Structural and functional relationships of human ferritin H and L chains deduced from cDNA clones

Ferritin - from iron, through inflammation and autoimmunity, to COVID-19

While it took decades to arrive to a conclusion that ferritin is more than an indicator of iron storage level, it took a short period of time through the COVID-19 pandemic to wonder what the reason behind high levels of ferritin in patients with severe COVID-19 might be. Unsurprisingly, acute phase reactant was not a satisfactory explanation. Moreover, the behavior of ferritin in patients with severe COVID-19 and the subsequent high mortality rates in patients with high ferritin levels necessitated further investigations to understand the role of ferritin in the diseases. Ferritin was initially described to accompany various acute infections, both viral and bacterial, indicating an acute response to inflammation. However, with the introduction of the hyperferritinemic syndrome connecting four severe pathological conditions such as adult-onset Still's disease, macrophage activation syndrome, catastrophic antiphospholipid syndrome, and septic shock added another aspect of ferritin where it could have a pathogenetic role rather than an extremely elevated protein only. In fact, suggesting that COVID-19 is a new member in the spectrum of hyperferritinemic syndrome besides the four mentioned conditions could hopefully direct further search on the pathogenetic role of ferritin. Doubtlessly, improving our understanding of those aspects of ferritin would enormously contribute to better coping with severe diseases in terms of treatment and prevention of complications. The origin, history, importance, and the advances of searching the role of ferritin in various pathological and clinical processes are presented hereby in our article. In addition, the implications of ferritin in COVID-19 are addressed.

Iron as the concert master in the pathogenic orchestra playing in sporadic Parkinson's disease

About 60 years ago, the discovery of a deficiency of dopamine in the nigro-striatal system led to a variety of symptomatic therapeutic strategies to supplement dopamine and to substantially improve the quality of life of patients with Parkinson's disease (PD). Since these seminal developments, neuropathological, neurochemical, molecular biological and genetic discoveries contributed to elucidate the pathology of PD. Oxidative stress, the consequences of reactive oxidative species, reduced antioxidative capacity including loss of glutathione, excitotoxicity, mitochondrial dysfunction, proteasomal dysfunction, apoptosis, lysosomal dysfunction, autophagy, suggested to be causal for ɑ-synuclein fibril formation and aggregation and contributing to neuroinflammation and neural cell death underlying this devastating disorder. However, there are no final conclusions about the triggered pathological mechanism(s) and the follow-up of pathological dysfunctions. Nevertheless, it is a fact, that iron, a major component of oxidative reactions, as well as neuromelanin, the major intraneuronal chelator of iron, undergo an age-dependent increase. And ageing is a major risk factor for PD. Iron is significantly increased in the substantia nigra pars compacta (SNpc) of PD. Reasons for this finding include disturbances in iron-related import and export mechanisms across the blood-brain barrier (BBB), localized opening of the BBB at the nigro-striatal tract including brain vessel pathology. Whether this pathology is of primary or secondary importance is not known. We assume that there is a better fit to the top-down hypotheses and pathogens entering the brain via the olfactory system, then to the bottom-up (gut-brain) hypothesis of PD pathology. Triggers for the bottom-up, the dual-hit and the top-down pathologies include chemicals, viruses and bacteria. If so, hepcidin, a regulator of iron absorption and its distribution into tissues, is suggested to play a major role in the pathogenesis of iron dyshomeostasis and risk for initiating and progressing ɑ-synuclein pathology. The role of glial components to the pathology of PD is still unknown. However, the dramatic loss of glutathione (GSH), which is mainly synthesized in glia, suggests dysfunction of this process, or GSH uptake into neurons. Loss of GSH and increase in SNpc iron concentration have been suggested to be early, may be even pre-symptomatic processes in the pathology of PD, despite the fact that they are progression factors. The role of glial ferritin isoforms has not been studied so far in detail in human post-mortem brain tissue and a close insight into their role in PD is called upon. In conclusion, "iron" is a major player in the pathology of PD. Selective chelation of excess iron at the site of the substantia nigra, where a dysfunction of the BBB is suggested, with peripherally acting iron chelators is suggested to contribute to the portfolio and therapeutic armamentarium of anti-Parkinson medications.

Ferritin heavy chain (FTH1) exerts significant antigrowth effects in breast cancer cells by inhibiting the expression of c-MYC

Overexpression of ferritin heavy chain (FTH1) often associates with good prognosis in breast cancer (BCa), particularly in the triple‐negative subtype (triple‐negative breast cancer). However, the mechanism by which FTH1 exerts its possible tumor suppressor effects in BCa is not known. Here, we examined the bearing of FTH1 silencing or overexpression on several aspects of BCa cell growth in vitro. FTH1 silencing promoted cell growth and mammosphere formation, increased c‐MYC expression, and reduced cell sensitivity to chemotherapy. In contrast, FTH1 overexpression inhibited cell growth, decreased c‐MYC expression, and sensitized cancer cells to chemotherapy; silencing of c‐MYC recapitulated the effects of FTH1 overexpression. These findings show for the first time that FTH1 suppresses tumor growth by inhibiting the expression of key oncogenes, such as c‐MYC.

Innovative therapies for neuroblastoma: The surprisingly potent role of iron chelation in up-regulating metastasis and tumor suppressors and down-regulating the key oncogene, N-myc

Iron is an indispensable requirement for essential biological processes in cancer cells. Due to the greater proliferation of neoplastic cells, their demand for iron is considerably higher relative to normal cells, making them highly susceptible to iron depletion. Understanding this sensitive relationship led to research exploring the effect of iron chelation therapy for cancer treatment. The classical iron-binding ligand, desferrioxamine (DFO), has demonstrated effective anti-proliferative activity against many cancer-types, particularly neuroblastoma tumors, and has the surprising activity of down-regulating the potent oncogene, N-myc, which is a major oncogenic driver in neuroblastoma. Even more significant is the ability of DFO to simultaneously up-regulate the potent metastasis suppressor, N-myc downstream-regulated gene-1 (NDRG1), which plays a plethora of roles in suppressing a variety of oncogenic signaling pathways. However, DFO suffers the disadvantage of demonstrating poor membrane permeability and short plasma half-life, requiring administration by prolonged subcutaneous or intravenous infusions. Considering this, the specifically designed di-2-pyridylketone thiosemicarbazone (DpT) series of metal-binding ligands was developed in our laboratory. The lead agent from the first generation DpT series, di-2-pyridylketone-4,4-dimethyl-3-thiosemicarbazone (Dp44mT), showed exceptional anti-cancer properties compared to DFO. However, it exhibited cardiotoxicity in mouse models at higher dosages. Therefore, a second generation of agents was developed with the lead compound being di-2-pyridylketone-4-cyclohexyl-4-methyl-3-thiosemicarbazone (DpC) that progressed to Phase I clinical trials. Importantly, DpC showed better anti-proliferative activity than Dp44mT and no cardiotoxicity, demonstrating effective anti-cancer activity against neuroblastoma tumors in vivo.

