Transcriptional regulation of the human H ferritin-encoding gene (FERH) in G418-treated cells: role of the B-box-binding factor

Ferritin Heavy Chain Binds Peroxiredoxin 6 and Inhibits Cell Proliferation and Migration

The H Ferritin subunit (FTH1), as well as regulating the homeostasis of intracellular iron, is involved in complex pathways that might promote or inhibit carcinogenesis. This function may be mediated by its ability to interact with different molecules. To gain insight into the FTH1 interacting molecules, we analyzed its interactome in HEK293T cells. Fifty-one proteins have been identified, and among them, we focused our attention on a member of the peroxiredoxin family (PRDX6), an antioxidant enzyme that plays an important role in cell proliferation and in malignancy development. The FTH1/PRDX6 interaction was further supported by co-immunoprecipitation, in HEK293T and H460 cell lines and by means of computational methods. Next, we demonstrated that FTH1 could inhibit PRDX6-mediated proliferation and migration. Then, the results so far obtained suggested that the interaction between FTH1/PRDX6 in cancer cells might alter cell proliferation and migration, leading to a less invasive phenotype.

Caffeine Positively Modulates Ferritin Heavy Chain Expression in H460 Cells: Effects on Cell Proliferation

Both the methylxanthine caffeine and the heavy subunit of ferritin molecule (FHC) are able to control the proliferation rate of several cancer cell lines. While caffeine acts exclusively as a negative modulator of cell proliferation, FHC might reduce or enhance cell viability depending upon the different cell type. In this work we have demonstrated that physiological concentrations of caffeine reduce the proliferation rate of H460 cells: along with the modulation of p53, pAKT and Cyclin D1, caffeine also determines a significant FHC up-regulation through the activation of its transcriptional efficiency. FHC plays a central role in the molecular pathways modulated by caffeine, ending in a reduced cell growth, since its specific silencing by siRNA almost completely abolishes caffeine effects on H460 cell proliferation. These results allow the inclusion of ferritin heavy subunits among the multiple molecular targets of caffeine and open the way for studying the relationship between caffeine and intracellular iron metabolism.

The association between the levels of serum ferritin and sex hormones in a large scale of Chinese male population

BACKGROUND

The ferritin is an important participant of iron-storage but its regulation and related factors were not well defined. The present objective was to explore the potential association between serum ferritin levels and sex hormones.

METHODS

1999 Chinese men in the Fangchenggang Area Male Health and Examination Survey (FAMHES) were recruited in this cross-sectional study. Levels of serum ferritin, total testosterone (free testosterone was calculated from the total one), estradiol and sex hormone-binding protein were detected in venous blood samples. The effects of age, BMI, smoking as well as alcohol consumption were analyzed on ferritin levels, respectively, and then the Pearson's correlation analysis was used to evaluate the association between ferritin levels and sex hormones adjusting for the above factors.

RESULTS

The age, BMI and alcohol consumption significantly affected serum ferritin levels, but there was no significant difference between smokers and nonsmokers. Ferritin levels were significantly and negatively associated with total testosterone (R = -0.205, P< 0.001), sex hormone-binding protein (R = -0.161, P<0.001) and free testosterone (R = -0.097, P<0.001). After age and alcohol consumption were adjusted, the above associations were still significant (R = -0.200, -0.181 and -0.083, respectively, all P<0.001). However, there was only borderline negative association between ferritin levels and estradiol (adjusted R = -0.039, P = 0.083).

CONCLUSION

The large scale of epidemic results showed the significantly negative associations between serum ferritin levels and sex hormones, which may provide more clues to explore the potential regulation and biological mechanism of ferritin.

