A single promoter directs both housekeeping and erythroid preferential expression of the human ferrochelatase gene

Regulation of the expression of ferrochelatase in a murine model of diabetes mellitus type I

Background

Diabetes produces changes on cellular hemeprotein metabolism. The last enzyme of heme biosynthetic pathway is ferrochelatase (FECH), an enzyme that catalyzes the insertion of ferrous ion into protoporphyrin IX to produce heme. The aim of this work was to investigate whether FECH expression can be other key point in the regulation of heme biosynthesis in diabetic animals.

Methods

Mice were rendered diabetic with streptozotocin (STZ, 170 mg/kg body weight i.p. for 15 days). Liver FECH protein and mRNA levels were evaluated by Western blot and Northern blot respectively. Vanadate was used as a hypoglycemic agent. The levels of the transcription factor Sp1 bound to the FECH promoter were assessed by chromatin immunoprecipitation (ChIP).

Results

Hyperglycemia caused an increase in FECH mRNA levels but no changes in FECH protein expression. ChIP analysis revealed that the increase in FECH mRNA levels was due to enhanced Sp1 binding to the FECH promoter in diabetic animals, which was reduced by vanadate administration.

Conclusions

In diabetic animals, enhanced binding of Sp1 to the FECH promoter may be responsible for the increase in FECH mRNA levels. However, this increase was not reflected in the amount of FECH protein, which would confirm that FECH could be another control point in heme synthesis.

RNA-Based Biomarkers of Iron Metabolism in Dried Blood Spots for Detecting Recombinant Human Erythropoietin in Doping Control

Erythropoietin (EPO) abuse in sports has been a major challenge in doping analysis for decades. Although the Athlete Biological Passport (ABP) serves as an indirect method for EPO detection, it requires continual improvement to increase its sensitivity and reliability. Biomarkers related to iron metabolism and erythropoiesis as complementary parameters to enhance the ABP hematology module have the potential to improve its ability to detect EPO indirectly. In this study, RNA was extracted from dried blood spot (DBS) samples collected over 28 days (days 0, 1, 3, 5, 7, 9, 11, 13, 21, and 28) following the administration of therapeutic doses of recombinant human EPO (Yibiao, 50 IU/kg per dose, administered subcutaneously twice). The expression of four genes, namely, mitoferrin 1 (MFRN1), ferrochelatase (FECH), ferroportin (FPN), and ferritin heavy chain (FTH), was analyzed. The results revealed significant expression changes, with MFRN1 demonstrating peak increases of 2.43-fold, and presented detection windows extending beyond Day 9, providing greater sensitivity and longer detection windows than traditional ABP parameters do. The integration of MFRN1 into the ABP framework has the potential to increase the detection of EPO misuse in athletes.

Spatiotemporal expression and control of haemoglobin in space

It is now widely recognised that the environment in space activates a diverse set of genes involved in regulating fundamental cellular pathways. This includes the activation of genes associated with blood homoeostasis and erythropoiesis, with a particular emphasis on those involved in globin chain production. Haemoglobin biology provides an intriguing model for studying space omics, as it has been extensively explored at multiple -omic levels, spanning DNA, RNA, and protein analyses, in both experimental and clinical contexts. In this study, we examined the developmental expression of haemoglobin over time and space using a unique suite of multi-omic datasets available on NASA GeneLab, from the NASA Twins Study, the JAXA CFE study, and the Inspiration4 mission. Our findings reveal significant variations in globin gene expression corresponding to the distinct spatiotemporal characteristics of the collected samples. This study sheds light on the dynamic nature of globin gene regulation in response to the space environment and provides valuable insights into the broader implications of space omics research.

Heme Biosynthetic Gene Expression Analysis With dPCR in Erythropoietic Protoporphyria Patients

Background: The heme biosynthesis (HB) involves eight subsequent enzymatic steps. Erythropoietic protoporphyria (EPP) is caused by loss-of-function mutations in the ferrochelatase (FECH) gene, which in the last HB step inserts ferrous iron into protoporphyrin IX (PPIX) to form heme.

Aim and method: The aim of this work was to for the first time analyze the mRNA expression of all HB genes in peripheral blood samples of patients with EPP having the same genotype FECH c.[215dupT]; [315-48T > C] as compared to healthy controls by highly sensitive and specific digital PCR assays (dPCR).

Results: We confirmed a decreased FECH mRNA expression in patients with EPP. Further, we found increased ALAS2 and decreased ALAS1, CPOX, PPOX and HMBS mRNA expression in patients with EPP compared to healthy controls. ALAS2 correlated with FECH mRNA expression (EPP: r = 0.63, p = 0.03 and controls: r = 0.68, p = 0.02) and blood parameters like PPIX (EPP: r = 0.58 p = 0.06).

Conclusion: Our method is the first that accurately quantifies HB mRNA from blood samples with potential applications in the monitoring of treatment effects of mRNA modifying therapies in vivo, or investigation of the HB pathway and its regulation. However, our findings should be studied in separated blood cell fractions and on the enzymatic level.

Zebrafish as a model system to delineate the role of heme and iron metabolism during erythropoiesis

Coordination of iron acquisition and heme synthesis is required for effective erythropoiesis. The small teleost zebrafish (Danio rerio) is an ideal vertebrate animal model to replicate various aspects of human physiology and provides an efficient and cost-effective way to model human pathophysiology. Importantly, zebrafish erythropoiesis largely resembles mammalian erythropoiesis. Gene discovery by large-scale forward mutagenesis screening has identified key components in heme and iron metabolism. Reverse genetic screens, using morpholino-knockdown and CRISPR/Cas9, coupled with the genetic tractability of the developing embryo have further accelerated functional studies. Ultimately, the ex utero development of zebrafish embryos combined with their transparency and developmental plasticity could provide a deeper understanding of the role of iron and heme metabolism during early vertebrate embryonic development.

Emerging Regulatory Role of Nrf2 in Iron, Heme, and Hemoglobin Metabolism in Physiology and Disease

Iron has played an important role in energy production since the beginning of life, as iron-catalyzed redox reactions are required for energy production. Oxygen, a highly efficient electron acceptor with high reduction potential, facilitates highly efficient energy production in eukaryotic cells. However, the increasing atmospheric oxygen concentration produces new threats to the organism, as oxygen reacts with iron and produces reactive oxygen species unless its levels are strictly regulated. As the size of multicellular organisms increases, these organisms must transport oxygen to the peripheral tissues and begin to employ red blood cells containing hemoglobin. This system is potentially a double-edged sword, as hemoglobin autoxidation occurs at a certain speed and releases free iron into the cytoplasm. Nrf2 belongs to the CNC transcription factor family, in which NF-E2p45 is the founding member. NF-E2p45 was first identified as a transcription factor that binds to the erythroid gene regulatory element NF-E2 located in the promoter region of the heme biosynthetic porphobilinogen deaminase gene. Human Nrf2 was also identified as a transcription factor that binds to the regulatory region of the β-globin gene. Despite these original findings, NF-E2p45 and Nrf2 knockout mice exhibit few erythroid phenotypes. Nrf2 regulates the expression of a wide range of antioxidant and detoxification enzymes. In this review article, we describe and discuss the roles of Nrf2 in various iron-mediated bioreactions and its possible coevolution with iron and oxygen.

Synthesis, delivery and regulation of eukaryotic heme and Fe-S cluster cofactors

In humans, the bulk of iron in the body (over 75%) is directed towards heme- or Fe-S cluster cofactor synthesis, and the complex, highly regulated pathways in place to accomplish biosynthesis have evolved to safely assemble and load these cofactors into apoprotein partners. In eukaryotes, heme biosynthesis is both initiated and finalized within the mitochondria, while cellular Fe-S cluster assembly is controlled by correlated pathways both within the mitochondria and within the cytosol. Iron plays a vital role in a wide array of metabolic processes and defects in iron cofactor assembly leads to human diseases. This review describes progress towards our molecular-level understanding of cellular heme and Fe-S cluster biosynthesis, focusing on the regulation and mechanistic details that are essential for understanding human disorders related to the breakdown in these essential pathways.

Biology of Heme in Mammalian Erythroid Cells and Related Disorders

Heme is a prosthetic group comprising ferrous iron (Fe(2+)) and protoporphyrin IX and is an essential cofactor in various biological processes such as oxygen transport (hemoglobin) and storage (myoglobin) and electron transfer (respiratory cytochromes) in addition to its role as a structural component of hemoproteins. Heme biosynthesis is induced during erythroid differentiation and is coordinated with the expression of genes involved in globin formation and iron acquisition/transport. However, erythroid and nonerythroid cells exhibit distinct differences in the heme biosynthetic pathway regulation. Defects of heme biosynthesis in developing erythroblasts can have profound medical implications, as represented by sideroblastic anemia. This review will focus on the biology of heme in mammalian erythroid cells, including the heme biosynthetic pathway as well as the regulatory role of heme and human disorders that arise from defective heme synthesis.