Pathogenesis, Diagnosis, and Clinical Implications of Hereditary Hemochromatosis-The Cardiological Point of View

Hereditary hemochromatosis (HH) is a genetic disease leading to excessive iron absorption, its accumulation, and oxidative stress induction causing different organ damage, including the heart. The process of cardiac involvement is slow and lasts for years. Cardiac pathology manifests as an impaired diastolic function and cardiac hypertrophy at first and as dilatative cardiomyopathy and heart failure with time. From the moment of heart failure appearance, the prognosis is poor. Therefore, it is crucial to prevent those lesions by upfront therapy at the preclinical phase of the disease. The most useful diagnostic tool for detecting cardiac involvement is echocardiography. However, during an early phase of the disease, when patients do not present severe abnormalities in serum iron parameters and severe symptoms of other organ involvement, heart damage may be overlooked due to the lack of evident signs of cardiac dysfunction. Considerable advancement in echocardiography, with particular attention to speckle tracking echocardiography, allows detecting discrete myocardial abnormalities and planning strategy for further clinical management before the occurrence of substantial heart damage. The review aims to present the current state of knowledge concerning cardiac involvement in HH. In addition, it could help cardiologists and other physicians in their everyday practice with HH patients.

Ciclopirox olamine induces ferritinophagy and reduces cyst burden in polycystic kidney disease

Despite the recent launch of tolvaptan, the search for safer polycystic kidney disease (PKD) drugs continues. Ciclopirox (CPX) or its olamine salt (CPX-O) is contained in a number of commercially available antifungal agents. CPX is also reported to possess anticancer activity. Several mechanisms of action have been proposed, including chelation of iron and inhibition of iron-dependent enzymes. Here, we show that CPX-O inhibited in vitro cystogenesis of primary human PKD cyst-lining epithelial cells cultured in a 3D collagen matrix. To assess the in vivo role of CPX-O, we treated PKD mice with CPX-O. CPX-O reduced the kidney-to-body weight ratios of PKD mice. The CPX-O treatment was also associated with decreased cell proliferation, decreased cystic area, and improved renal function. Ferritin levels were markedly elevated in cystic kidneys of PKD mice, and CPX-O treatment reduced renal ferritin levels. The reduction in ferritin was associated with increased ferritinophagy marker nuclear receptor coactivator 4, which reversed upon CPX-O treatment in PKD mice. Interestingly, these effects on ferritin appeared independent of iron. These data suggest that CPX-O can induce ferritin degradation via ferritinophagy, which is associated with decreased cyst growth progression in PKD mice. Most importantly these data indicate that CPX-O has the potential to treat autosomal dominant PKD.

Ferritin as a Platform for Creating Antiviral Mosaic Nanocages: Prospects for Treating COVID-19

Infectious diseases are a continues threat to human health and the economy worldwide. The latest example is the global pandemic of COVID-19 caused by SARS-CoV-2. Antibody therapy and vaccines are promising approaches to treat the disease; however, they have bottlenecks: they might have low efficacy or narrow breadth due to the continuous emergence of new strains of the virus or antibodies could cause antibody-dependent enhancement (ADE) of infection. To address these bottlenecks, I propose the use of 24-meric ferritin for the synthesis of mosaic nanocages to deliver a cocktail of antibodies or nanobodies alone or in combination with another therapeutic, like a nucleotide analogue, to mimic the viral entry process and deceive the virus, or to develop mosaic vaccines. I argue that available data showing the effectiveness of ferritin-antibody conjugates in targeting specific cells and ferritin-haemagglutinin nanocages in developing influenza vaccines strongly support my proposals.

Ferritins in Kidney Disease

Ferritins are evolutionarily conserved proteins that regulate cellular iron metabolism. It is the only intracellular protein that is capable of storing large quantities of iron. Although the ratio of different subunits determines the iron content of each ferritin molecule, the exact mechanism that dictates organization of these subunits still is unclear. In this review, we address renal ferritin expression and its implication in kidney disease. Specifically, we address the role of ferritin subunits in preventing kidney injury and also promoting tolerance against infection-associated kidney injury. We describe functions for ferritin that are independent of its ability to ferroxidize and store iron. We further discuss the implications of ferritin in body fluids, including blood and urine, during inflammation and kidney disease. Although there are several in-depth review articles on ferritin in the context of iron metabolism, we chose to focus on the role of ferritin particularly in kidney health and disease and highlight unanswered questions in the field.

Transcriptome analysis reveals the pigmentation-related genes in two shell color strains of the Manila clam Ruditapes philippinarum

The Manila clam, Ruditapes philippinarum, is an ecologically and economically important marine bivalve species. In this study, we conducted transcriptomic sequencing of two different shell color strains (O and Z) before color appearance (uncolored juvenile clam) and pigmented shell color (colored juvenile clam) and investigated the analysis of the differential expression patterns of specific genes associated with pigmentation by RNA-seq and time course qPCR analysis. The transcription level of 16 differentially expressed genes (DEGs) related with shell color was analyzed by qRT-PCR to validate the performance of RNA-seq from Illumina sequence data where most of them were up-regulated. Two genes were down-regulated after the occurrence of zebra clam stripes compared with uncolored zebra clam. The trend of gene expression obtained by qPCR was basically consistent with that of RNA-seq. The synthesis of melanin in bivalves plays potential roles in the pigmentation of the shell and is closely related to the formation of the surface pattern. The porphyrin metabolism combined with tyrosinase and melanogenesis signaling pathway is a novel finding in shell color determination of R. philippinarum. This study sheds light on the pigmentation and coloration mechanism of the Manila clam.

Identification of multiple ferritin genes in Macrobrachium nipponense and their involvement in redox homeostasis and innate immunity

Based on the transcriptome database, we screened out four ferritin subunit genes (MnFer2-5) from the oriental river prawn Macrobrachium nipponense, which encode two non-secretory and two secretory peptides. MnFer2 and 4 possess a strictly conserved ferroxidase site, and MnFer3 has a non-typical ferroxidase site. MnFer5 seems to be a number of ferritin families, which has a distinct dinuclear metal binding motif, but lacks an iron ion channel, a ferroxidase site and a nucleation site. Diverse tissue-specific transcriptions of the four genes indicate their functional diversity in the prawn. Among them, MnFer2 is mainly expressed in hepatopancreas and intestines, MnFer3 and 4 are predominantly expressed in gills, and MnFer5 is widely expressed in various tissues with high presence in intestines, hepatopancreas and haemocytes. The transcription of all the four MnFer genes can be strongly induced by doxorubicin, indicating the involvement of these ferritin subunits in protection from oxidative stress. Upon Aeromonas hydrophila infection, only MnFer5 is persistently up-regulated, while other subunits including MnFer2-4 are down-regulated during the early stage, followed by recovery and even a slight increase at 48 h post bacterial challenge. Moreover, the iron binding capacity of recombinant MnFer2 is also demonstrated in vitro. The E. coli expressing MnFer2 displays increased resistance to hydrogen peroxidase cytotoxicity. These results suggest a protective role of ferritins from M. nipponense in iron homeostasis, redox biology and antibacterial immunity and shed light on the molecule evolution of crustacean ferritin subunits.

