Regulation of the genes for heme pathway enzymes in erythroid and in non-erythroid cells

Application of fluorescent probe for labile heme quantification in physiological dynamics

Heme is an essential prosthetic molecule for life activities and is well known to act as the active center of many proteins, however, labile heme (LH) released from proteins is a harmful molecule that produces reactive oxygen species and must be strictly controlled. Recently, LH has been suggested to function as an important molecule for diverse physiological responses. Quantitative analysis of the intracellular dynamics of LH is essential for understanding its physiological functions, a substantially practical method has not been established. Here, we successfully developed an alternative method that can be used to complement quantification of the dynamics of intracellular LH using H-FluNox, an activity-based specific fluorescent probe recently constructed. Our newly established method should be effective in elucidating the physiological functions of LH.

Do Mammalian Cells Really Need to Export and Import Heme?

Heme is a cofactor that is essential to almost all forms of life. The production of heme is a balancing act between the generation of the requisite levels of the end-product and protection of the cell and/or organism against any toxic substrates, intermediates and, in this case, end-product. In this review, we provide an overview of our understanding of the formation and regulation of this metallocofactor and discuss new research on the cell biology of heme homeostasis, with a focus on putative transmembrane transporters now proposed to be important regulators of heme distribution. The main text is complemented by a discussion dedicated to the intricate chemistry and biochemistry of heme, which is often overlooked when new pathways of heme transport are conceived.

Haem Biosynthesis and Antioxidant Enzymes in Circulating Cells of Acute Intermittent Porphyria Patients

The aims of the present study were to explore the expression pattern of haem biosynthesis enzymes in circulating cells of patients affected by two types of porphyria (acute intermittent, AIP, and variegate porphyria, VP), together with the antioxidant enzyme pattern in AIP in order to identify a possible situation of oxidative stress. Sixteen and twelve patients affected by AIP and VP, respectively, were analysed with the same numbers of healthy matched controls. Erythrocytes, neutrophils and peripheral blood mononuclear cells (PBMCs) were purified from blood, and RNA and proteins were extracted for quantitative real time PCR (qRT-PCR) and Western-blot analysis, respectively. Porhobilinogen deaminase (PBGD) and protoporphyrinogen oxidase (PPOX) gene and protein expression was analysed. Antioxidant enzyme activity and gene expression were additionally determined in blood cells, together with protein carbonyl content in plasma. PBMCs isolated from AIP patients presented low mRNA levels of PBGD when compared to controls, while PBMCs isolated from VP patients presented a decrease in PPOX mRNA. PPOX protein content was higher in AIP patients and lower in VP patients, compared to healthy controls. Regarding antioxidant enzymes, PBMCs and erythrocyte superoxide dismutase (SOD) presented statistically significant higher activity in AIP patients compared to controls, while catalase activity tended to be lower in these patients. No differences were observed regarding antioxidant gene expression in white blood cells. Circulating cells in AIP and VP patients present altered expression of haem biosynthetic enzymes, which could be useful for the differential diagnosis of these two types of porphyria in certain difficult cases. AIP patients present a condition of potential oxidative stress similar to VP patients, evidenced by the post-transcriptional activation of SOD and possible catalase impairment.

Continuous de novo biosynthesis of haem and its rapid turnover to bilirubin are necessary for cytoprotection against cell damage

It is well known that haem serves as the prosthetic group of various haemoproteins that function in oxygen transport, respiratory chain, and drug metabolism. However, much less is known about the functions of the catabolites of haem in mammalian cells. Haem is enzymatically degraded to iron, carbon monoxide (CO), and biliverdin, which is then converted to bilirubin. Owing to difficulties in measuring bilirubin, however, the generation and transport of this end product remain unclear despite its clinical importance. Here, we used UnaG, the recently identified bilirubin-binding fluorescent protein, to analyse bilirubin production in a variety of human cell lines. We detected a significant amount of bilirubin with many non-blood cell types, which was sensitive to inhibitors of haem metabolism. These results suggest that there is a basal level of haem synthesis and its conversion into bilirubin. Remarkably, substantial changes were observed in the bilirubin generation when cells were exposed to stress insults. Since the stress-induced cell damage was exacerbated by the pharmacological blockade of haem metabolism but was ameliorated by the addition of biliverdin and bilirubin, it is likely that the de novo synthesis of haem and subsequent conversion to bilirubin play indispensable cytoprotective roles against cell damage.