Regulation and function of the NFE2 transcription factor in hematopoietic and non-hematopoietic cells

The NFE2 transcription factor was identified over 25 years ago. The NFE2 protein forms heterodimers with small MAF proteins, and the resulting complex binds to regulatory elements in a large number of target genes. In contrast to other CNC transcription family members including NFE2L1 (NRF1), NFE2L2 (NRF2) and NFE2L3 (NRF3), which are widely expressed, earlier studies had suggested that the major sites of NFE2 expression are hematopoietic cells. Based on cell culture studies it was proposed that this protein acts as a critical regulator of globin gene expression. However, the knockout mouse model displayed only mild erythroid abnormalities, while the major phenotype was a defect in megakaryocyte biogenesis. Indeed, absence of NFE2 led to severely impaired platelet production. A series of recent data, also summarized here, shed new light on the various functional roles of NFE2 and the regulation of its activity. NFE2 is part of a complex regulatory network, including transcription factors such as GATA1 and RUNX1, controlling megakaryocytic and/or erythroid cell function. Surprisingly, it was recently found that NFE2 also has a role in non-hematopoietic tissues, such as the trophoblast, in which it is also expressed, as well as the bone, opening the door to new research areas for this transcription factor. Additional data showed that NFE2 function is controlled by a series of posttranslational modifications. Important strides have been made with respect to the clinical significance of NFE2, linking this transcription factor to hematological disorders such as polycythemias.

Iron availability modulates aberrant splicing of ferrochelatase through the iron- and 2-oxoglutarate dependent dioxygenase Jmjd6 and U2AF(65.)

Erythropoietic protoporphyria (EPP) results from partial deficiency of ferrochelatase (FECH). Genetically, EPP patients differ from asymptomatic mutation carriers at the unmutated FECH allele, the expression of which is modulated by single nucleotide polymorphism IVS3-48C/T. The IVS3-48C genotype, which is present among patients, leads to correct splicing of 60% of the pre-mRNA and to alternative splicing of 40%, the latter mRNA-product being destroyed by nonsense-mediated decay. An IVS3-48T genotype generates 80% correct and 20% aberrant products. Our study demonstrated that under iron deficient conditions, the aberrant splice product was increased to 56% and 50% of total FECH mRNA in erythroleukemic K562 and lymphoblastoid cell lines, respectively, both being homozygous for IVS3-48T. Concomitantly, FECH protein was decreased. Iron deficiency had less effect on the FECH splice ratio in an IVS3-48C/C lymphoblastoid cell line. Effects similar to iron deficiency were generated by siRNA knockdown of either splicing factor U2AF(65) or Fe(II)- and 2-oxoglutarate-dependent dioxygenase Jumonji domain-containing protein 6 (Jmjd6), which interacts with U2AF(65) by lysyl-hydroxylation. Based on these results, we propose that the availability of iron, a co-factor of Jmjd6, modulates U2AF(65)-lysyl-hydroxylation. This in turn, influences the relative amounts of correct and aberrant FECH mRNA splice products and thus, regulates the FECH enzyme activity.

One ring to rule them all: trafficking of heme and heme synthesis intermediates in the metazoans

The appearance of heme, an organic ring surrounding an iron atom, in evolution forever changed the efficiency with which organisms were able to generate energy, utilize gasses and catalyze numerous reactions. Because of this, heme has become a near ubiquitous compound among living organisms. In this review we have attempted to assess the current state of heme synthesis and trafficking with a goal of identifying crucial missing information, and propose hypotheses related to trafficking that may generate discussion and research. The possibilities of spatially organized supramolecular enzyme complexes and organelle structures that facilitate efficient heme synthesis and subsequent trafficking are discussed and evaluated. Recently identified players in heme transport and trafficking are reviewed and placed in an organismal context. Additionally, older, well established data are reexamined in light of more recent studies on cellular organization and data available from newer model organisms. This article is part of a Special Issue entitled: Cell Biology of Metals.

ATP-dependent mitochondrial porphyrin importer ABCB6 protects against phenylhydrazine toxicity

Abcb6 is a mammalian mitochondrial ATP-binding cassette (ABC) transporter that regulates de novo porphyrin synthesis. In previous studies, haploinsufficient (Abcb6(+/-)) embryonic stem cells showed impaired porphyrin synthesis. Unexpectedly, Abcb6(-/-) mice derived from these stem cells appeared phenotypically normal. We hypothesized that other ATP-dependent and/or -independent mechanisms conserve porphyrins. Here, we demonstrate that Abcb6(-/-) mice lack mitochondrial ATP-driven import of coproporphyrin III. Gene expression analysis revealed that loss of Abcb6 results in up-regulation of compensatory porphyrin and iron pathways, associated with elevated protoporphyrin IX (PPIX). Phenylhydrazine-induced stress caused higher mortality in Abcb6(-/-) mice, possibly because of sustained elevation of PPIX and an inability to convert PPIX to heme despite elevated ferrochelatase levels. Therefore, Abcb6 is the sole ATP-dependent porphyrin importer, and loss of Abcb6 produces up-regulation of heme and iron pathways necessary for normal development. However, under extreme demand for porphyrins (e.g. phenylhydrazine stress), these adaptations appear inadequate, which suggests that under these conditions Abcb6 is important for optimal survival.

[Inheritance in erythropoietic protoporphyria]

Erythropoietic protoporphyria (EPP) is an inherited disorder of heme biosynthesis that results from an accumulation of protoporphyrin IX in erythroid cells, plasma, skin and liver. EPP leads to acute photosensitivity and, in about 2% of patients, liver disease. EPP is a complex syndrome in which two genes are independently involved: FECH and ALAS2. More than 96% of unrelated EPP patients have ferrochelatase (FECH) deficiency (MIM 177000). Four percent of them present with autosomal recessive inheritance with two mutated FECH alleles. In dominant cases (95%) the inheritance of a common hypomorphic IVS3-48C FECH allele trans to a deleterious FECH mutation reduces FECH activity below a critical threshold. The frequency of the IVS3-48C allele differs widely from the Japanese (45%), to Black West Africans (<1%) populations. These differences in the frequency of this single common SNP account for the prevalence of overt EPP in different countries and for the absence of EPP in Black Africans. The phylogenic origin of the IVS3-48C haplotypes strongly suggests that the IVS3-48C allele arose from a single recent mutational event that occurred 60 Kyears ago. Acquired somatic mutation of FECH secondary to myeloid disease may also exceptionally cause EPP (<1%). Finally, about 4% of unrelated EPP patients have X-linked dominant protoporphyria (XLDPP) (MIM 300752) caused by gain-of-function mutations in the ALAS2 gene leading to an increased erythroid heme biosynthesis and subsequently an accumulation of protoporphyrin without any FECH deficiency.

GATA-1 binding sites in exon 1 direct erythroid-specific transcription of PPOX

We investigated erythroid-specific expression of the human PPOX gene. This gene encodes protoporphyrinogen oxidase, which is involved in synthesizing heme for red blood cells and heme as a cofactor for the respiratory cytochromes. In vitro luciferase transfection assays in human uninduced and hemin induced erythroleukemic K562 cells showed that the presence of exon 1 increased promoter activity fourfold as compared to reporter constructs lacking this exon. This transcriptional regulation was mediated by two GATA-1 sites in exon 1. Electrophoretic mobility shift and chromatin immunoprecipitation assays demonstrated that both GATA sites were able to bind GATA-1 in vitro and in vivo. Exon 1 did not affect promoter activity in human hepatoma HepG2 cells and U937 monocytic cells but its presence decreased promoter activity in HeLa human cervical carcinoma cells. We conclude that the GATA-1 binding sites in exon 1 constitute key regulatory elements in differential expression of PPOX in erythroid and non-erythroid cells.