Magnetoferritin: Process, Prospects, and Their Biomedical Applications

Ferritin is a spherical iron storage protein composed of 24 subunits and an iron core. Using biomimetic mineralization, magnetic iron oxide can be synthesized in the cavity of ferritin to form magnetoferritin (MFt). MFt, also known as a superparamagnetic protein, is a novel magnetic nanomaterial with good biocompatibility and flexibility for biomedical applications. Recently, it has been demonstrated that MFt had tumor targetability and a peroxidase-like catalytic activity. Thus, MFt, with its many unique properties, provides a powerful platform for tumor diagnosis and therapy. In this review, we discuss the biomimetic synthesis and biomedical applications of MFt.

Up-regulated ferritin in periodontitis promotes inflammatory cytokine expression in human periodontal ligament cells through transferrin receptor via ERK/P38 MAPK pathways

OBJECTIVE

Ferritin, an iron-binding protein, is ubiquitous and highly conserved; it plays a crucial role in inflammation, which is the main symptom of periodontitis. Full-length cDNA library analyses have demonstrated abundant expression of ferritin in human periodontal ligament. The aims of the present study were to explore how ferritin is regulated by local inflammation, and to investigate its functions and mechanisms of action in the process of periodontitis.

METHODS

Human gingival tissues were collected from periodontitis patients and healthy individuals. Experimental periodontitis was induced by ligature of second molars in mice. The expression of ferritin light polypeptide (FTL) and ferritin heavy polypeptide (FTH) were assessed by immunohistochemistry. Meanwhile, after stimulating human periodontal ligament cells (HPDLCs) with P. gingivalis-lipopolysaccharide (LPS), interleukin (IL)-6, and tumor necrosis factor-α (TNF-α), the expression of FTH and FTL were measured. Then, IL-6 and IL-8 were measured after incubation with different concentrations of apoferritin (iron-free ferritin) and several intracellular signaling pathway inhibitors, or after knockdown of the transferrin receptor.

RESULTS

Both FTH and FTL were substantially higher in inflamed periodontal tissues than in healthy tissues. The location of the elevated expression correlated well with the extent of inflammatory infiltration. Moreover, expression of FTH and FTL were enhanced after stimulation with P. gingivalis-LPS, IL-6, TNF-α. Apoferritin induced the production of IL-6 and IL-8 in a dose-dependent manner partly through binding to the transferrin receptor and activating ERK/P38 signaling pathways in HPDLCs.

CONCLUSIONS

Ferritin is up-regulated by inflammation and exhibits cytokine-like activity in HPDLCs inducing a signaling cascade that promotes expression of pro-inflammatory cytokines associated with periodontitis.

A piRNA utilizes HILI and HIWI2 mediated pathway to down-regulate ferritin heavy chain 1 mRNA in human somatic cells

The piwi interacting RNAs (piRNAs) are small non-coding RNAs that specifically bind to the PIWI proteins, a functional requirement. The piRNAs regulate germline development, transposons control, and gene expression. However, piRNA-mediated post-transcriptional gene regulation in human somatic cells is not well understood. We discovered a human piRNA (piR-FTH1) which has a complementary sequence in the ferritin heavy chain 1 (Fth1) mRNA. We demonstrated that expression of piR-FTH1 and Fth1 are inversely correlated in the tested tumor cell lines. We found that piR-FTH1 negatively regulates the Fth1 expression at post-transcriptional level in triple negative breast cancer (TNBC) cells. Additionally, we confirmed that transfected piR-FTH1 knocks down the Fth1 mRNA via the HIWI2 and HILI mediated mechanism. piR-FTH1 mediated Fth1 repression also increased doxorubicin sensitivity by a remarkable 20-fold in TNBC cells. Since the current piRNA-mediated knockdowns of target mRNA are mostly reported in germ line cells, piRNA-mediated post-transcriptional gene regulation in somatic cells is rather unique in its application and mechanistically uses an alternative pathway to siRNA and miRNA. This work begins to lay the groundwork with a broader impact on treatment of various diseases that are linked to elevated levels of specific mRNAs which have a piRNA target.

Significance of serum ferritin as a prognostic factor in advanced hepatobiliary cancer patients treated with Korean medicine: a retrospective cohort study

Background

Advanced hepatobiliary cancers are highly lethal cancers that require precise prediction in clinical practice. Serum ferritin level increases in malignancy and high serum ferritin level is associated with poor survival in various cancers. This study aimed to identify whether serum ferritin could independently predict the overall survival (OS) of patients with advanced hepatobiliary cancers.

Methods

The retrospective cohort study was performed by reviewing medical records of patients with advanced hepatobiliary cancers from June 2006 to September 2016. The demographic and clinicopathological characteristics as well as the biochemical markers were evaluated at the initiation of Korean medicine (KM) treatment. The OS was calculated using Kaplan-Meier estimates. The Cox proportional hazard model was used to identify the independent prognostic significance of serum ferritin for survival.

Results

The median OS of all subjects was 5.1 months (range, 0.5–114.9 months). The median OS of group with low ferritin levels and that with high ferritin levels was 7.5 months (range, 0.7–114.9 months) and 2.8 months (range, 0.5–22.8 months), respectively (P < 0.001). The results of the univariate analysis showed that the Eastern Cooperative Oncology Group Performance Status (ECOG-PS) (P = 0.002), tumor type (P = 0.001), prior treatment (P = 0.023), serum ferritin (P < 0.001), hemoglobin (P = 0.002), total bilirubin (P = 0.002), gamma-glutamyl transpeptidase (P = 0.007), albumin (P = 0.013), white blood cell (P = 0.002), and C-reactive protein (CRP) (P < 0.001) were significant factors for the patients’ survival outcome. On multivariate analysis controlling confounding factors, ferritin (P = 0.041), CRP (P = 0.010), ECOG-PS (P = 0.010), and tumor type (P = 0.018) were identified as independent prognostic factors for survival.

Conclusions

These results indicate that serum ferritin is a valid clinical biochemical marker to predict survival of patients with advanced hepatobiliary cancers.

Study of manganese binding to the ferroxidase centre of human H-type ferritin

Ferritins are ubiquitous and conserved proteins endowed with enzymatic ferroxidase activity, that oxidize Fe(II) ions at the dimetal ferroxidase centre to form a mineralized Fe(III) oxide core deposited within the apo-protein shell. Herein, the in vitro formation of a heterodimetal cofactor constituted by Fe and Mn ions has been investigated in human H ferritin (hHFt). Namely, Mn and Fe binding at the hHFt ferroxidase centre and its effects on Fe(II) oxidation have been investigated by UV-Vis ferroxidation kinetics, fluorimetric titrations, multifrequency EPR, and preliminary Mössbauer spectroscopy. Our results show that in hHFt, both Fe(II) and Mn(II) bind the ferroxidase centre forming a Fe-Mn cofactor. Moreover, molecular oxygen seems to favour Mn(II) binding and increases the ferroxidation activity of the Mn-loaded protein. The data suggest that Mn influences the Fe binding and the efficiency of the ferroxidation reaction. The higher efficiency of the Mn-Fe heterometallic centre may have a physiological relevance in specific cell types (i.e. glia cells), where the concentration of Mn is the same order of magnitude as iron.