Heme as key regulator of major mammalian cellular functions: molecular, cellular, and pharmacological aspects

Heme (iron protoporphyrin IX) exists as prosthetic group in several hemoproteins, which include respiration cytochromes, gas sensors, P450 enzymes (CYPs), catalases, peroxidases, nitric oxide synthases (NOS), guanyl cyclases, and even transcriptional factors. Hemin (the oxidized form of iron protoporphyrin IX) on the other hand is an essential regulator of gene expression and growth promoter of hematopoietic progenitor cells. This review is focused on the major developments occurred in this field of heme biosynthesis and catabolism and their implications in our understanding the pathogenesis of heme-related disorders like anemias, acute porphyrias, hematological malignancies (leukemias), and other disorders. Heme is transported into hematopoietic cells and enters the nucleus where it activates gene expression by removing transcriptional potential repressors, like Bach1, from enhancer DNA sequences. Evidence also exists to indicate that heme acts like a signaling ligand in cell respiration and metabolism, stress response adaptive processes, and even transcription of several genes. Impaired heme biosynthesis or heme deficiency lead to hematological disorders, tissue degeneration, and aging, while heme prevents cell damage via activation of heme oxygenase-1 (HO-1) gene. Therefore, heme, besides being a key regulator of mammalian functions, can be also a useful therapeutic agent alone or in combination with other drugs in several heme-related disorders.

Early apoptotic features of K562 cell death induced by 5-aminolaevulinic acid-based photodynamic therapy

5-Aminolaevulinic acid-based photodynamic therapy (ALA-PDT) is used to eliminate cancerous cells through photoactivation of endogenously formed protoporphyrin IX (PPIX) following the administration of PPIX precursor, 5-aminolaevulinic acid (ALA). We report on the kinetics of PPIX accumulation and the mechanism of cytotoxic effects of ALA-PDT studied in the chronic myelogenous leukaemia derived cell line K562. The PPIX distribution and, consequently, cytotoxic effects were found to be heterogenous. A subpopulation of K562 cells accumulating PPIX to a lesser extent exhibits only transient cell cycle arrest. A fraction of cells, probably those with higher PPIX accumulation, are irreversibly damaged by ALA-PDT. We detected several signs of an early apoptosis: lowering of Bcl-xL expression, decrease of the mitochondrial and plasma membrane potential, the cytochrome c release into the cytoplasm, and the unmasking of the mitochondrial antigen 7A6. However, late apoptotic events were lacking: neither caspase-3 activation nor DNA fragmentation occurred. Instead, rapidly progressing cell necrosis resulting from plasma membrane damage was observed. We suggest that the high level of the antiapoptotic heat-shock proteins HSP70 and HSP27 found by us in the K562 cells is responsible for the inhibition of the apoptotic process upstream of caspases activation.

5-aminolevulinic acid-based photodynamic therapy in leukemia cell HL60

A study to explore the optimal experimental parameters and the photosensitization of 5-aminolevulinic acid (ALA)-based photodynamic therapy (PDT) in promyelocytic leukemia cell HL60 has been conducted, in which HL60 cells and their control groups, peripheral blood mononuclear cell (PBMC), first are incubated with different concentrations of ALA in dark for different periods of time and then followed by irradiating with different wavebands for different fluences. Fluorescence microscope and spectrofluorometer have been used to detect the fluorescence of protoporphyrin IX (PpIX) endogenously produced by ALA. The response of the cells to ALA-PDT was evaluated by the 3-(4,5-dimethyl-2-thiazolyl)-2-5-diphenyl-2H-tetrazolium bromide (MTT) assay (interval between irradiation and the MTT assay is 24 h) and by flow cytometry (the length of time between irradiation and the flow assay is 30 min). MTT results will reflect the relative number of metabolically active mitochondria in the population. Propidium iodide uptake in flow cytometry will test for membrane damage. The results of parameter experiments were obtained: 1 x 10(5)/mL HL60 cell was first incubated with 1 mmol/L ALA in dark for 4 h and the maximum fluorescence of PpIX level appeared; then irradiated with 410 nm (4 mW/cm2) for 14.4 J/cm2 and maximum photodamage to membrane and mitochondrial function of HL60 cell resulted. With the normal granulocytes, such response was not detected. Therefore a hypothetical idea can be brought forward that ALA-based PDT can be used for inactivation of leukemia cell HL60 and these optimal parameters may be useful for clinical application.

