored the role of this C-terminal region in the pathogenesis of X-linked sideroblastic anemia.

Roles of porphyrin and iron metabolisms in the δ-aminolevulinic acid (ALA)-induced accumulation of protoporphyrin and photodamage of tumor cells.

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 protoporphyrin.

Hereditary sideroblastic anemia: pathophysiology and gene mutations.

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.

Hypoxemia induces expression of heme oxygenase-1 and heme oxygenase-2 proteins in the mouse myocardium.

Heme oxygenase (HO) catalyzes oxidative breakdown of heme, and constitutes two isozymes, HO-1 and HO-2. Here, we explored the tissue-specific regulation of expression of HO-1 and HO-2 under hypoxemia. There was no significant change in the overall expression levels of HO-1 and HO-2 mRNAs and proteins in the lung during adaptation of C57BL/6 mice to normobaric hypoxia (10% O(2)).

Functional expression of heme oxygenase-1 in human differentiated epidermis and its regulation by cytokines.

Although heme oxygenase-1 (HO-1) is induced in keratinocytes after UV radiation, HO-1 expression during normal epidermal differentiation has not yet been reported. We showed by real-time PCR, western blotting, and ELISA that HO-1 mRNA and protein expression by cultured normal human keratinocytes was upregulated during epidermal differentiation induced by a high-calcium medium. Immunohistochemical staining and in situ hybridization showed the graduated expression of HO-1 in the upper epidermis, which was accompanied by suprabasal HO-1 mRNA expression, and the accumulation of bilirubin (BR) in the stratum corneum.

Induction of lipocalin-type prostaglandin D synthase in mouse heart under hypoxemia.

Hypoxemia is a common manifestation of various disorders and generates pressure overload to the heart. Here we analyzed the expression of lipocalin-type prostaglandin D synthase (L-PGDS) in the heart of C57BL/6 mice kept under normobaric hypoxia (10% O2) that generates hemodynamic stress. Northern and Western blot analyses revealed that the expression levels of L-PGDS mRNA and protein were significantly increased (> twofold) after 14 days of hypoxia, compared to the mice kept under normoxia.

Hypoxia induces erythroid-specific 5-aminolevulinate synthase expression in human erythroid cells through transforming growth factor-beta signaling.

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.

Hypoxia decreases the expression of the two enzymes responsible for producing linear and cyclic tetrapyrroles in the heme biosynthetic pathway.

Heme is synthesized in all cell types in aerobic organisms. Hydroxymethylbilane synthase (HMBS) and uroporphyrinogen III synthase (UROS) catalyze two consecutive reactions in the heme biosynthetic pathway, generating the first linear and the first cyclic tetrapyrroles, respectively. Each of the HMBS and UROS genes contains the two separate promoters that generate ubiquitous and erythroid-specific mRNAs.

Hemin reduces cellular sensitivity to imatinib and anthracyclins via Nrf2.

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.

Leishmania spp.: delta-aminolevulinate-inducible neogenesis of porphyria by genetic complementation of incomplete heme biosynthesis pathway.

To further develop the Leishmania model for porphyria based on their deficiencies in heme biosynthesis, three Old World species were doubly transfected as before for Leishmania amazonensis with cDNAs, encoding the 2nd and 3rd enzymes in the pathway. Expression of the transgenes was verified immunologically at the protein level and functionally by uroporphyrin neogenesis that occurs only after exposure of the double-transfectants to delta-aminolevulinate. All species examined were equally deficient in heme biosynthesis, as indicated by the accumulation of uroporphyrin as the sole porphyrin and the production of coproporphyrin upon further transfection of one representative species with the downstream gene.

Heme as a magnificent molecule with multiple missions: heme determines its own fate and governs cellular homeostasis.

Heme is a prosthetic group of various types of proteins, such as hemoglobin, myoglobin, cytochrome c, cytochrome p450, catalase and peroxidase. In addition, heme is involved in a variety of biological events by modulating the function or the state of hemoproteins. For example, protein synthesis is inhibited in erythroid cells under heme deficiency, as the consequence of the activation of heme-regulated inhibitor (HRI).