Metal ion assisted interface re-engineering of a ferritin nanocage for enhanced biofunctions and cancer therapy

The bottom-up self-assembly of protein subunits into supramolecular nanoarchitectures is ubiquitously exploited to recapitulate and expand the features of natural proteins to advance nanoscience in medicine. Various chemical and biological re-engineering approaches are available to render diverse functions in the given proteins. They are, unfortunately, capable of compromising protein integrity and stability after extensive modifications. In this study, we introduce a new protein re-engineering method, metal ion assisted interface re-engineering (MAIR), to serve as a robust and universal strategy to extend the functions of self-assembly proteins by boosting structural features to advance their diverse biomedical applications. In particular, the MAIR strategy was applied to a widely used natural protein, ferritin, as a model protein to coordinate with copper ions in its mutagenic artificial metal binding domain. Structure directed rational protein mutagenesis was carried out at the C2 interface amino acid residues of the ferritin subunit for metal ion coordination site optimization. Copper binding at the artificial binding pocket was highly specific over the other divalent ions present in physiological fluids, and the structurally embedded copper ion in turn strengthened the overall protein integrity and stability. In the presence of isotopic copper-64, the interface re-engineered ferritin worked as a chelator-free molecular nanoprobe with an extraordinarily high specific activity to allow PET imaging of tumors in live animals. We also found that the re-engineered ferritin coordinating with copper ions demonstrates high drug loading capacity of a widely used anti-cancer agent, doxorubicin (DOX), to achieve significant drug retention at the tumor site and enhance tumor regression for improved anti-cancer effects. The MAIR approach, thus, exploited the copper ion to facilitate efficient one-step labeling of mutant ferritin derivatives for simultaneous molecular imaging and drug delivery. The reported interface re-engineering strategy provides an unparalleled opportunity to expand protein biofunctions to serve as a new theranostic agent in cancer research.

The Ferritin Superfamily

Iron is very important in many biological processes and the ferritin protein family has evolved to store iron and to maintain cellular iron homeostasis. The deletion of the coding gene for the H subunit of ferritin leads to early embryonic death in mice and mutations in the gene for the L subunits in humans has been observed in neurodegenerative diseases, such as neuroferritinopathy. Thus, understanding how ferritin works is imperative and many studies have been conducted to delineate the molecular mechanism of ferritins and bacterioferritins. In the ferritin protein family, it is clear that a catalytic center for iron oxidation, the routes for iron to reach this center and the ability to nucleate an iron core, are common requirements for all ferritins. However, there are differences in the structural and mechanistic details of iron oxidation and mineralization. Although a common mechanism has been proposed for all ferritins, this mechanism needs to be further explored. There is a mechanistic diversity related to structural variation in the ferritin protein family. It is clear that other factors appear to affect the mechanism of iron oxidation and mineralization. This review focusses on the structural features of the ferritin protein family and its role in the mechanism of iron mineralization.

Self-assembly is prerequisite for catalysis of Fe(II) oxidation by catalytically active subunits of ferritin

Fe(III) storage by ferritin is an essential process of the iron homeostasis machinery. It begins by translocation of Fe(II) from outside the hollow spherical shape structure of the protein, which is formed as the result of self-assembly of 24 subunits, to a di-iron binding site, the ferroxidase center, buried in the middle of each active subunit. The pathway of Fe(II) to the ferroxidase center has remained elusive, and the importance of self-assembly for the functioning of the ferroxidase center has not been investigated. Here we report spectroscopic and metal ion binding studies with a mutant of ferritin from Pyrococcus furiosus (PfFtn) in which self-assembly was abolished by a single amino acid substitution. We show that in this mutant metal ion binding to the ferroxidase center and Fe(II) oxidation at this site was obliterated. However, metal ion binding to a conserved third site (site C), which is located in the inner surface of each subunit in the vicinity of the ferroxidase center and is believed to be the path for Fe(II) to the ferroxidase center, was not disrupted. These results are the basis of a new model for Fe(II) translocation to the ferroxidase center: self-assembly creates channels that guide the Fe(II) ions toward the ferroxidase center directly through the protein shell and not via the internal cavity and site C. The results may be of significance for understanding the molecular basis of ferritin-related disorders such as neuroferritinopathy in which the 24-meric structure with 432 symmetry is distorted.

Cytoprotective effects of ferritin on doxorubicin-induced breast cancer cell death

Ferritin is a major iron storage protein and essential for iron homeostasis. It has a wide range of functions in the body including iron delivery, immunosuppression, angiogenesis, and cell proliferation. Ferritin is overexpressed in many cancer cells, but its precise role in cancer is unclear. In the present study, we examined the functional roles of ferritin in protecting the MCF-7 breast cancer cell line against treatment with the chemotherapeutic agent doxorubicin. The effects of ferritin (human liver ferritin) and doxorubicin on the human MCF-7 breast cancer cell line were evaluated using the cell viability assay. The impact of decreasing ferritin light chain (FTL) and ferritin heavy chain (FTH) expression on doxorubicin sensitivity was assessed using siRNA. Reactive oxygen species (ROS) was also measured using the fluorescence probe CM-H2DCFDA. The mechanism of modulated chemosensitivity was evaluated by western blot analysis. Ferritin treatment activated MCF-7 cell proliferation in a concentration- and time-dependent manner. While treatment with doxorubicin alone significantly increased intracelullar ROS production, the addition of ferritin decreased this ROS formation, thereby reducing doxorubicin‑induced MCF-7 cell death. The inhibition of FTL and FTH by siRNA sensitized cells to doxorubicin. Treatment with doxorubicin alone significantly induced the cell cycle‑dependent kinase inhibitor protein p21, whereas ferritin reduced p21 expression. Thus, ferritin plays a critical role in protecting MCF-7 cells against the chemotherapeutic drug doxorubicin. A targeted reduction of ferritin may be a useful strategy for overcoming chemoresistance in breast cancer.

The significance of ferritin in cancer: anti-oxidation, inflammation and tumorigenesis

The iron storage protein ferritin has been continuously studied for over 70years and its function as the primary iron storage protein in cells is well established. Although the intracellular functions of ferritin are for the most part well-characterized, the significance of serum (extracellular) ferritin in human biology is poorly understood. Recently, several lines of evidence have demonstrated that ferritin is a multi-functional protein with possible roles in proliferation, angiogenesis, immunosuppression, and iron delivery. In the context of cancer, ferritin is detected at higher levels in the sera of many cancer patients, and the higher levels correlate with aggressive disease and poor clinical outcome. Furthermore, ferritin is highly expressed in tumor-associated macrophages which have been recently recognized as having critical roles in tumor progression and therapy resistance. These characteristics suggest ferritin could be an attractive target for cancer therapy because its down-regulation could disrupt the supportive tumor microenvironment, kill cancer cells, and increase sensitivity to chemotherapy. In this review, we provide an overview of the current knowledge on the function and regulation of ferritin. Moreover, we examine the literature on ferritin's contributions to tumor progression and therapy resistance, in addition to its therapeutic potential.