Differentiation-dependent photodynamic therapy regulated by porphobilinogen deaminase in B16 melanoma

Protoporphyrin IX (PpIX) synthesis by malignant cells is clinically exploited for photodiagnosis and photodynamic therapy following administration of 5-aminolevulinic acid (ALA). The expression and activity of the housekeeping porphobilinogen deaminase (PBGD) was correlated to PpIX synthesis in differentiating B16 melanoma cells. Differentiation was stimulated by two inducers, butyrate and hexamethylene bisacetamide (HMBA), both of which promote the formation of typical melanosomes and melanin, as well as morphological changeover. A marked decrease in total PBGD activity and PpIX synthesis was observed following stimulation by butyrate, while HMBA induced an opposite effect. In contrast, ferrochelatase levels remained unchanged. Photodynamic inactivation of the cells undergoing differentiation was largely dependent on the PpIX accumulation, which was modulated by the two inducers butyrate and HMBA. Fluorescence immunostaining with anti-PBGD antibodies revealed a major PBGD fraction in the nucleus and a minor fraction in the cytosol. This nuclear localisation pattern was confirmed by expression of PBGD fused to green fluorescence protein. We suggest that efficient photodynamic therapy of cancer facilitated by ALA administration can be enhanced using combined therapeutic modalities.

Mitochondrial and endoplasmic reticulum stress-induced apoptotic pathways are activated by 5-aminolevulinic acid-based photodynamic therapy in HL60 leukemia cells

We studied the mechanism of the cytotoxic effects of 5-aminolevulinic acid-based photodynamic therapy (ALA-PDT; induction with 1 mM ALA for 4 h followed by a blue light dose of 18 J/cm(2)) on the human promyelocytic leukemia cell line HL60 using biochemical and electron microscopy methods. The disruption of mitochondrial membrane potential, deltapsi(m), was paralleled by a decrease in ATP level, unmasking of the mitochondrial antigen 7A6, release of cytochrome c into the cytoplasm, activation of caspases 9 and 3 and cleavage of poly(ADP-ribose) polymerase (PARP). This was followed by DNA fragmentation. These data suggest that ALA-PDT activates the mitochondrial apoptotic pathway. The level of endoplasmic reticulum Ca(2+)-binding chaperones ERp57 and ERp72 and of anti-apoptotic proteins Bcl-2 and Bcl-x(L) was decreased whereas that of Ca(2+)-binding protein calmodulin and the stress protein HSP60 was elevated following ALA-PDT. Inhibition of the initiator caspase 9, execution caspase 3 and Ca(2+)-dependent protease m-calpain, did not prevent DNA fragmentation. We conclude that, in our in vitro model, ALA-based photodynamic treatment initiates several signaling processes in HL60 cells that lead to rapidly progressing apoptosis, which is followed by slow necrosis. Two apoptotic processes proceed in parallel, one representing the mitochondrial pathway, the other involving disruption of calcium homeostasis and activation of the endoplasmic reticulum stress-mediated pathway.