Transcriptional up-regulation of a novel ferritin homolog in abalone Haliotis discus hannai Ino by dietary iron

A novel cDNA encoding ferritin (HdhNFT) was cloned from the hepatopancreas of abalone, Haliotis discus hannai Ino. The deduced protein contains 171 amino acid residues with a predicted molecular mass (MW) about 19.8 kDa and theoretical isoelectric point (pI) of 4.792. Amino acid alignment revealed that HdhNFT shared high similarity with other known ferritins. The HdhNFT contained a highly conserved motif for the ferroxidase center, which consists of seven residues of a typical vertebrate heavy-chain ferritin with a typical stem-loop structure. HdhNFT mRNA contains a 27 bp iron-responsive element (IRE) in the 5'-untranslated region. This IRE exhibited 82.14% similarity with abalone H. discus discus and 78.57% similarity with Pacific oyster Crassostrea gigas IREs. By real-time PCR assays, the mRNA transcripts of HdhNFT were found to be higher expressed in kidney, hepatopancreas, gill, mantle and muscle than in haemocytes and gonad. Moreover, mRNA expression levels of HdhNFT in the hepatopancreas and haemocytes were measured by real-time PCR in abalone fed with graded levels of dietary iron (29.2, 65.7, 1267.2 and 6264.7 mg/kg). Results showed that the expression of the HdhNFT mRNA increased with dietary iron contents. Furthermore, the maximum value of the HdhNFT mRNA was found in the treatment with 6264.7 mg/kg of dietary iron. These data indicated that dietary iron can up-regulate HdhNFT at transcriptional level in abalone.

Identification and molecular analysis of a ferritin subunit from red drum (Sciaenops ocellatus)

Ferritin is a conserved iron binding protein existing ubiquitously in prokaryotes and eukaryotes. In this study, the gene encoding a ferritin M subunit homologue (SoFer1) was cloned from red drum (Sciaenops ocellatus) and analyzed at expression and functional levels. The open reading frame of SoFer1 is 531 bp and preceded by a 5'-untranslated region that contains a putative Iron Regulatory Element (IRE) preserved in many ferritins. The deduced amino acid sequence of SoFer1 possesses both the ferroxidase center of mammalian H ferritin and the iron nucleation site of mammalian L ferritin. Expression of SoFer1 was tissue specific and responded positively to experimental challenges with Gram-positive and Gram-negative fish pathogens. Treatment of red drum liver cells with iron, copper, and oxidant significantly upregulated the expression of SoFer1 in time-dependent manners. To further examine the potential role of SoFer1 in antioxidation, red drum liver cells transfected transiently with SoFer1 were prepared. Compared to control cells, SoFer1 transfectants exhibited reduced production of reactive oxygen species following H(2)O(2) challenge. Finally, to examine the iron binding potential of SoFer1, SoFer1 was expressed in and purified from Escherichia coli as a recombinant protein. Iron-chelating analysis showed that purified recombinant SoFer1 was capable of iron binding. Taken together, these results suggest that SoFer1 is likely to be a functional ferritin involved in iron sequestration, host immune defence against bacterial infection, and antioxidation.

Production of recombinant protein and polyclonal mouse antiserum for ferritin from Sipuncula Phascolosoma esculenta

The iron storage protein, ferritin, plays a key role in iron metabolism, but its regulation and functions in many invertebrate species are still largely unknown. In our previous work, an inducible ferritin cDNA from Phascolosoma esculenta with a full-length of 1017 bp has been cloned. In this follow-up study, the deducted ferritin protein sequence was predicted to be a polypeptide of 175 amino acids with a molecular mass of 20.1955kDa and an isoelectric point of 5.08. The cDNA sequence of P. esculenta ferritin was constructed into pET system expression system and efficiently expressed in E. coli BL21 under IPTG induction. The recombinant ferritin was detected as a 24 kDa protein by SDS-PAGE. After purification directly from the gel, the recombinant ferritin was used to immunize mice and the anti-serum was prepared. The antibody displayed a strong immunological reactivity and specificity when used in Western-blot analysis. For the first time, our work provided a set of molecular tools essential for the further studies of ferritin protein functions in P. esculenta.

Adiponectin upregulates ferritin heavy chain in skeletal muscle cells

OBJECTIVE

Adiponectin is an adipocyte-derived protein that acts to reduce insulin resistance in the liver and muscle and also inhibits atherosclerosis. Although adiponectin reportedly enhances AMP-activated protein kinase and inhibits tumor necrosis factor-alpha action downstream from the adiponectin signal, the precise physiological mechanisms by which adiponectin acts on skeletal muscles remain unknown.