Ferritin stimulates breast cancer cells through an iron-independent mechanism and is localized within tumor-associated macrophages

Tumor-associated macrophages play a critical role in breast tumor progression; however, it is still unclear what effector molecular mechanisms they employ to impact tumorigenesis. Ferritin is the primary intracellular iron storage protein and is also abundant in circulation. In breast cancer patients, ferritin is detected at higher levels in both serum and tumor lysates, and its increase correlates with poor clinical outcome. In this study, we comprehensively examined the distribution of ferritin in normal and malignant breast tissue at different stages in tumor development. Decreased ferritin expression in cancer cells but increased infiltration of ferritin-rich CD68-positive macrophages was observed with increased tumor histological grade. Interestingly, ferritin stained within the stroma surrounding tumors suggesting local release within the breast. In cell culture, macrophages, but not breast cancer cells, were capable of ferritin secretion, and this secretion was further increased in response to pro-inflammatory cytokines. We next examined the possible functional significance of extracellular ferritin in a breast cancer cell culture model. Ferritin stimulated the proliferation of the epithelial breast cancer cell lines MCF7 and T47D. Moreover, this proliferative effect was independent of the iron content of ferritin and did not increase intracellular iron levels in cancer cells indicating a novel iron-independent function for this protein. Together, these findings suggest that the release of ferritin by infiltrating macrophages in breast tumors may represent an inflammatory effector mechanism by which ferritin directly stimulates tumorigenesis.

A novel mechanism of iron-core formation by Pyrococcus furiosus archaeoferritin, a member of an uncharacterized branch of the ferritin-like superfamily

Storage of iron in a nontoxic and bioavailable form is essential for many forms of life. Three subfamilies of the ferritin-like superfamily, namely, ferritin, bacterioferritin, and Dps (DNA-binding proteins from starved cells), are able to store iron. Although the function of these iron-storage proteins is constitutive to many organisms to sustain life, the genome of some organisms appears not to encode any of these proteins. In an attempt to identify new iron-storage systems, we have found and characterized a new member of the ferritin-like superfamily of proteins, which unlike the multimeric storage system of ferritin, bacterioferritin, and Dps is monomeric in the absence of iron. Monomers catalyze oxidation of Fe(II) and they store the Fe(III) product as they assemble to form structures comparable to those of 24-meric ferritin. We propose that this mechanism is an alternative method of iron storage by the ferritin-like superfamily of proteins in organisms that lack the regular preassociated 24-meric/12-meric ferritins.

Structural and functional analyses of chicken liver ferritin

Characterization of ferritins from different species has provided insight into iron regulation mechanisms and evolutionary relationships. Here, we examined chicken liver ferritin, which comprises only H subunit and has 14.8 µg of Fe/100 µg of protein. The chicken H subunit apo homopolymer showed the same iron uptake rate as bovine H subunit homopolymer expressed with a baculovirus expression system (0.31 and 0.28 mmol of Fe/min per micromole of protein for chicken and bovine H subunit, respectively). Chicken H subunit apo homopolymer showed a significantly higher biotinylated hemin-binding activity than liver holoferritin. Although bovine spleen apoferritin, which has an L (liver or light):H (heart or heavy) subunit ratio of 1:1, also shows a significantly higher biotinylated hemin-binding activity than its holoferritin, these biotinylated hemin-binding activities were markedly lower than those of both chicken holo- and apoferritins. Binding of chicken holo- and apoferritin with biotinylated hemin was strongly inhibited by hemin but not iron-free hemin, protoporphyrin IX, or Zn-protoporphyrin. These findings demonstrate that chicken ferritin comprises only an H subunit, possesses ferroxidase activity as in mammalian ferritin H subunits, and binds heme more strongly than mammalian ferritins.

The MrgA Multimeric Complex: a self-assembled nanostructure for inorganic synthesis

Utilization of protein cages in biomimetic chemistry allows for the deposition of inorganic materials within an organic construct, controlling the size and amount of material deposited within a constrained reaction environment. Previously, protein cages such as viral capsids and ferritins have been used in the constrained synthesis of inorganic materials. The MrgA protein displays a high sequence homology to both bacterial DNA-protecting proteins (Dps) found in many bacterial genera and Ferritin-like proteins (Flp), which have been shown to functionally sequester and store iron in a biologically available form. Here we demonstrate recombinant production, purification and characterization of the MrgA protein and provide evidence that this protein self-assembles to form a multimeric complex. This complex demonstrates characteristics similar to that of ferritin-like proteins such as resistance to iron toxicity, iron incorporation, and resistance to thermal and chemical denaturation. The ability to deposit iron within the putative internal cavity of this protein cage will allow the MrgA complex to be utilized as a spatially constrained reaction vessel for nanomaterial synthesis of other inorganic materials. From a materials science perspective, it will be interesting to see if these organic/inorganic hybrid materials can be harnessed for catalysis, nanomagnetics, and other applications.

Binding of mammalian and avian ferritins with biotinylated hemin: demonstration of preferential binding of the H subunit to heme

The binding of ferritin to heme has been well studied using commercial horse spleen apoferritin, which is almost entirely composed of the L subunit, suggesting that mammalian ferritins bind heme. The present study revealed that both mammalian holoferritins (commercial horse spleen ferritin and purified horse spleen, bovine spleen and canine liver ferritins with L/H subunit ratios of 4.0, 1.1, and 2.3, respectively) and their apoferritins bound biotinylated hemin; apoferritins had higher binding activity than holoferritins, except for canine holo- and apoferritins, which showed the same binding. Bovine ferritin H subunit homopolymers expressed by a baculovirus expression system showed heme binding and had higher binding activity to biotinylated hemin than the L subunit homopolymer expressed by the same system. These bindings were inhibited by heme but not by iron-free or Zn-protoporphyrin IX (Zn-PPIX). Purified chicken liver holoferritin was found to be composed of only H subunits and showed the highest binding activity with biotinylated hemin compared with mammalian holoferritins. The binding of chicken liver holoferritin to biotinylated hemin was also inhibited by heme but not by PPIX or Zn-PPIX. These results indicate that mammalian and avian ferritins bind heme and that the H subunit preferentially recognizes heme.

Design and characterization of a chimeric ferritin with enhanced iron loading and transverse NMR relaxation rate

This paper describes the design and characterization of a novel ferritin chimera. The iron storage protein ferritin forms a paramagnetic ferrihydrite core. This biomineral, when placed in a magnetic field, can decrease the transverse NMR relaxation times (T (2) and T (2)*) of nearby mobile water protons. Ferritin nucleic acid constructs have recently been studied as "probeless" magnetic resonance imaging (MRI) reporters. Following reporter expression, ferritin sequesters endogenous iron and imparts hypointensity to T (2)- and T (2)*-weighted images in an amount proportional to the ferritin iron load. Wild-type ferritin consists of various ratios of heavy H and light L subunits, and their ratio affects ferritin's stability and iron storage capacity. We report a novel chimeric ferritin with a fixed subunit stoichiometry obtained by fusion of the L and the H subunits (L*H and H*L) using a flexible linker. We characterize these supramolecular ferritins expressed in human cells, including their iron loading characteristics, hydrodynamic size, subcellular localization, and effect on solvent water T (2) relaxation rate. Interestingly, we found that the L*H chimera exhibits a significantly enhanced iron loading ability and T (2) relaxation compared to wild-type ferritin. We suggest that the L*H chimera may be useful as a sensitive MRI reporter molecule.