Molecular profiling of anemia in acute renal allograft rejection using DNA microarrays

Compromised renal function after renal allograft transplantation often results in anemia in the recipient. Molecular mechanisms leading to anemia during acute rejection are not fully understood; inadequate erythropoietin production and iron deficiency have been reported to be the main contributors. To increase our understanding of the molecular events underlying anemia in acute rejection, we analyzed the gene expression profiles of peripheral blood lymphocytes (PBL) from four pediatric renal allograft recipients with acute rejection and concurrent anemia, using DNA microarrays containing 9000 human cDNA clones (representing 7469 unique genes). In these anemic rejecting patients, an 'erythropoiesis cluster' of 11 down-regulated genes was identified, involved in hemoglobin transcription and synthesis, iron and folate binding and transport. Additionally, some alloimmune response genes were simultaneously down-regulated. An independent data set of 36 PBL samples, some with acute rejection and some with concurrence of acute rejection and anemia, were analyzed to support a possible association between acute rejection and anemia. In conclusion, analysis using DNA microarrays has identified a cluster of genes related to hemoglobin synthesis and/or erythropoeisis that was altered in kidneys with renal allograft rejection compared with normal kidneys. The possible relationship between alterations in the expression of this cluster, reduced renal function, the alloimmune process itself, and other influences on the renal transplant awaits further analysis.

Nuclear distribution of porphobilinogen deaminase (PBGD) in glioma cells: a regulatory role in cancer transformation?

Recently, considerable interest has been directed to red-fluorescence photodiagnosis of brain and other tumours during surgery using the protoporphyrin IX natural precursor, 5-aminolaevulinic acid. In the present study we focused on the role of the rate-limiting enzyme porphobilinogen deaminase in glioma C6 cell activity, differentiation and sub-cellular distribution. Over-expression of the human housekeeping porphobilinogen deaminase in the glioma cells, using the housekeeping-porphobilinogen deaminase plasmid, induced a G1 cell cycle attenuation accompanied by increases in enzyme activity and c6 differentiation toward astrocytes. Visualisation of subcellular localisation of the porphobilinogen deaminase using the independent techniques of fluorescence immuno-staining with specific anti-human porphobilinogen deaminase antibodies and cellular expression of porphobilinogen deaminase fused to green fluorescent protein, revealed (unexpectedly) a major fraction of porphobilinogen deaminase in the nucleus and only a minor fraction in the cytoplasm. Both C and N terminals of porphobilinogen deaminase fused to green fluorescent protein revealed a major fraction of the newly synthesized fused porphobilinogen deaminase in the nucleus. Furthermore, newborn rat brain cells grown in a primary culture showed the same localisation pattern of porphobilinogen deaminase in the nuclei. Stimulation of C6 glioma cell differentiation by butyrate induced a marked decrease in porphobilinogen deaminase both in the nucleus and in the cytoplasm as determined by Western blotting and fluorescence immuno-localisation. These findings suggest a possible dual role for housekeeping porphobilinogen deaminase in fast dividing glioma cells, one related to the porphyrin synthesis pathway and another coupled to nuclear function, which might be linked to tumorigenesis.

Human erythroid porphobilinogen deaminase exists in 2 splice variants

Human porphobilinogen deaminase (PBGD) is, reportedly, encoded by 2 distinct messenger RNAs (mRNAs) transcribing from a single gene. The ubiquitous form of the PBGD gene product is often used as an endogenous reference in gene expression studies because it is pseudogene free and has minimal transcriptional variability among tissues. A distinct erythroid-specific gene product has also been described because of the alternate splicing of the gene. Here is reported the existence of an additional erythroid-specific isoform of PBGD mRNA in primary cells.

Cloning of a coproporphyrinogen oxidase promoter regulatory element binding protein

Coproporphyrinogen oxidase [CPO] gene promoter regulatory element (CPRE) plays an important role in CPO gene regulation. To isolate a CPRE binding protein, we performed Southwestern screening of K562 cDNA expression library using CPRE as a probe and isolated a cDNA clone which encoded a novel protein, Klp1 (K562 cell-derived leucine-zipper-like protein 1). Klp1 mRNA was highly expressed in K562 cells, HeLa cells, and brain as a single transcript (1.4 kb). Gel mobility shift assays revealed that Klp1 specifically binds to CPRE. Computational analysis revealed that Klp1 has a leucine-zipper-like structure, a Leu-X-X-Leu-Leu motif, and a putative nuclear localization signal in the basic amino acid rich region. Transfection of the Klp1 expression vector into THP-1 cells resulted in transcriptional activation of a reporter construct containing CPRE. These results indicate that Klp1 is a DNA sequence-specific transcription factor that regulates gene expression of genes that contain CPRE in their regulatory region.