A 10376 bp deletion of FECH gene responsible for erythropoietic protoporphyria

Erythropoietic protoporphyria (EPP, MIM 177000) is an autosomal dominant disease with incomplete penetrance since the phenotypic expression requires coinheritance of a null allele and a wild-type low expressed allele of Ferrochelatase gene (FECH). In this study, we identify a peculiar mutation in a young Canadian patient of Italian origin. The patient had clinical and biochemical symptoms of EPP, the wild-type low expressed allele but at preliminary analysis no mutation in the promoter, in the entire coding region and in the splice junctions of the gene. Family studies of seven most common polymorphisms along the gene established absence of Mendelian segregation for the promoter polymorphism only. The intron 1 polymorphism appeared in heterozygosis suggesting an hypothetical deletion in the first region of the gene. In order to identify the size of this deletion, single nucleotide polymorphisms (SNPs) analysis was extended to the upstream N-asparaginyl-tRNA synthetase gene (NARS). We analyzed two polymorphisms in the last exon of this gene and a dizigous region was found in the patient. A Long-PCR with primers located in previously fixed heterozygous regions showed a 10,376 bp deletion (c.1-7887_67+2422del) that included a portion of the upstream intergenic region, the promoter, the exon 1 and a portion of intron 1. RNA analysis demonstrated that the lack of the entire promoter prevents the expression of the mutated allele, in fact the expression of the Ferrochelatase gene was decreased by half in the subjects carrying only the mutation compared to control.

Co-existence of two functional mutations on the same allele of the human ferrochelatase gene in erythropoietic protoporphyria

Erythropoietic protoporphyria (EPP) is an autosomal dominant disease with incomplete penetrance due to reduced activity of ferrochelatase (FECH), a mitochondrial enzyme that catalyzes the final step of the heme biosynthetic pathway. The clinical phenotype of EPP results from co-inheritance of a mutated allele and a wild-type low-expressed allele of the FECH gene. To date, more than 88 different mutations have been identified in the FECH gene of patients with EPP. There are evidences suggesting that an entire haplotype (-251G, IVS1-23T and IVS3-48C) reduces allele expression. In this study, we searched for the -251A/G, IVS1-23C/T and IVS3-48T/C polymorphisms in two unrelated Italian families with EPP. In all the patients, carrying the -250G>C mutation in the promoter region, the IVS3-48C on the other allele showed apparent homozygosity and absence of Mendelian segregation. By RNA and long polymerase chain reaction analysis, we identified a deletion of 5576 bp (g12490_18067), including exons 3 and 4, in cis with the -250G>C mutation in the promoter.

Biochemical abnormality in erythropoietic protoporphyria: cause and consequences

OBJECTIVES

Erythropoietic protoporphyria (EPP) is a genetic disorder in which deficient ferrochelatase (FECH) activity causes the excessive production and excretion of protoporphyrin. This in turn causes the major clinical manifestation of EPP, photosensitivity and, in some patients, hepatobiliary disease that may be severe. The objective of this study was to define genotypic determinants of phenotype in EPP.

METHODS

FECH activity was measured in 30 tissue samples from 26 patients with symptomatic EPP to determine the degree of deficient activity. FECH DNA analysis was also done in 26 families with EPP to identify mutations and examine for the presence of a polymorphism (IVS3-48c) that causes low gene expression.

RESULTS

The level of residual FECH activity that was measured in tissue samples of patients with symptomatic EPP was <or=30% of the mean normal level in all patients except one. Lowest levels (4-20% normal) were in patients with advanced EPP liver disease. Heterozygous FECH mutations were found in 45 individuals from 26 families with EPP. In 94% of the 32 symptomatic individuals, 15 of whom had liver disease, the polymorphism was present in the nonmutant allele. In 13 asymptomatic patients, the polymorphism was absent.

CONCLUSIONS

Patients with symptomatic EPP (photosensitivity with/without hepatobiliary disease) usually have a mutation in 1 FECH allele that alters enzyme structure/function, together with a polymorphism in the nonmutant allele that causes low gene expression. This leads to a significant reduction in FECH activity that causes symptomatic disease to develop because of the excess protoporphyrin produced.

Biosynthesis of heme in mammals

Most iron in mammalian systems is routed to mitochondria to serve as a substrate for ferrochelatase. Ferrochelatase inserts iron into protoporphyrin IX to form heme which is incorporated into hemoglobin and cytochromes, the dominant hemoproteins in mammals. Tissue-specific regulatory features characterize the heme biosynthetic pathway. In erythroid cells, regulation is mediated by erythroid-specific transcription factors and the availability of iron as Fe/S clusters. In non-erythroid cells the pathway is regulated by heme-mediated feedback inhibition. All of the enzymes in the heme biosynthetic pathway have been crystallized and the crystal structures have permitted detailed analyses of enzyme mechanisms. All of the genes encoding the heme biosynthetic enzymes have been cloned and mutations of these genes are responsible for a group of human disorders designated the porphyrias and for X-linked sideroblastic anemia. The biochemistry, structural biology and the mechanisms of tissue-specific regulation are presented in this review along with the key features of the porphyric disorders.

SOX2 is a dose-dependent regulator of retinal neural progenitor competence

Approximately 10% of humans with anophthalmia (absent eye) or severe microphthalmia (small eye) show haploid insufficiency due to mutations in SOX2, a SOXB1-HMG box transcription factor. However, at present, the molecular or cellular mechanisms responsible for these conditions are poorly understood. Here, we directly assessed the requirement for SOX2 during eye development by generating a gene-dosage allelic series of Sox2 mutations in the mouse. The Sox2 mutant mice display a range of eye phenotypes consistent with human syndromes and the severity of these phenotypes directly relates to the levels of SOX2 expression found in progenitor cells of the neural retina. Retinal progenitor cells with conditionally ablated Sox2 lose competence to both proliferate and terminally differentiate. In contrast, in Sox2 hypomorphic/null mice, a reduction of SOX2 expression to <40% of normal causes variable microphthalmia as a result of aberrant neural progenitor differentiation. Furthermore, we provide genetic and molecular evidence that SOX2 activity, in a concentration-dependent manner, plays a key role in the regulation of the NOTCH1 signaling pathway in retinal progenitor cells. Collectively, these results show that precise regulation of SOX2 dosage is critical for temporal and spatial regulation of retinal progenitor cell differentiation and provide a cellular and molecular model for understanding how hypomorphic levels of SOX2 cause retinal defects in humans.

Cloning and functional characterization of the rat alpha2B-adrenergic receptor gene promoter region: Evidence for binding sites for erythropoiesis-related transcription factors GATA1 and NF-E2

In the rat, the alpha2B-adrenergic receptor (alpha2B-AR) is encoded by the rat non-glycosylated (RNG) gene and is primarily expressed in the kidney, brain and liver of adult animals. High levels of alpha2B-AR are also found during fetal life in the placenta, liver and blood, where it is borne by cells of the erythropoietic lineage. As a first step to define the mechanisms responsible for the spatio-temporal pattern of alpha2B-AR expression, a genomic fragment containing 2.8 kb of the 5'-flanking region, the ORF and approximately 20 kb of the 3'-flanking region of the RNG gene was isolated. RNase protection assays performed on RNA from placenta or kidney using a series of riboprobes permitted to locate the transcription start site 372 bases upstream from the start codon. Transient transfection of various cells, including rat proximal tubule in primary culture, with constructs containing luciferase as a reporter gene demonstrated that: (i) the 5'-flanking region exhibited a strong and sense-dependent transcriptional activity and (ii) the 332 bp fragment (-732/-401 relative to the start codon), which lacks a TATA box but contains Sp1 sites, is sufficient to drive expression. Analysis of chromatin susceptibility to DNaseI digestion identified two hypersensitive sites (HS1 and HS2) located 1.7 and 1.0 kb, respectively, upstream from ATG and containing recognition sequences for erythroid transcription factors. EMSA showed specific binding of GATA1 and NF-E2 to these elements. Taken together, the results suggest that the chromatin environment in the vicinity of these boxes plays a critical role for alpha2B-AR expression during fetal life.

A point mutation affecting an SP1 binding site in the promoter of the ferrochelatase gene impairs gene transcription and causes erythropoietic protoporphyria

OBJECTIVE

Clinical manifestation of erythropoietic protoporphyria (EPP) results from coinheritance of a mutated allele and a wild-type low-expressed allele of the ferrochelatase (FECH) gene. Currently, up to 90 different mutations affecting the coding region or splicing junctions of the FECH gene have been identified. Despite the high molecular heterogeneity, no functional mutations have been previously reported in the promoter region. The weaker allele expression has been controversially associated to the presence of different intragenic polymorphisms.

METHODS

We applied a two-step screening strategy using denaturing gradient gel electrophoresis followed by direct sequencing in order to rapidly identify FECH gene mutations in Italian EPP patients. We identified two unrelated subjects showing a normal FECH coding region but a single G>C base substitution at position -250 in the FECH promoter and the -251G, IVS1-23T, and IVS3-48C polymorphisms in trans to the substitution. To investigate the effect of the -250G>C mutation on protein binding to the FECH promoter, we conducted electro mobility shift assay (EMSA) and supershift analysis. To determine its effect on the transcriptional activity, K562 and Jurkat cell lines were transiently transfected.