Comparative study on iron release from soybean (Glycine max) seed ferritin induced by anthocyanins and ascorbate

Anthocyanins have received much attentions due to their various activities. Phytoferritin represents a novel alternative for iron supplementation. In the present study, it was found that all tested anthocyanins such as cyanidin (Cy), delphinidin (Dp), delphinidin-3-O-glucoside (Dp3glc), malvidin (Mv), petunidin (Pt), and petunidin-3-O-glucoside (Pt3glc) had a strong interaction with SSF, respectively, resulting in iron release from soybean seed ferritin (SSF) just as for ascorbate. The order of iron release from SSF is as follows: Dp>Cy>Pt>Mv>Dp3glc>Pt3glc. Their ability to liberate iron from SSF is associated with the size of the molecules and the chemical structures but mainly depends on their chelating activity with Fe2+. Interestingly, these pigments inhibited SSF degradation during the iron release to different extents while ascorbate did not. The difference in protective effects on SFF between ascorbate and the anthocyanins is in good agreement with their different Fe2+-chelating activities.

Sequence analysis of canine and equine ferritin H and L subunit cDNAs

Canine and equine ferritin H and L subunit cDNA clones were obtained using reverse transcriptase-polymerase chain reaction (RT-PCR) and TA cloning from various tissues. Canine liver and spleen ferritin H subunit cDNA clones contained an open reading frame for the same 182-amino acid protein as that reported in canine brain ferritin H subunit cDNA although there were substitutions in the 3'-noncoding regions. Ferritin L subunit cDNA clones from canine liver, spleen, and kidney showed identical coding sequences encoding the 174-amino acid protein except for a single nucleotide substitution in kidney (C474G). The H subunit nucleotide sequences of equine leukocyte and spleen were identical to the fragment encoding the 181-amino acid protein in equine peripheral blood mononuclear cells, with the exception of one substitution seen in both leukocyte and spleen sequences (C234T). The nucleotide sequence of equine leukocyte ferritin L subunit showed 7 substitutions compared with the published equine liver L subunit sequence with two substitutions at positions 281 and 282 resulting in an amino acid substitution of P94L. The amino acid residues involved in the ferroxidase center and in iron nucleation were perfectly conserved in H and L subunits of canine and equine ferritins, respectively.

A general map of iron metabolism and tissue-specific subnetworks

Iron is required for survival of mammalian cells. Recently, understanding of iron metabolism and trafficking has increased dramatically, revealing a complex, interacting network largely unknown just a few years ago. This provides an excellent model for systems biology development and analysis. The first step in such an analysis is the construction of a structural network of iron metabolism, which we present here. This network was created using CellDesigner version 3.5.2 and includes reactions occurring in mammalian cells of numerous tissue types. The iron metabolic network contains 151 chemical species and 107 reactions and transport steps. Starting from this general model, we construct iron networks for specific tissues and cells that are fundamental to maintaining body iron homeostasis. We include subnetworks for cells of the intestine and liver, tissues important in iron uptake and storage, respectively, as well as the reticulocyte and macrophage, key cells in iron utilization and recycling. The addition of kinetic information to our structural network will permit the simulation of iron metabolism in different tissues as well as in health and disease.

Sequence analysis of dolphin ferritin H and L subunits and possible iron-dependent translational control of dolphin ferritin gene

Background

Iron-storage protein, ferritin plays a central role in iron metabolism. Ferritin has dual function to store iron and segregate iron for protection of iron-catalyzed reactive oxygen species. Tissue ferritin is composed of two kinds of subunits (H: heavy chain or heart-type subunit; L: light chain or liver-type subunit). Ferritin gene expression is controlled at translational level in iron-dependent manner or at transcriptional level in iron-independent manner. However, sequencing analysis of marine mammalian ferritin subunits has not yet been performed fully. The purpose of this study is to reveal cDNA-derived amino acid sequences of cetacean ferritin H and L subunits, and demonstrate the possibility of expression of these subunits, especially H subunit, by iron.

Methods

Sequence analyses of cetacean ferritin H and L subunits were performed by direct sequencing of polymerase chain reaction (PCR) fragments from cDNAs generated via reverse transcription-PCR of leukocyte total RNA prepared from blood samples of six different dolphin species (Pseudorca crassidens, Lagenorhynchus obliquidens, Grampus griseus, Globicephala macrorhynchus, Tursiops truncatus, and Delphinapterus leucas). The putative iron-responsive element sequence in the 5'-untranslated region of the six different dolphin species was revealed by direct sequencing of PCR fragments obtained using leukocyte genomic DNA.

Results

Dolphin H and L subunits consist of 182 and 174 amino acids, respectively, and amino acid sequence identities of ferritin subunits among these dolphins are highly conserved (H: 99–100%, (99→98) ; L: 98–100%). The conserved 28 bp IRE sequence was located -144 bp upstream from the initiation codon in the six different dolphin species.

Conclusion

These results indicate that six different dolphin species have conserved ferritin sequences, and suggest that these genes are iron-dependently expressed.

The unusual co-assembly of H- and M-chains in the ferritin molecule from the Antarctic teleosts Trematomus bernacchii and Trematomus newnesi

Ferritins from the liver and spleen of the cold-adapted Antarctic teleosts Trematomus bernacchii and Trematomus newnesi have been isolated and characterized. Interestingly, only H- and M-chains are expressed and no L-chains. The H-chains contain the conserved ferroxidase center residues while M-chains harbor both the ferroxidase center and the micelle nucleation site ligands. Ferritins have an organ-specific subunit composition, they are: M homopolymers in spleen and H/M heteropolymers in liver. The M-chain homopolymer mineralizes iron at higher rate with respect to the H/M heteropolymer, which however is endowed with a lower activation energy for the iron incorporation process, indicative of a higher local flexibility. These findings and available literature data on ferritin expression in fish point to the role of tissue-specific expression of different chains in modulating the iron oxidation/mineralization process.

Hepatitis C virus-induced reactive oxygen species raise hepatic iron level in mice by reducing hepcidin transcription

BACKGROUND & AIMS

Despite abundant clinical evidence, the mechanisms by which hepatic iron overload develops in patients with hepatitis C virus (HCV)-associated chronic liver disease remain unknown. The aim of this study was to investigate how hepatic iron overload develops in the presence of HCV proteins.

METHODS

Male transgenic mice expressing the HCV polyprotein and nontransgenic control mice (C57BL/6) were assessed for iron concentrations in the liver, spleen, and serum and iron regulatory molecules in vivo and ex vivo.

RESULTS

Transgenic mice had increased hepatic and serum iron concentrations, decreased splenic iron concentration, and lower hepcidin expression in the liver accompanied by higher expression of ferroportin in the duodenum, spleen, and liver. In response to hepatocellular iron excess, transferrin receptor 1 expression decreased and ferritin expression increased in the transgenic liver. Transgenic mice showed no inflammation in the liver but preserved the ability to induce hepcidin in response to proinflammatory cytokines induced by lipopolysaccharide. Hepcidin promoter activity and the DNA binding activity of CCAAT/enhancer-binding protein alpha (C/EBP) were down-regulated concomitant with increased expression of C/EBP homology protein, an inhibitor of C/EBP DNA binding activity, and with increased levels of reactive oxygen species in transgenic mice at the ages of 8 and 14 months.