RESEARCH DESIGN AND METHODS

We treated murine primary skeletal muscle cells with recombinant full-length human adiponectin for 12 h and searched, using two-dimensional electrophoresis, for proteins upregulated more than threefold by adiponectin compared with untreated cells.

RESULTS

We found one protein that was increased 6.3-fold with adiponectin incubation. MALDI-TOF (matrix-assisted laser desorption/ionization-top of flight) mass spectrometric analysis identified this protein as ferritin heavy chain (FHC). When murine primary skeletal muscle cells were treated with adiponectin, IkappaB-alpha phosphorylation was observed, suggesting that adiponectin stimulates nuclear factor (NF)-kappaB activity. In addition, FHC upregulation by adiponectin was inhibited by NF-kappaB inhibitors. These results suggest NF-kappaB activation to be involved in FHC upregulation by adiponectin. Other NF-kappaB target genes, manganese superoxide dismutase (MnSOD) and inducible nitric oxide synthase (iNOS), were also increased by adiponectin treatment. We performed a reactive oxygen species (ROS) assay using CM-H(2)DCFDA fluorescence and found that ROS-reducing effects of adiponectin were abrogated by FHC or MnSOD small-interfering RNA induction.

CONCLUSIONS

We have demonstrated that adiponectin upregulates FHC in murine skeletal muscle tissues, suggesting that FHC elevation might partially explain how adiponectin protects against oxidative stress in skeletal muscles.

Two ferritin subunits from disk abalone (Haliotis discus discus): cloning, characterization and expression analysis

Ferritin plays a key role in cellular iron metabolism, which includes iron storage and detoxification. From disk abalone, Haliotis discus discus, the cDNA that encodes the two ferritin subunits abalone ferritin subunit 1 (Abf1) and abalone ferritin subunit 2 (Abf2) were cloned. The complete cDNA coding sequences for Abf1 and Abf2 contained 621 and 549 bp, encoding for 207 and 183 amino acid residues, respectively. The H. discus discus Abf2 subunit contained a highly conserved motif for the ferroxidase center, which consists of seven residues of a typical vertebrate heavy-chain ferritin with a typical stem-loop structure. Abf2 mRNA contains a 27 bp iron-responsive element (IRE) in the 5'UTR position. This IRE exhibited 96% similarity with pearl and Pacific oyster and 67% similarity with human H type IREs. However, the Abf1 subunit had neither ferroxidase center residues nor the IRE motif sequence; instead, it contained iron-binding region signature 2 (IBRS) residues. Recombinant Abf1 and Abf2 proteins were purified and the respective sizes were about 24 and 21 kDa. Abf1 and Abf2 exhibited iron-chelating activity 44.2% and 22.0%, respectively, at protein concentration of 6 microg/ml. Analysis of tissue-specific expression by RT-PCR revealed that Abf1 and Abf2 ferritin mRNAs were expressed in various abalone tissues, such as gill, mantle, gonad, foot and digestive tract in a wide distribution profile, but Abf2 expression was more prominent than Abf1.

Neomycin and puromycin affect gene expression in Giardia lamblia stable transfection

Two systems for stable transfection of Giardia have been established using selection either by neomycin or by puromycin. We asked if these selection systems themselves influenced expression of endogenous giardial genes. Northern blot analysis showed a approximately 1.4 to approximately 7-fold increase in the encystation-induced cyst wall protein 1 (cwp1), cwp2, and gmyb2 gene transcripts in the drug selected cell lines during vegetative growth, compared with untransfected cells. However, the levels of the constitutive ran, lrp3, or alpha2-tubulin gene transcripts decreased slightly or did not change in these stably transfected cell lines. Part of the effect could be due to drug selection, since treatment of untransfected cells with G418 or puromycin also had similar effects. Nuclear run-on assays showed that part of the effect comes from an increase in transcription initiation rate. The levels of CWP and cyst formation during vegetative growth also increased in the transfected cell lines. Using proteomic technologies, we identified eight genes whose expression is upregulated in neomycin selected cell lines, including phosphoglycerate kinase, glyceraldehyde-3-phosphate dehydrogenase, ornithine carbamoyltransferase, carbamate kinase, orf 16424, cyclophilin, co-chaperone-like p21, and bip. Six of these are also upregulated in puromycin selected cell lines. Our results indicate that transfection and drug selection, per se, can alter expression of genes involved in metabolism, protein folding, and differentiation status in Giardia.