RESULTS

EMSA showed that the -250G>C mutation results in the loss of an SP1 binding site, and transient transfection assays demonstrated that such mutation strongly impairs promoter activity. Moreover, we showed that the -251A>G polymorphism, although unable to affect SP1 binding, displays a significant reduction in the transcriptional activity of the promoter.

CONCLUSION

This is the first report of a mutation in the FECH promoter affecting binding of a transcription factor and causing EPP phenotype.

Molecular studies of liver disease in erythropoietic protoporphyria

GOALS

The goal of this study was to define molecular determinants of liver disease in erythropoietic protoporphyria (EPP).

BACKGROUND

EPP is a genetic disorder in which deficient ferrochelatase activity causes excessive production of protoporphyrin, which is excreted in bile. Some patients develop liver disease that necessitates transplantation.

STUDY

Ferrochelatase gene analysis was done in 25 families with EPP to identify mutations and a polymorphism (IVS3-48c) that causes low gene expression. Expression of multiple hepatic genes was also examined by DNA microarray analysis in patients who had liver transplantation to identify genes with altered regulation.

RESULTS

Heterozygous ferrochelatase mutations were found in 43 individuals. In 94% of 31 symptomatic patients, 15 of whom had liver disease, the polymorphism was also present in the nonmutant allele. Explanted liver of patients who had transplantation showed significant change in expression of several genes involved in wound healing, organic anion transport, and oxidative stress.

CONCLUSIONS

Patients with EPP who develop liver disease usually have a mutation in one ferrochelatase allele that alters enzyme function, together with a polymorphism in the nonmutant allele that causes low gene expression. This results in significant increase in the hepatobiliary excretion of protoporphyrin, which can damage the liver through both cholestatic injury and oxidative stress.

Two promoters control the mouse Nmp4/CIZ transcription factor gene

Nmp4/CIZ proteins (nuclear matrix protein 4/cas interacting zinc finger protein) contribute to gene regulation in bone, blood, and testis. In osteoblasts, they govern the magnitude of gene response to osteotropic factors like parathyroid hormone (PTH). Nmp4/CIZ is recurrently involved in acute leukemia and it has been implicated in spermatogenesis. However, these conserved proteins, derived from a single gene, are expressed in numerous tissues indicative of a more generalized housekeeping function in addition to their tissue-specific roles. To address how Nmp4/CIZ expression is governed, we characterized the 5' regulatory region of the mouse Nmp4 gene, located on chromosome 6. Two adjacent promoters P(1) [-2521 nucleotide (nt)/-597 nt] and P(2) (-2521 nt/+1 nt) initiate transcription of alternative first exons (U(1) and U(2)). Both promoters lack TATA and CCAAT boxes but contain initiator sites and CpG islands. Northern analysis revealed expression of both U(1) and U(2) in numerous adult tissues consistent with the constitutive and ubiquitous activity of a housekeeping gene. Sequence analysis identified numerous potential transcription factor-binding sites significant to osteogenesis, hematopoeisis, and gonadal development. The promoters are active in both osteoblast-like cells and in the M12 B-lymphocyte cell line. Low doses of PTH attenuated P(1)/P(2) activity in osteoblast-like cells. The Nmp4/CIZ promoters are autoregulated and deletion analysis identified regions that drive P(1) and P(2) basal activities as well as regions that contain positive and negative regulatory elements affecting transcription. The Nmp4/CIZ promoters comprise a genomic regulatory architecture that supports constitutive expression as well as cell- and tissue-specific regulation.

Hypermethylation of the wild-type ferrochelatase allele is closely associated with severe liver complication in a family with erythropoietic protoporphyria

Erythropoietic protoporphyria (EPP) is an inherited disorder of heme biosynthesis caused by cellular decreases in ferrochelatase (FECH) activity. Clinical expression of this disorder usually requires coinheritance of a mutant FECH allele and a normal FECH allele expressed at a low level. In this study, we investigated the methylation status of a normal, but poorly expressed, FECH gene in a single Japanese family with EPP. In this family, the proband died from liver failure, whereas the mother and sister exhibited overt EPP with mild liver dysfunction. A splicing mutation (IVS9+1g-->a) in the FECH gene, which produces a mutant FECH transcript lacking exon 9, was detected in the maternal allele of the proband and his sister. All subjects, including the father, who did not exhibit EPP, possessed the IVS3-48c/c genotype. This allele increases the proportion of aberrantly spliced mRNA, resulting in reduced FECH activity. Normal FECH transcripts were, however, detected in the mother and sister, but not in the proband. The CpG sites in the region from bases -78 to -31 were partially methylated in the proband and his father, but not in his mother or sister. Additionally, CpG methylation within this region reduced transcription of the FECH gene. These results suggest that whereas the combination of a maternal IVS9+1a allele and a paternal IVS3-48c allele results in overt EPP, CpG methylation of the FECH gene promoter, likely inherited from the father, increases the severity of EPP, leading to fatal liver failure, as seen in the proband.

Regulation of ferrochelatase gene expression by hypoxia

Ferrochelatase (FECH), the last enzyme of the heme biosynthetic pathway, catalyzes the insertion of iron into protoporphyrin to form heme. This pathway provides heme for hemoglobin and other essential hemoproteins. The regulatory role of oxygen in the pathway has not been clearly established. In this study, we examined whether FECH gene expression is upregulated during hypoxia by a mechanism which involves the hypoxia-inducible factor 1 (HIF-1). Two HIF-1 binding motifs were identified within the -150 bp FECH minimal promoter sequence. Exposure of HEL, K562, and Hep-G2 cells to hypoxia for 18 hours resulted in a significant increase in FECH mRNA expression (p < 0.05). Hypoxia also transactivated the minimal promoter for the FECH gene in the cells. Transient co-expression of wild-type HIF-1alpha or a dominant negative HIF-1alpha with the FECH minimal promoter luciferase construct stimulated or blocked FECH promoter activity, respectively. Expression of the von Hippel-Lindau (VHL) tumor suppressor factor blocked the expression of both FECH mRNA and HIF-1alpha protein during normoxic culture of renal carcinoma cell line (RCC4). The results suggest that the FECH gene is a target for HIF-1 during hypoxia.

Transcriptional regulation of the human HFE gene indicates high liver expression and erythropoiesis coregulation

The human HFE gene is clearly involved in hereditary hemochromatosis, a common autosomal recessive genetic disorder of iron homeostasis. However, the precise role of the HFE protein is still undefined. Here, to obtain new insight, we analyzed the transcriptional regulation of HFE gene and defined the functional organization of the HFE promoter. Both in vitro transcription and reporter gene assay in transient transfection evidenced a high liver expression of the HFE mRNA. The 5' end analysis of mRNA showed two major initiation sites localized at -265 and -195 directed by TATA-like sequences and a window of initiation within the -120 to -10 GC-rich region upstream of the first coding nucleotide. Positive cis-regulating elements were characterized within the -1057/-8 region, and a negative one extending upstream (-1485/-1057) was identified. DNase I footprinting analysis and gel shift assay revealed several protein binding sites, and subsequent functional analysis evidenced transactivation of HFE by liver-enriched C/EBPalpha, erythropoietic-specific GATA-1, and ubiquitous Sp1 transcription factors. These data bring some evidence of a role of HFE in the liver and a coregulation with erythropoiesis as other genes involved in iron homeostasis.

Genotypic determinants of phenotype in North American patients with erythropoietic protoporphyria

Erythropoietic protoporphyria (EPP) is characterized by excess accumulation of protoporphyrin, which is due to deficient activity of the enzyme ferrochelatase (FECH). This results in photosensitivity and in some patients liver disease which may necessitate liver transplantation. The aim of this study was to delineate the abnormalities in the FECH gene which cause phenotypic expression in EPP. We identified 43 individuals from 25 North American families with EPP who were heterozygous for various FECH mutations, but the mutations did not adequately explain the variable phenotype. We also examined the presence of an intron polymorphism (IVS3-48c) in the FECH gene which was shown to cause the formation of aberrantly spliced FECH mRNA. FECH DNA analysis demonstrated that 94% of 31 symptomatic individuals with FECH mutations were heterozygous for IVS3-48c, whereas 12 asymptomatic individuals with FECH mutations were homozygous for IVS3-48t. Haplotype analysis in four families showed that symptomatic members had the IVS3-48c polymorphism in the non-mutant FECH allele. Sequencing of the proximal FECH gene promoter showed no additional changes which might affect gene expression. The levels of normal FECH mRNA, measured by relative quantitative RT-PCR, and FECH enzyme activity were correspondingly lower in the cultured lymphoblasts of family members with the IVS3-48c polymorphism. These results indicate that symptomatic disease in most North American patients with EPP is explained by the inheritance of a mutation in one FECH allele which causes a structural alteration in the protein, together with a low expressing non-mutant FECH allele which is caused by the IVS3-48c polymorphism.