CONCLUSIONS

HCV-induced reactive oxygen species may down-regulate hepcidin transcription through inhibition of C/EBPalpha DNA binding activity by C/EBP homology protein, which in turn leads to increased duodenal iron transport and macrophage iron release, causing hepatic iron accumulation.

Ferritin L and H subunits are differentially regulated on a post-transcriptional level

Ferritin plays an important role in the storage and release of iron, an element utilized in cellular processes such as respiration, gene regulation, and DNA replication and repair. Ferritin in animals is composed of 24 ferritin L (FTL) and ferritin H (FTH) subunits in ratios that vary in different cell types. Because the subunits are not functionally interchangeable, both L and H units are critical for maintaining iron homeostasis and protecting against iron overload. FTL and FTH are regulated primarily at a post-transcriptional level in response to cellular iron concentrations. Individual regulation of FTL and FTH is of much interest, and although transcriptional differences between FTL and FTH have been shown, differences in their post-transcriptional regulation have not been evaluated. We report here that FTL and FTH are differentially regulated in 1% oxygen on a post-transcriptional level. We have designed a quantitative assay system sensitive enough to detect differences between FTL and FTH iron regulatory elements (IREs) that a standard electrophoretic mobility shift assay does not. The FTL IRE is the primary responder in the presence of an iron donor in hypoxic conditions, and this response is reflected in endogenous FTL protein levels. These results provide evidence that FTL and FTH subunits respond independently to cellular iron concentrations and underscore the importance of evaluating FTL and FTH IREs separately.

Molecular, physiological and clinical aspects of the iron storage protein ferritin

Oxidative stress is a major factor in inflammatory, malignant and metabolic diseases in domestic and farm animals. Oxidative stress-mediated damage depends on the level of cellular and total body iron status because an excess iron (Fe(2+)) pool produces the most harmful free radicals (hydroxyls) through the Fenton reaction. Ferritin is a ubiquitous and conserved iron storage protein that plays a central role in iron metabolism and has the dual function of storing iron in bioavailable and non-toxic forms. Intracellular ferritin synthesis is controlled at translational and transcriptional levels in both an iron-dependent and an iron-independent manner. Ferritin is also found in extracellular fluids such as serum, synovial fluids and milk. Although serum ferritin is a sensitive indicator of body iron stores, the extracellular ferritins are elevated in inflammatory or malignant disease. Circulating ferritin interacts with ferritin-binding protein to form a complex, which is rapidly cleared from the body. This review describes recent research of physiological and clinical significance of ferritin and its application to future veterinary medicine.

Ferritin and ferritin isoforms II: protection against uncontrolled cellular proliferation, oxidative damage and inflammatory processes

Ferritin is a major iron storage protein involved in the regulation of iron availability. Each ferritin molecule comprises 24 subunits. Various combinations of H-subunits and L-subunits make up the 24-subunit protein structure and these ferritin isoforms differ in their H-subunit to L-subunit ratio, as well as in their metabolic properties. Ferritin is an acute-phase protein and its expression is up-regulated in conditions such as uncontrolled cellular proliferation, in any condition marked by excessive production of toxic oxygen radicals, and by infectious and inflammatory processes. Under such conditions ferritin up-regulation is predominantly stimulated by increased reactive oxygen radical production and by cytokines. The major function of ferritin in these conditions is to reduce the bio-availability of iron in order to stem uncontrolled cellular proliferation and excessive production of reactive oxygen radicals. Ferritin is not, however, indiscriminately up-regulated in these conditions as a marked shift towards a predominance in H-subunit rich ferritins occurs. Preliminary indications are that, while the L-subunit primarily fulfils the conventional iron storage role, the H-subunit functions primarily as rapid regulator of iron availability, and perhaps indirectly as regulator of other cellular processes. It is suggested that the optimum differential expression of the two subunits differ for different cells and under different conditions and that the expression of appropriate isoferritins offers protection against uncontrolled cellular proliferation, oxidative stress and against side effects of infectious and inflammatory conditions.

The N-terminal Extensions of Deinococcus radiodurans Dps-1 Mediate DNA Major Groove Interactions as well as Assembly of the Dodecamer

Dps (DNA protection during starvation) proteins play an important role in the protection of prokaryotic macromolecules from damage by reactive oxygen species. Previous studies have suggested that the lysine-rich N-terminal tail of Dps proteins participates in DNA binding. In comparison with other Dps proteins, Dps-1 from Deinococcus radiodurans has an extended N terminus comprising 55 amino acids preceding the first helix of the 4-helix bundle monomer. In the crystal structure of Dps-1, the first approximately 30 N-terminal residues are invisible, and the remaining 25 residues form a loop that harbors a novel metal-binding site. We show here that deletion of the flexible N-terminal tail obliterates DNA/Dps-1 interaction. Surprisingly, deletion of the entire N terminus also abolishes dodecameric assembly of the protein. Retention of the N-terminal metal site is necessary for formation of the dodecamer, and metal binding at this site facilitates oligomerization of the protein. Electrophoretic mobility shift assays using DNA modified with specific major/minor groove reagents further show that Dps-1 interacts through the DNA major groove. DNA cyclization assays suggest that dodecameric Dps-1 does not wrap DNA about itself. A significant decrease in DNA binding affinity accompanies a reduction in duplex length from 22 to 18 bp, but only for dodecameric Dps-1. Our data further suggest that high affinity DNA binding depends on occupancy of the N-terminal metal site. Taken together, the mode of DNA interaction by dodecameric Dps-1 suggests interaction of two metal-anchored N-terminal tails in successive DNA major grooves, leading to DNA compaction by formation of stacked protein-DNA layers.

Ferritin and ferritin isoforms I: Structure-function relationships, synthesis, degradation and secretion

Ferritin is the intracellular protein responsible for the sequestration, storage and release of iron. Ferritin can accumulate up to 4500 iron atoms as a ferrihydrite mineral in a protein shell and releases these iron atoms when there is an increase in the cell's need for bioavailable iron. The ferritin protein shell consists of 24 protein subunits of two types, the H-subunit and the L-subunit. These ferritin subunits perform different functions in the mineralization process of iron. The ferritin protein shell can exist as various combinations of these two subunit types, giving rise to heteropolymers or isoferritins. Isoferritins are functionally distinct and characteristic populations of isoferritins are found depending on the type of cell, the proliferation status of the cell and the presence of disease. The synthesis of ferritin is regulated both transcriptionally and translationally. Translation of ferritin subunit mRNA is increased or decreased, depending on the labile iron pool and is controlled by an iron-responsive element present in the 5'-untranslated region of the ferritin subunit mRNA. The transcription of the genes for the ferritin subunits is controlled by hormones and cytokines, which can result in a change in the pool of translatable mRNA. The levels of intracellular ferritin are determined by the balance between synthesis and degradation. Degradation of ferritin in the cytosol results in complete release of iron, while degradation in secondary lysosomes results in the formation of haemosiderin and protection against iron toxicity. The majority of ferritin is found in the cytosol. However, ferritin with slightly different properties can also be found in organelles such as nuclei and mitochondria. Most of the ferritin produced intracellularly is harnessed for the regulation of iron bioavailability; however, some of the ferritin is secreted and internalized by other cells. In addition to the regulation of iron bioavailability ferritin may contribute to the control of myelopoiesis and immunological responses.