Protein changes in HL60 leukemia cells associated with 5-aminolevulinic acid-based photodynamic therapy. Early effects on endoplasmic reticulum chaperones

Using two-dimensional electrophoresis we investigated the effect of 5-aminolevulinic acid (ALA)-based photodynamic therapy (PDT; induction with 1 mM ALA for 4 h followed by blue light dose of 18 J/cm2) on the protein expression in HL60 leukemia cells. ALA-PDT resulted in extensive qualitative and quantitative changes in the protein pattern of HL60 cell lysates. Of more than 1350 protein spots recognized on the protein maps of ALA-induced cells, seven proteins were enhanced and 17 suppressed following irradiation. Three of these, calreticulin precursor, p58 microsomal protein (ERp57) and protein disulfide isomerase (p55) have been identified by matrix-assisted laser desorption and ionization-mass spectrometry and the pI/molecular weight parameters of the affected proteins were estimated by computer analysis. The findings suggest participation of endoplasmic reticulum Ca(2+)-binding chaperones and/or Ca2+ signaling in ALA-PDT mediated cytotoxicity.

MPTP selectively induces haem oxygenase-1 expression in striatal astrocytes

Parkinson's disease (PD) is characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta with accompanying evidence of increased oxidative damage, deficits in mitochondrial function and iron deposition. Recently, haem oxygenase-1 levels were reported to be elevated in PD brains. Because this enzyme is involved in the response to oxidative stress and is critical for cellular haem and iron homeostasis, it could play a role in the pathogenesis of PD. Therefore, we investigated the expression of haem oxygenase isoform 1 (HO-1) in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. MPTP triggered a relatively rapid and persistent increase in HO-1 mRNA exclusively in the mouse striatum. In situ hybridization and immunohistochemistry showed HO-1 to be localized to striatal astrocytes. The induction of HO-1 by MPTP was blocked by selegiline and GBR-12909, indicating the protoxin had to be metabolized by monoamine oxidase B and taken up by dopaminergic neurons to exert its action in astrocytes. MPTP did not alter the expression of other enzymes of haem synthesis or degradation nor were the levels of mRNA for haem or iron-binding proteins changed. Thus, expression of HO-1 was not part of a cellular program involving haem biosynthesis or homeostasis. In addition, heat shock proteins were not induced by MPTP. Thus, MPTP elicited a selective transcriptional response in striatal astrocytes. This response appears to be mediated by molecules released from affected dopaminergic nerve terminals in the striatum acting upon neighbouring astrocytes. This signalling pathway and its potential relevance to PD are discussed.

[Hepatic porphyrias and alcohol]

Alcohol has an porphyrinogenic action and can cause a disturbance of porphyrin metabolism in healthy people as well as lead to a biochemical and clinical manifestation of acute and chronic hepatic porphyrias, especially acute intermittent porphyria and porphyria cutanea tarda. After excessive consumption of alcohol a temporary, clinically asymptomatic secondary hepatic coproporphyrinuria in man can be observed, which can become persistent in cases of alcohol-induced liver damage. Nowadays alcohol-liver-porphyrinuria syndrome is the first to be mentioned in secondary hepatic disturbances of porphyrin metabolism. In people with a genetic lack of uroporphyrinogen-decarboxylase alcohol is able to transform an asymptomatic coproporphyrinuria into a chronic hepatic porphyria or porphyria cutanea tarda. From experimental and clinical studies the conclusion can be drawn that alcohol inhibits the enzymes delta-aminolevulinic-acid-dehydratase (synonym: porphobilinogen-synthase), uroporphyrinogen-decarboxylase and coproporphyrinogen-oxidase and induces delta-aminolevulinic-acid-synthase in the liver. Abstinence of alcohol is a therapeutically and prophylactically important measurement in all types of hepatic porphyrias. For clinical experience follows that in cases with chronic consumption of alcohol, fatty liver, alcohol induced hepatitis and liver cirrhosis porphyrin studies in urine should be made to notice a hepatic porphyria in the latent phase very early. When dealing with abdominal and cutaneous symptoms in clinical context with consumption of alcohol one has to exclude hepatic porphyria differential diagnostically.