Picosecond-hetero-FRET microscopy to probe protein-protein interactions in live cells

By using a novel time- and space-correlated single-photon counting detector, we show that fluorescence resonance energy transfer (FRET) between cyan fluorescent protein (CFP) and yellow fluorescent protein (YFP) fused to herpes simplex virus thymidine kinase (TK) monomers can be used to reveal homodimerization of TK in the nucleus and cytoplasm of live cells. However, the quantification of energy transfer was limited by the intrinsic biexponential fluorescence decay of the donor CFP (lifetimes of 1.3 +/- 0.2 ns and 3.8 +/- 0.4 ns) and by the possibility of homodimer formation between two TK-CFP. In contrast, the heterodimerization of the transcriptional factor NF-E2 in the nucleus of live cells was quantified from the analysis of the fluorescence decays of GFP in terms of 1) FRET efficiency between GFP and DsRed chromophores fused to p45 and MafG, respectively, the two subunits of NF-E2 (which corresponds to an interchromophoric distance of 39 +/- 1 A); and 2) fractions of GFP-p45 bound to DsRed-MafG (constant in the nucleus, varying in the range of 20% to 70% from cell to cell). The picosecond resolution of the fluorescence kinetics allowed us to discriminate between very short lifetimes of immature green species of DsRed-MafG and that of GFP-p45 involved in FRET with DsRed-MafG.

Erythroid expression of the human alpha-spectrin gene promoter is mediated by GATA-1- and NF-E2-binding proteins

alpha-Spectrin is a highly expressed membrane protein critical for the flexibility and stability of the erythrocyte. Qualitative and quantitative defects of alpha-spectrin are present in the erythrocytes of many patients with abnormalities of red blood cell shape including hereditary spherocytosis and elliptocytosis. We wished to determine the regulatory elements that determine the erythroid-specific expression of the alpha-spectrin gene. We mapped the 5' end of the alpha-spectrin erythroid cDNA and cloned the 5' flanking genomic DNA containing the putative alpha-spectrin gene promoter. Using transfection of promoter/reporter plasmids in human tissue culture cell lines, in vitro DNase I footprinting analyses, and gel mobility shift assays, an alpha-spectrin gene erythroid promoter with binding sites for GATA-1- and NF-E2-related proteins was identified. Both binding sites were required for full promoter activity. In transgenic mice, a reporter gene directed by the alpha-spectrin promoter was expressed in yolk sac, fetal liver, and erythroid cells of bone marrow but not adult reticulocytes. No expression of the reporter gene was detected in nonerythroid tissues. We conclude that this alpha-spectrin gene promoter contains the sequences necessary for low level expression in erythroid progenitor cells.

The role of c-Myb and Sp1 in the up-regulation of methionine adenosyltransferase 2A gene expression in human hepatocellular carcinoma

Liver-specific and non-liver-specific methionine adenosyltransferase (MAT) are products of two genes, MAT1A and MAT2A, respectively, that catalyze the formation of S-adenosylmethionine. We showed a switch from MAT1A to MAT2A expression at the transcriptional level in human hepatocellular carcinoma (HCC) that facilitates cancer cell growth. The purpose of the present study was to better understand the molecular mechanism of increased MAT2A expression in HCC. In vitro DNase I footprinting analysis revealed two protected sites (-354 to -312 and -73 to -28) using nuclear proteins from HCC and HepG2 cells, but not normal liver. These sites are also protected in HepG2 cells on in vivo DNase I footprinting analysis. These protected sites contain consensus binding sites for c-Myb and Sp1. In HCC, the mRNA levels of c-myb and Sp1 and binding to their respective sites increased. Mutation of the c-Myb or Sp1 site reduced MAT2A promoter activity by 67% and 50%, respectively. The importance of these cis-acting elements and trans-activating factors was confirmed using heterologous promoter and expression vectors. Increased expression of c-Myb and Sp1 and binding to the MAT2A promoter contribute to transcriptional up-regulation of MAT2A in HCC.-Yang, H., Huang, Z.-Z., Wang, J., Lu, S. C. The role of c-Myb and Sp1 in the up-regulation of methionine adenosyltransferase 2A gene expression in human hepatocellular carcinoma.

Negative regulatory regions of the PAT1 promoter of Hz-1 virus contain GATA elements which associate with cellular factors and regulate promoter activity

The persistence-associated transcript 1 (PAT1) is actively expressed during persistent infection with Hz-1 virus, while transcription of the rest of the viral genes is shut down. Previously, results of a series deletion of the PAT1 promoter suggested that the regions from nucleotides -312 to -212 and nucleotides -158 to -90 negatively regulate the promoter activity. Here, the negative regulatory effect of the -312/-90 fragment was confirmed using a heterologous IE0 promoter of Autographa californica multiple nucleopolyhedrovirus. Further, the negative regulation of the -312 to -212 region was orientation-independent. The results of electrophoresis mobility shift assays showed that cellular protein(s) bind specifically to DNA fragments -312/-212 and -158/-90. In each of these fragments, a GATA element was identified by computer-assisted analysis. Mutating both GATA elements in the -312/-90 fragment completely eliminated its negative effect on IE0 promoter activity, while mutating only one of these elements had little or no effect. Together, these results suggest that the GATA element has a negative regulatory role on the IE0 and PAT1 promoters.

p45(NFE2) is a negative regulator of erythroid proliferation which contributes to the progression of Friend virus-induced erythroleukemias

In previous studies, we identified a common site of retroviral integration designated Fli-2 in Friend murine leukemia virus (F-MuLV)-induced erythroleukemia cell lines. Insertion of F-MuLV at the Fli-2 locus, which was associated with the loss of the second allele, resulted in the inactivation of the erythroid cell- and megakaryocyte-specific gene p45(NFE2). Frequent disruption of p45(NFE2) due to proviral insertion suggests a role for this transcription factor in the progression of Friend virus-induced erythroleukemias. To assess this possibility, erythroleukemia was induced by F-MuLV in p45(NFE2) mutant mice. Since p45(NFE2) homozygous mice mostly die at birth, erythroleukemia was induced in +/- and +/+ mice. We demonstrate that +/- mice succumb to the disease moderately but significantly faster than +/+ mice. In addition, the spleens of +/- mice were significantly larger than those of +/+ mice. Of the 37 tumors generated from the +/- and +/+ mice, 10 gave rise to cell lines, all of which were derived from +/- mice. Establishment in culture was associated with the loss of the remaining wild-type p45(NFE2) allele in 9 of 10 of these cell lines. The loss of a functional p45(NFE2) in these cell lines was associated with a marked reduction in globin gene expression. Expression of wild-type p45(NFE2) in the nonproducer erythroleukemic cells resulted in reduced cell growth and restored the expression of globin genes. Similarly, the expression of p45(NFE2) in these cells also slows tumor growth in vivo. These results indicate that p45(NFE2) functions as an inhibitor of erythroid cell growth and that perturbation of its expression contributes to the progression of Friend erythroleukemia.

Human uroporphyrinogen-III synthase: genomic organization, alternative promoters, and erythroid-specific expression

Uroporphyrinogen-III (URO) synthase is the heme biosynthetic enzyme defective in congenital erythropoietic porphyria. The approximately 34-kb human URO-synthase gene (UROS) was isolated, and its organization and tissue-specific expression were determined. The gene had two promoters that generated housekeeping and erythroid-specific transcripts with unique 5'-untranslated sequences (exons 1 and 2A) followed by nine common coding exons (2B to 10). Expression arrays revealed that the housekeeping transcript was present in all tissues, while the erythroid transcript was only in erythropoietic tissues. The housekeeping promoter lacked TATA and SP1 sites, consistent with the observed low level expression in most cells, whereas the erythroid promoter contained GATA1 and NF-E2 sites for erythroid specificity. Luciferase reporter assays demonstrated that the housekeeping promoter was active in both erythroid K562 and HeLa cells, while the erythroid promoter was active only in erythroid cells and its activity was increased during hemin-induced erythroid differentiation. Thus, human URO-synthase expression is regulated during erythropoiesis by an erythroid-specific alternative promoter.