Detection and functional analysis of an SNP in the promoter of the human ferritin H gene that modulates the gene expression

The H ferritin promoter spans approximately 150 bp, upstream of the transcription start and is composed by two cis-elements in position -132 (A box) and -62 (B-box), respectively. The A box is recognized by the transcription factor Sp1, and the B-box by a protein complex called Bbf, which includes the CAAT binding factor NF-Y. In this study we performed a functional analysis of an H ferritin promoter allele carrying a G to T substitution adjacent to the Bbf binding site, in position -69. In vitro studies with reporter constructs revealed a significantly reduced transcriptional activity of this allele compared to that of the w.t. promoter that was mirrored by a decrease in Bbf binding. In vivo, this variant genotype is accompanied by a reduced amount of the H mRNA in peripheral blood lymphocytes.

Evaluation of gene expression in pigs selected for enhanced reproduction using differential display PCR: II. Anterior pituitary

The objective of this study was to identify differentially expressed genes in the anterior pituitary (AP) of sows selected for enhanced reproductive phenotypes. Selection in the Index (I) line was based on an index of ovulation rate and embryo survival, whereas random selection was used in the Control (C) line. Average numbers of fully formed piglets at birth were 12.5 +/- 1.5 and 9.9 +/- 2.0 for Line I and C sows used in this study, respectively. In order to induce luteolysis and synchronize follicle development, sows were injected (i.m.) with 2 mL of prostaglandin F2alpha analog between d 12 and 14 of the estrous cycle. Tissue was harvested 2 d (d2) or 4 d (d4) after injection, resulting in four experimental groups: Cd2 (n = 6), Cd4 (n = 4), Id2 (n = 6), and Id4 (n = 7). Differential display PCR (ddPCR) was used to search for transcriptional changes between selection lines in the AP, using samples within line but pooled across days. Northern hybridization was used to confirm ddPCR results. For ddPCR, two pools were used from each line (C and I). Three genes were confirmed to be differentially expressed between Lines I and C: G-beta like protein, ferritin heavy-chain, and follicle stimulating hormone beta subunit, whereas many other expressed sequence tags were observed to be differentially expressed but still require confirmation. Our findings indicate that long-term selection to increase ovulation rate and decrease embryo mortality has altered transcriptional patterns in the anterior pituitary, most likely as correlated responses.

Transcription factor NF-Y regulates differentiation of CaCo-2 cells

The CaCo-2 cell line is used to study the molecular mechanisms underlying differentiation of intestinal epithelial cells. These cells undergo a gradual differentiation process that is growth-related and depends on cellular density. CaCo-2 cells acquire a morphological polarity and express such markers of mature enterocytes as sucrase-isomaltase, apolipoproteins, alkaline phosphatase, and H-ferritin. Because the NF-Y transcription factor is required for H-ferritin gene expression, we investigated whether it is involved in the expression of the other CaCo-2 differentiation markers. We observed that subunit NF-YA increases during CaCo-2 differentiation and that the constitutive expression of NF-YA, obtained in stably transfected CaCo-2 cells, results in the expression of differentiation markers. In fact, sucrase-isomaltase, apolipoprotein A1, and H-ferritin were constitutively expressed in NF-YA-transfected cells and their levels did not increase during prolonged culture, while these markers were not expressed in mock-transfected CaCo-2 cells or transfected with an inactive NF-YA expression vector until the onset of differentiation.

The B subunit of the CAAT-binding factor NFY binds the central segment of the Co-activator p300

We report that the heterotrimeric transcription factor NFY or "CAAT-binding factor" binds the -60 region of the human H ferritin promoter, the B site. DNA binding analysis with specific antibodies demonstrates that NFY/B/C subunits tightly bind this site and that NFY/C subunit is masked in vivo by binding with other protein(s). NFY binds the co-activator p300. Specifically, the NFY/B subunit interacts with the central segment of p300 in vivo and in vitro. cAMP substantially increases the formation of the NFY.p300 complex. Taken together these data provide a general model of cAMP induction of non-CRE-containing promoters and suggest that the NFY-B.p300 complex is located at the 5' end of the promoter and the NFY-B.C. TFIIB on the 3' end toward the transcription start site.