Porphyrins, porphyrias, cancer and photodynamic therapy--a model for carcinogenesis

Porphyrins are the only and most powerful photosensitizers synthesized internally. To understand better the involvement of porphyrins in photosensitization reactions, the heme biosynthetic pathway is first described, as well as the main features of its regulation in both erythroid and hepatic cells. Most disorders of porphyrin metabolism, known as porphyrias, are characterized by porphyrin accumulation. A full discussion of these diseases, their classification and relevant biochemical and clinical signs are presented. Abnormalities in heme biosynthesis in disorders other than porphyrias, such as iron-deficient and sideroblastic anemias, lead poisoning, hereditary tyrosinemia, chronic renal disease and alcoholism, are briefly considered. A complete survey of the experimental research on the biosynthesis of porphyrins in tumors and of the important association between cancer and porphyrias is dealt with. The link to photodynamic therapy (PDT) emerges naturally and this is treated from the point of view of using porphyrins endogenously formed by the tumors for their localization and PDT. Finally, considering the nature of the alterations occurring in heme metabolism in tumors, and porphyrias and their ubiquity, a model is discussed where the abnormality of heme synthesis is involved in the initiating lesion of carcinogenesis. The model strongly predicts that the incidence of cancer will be high in cells with abnormal heme metabolism, suggesting that porphyric patients may be at greater risk of the development of cancer.

Mitochondrial actaptations to chronic muscle use: Effect of iron deficiency

1. The effects of chronic muscle use on mitochondrial structure, enzymes and gene expression is reviewed. The role of iron deficiency in modulating this adaptation is discussed. 2. Chronic muscle use and disuse alter mitochondrial composition and affect mitochondrial subpopulations differentially. This has implications for an understanding of organelle assembly. 3. Iron deficiency decreases mitochondrial functional mass within muscle by reducing the level of heme and non-heme iron-containing components. This alters the metabolic response during exercise and results in a reduced endurance performance. 4. Both iron deficiency and chronic muscle use represent contrasting experimental models for the study of mitochondrial function and biogenesis.

Sequential activation of genes for heme pathway enzymes during erythroid differentiation of mouse Friend virus-transformed erythroleukemia cells

Changes in the level of transcripts encoding enzymes of the heme biosynthetic pathway as well as those encoding ubiquitous proteins were examined in murine Friend virus-transformed erythroleukemia cells during erythroid cell differentiation induced by chemicals including dimethyl sulfoxide (DMSO). Early changes following DMSO treatment were marked decreases in mRNAs for three ubiquitous proteins, i.e., a 70 kDa heat shock protein (less than 6 h), heme oxygenase and nonspecific delta-aminolevulinate synthase (ALAS) (less than 12 h). These changes were followed by sequential increases in mRNAs for enzymes in the heme biosynthetic pathway. Namely, mRNAs for the erythroid-specific ALAS, delta-aminolevulinate dehydratase, porphobilinogen deaminase and uroporphyrinogen decarboxylase started to increase at 12, 18, 18-24 and 24 h, respectively. Nuclear runoff studies revealed that these changes are largely transcriptional. Treatments with other inducers of erythroid differentiation, e.g., hexamethylene bisacetamide, n-butyric acid and N'-methylnicotinamide, also showed similar effects on mRNAs as those following DMSO. These findings suggest that both suppression of ubiquitous genes and activation of heme pathway enzyme genes are associated with erythroid differentiation, and the former occurs preceding changes in the latter.