The human ankyrin-1 gene is selectively transcribed in erythroid cell lines despite the presence of a housekeeping-like promoter

To begin to study the sequence variations identified in the 5′ flanking genomic DNA of the ankyrin gene in ankyrin-deficient hereditary spherocytosis patients and to provide additional insight into our understanding of the regulation of genes encoding erythrocyte membrane proteins, we have identified and characterized the erythroid promoter of the human ankyrin-1 gene. This compact promoter has characteristics of a housekeeping gene promoter, including very high G+C content and enzyme restriction sites characteristic of an HTF-island, no TATA, InR, or CCAAT consensus sequences, and multiple transcription initiation sites. In vitro DNAseI footprinting analyses revealed binding sites for GATA-1, CACCC-binding, and CGCCC-binding proteins. Transfection of ankyrin promoter/reporter plasmids into tissue culture cell lines yielded expression in erythroid, but not muscle, neural, or HeLa cells. Electrophoretic mobility shift assays, including competition and antibody supershift experiments, demonstrated binding of GATA-1, BKLF, and Sp1 to core ankyrin promoter sequences. In transfection assays, mutation of the Sp1 site had no effect on reporter gene expression, mutation of the CACCC site decreased expression by half, and mutation of the GATA-1 site completely abolished activity. The ankyrin gene erythroid promoter was transactivated in heterologous cells by forced expression of GATA-1 and to a lesser degree BKLF.

The human ankyrin-1 gene is selectively transcribed in erythroid cell lines despite the presence of a housekeeping-like promoter

To begin to study the sequence variations identified in the 5′ flanking genomic DNA of the ankyrin gene in ankyrin-deficient hereditary spherocytosis patients and to provide additional insight into our understanding of the regulation of genes encoding erythrocyte membrane proteins, we have identified and characterized the erythroid promoter of the human ankyrin-1 gene. This compact promoter has characteristics of a housekeeping gene promoter, including very high G+C content and enzyme restriction sites characteristic of an HTF-island, no TATA, InR, or CCAAT consensus sequences, and multiple transcription initiation sites. In vitro DNAseI footprinting analyses revealed binding sites for GATA-1, CACCC-binding, and CGCCC-binding proteins. Transfection of ankyrin promoter/reporter plasmids into tissue culture cell lines yielded expression in erythroid, but not muscle, neural, or HeLa cells. Electrophoretic mobility shift assays, including competition and antibody supershift experiments, demonstrated binding of GATA-1, BKLF, and Sp1 to core ankyrin promoter sequences. In transfection assays, mutation of the Sp1 site had no effect on reporter gene expression, mutation of the CACCC site decreased expression by half, and mutation of the GATA-1 site completely abolished activity. The ankyrin gene erythroid promoter was transactivated in heterologous cells by forced expression of GATA-1 and to a lesser degree BKLF.

Analysis of ferrochelatase expression during hematopoietic development of embryonic stem cells

Ferrochelatase, the last enzyme in the heme pathway, chelates protoporphyrin IX and iron to form heme and is mutated in protoporphyria. The ferrochelatase gene is expressed in all tissues at low levels to provide heme for essential heme-containing proteins and is up-regulated during erythropoiesis for the synthesis of hemoglobin. The human ferrochelatase promoter contains 2 Sp1 cis-elements and GATA and NF–E2 sites, all of which bind their cognatetrans-acting factors in vitro. To investigate the role of these elements during erythropoiesis, we introduced expression of the green fluorescent protein (EGFP) transgenes driven by various ferrochelatase promoter fragments into a single locus in mouse embryonic stem cells. EGFP expression was monitored during hematopoietic differentiation in vitro using flow cytometry. We show that a promoter fragment containing the Sp1 sites, the NF–E2 and GATA elements, was sufficient to confer developmental-specific expression of the EGFP transgene, with an expression profile identical to that of the endogenous gene. In this system the −0.275 kb NF–E2 cis-element is required for erythroid-enhanced expression, the GATA cis-element functions as a stage-specific repressor and enhancer, and elements located between −0.375kb and −1.1kb are necessary for optimal levels of expression. Ferrochelatase mRNA increased before the primitive erythroid-cell stage without a concomitant increase in ferrochelatase protein, suggesting the presence of a translational control mechanism. Because of the sensitivity of this system, we were able to assess the effect of an A-to-G polymorphism identified in the promoters of patients with protoporphyria. There was no effect of the G haplotype on transcriptional activity of the −1.1 kb transgene.

Analysis of ferrochelatase expression during hematopoietic development of embryonic stem cells

Ferrochelatase, the last enzyme in the heme pathway, chelates protoporphyrin IX and iron to form heme and is mutated in protoporphyria. The ferrochelatase gene is expressed in all tissues at low levels to provide heme for essential heme-containing proteins and is up-regulated during erythropoiesis for the synthesis of hemoglobin. The human ferrochelatase promoter contains 2 Sp1 cis-elements and GATA and NF–E2 sites, all of which bind their cognatetrans-acting factors in vitro. To investigate the role of these elements during erythropoiesis, we introduced expression of the green fluorescent protein (EGFP) transgenes driven by various ferrochelatase promoter fragments into a single locus in mouse embryonic stem cells. EGFP expression was monitored during hematopoietic differentiation in vitro using flow cytometry. We show that a promoter fragment containing the Sp1 sites, the NF–E2 and GATA elements, was sufficient to confer developmental-specific expression of the EGFP transgene, with an expression profile identical to that of the endogenous gene. In this system the −0.275 kb NF–E2 cis-element is required for erythroid-enhanced expression, the GATA cis-element functions as a stage-specific repressor and enhancer, and elements located between −0.375kb and −1.1kb are necessary for optimal levels of expression. Ferrochelatase mRNA increased before the primitive erythroid-cell stage without a concomitant increase in ferrochelatase protein, suggesting the presence of a translational control mechanism. Because of the sensitivity of this system, we were able to assess the effect of an A-to-G polymorphism identified in the promoters of patients with protoporphyria. There was no effect of the G haplotype on transcriptional activity of the −1.1 kb transgene.

Transcriptional regulation of the murine erythroid-specific 5-aminolevulinate synthase gene

5-Aminolevulinate synthase (ALAS) catalyzes the first step of the heme biosynthetic pathway in mammalian cells. Separate genes encode the two isoforms: ubiquitously expressed ALAS (ALAS1) and erythroid-specific ALAS (ALAS2). Transcription of the ALAS2 gene is only activated during erythroid cell differentiation. This stimulation allows for the formation of hemoglobin-specific heme. The 5'-flanking region of the mouse ALAS2 gene was studied in order to define its erythroid-specific function in transcriptional activation. Putative binding sites for the erythroid-specific nuclear factors GATA-1, NF-E2, and EKLF were identified within the first 300bp region of the mouse ALAS2 5'-flanking region. However, this 300bp region alone did not efficiently activate transient expression in erythroid MEL and K562 cell lines. Additional DNA regulatory sequences found within 300-718bp upstream of the transcription start site were required for maximal transcriptional activation, even though these regions stimulated similar expression in the non-erythroid HeLa and NIH/3T3 cells. This suggests that cis-acting elements present in the 5'-flanking region are not responsible for maintenance of transcriptional silencing in non-erythroid cell lines and that tissue-specific regulation of ALAS2 depends on other regions of the gene or on chromatin remodeling. A putative hypoxia inducible factor 1 (HIF-1) response element was identified within the 300-718bp upstream region. Significantly, two proximal GATA-1-binding sites (-118/-113 and -98/-93) and a region located within -518 to -315bp of the mouse ALAS2 promoter were essential for transcriptional activation during chemically induced differentiation of MEL cells, implying their importance in conferring erythroid specificity to the ALAS2 transcriptional activation. This is the first study to delimit the cis-acting region responsible for activation of the ALAS2 promoter upon dimethyl-sulfoxide induction in MEL cells.

Uroporphyrinogen III synthase. An alternative promoter controls erythroid-specific expression in the murine gene

Uroporphyrinogen III synthase (URO-synthase, EC 4.2.1.75) is the fourth enzyme of the heme biosynthetic pathway and is the defective enzyme in congenital erythropoietic porphyria. To investigate the erythroid-specific expression of murine URO-synthase, the cDNA and approximately 24-kilobase genomic sequences were isolated and characterized. Three alternative transcripts were identified containing different 5'-untranslated regions (5'-UTRs), but identical coding exons 2B through 10. Transcripts with 5'-UTR exon 1A alone or fused to exon 1B were ubiquitously expressed (housekeeping), whereas transcripts with 5'-UTR exon 2A were only present in erythroid cells (erythroid-specific). Analysis of the TATA-less housekeeping promoter upstream of exon 1A revealed binding sites for ubiquitously expressed transcription factors Sp1, NF1, AP1, Oct1, and NRF2. The TATA-less erythroid-specific promoter upstream of exon 2A had nine putative GATA1 erythroid enhancer binding sites. Luciferase promoter/reporter constructs transfected into NIH 3T3 and mouse erythroleukemia cells indicated that the housekeeping promoter was active in both cell lines, while the erythroid promoter was active only in erythroid cells. Site-specific mutagenesis of the first GATA1 binding site markedly reduced luciferase activity in K562 cells (<5% of wild type). Thus, housekeeping and erythroid-specific transcripts are expressed from alternative promoters of a single mouse URO-synthase gene.