P/CAF/p300 complex binds the promoter for the heavy subunit of ferritin and contributes to its tissue-specific expression

We analysed the role of the nuclear protein P/CAF in regulating the transcription of the gene for human heavy (H) ferritin in given cell types. P/CAF is a histone acetylase, recruited to specific promoters via interaction with the co-activator molecule p300/CREB-binding protein (CBP). Histone acetylation promoted by P/CAF destabilizes the nucleosome structure, thus contributing to activation of transcription. The transcription of the H ferritin gene is regulated by the transcription factor B-box-binding factor (Bbf), which bridges RNA polymerase II via p300/CBP. Northern blot analyses of RNA species from various human tissues and cell lines demonstrate that the H ferritin gene is expressed at high levels in cells containing high levels of the P/CAF transcript. Moreover, transient overexpression of P/CAF in cells constitutively expressing low levels of this protein activates transcription driven by the region of the H promoter interacting with Bbf. The involvement of p300/CBP in the possible P/CAF-mediated regulation of H promoter was also explored by evaluating the phenomenon in the presence of the oncoprotein E1A. The results of these experiments demonstrate that P/CAF activates the H promoter also in the presence of limited amounts of p300/CBP. We argue that P/CAF is a component of the basal transcription apparatus of the H ferritin gene and that the relative amounts of the P/CAF protein in different cell types could account for the cell-specific control of the H ferritin gene transcription.

Okadaic acid stimulates H ferritin transcription in HeLa cells by increasing the interaction between the p300 CO-activator molecule and the transcription factor Bbf

The transcription of the human H ferritin gene is regulated by a transcription factor, called Bbf, which binds an enhancer element located in the -100/+1 region of the H promoter. To evaluate a possible role of Bbf phosphorylation on the promoter efficiency, we exposed HeLa cells to the phosphatase inhibitor okadaic acid (OA). The okadaic acid treatment increased about 4-fold the transcription driven by the -100/+1 region of the H promoter. However, the DNA binding activity of Bbf was not modified by OA, as assessed by EMSA. Immunoprecipitation experiments demonstrated that the OA-treatment stimulates and/or stabilizes the complex between Bbf and the nuclear protein p300, most probably by inducing the phosphorylation state of the complex. Bbf depends on the p300 molecule to trigger RNA polymerase II and thus transcription of the H ferritin gene.

A common mechanism underlying the E1A repression and the cAMP stimulation of the H ferritin transcription

Transcription of the H ferritin gene in vivo is stimulated by cAMP and repressed by the E1A oncoprotein. We report here the identification of the cis-element in the human promoter responsive to both cAMP- and E1A-mediated signals. This promoter region is included between positions -62 to -45 and binds a approximate 120-kDa transcription factor called Bbf. Bbf forms a complex in vivo with the coactivator molecules p300 and CBP. Recombinant E1A protein reduces the formation of these complexes. In vivo overexpression of p300 in HeLa cells reverses the E1A-mediated inhibition of the ferritin promoter transcription driven by Bbf. These data suggest the existence of a common mechanism for the cAMP activation and the E1A-mediated repression of H ferritin transcription.

Ferritin mRNAs in Schistosoma mansoni do not have iron-responsive elements for post-transcriptional regulation

Schistosoma mansoni possesses two isoforms of ferritin, soma and yolk ferritin. The soma ferritin occurs at a low level in most cells of both genders, whereas the yolk ferritin is a female-specific gene product that is expressed at high level in the vitellarium. In higher animals, ferritin mRNA is regulated by iron via the interaction of cytoplasmic binding proteins (IRPs) with a specific sequence element in the 5' untranslated region (UTR) referred to as the iron-responsive element (IRE). Sequence studies of the 5' UTRs, gel retardation assays, and hybridization experiments show that neither ferritin mRNAs of S. mansoni is regulated by an IRE/IRP mechanism. It is suggested that ferritins in schistosomes are controlled only at the transcriptional level.