NF-kappaB inhibits expression of the alpha1(I) collagen gene

Fibrosis results from an increase in the synthesis and deposition of type I collagen. Fibrosis is frequently associated with inflammation, which is accompanied by increased levels of tumor necrosis factor-alpha (TNFalpha) and activation of the transcription factor NF-kappaB. However, several agents known to activate NF-kappaB, such as phorbol 12-myristate 13-acetate (PMA) and TNFalpha, result in decreased expression of type I collagen. Therefore, we directly examined the effects of NF-kappaB on alpha1(I) collagen gene expression in two collagen-producing cells, NIH 3T3 fibroblasts and hepatic stellate cells (HSCs). Transient transfections of NIH 3T3 cells or HSCs using NF-kappaB p50, p65, and c-Rel expression plasmids with collagen reporter gene plasmids demonstrated a strong inhibitory effect on transcription of the collagen gene promoter. Dose-response curves showed that p65 was a stronger inhibitor of collagen gene expression than was NF-kappaB p50 or c-Rel (maximum inhibition 90%). Transient transfections with reporter gene plasmids containing one or two Spl binding sites demonstrated similar inhibitory effects of NF-kappaB p65 on the activity of these reporter genes, suggesting that the inhibitory effects of NF-kappaB p65 are mediated through the critical Spl binding sites in the alpha1(I) collagen gene promoter. Cotransfection experiments using either a super-repressor I[ke]B or Spl partially blocked the inhibitory effects of p65 on collagen reporter gene activity. Coimmunoprecipitation experiments demonstrated that NF-kappaB and Spl do interact in vivo. Nuclear run-on assays showed that NF-kappaB p65 inhibited transcription of the endogenous alpha1(I) collagen gene. Together, these results demonstrate that NF-kappaB decreases transcription of the alpha1(I) collagen gene.

FKLF, a novel Krüppel-like factor that activates human embryonic and fetal beta-like globin genes

A cDNA encoding a novel Krüppel-type zinc finger protein, FKLF, was cloned from fetal globin-expressing human fetal erythroid cells. The deduced polypeptide sequence composed of 512 amino acids revealed that, like Sp1 and EKLF, FKLF has three contiguous zinc fingers at the near carboxyl-terminal end. A long amino-terminal domain is characterized by the presence of two acidic and two proline-rich regions. Reverse transcription (RT)-PCR assays using various cell lines demonstrated that the FKLF mRNA is expressed predominantly in erythroid cells. FKLF message is detectable by RT-PCR in fetal liver but not in adult bone marrow cells. As predicted from its structural features, FKLF is a transcriptional activator. In luciferase assays FKLF activated the gamma- and epsilon-globin gene promoters, and, to a much lower degree, the beta-globin promoter. Studies of HS2-gamma gene reporter constructs carrying CACCC box deletions revealed that the CACCC box sequence of the gamma gene promoter mediates the activation of the gamma gene by FKLF. Other erythroid promoters (GATA-1, glycophorin B, ferrochelatase, porphobilinogen deaminase, and 5-aminolevulinate synthase) containing CACCC elements or GC-rich potential Sp1-binding sites were activated minimally, if at all, by FKLF, indicating that FKLF is not a general activator of genes carrying the CACCC motifs. Transfection of K562 cells with FKLF cDNA enhanced the expression of the endogenous epsilon- and gamma-globin genes, suggesting an in vivo role of FKLF in fetal and embryonic globin gene expression. Our results indicate that the protein potentially encoded by the FKLF cDNA acts as a transcriptional activator of embryonic and fetal beta-like globin genes.

Inheritance in Erythropoietic Protoporphyria: A Common Wild-Type Ferrochelatase Allelic Variant With Low Expression Accounts for Clinical Manifestation

Erythropoietic protoporphyria (EPP) is a rare autosomal dominant disorder of heme biosynthesis characterized by partial decrease in ferrochelatase (FECH; EC 4.99.1.1) activity with protoporphyrin overproduction and consequent painful skin photosensitivity and rarely liver disease. EPP is normally inherited in an autosomal dominant pattern with low clinical penetrance; the many different mutations that have been identified are restricted to one FECH allele, with the other one being free of any mutations. However, clinical manifestations of dominant EPP cannot be simply a matter ofFECH haploinsufficiency, because patients have enzyme levels that are lower than the expected 50%. From RNA analysis in one family with dominant EPP, we recently suggested that clinical expression required coinheritance of a normal FECH allele with low expression and a mutant FECH allele. We now show that (1) coinheritance of a FECH gene defect and a wild-type low-expressed allele is generally involved in the clinical expression of EPP; (2) the low-expressed allelic variant was strongly associated with a partial 5′ haplotype [−251G IVS1−23T IVS2μsatA9] that may be ancestral and was present in an estimated 10% of a control group of Caucasian origin; and (3) haplotyping allows the absolute risk of developing the disease to be predicted for those inheriting FECH EPP mutations. EPP may thus be considered as an inherited disorder that does not strictly follow recessive or dominant rules. It may represent a model for phenotype modulation by mild variation in expression of the wild-type allele in autosomal dominant diseases.

Structure and transcriptional regulation of the mouse ferrochelatase gene

Ferrochelatase (EC.4.99.1.1), the final step in the biosynthesis of heme, is widely expressed in various tissues and is induced in erythroid cells. We determined the structure of the mouse ferrochelatase gene after isolation and characterization of lambda phage clones mapping discrete regions of the cDNA. The gene spans about 25 kb and consists of 11 exons. The exon/intron boundary sequences conform to consensus acceptor (GTn)/donor (nAG) sequences, and exons in the gene encode functional protein domains. The promoter region contains multiple Sp1 sites, a CACCC box and GATA-1 binding sites. Function analysis of the promoter by transient transfection assay demonstrated that one Sp1 binding site located at -37/-32 is essential for basic expression of the ferrochelatase gene in both mouse erythroleukemia (MEL) and non-erythroid EL4 cells. In addition, the region (-66/-51) containing a CACCC box and the neighboring GC box partly contributes to the inducible activity of the reporter in MEL cells upon induction with dimethylsulfoxide. It appears that at least two promoter regions of the mouse ferrochelatase gene function in basic and inducible expression.

Targeted disruption of the mouse ferrochelatase gene producing an exon 10 deletion

Protoporphyria is a disease characterized by a deficiency in ferrochelatase, the terminal enzyme in the heme biosynthetic pathway, which catalyzes the chelation of iron and protoporphyrin to form heme. Clinical symptoms arise from an accumulation of protoporphyrin behind the partial enzyme block and include photosensitivity and sometimes hepatobiliary disease. Protoporphyria is described as an dominant disease, yet patients exhibit decreased ferrochelatase activities of 15-30% of normal, not 50% as might be expected. Missense, nonsense, and splicing mutations have been identified in ferrochelatase cDNA from protoporphyric patients. In this study we introduce an exon 10 deletion, an analogous mutation to that described in some protoporphyric patients, into the mouse embryonic stem (ES) cell genome via homologous recombination. Targeted ES cells were confirmed by Southern blot analysis. Expression of wild-type and exon 10-deleted mRNA was demonstrated by reverse transcriptase-polymerase chain reaction (RT-PCR) and cDNA sequencing. Ferrochelatase levels were analyzed by immunoblotting. Ferrochelatase activity was measured by the chelation of zinc and mesoporphyrin, and by the decrease in protoporphyrin accumulation after adding delta-aminolevulinic acid. In the exon 10 +/- ES cells there is expression of both wild-type and exon 10-deleted mRNA, a 50% decrease in cross-reactive material with an anti-ferrochelatase antibody, and an approximate 50% decrease in ferrochelatase activity compared to wild-type ES cells. Therefore, an exon 10 deletion alone is insufficient to decrease ferrochelatase activity to the levels in protoporphyric patients. This suggests that requirement of an additional mutation to decrease the expression of the wild-type allele.

Analysis of the Human Ferrochelatase Promoter in Transgenic Mice

Ferrochelatase catalyzes the chelation of ferrous iron and protoporphyrin to form heme. It is expressed as a housekeeping gene in all cells, but is upregulated during erythropoiesis. Ferrochelatase activity is deficient in the inherited disease protoporphyria as a result of heterogeneous mutations. Although human ferrochelatase is transcribed from a single promoter in both nonerythroid and erythroid cells, previous studies using transient transfection assays failed to demonstrate erythroid-specific increased expression from 4.0 kb of the human ferrochelatase promoter containing the erythroidcis-elements, GATA and NF-E2. The present study analyzes the in vivo regulation of the ferrochelatase gene to provide insights into the mechanism of its erythroid-specific enhancement. Transgenic (TG) mouse lines were generated in which the luciferase reporter gene was driven by either a 150-bp ferrochelatase minimal promoter (−0.15 TG) or by a 4.0 kb extended 5′ upstream region (−4.0 TG). Expression of the −4.0 TG transgene was generally consistent with the endogenous gene during embryonic development and in nonerythroid and erythroid tissues as demonstrated by Northern blotting and mRNA in situ hybridization. The −4.0 TG was expressed at a higher level than the −0.15 TG in nonerythroid and erythroid tissues, including during extramedullary erythropoiesis induced by n-acetylphenylhydrazine injection. The enhanced erythroid expression of the −4.0 TG correlates with the appearance of a DNase I hypersensitive site in the 5′ flanking region of the transgene. Therefore, in the context of chromosomal integration, the 5′ flanking region of the ferrochelatase gene is necessary and sufficient to confer high levels of transgene expression in erythroid tissue.

GATA-1 dominantly activates a program of erythroid gene expression in factor-dependent myeloid FDCW2 cells

Erythrocyte development has previously been shown to depend upon the expression of the lineage-restricted trans-acting factor GATA-1. Despite predicted roles for this factor during early development, GATA-1-deficient cells in chimeric mice and embryonic stem cell cultures mature to a late proerythroblast stage and express at least certain genes that normally are thought to be regulated by GATA-1 (including erythroid Krüppel-like factor [EKLF] and the erythropoietin [Epo] receptor). Opportunities to test roles for GATA-1 in erythroid gene activation in these systems therefore are limited. In the present study, in an alternate approach to test the function of GATA-1, GATA-1 has been expressed together with the Epo receptor in myeloid FDCW2 cells and the resulting effects on cytokine-dependent proliferation and erythroid gene expression have been assessed. GATA-1 expression at low levels delayed FDCW2ER cell cycle progression at the G1 phase specifically during Epo-induced mitogenesis. Upon expression of GATA-1 at increased levels, proliferation in response to Epo, interleukin-3 (IL-3), and stem cell factor was attenuated and endogenous GATA-1, EKLF and betamaj-globin gene expression was activated. Friend of GATA-1 (FOG) transcript levels also were enhanced, and ets-1 and c-mpl but not Epo receptor gene expression was induced. Finally, in FDCW2 cells expressing increased levels of GATA-1 and a carboxyl-terminally truncated Epo receptor, Epo (with respect to IL-3 as a control) was shown to markedly promote globin transcript expression. Thus, novel evidence for select hierarchical roles for GATA-1 and Epo in erythroid lineage specification is provided.

Cruciform-extruding regulatory element controls cell-specific activity of the tyrosine hydroxylase gene promoter

Tyrosine hydroxylase (TH) is expressed specifically in catecholaminergic cells. We have identified a novel regulatory sequence in the upstream region of the bovine TH gene promoter formed by a dyad symmetry element (DSE1;-352/-307 bp). DSE1 supports TH promoter activity in TH-expressing bovine adrenal medulla chromaffin (BAMC) cells and inhibits promoter activity in non-expressing TE671 cells. DNase I footprinting of relaxed TH promoter DNA showed weak binding of nuclear BAMC cell proteins to a short sequence in the right DSE1 arm. In BAMC cells, deletion of the right arm markedly reduced the expression of luciferase from the TH promoter. However, deletion of the left DSE1 arm or its reversed orientation (RevL) also inactivated the TH promoter. In supercoiled TH promoter, DSE1 assumes a cruciform-like conformation i.e., it binds cruciform-specific 2D3 antibody, and S1 nuclease-cleavage and OsO4-modification assays have identified an imperfect cruciform extruded by the DSE1. DNase I footprinting of supercoiled plasmid showed that cruciformed DSE1 is targeted by nuclear proteins more efficiently than the linear duplex isomer and that the protected site encompasses the left arm and center of DSE1. Our results suggest that the disruption of intrastrand base-pairing preventing cruciform formation and protein binding to DSE1 is responsible for its inactivation in DSE1 mutants. DSE1 cruciform may act as a target site for activator (BAMC cells) and repressor (TE671) proteins. Its extrusion emerges as a novel mechanism that controls cell-specific promoter activity.

The comparative genomic structure and sequence of the surfeit gene homologs in the puffer fish Fugu rubripes and their association with CpG-rich islands

The puffer fish Fugu rubripes (Fugu) has a compact genome approximately one-seventh the size of man, mainly owing to small intron size and the presence of few dispersed repetitive DNA elements, which greatly facilitates the study of its genes at the genomic level. It has been shown previously that, whereas the Surfeit genes are tightly clustered at a single locus in mammals and birds, the genes are found at three separate loci in the Fugu genome. Here, Fugu gene homologs of all six Surfeit genes (Surf-1 to Surf-6) have been cloned and sequenced, and their gene structure has been compared with that of their mammalian and avian homologs. The predicted protein products of each gene are well conserved between vertebrate species, and in most cases their gene structures are identical to their mammalian and avian homologs except for the Fugu Surf-6 gene, which was found to lack an intron present in the mouse gene. In addition, we have identified conserved regulatory elements at the 5' and 3' ends of the Surf-3/rpL7a gene by comparison with the mammalian and chicken Surf-3/rpL7a gene homologs, including the presence of a polypyrimidine tract at the extreme 5' end of this ribosomal protein gene. The Fugu Surfeit gene homologs appear to be associated with CpG-rich islands, like the Surfeit genes in higher vertebrates, but these Fugu CpG islands are similar to the nonclassical islands characteristic of other fish species. Our observations support the use of the Fugu genome to study vertebrate gene structure, to predict the structure of mammalian genes, and to identify vertebrate regulatory elements. [The sequence data described in this paper have been submitted to the data library under accession nos. Y15170 (Surf-2, Surf-4), Y15171 (Surf-3, Surf-1, Surf-6), and Y15172 (Surf-5.)]

Transcriptional regulation of the human erythroid 5-aminolevulinate synthase gene. Identification of promoter elements and role of regulatory proteins

We have characterized the 5'-flanking region of the human erythroid-specific 5-amino levulinate synthase (ALAS) gene (the ALAS2 gene) and shown that the first 300 base pairs of promoter sequence gives maximal expression in erythroid cells. Transcription factor binding sites clustered within this promoter sequence include GATA motifs and CACCC boxes, critical regulatory sequences of many erythroid cell-expressed genes. GATA sites at -126/-121 (on the noncoding strand) and -102/-97 were each recognized by GATA-1 protein in vitro using erythroid cell nuclear extracts. Promoter mutagenesis and transient expression assays in erythroid cells established that both GATA-1 binding sites were functional and exogenously expressed GATA-1 increased promoter activity through these sites in transactivation experiments. A noncanonical TATA sequence at the expected TATA box location (-30/-23) bound GATA-1- or TATA-binding protein (TBP) in vitro. Conversion of this sequence to a canonical TATA box reduced expression in erythroid cells, suggesting a specific role for GATA-1 at this site. However, expression was also markedly reduced when the -30/-23 sequence was converted to a consensus GATA-1 sequence (that did not bind TBP in vitro), suggesting that a functional interaction of both factors with this sequence is important. A sequence comprising two overlapping CACCC boxes at -59/-48 (on the noncoding strand) was demonstrated by mutagenesis to be functionally important. This CACCC sequence bound Sp1, erythroid Krüppel-like factor, and basic Krüppel-like factor in vitro, while in transactivation experiments erythroid Krüppel-like factor activated ALAS2 promoter expression through this sequence. A sequence at -49/-39 with a 9/11 match to the consensus for the erythroid specific factor NF-E2 was not functional. Promoter constructs with 5'-flanking sequence from 293 base pairs to 10.3 kilobase pairs expressed efficiently in COS-1 cells as well as in erythroid cells, indicating that an enhancer sequence located elsewhere or native chromatin structure may be required for the tissue-restricted expression of the gene in vivo.