The ferritins: molecular properties, iron storage function and cellular regulation

The iron storage protein, ferritin, plays a key role in iron metabolism. Its ability to sequester the element gives ferritin the dual functions of iron detoxification and iron reserve. The importance of these functions is emphasised by ferritin's ubiquitous distribution among living species. Ferritin's three-dimensional structure is highly conserved. All ferritins have 24 protein subunits arranged in 432 symmetry to give a hollow shell with an 80 A diameter cavity capable of storing up to 4500 Fe(III) atoms as an inorganic complex. Subunits are folded as 4-helix bundles each having a fifth short helix at roughly 60 degrees to the bundle axis. Structural features of ferritins from humans, horse, bullfrog and bacteria are described: all have essentially the same architecture in spite of large variations in primary structure (amino acid sequence identities can be as low as 14%) and the presence in some bacterial ferritins of haem groups. Ferritin molecules isolated from vertebrates are composed of two types of subunit (H and L), whereas those from plants and bacteria contain only H-type chains, where 'H-type' is associated with the presence of centres catalysing the oxidation of two Fe(II) atoms. The similarity between the dinuclear iron centres of ferritin H-chains and those of ribonucleotide reductase and other proteins suggests a possible wider evolutionary linkage. A great deal of research effort is now concentrated on two aspects of ferritin: its functional mechanisms and its regulation. These form the major part of the review. Steps in iron storage within ferritin molecules consist of Fe(II) oxidation, Fe(III) migration and the nucleation and growth of the iron core mineral. H-chains are important for Fe(II) oxidation and L-chains assist in core formation. Iron mobilisation, relevant to ferritin's role as iron reserve, is also discussed. Translational regulation of mammalian ferritin synthesis in response to iron and the apparent links between iron and citrate metabolism through a single molecule with dual function are described. The molecule, when binding a [4Fe-4S] cluster, is a functioning (cytoplasmic) aconitase. When cellular iron is low, loss of the [4Fe-4S] cluster allows the molecule to bind to the 5'-untranslated region (5'-UTR) of the ferritin m-RNA and thus to repress translation. In this form it is known as the iron regulatory protein (IRP) and the stem-loop RNA structure to which it binds is the iron regulatory element (IRE). IREs are found in the 3'-UTR of the transferrin receptor and in the 5'-UTR of erythroid aminolaevulinic acid synthase, enabling tight co-ordination between cellular iron uptake and the synthesis of ferritin and haem. Degradation of ferritin could potentially lead to an increase in toxicity due to uncontrolled release of iron. Degradation within membrane-encapsulated "secondary lysosomes' may avoid this problem and this seems to be the origin of another form of storage iron known as haemosiderin. However, in certain pathological states, massive deposits of "haemosiderin' are found which do not arise directly from ferritin breakdown. Understanding the numerous inter-relationships between the various intracellular iron complexes presents a major challenge.

Transcriptional activation of the H-ferritin gene in differentiated Caco-2 cells parallels a change in the activity of the nuclear factor Bbf

In this paper, we examine the mechanisms that regulate the expression of the heavy (H) ferritin subunit in the colon carcinoma Caco-2 cell line allowed to differentiate spontaneously in vitro. The differentiation process of these cells in continuous culture is accompanied by an accumulation of the mRNA coding for the apoferritin H chain. The analysis of Caco-2 subclones stably transfected with an H-chain promoter-chloramphenicol acetyltransferase (CAT) construct revealed that the mRNA increase is paralleled by an enhanced transcription of the H gene, driven by the -100 to +4 region of the H promoter. The H gene transcriptional activation seems to be a specific feature of differentiated Caco-2 cells, since the activity of other promoters did not change upon differentiation. The -100 to +4 region of the H promoter binds a transcription factor called Bbf (B-box binding factor); electrophoretic-mobility-shift-assay analyses showed that the retarded complex due to Bbf-H promoter interaction is significantly increased in the differentiated cells. We propose that the activation of H-ferritin gene expression may be associated with the establishment of a differentiated phenotype in Caco-2 cells, and that the H-ferritin gene transcriptional up-regulation is accompanied by a modification in the activity of the transcription factor Bbf.