The ferritin family of iron storage proteins

The ferritins are a family of proteins produced in a variety of amounts and types depending on the state of development of an animal, or the state of differentiation of a particular cell type, or the environment. Iron storage is the main function of the ferritins when iron is needed for intracellular use (housekeeping) for iron proteins such as ribonucleotide reductase, cytochromes, oxidases, nitrogenases, or photosynthetic reaction centers or for extracellular use by other cells (specialized). Under abnormal conditions, such as the breach of transferrin-receptor-controlled incorporation of iron, ferritin can also serve to detoxify excess intracellular iron. The structure of ferritin is very complex, consisting of a protein coat of 24 polypeptide subunits, approximately 20 kDa, which surrounds an inorganic phase of hydrous ferric oxide. The polypeptide subunits, bundles of four alpha helices, display remarkable conservation of sequence among plants and animals, which is probably related to the necessity of forming the hollow sphere pierced by 14 channels through which iron may pass. In spite of the conserved regions of sequence, there are multiple genes for ferritin polypeptide subunits within an organism; at the moment three distinct subunit types, H H'(or M), and L, have been identified which are expressed in a cell-specific fashion. How many different subunit types exist, the influence on function, and the number of genes required to encode them are currently being actively investigated. Not only does the protein coat of ferritin display variations, the inorganic phase of ferritin can vary as well. For instance, differences can occur in the number of Fe atoms (up to 4500), as well as in the phosphorus content and in the degree of hydration and order. Such observations have depended on the use of a variety of physical techniques such as X-ray diffraction, EXAFS, and Mössbauer spectroscopy. The same approaches, as well as EPR spectroscopy, have been used to monitor the path taken by Fe as it passes from mononuclear Fe(II) outside the protein coat to polynuclear Fe(III) inside the protein coat. Both mononuclear Fe(II) and Fe(III) have been observed, as well as dimeric Fe(II)-O-Fe(III), and Fe(III)-oxo bridged clusters attached to the protein. A possible protein site for the Fe(III) cluster is a groove on the inner surface of the dimeric interface, suggested by the structure and from the affect of natural cross-links between subunit pairs.(ABSTRACT TRUNCATED AT 400 WORDS)

Coordinate Inhibition of Cytokine-mediated Induction of Ferritin H, Manganese Superoxide Dismutase, and Interleukin-6 by the Adenovirus E1A Oncogene

Adenovirus E1A sensitizes cells to the cytotoxic action of tumor necrosis factor alpha (TNF-alpha). This effect has been attributed to direct blockade of NF-kappaB activation, as well as to increased activation of components of the apoptotic pathway and decreases in inhibitors of apoptosis. In this report we evaluated the mechanism by which E1A modulates the expression of the cytokine-inducible cytoprotective genes manganese superoxide dismutase (MnSOD), interleukin-6 (IL-6), and ferritin heavy chain (FH). We observed that E1A blocks induction of MnSOD, IL-6, and FH by TNF-alpha or IL-1alpha. Because NF-kappaB plays a role in cytokine-dependent induction of MnSOD, IL-6, and FH, we assessed the effect of E1A on NF-kappaB in cells treated with TNF. IkappaB, the inhibitor of NF-kappaB, was degraded similarly in the presence and absence of E1A. TNF induced a quantitatively and temporally equivalent activation of NF-kappaB in control and E1A-transfected cells. However, TNF-dependent acetylation of NF-kappaB was diminished in cells expressing E1A. E1A mutants unable to bind p400 or the Rb family proteins were still capable of repressing TNF-dependent induction of FH. However, mutants of E1A that abrogated binding of p300/CBP blocked the ability of E1A to repress TNF-dependent induction of FH. These results suggest that p300/CBP is a critical control point in NF-kappaB-dependent transcriptional regulation of cytoprotective genes by cytokines.

Ferritin contributes to melanoma progression by modulating cell growth and sensitivity to oxidative stress

PURPOSE

Employing an in vitro model system of human melanoma progression, we previously reported ferritin light chain (L-ferritin) gene overexpression in the metastatic phenotype. Here, we attempted to characterize the role of ferritin in the biology of human melanoma and in the progression of this disease.

EXPERIMENTAL DESIGN

Starting from the LM human metastatic melanoma cell line, we engineered cell clones in which L-ferritin gene expression was down-regulated by the stable expression of a specific antisense construct. These cells were then assayed for their growth capabilities, chemoinvasive properties, and sensitivity to oxidative stress. Additionally, ferritin protein content in primary and metastatic human melanomas was determined by immunohistochemistry.

RESULTS

Artificial L-ferritin down-regulation in the LM cells strongly inhibited proliferation and chemoinvasion in vitro and cell growth in vivo. In addition, L-ferritin down-regulated cells displayed enhanced sensitivity to oxidative stress and to apoptosis. Concurrently, immunohistochemical analysis of a human melanoma tissue array revealed that ferritin expression level in metastatic lesions was significantly higher (P < 0.0001) than in primary melanomas. Furthermore, ferritin expression was constantly up-regulated in autologous lymph node melanoma metastases when compared with the respective primary tumors in a cohort of 11 patients.

CONCLUSIONS

These data suggest that high ferritin expression can enhance cell growth and improve resistance to oxidative stress in metastatic melanoma cells by interfering with their cellular antioxidant system. The potential significance of these findings deserves to be validated in a clinical setting.

Differential DNA binding and protection by dimeric and dodecameric forms of the ferritin homolog Dps from Deinococcus radiodurans

Bacterial iron storage proteins such as ferritin serve as intracellular iron reserves. Members of the DNA protection during starvation (Dps) family of proteins are structurally related to ferritins, and their function is to protect the genome from iron-induced free radical damage. Some members of the Dps family bind DNA and are thought to do so only as fully assembled dodecamers. We present the cloning and characterization of a Dps homolog encoded by the radiation-resistant eubacterium Deinococcus radiodurans and show that DNA binding does not require its assembly into a dodecamer. D.radiodurans Dps-1, the product of gene DR2263, adopts a stably folded conformation, as demonstrated by circular dichroism spectroscopy, and undergoes a transition to a disordered state with a melting temperature of 69.2(+/-0.1) degrees C. While a dimeric form of Dps-1 is observed under low-salt conditions, a dodecameric assembly is highly favored at higher concentrations of salt. Both oligomeric forms of Dps-1 exhibit ferroxidase activity, and Fe(II) oxidation/mineralization is seen for dodecameric Dps-1. Notably, addition of Ca(2+) (to millimolar concentrations) to dodecameric Dps-1 can result in the reduction of bound Fe(III). Dimeric Dps-1 protects DNA from both hydroxyl radical cleavage and from DNase I-mediated cleavage; however, dodecameric Dps-1 is unable to provide efficient protection against hydroxyl radical-mediated DNA cleavage. While dodecameric Dps-1 does bind DNA, resulting in formation of large aggregates, cooperative DNA binding by dimeric Dps-1 leads to formation of protein-DNA complexes of finite stoichiometry.

Iron-oxo clusters biomineralizing on protein surfaces: structural analysis of Halobacterium salinarum DpsA in its low- and high-iron states

The crystal structure of the Dps-like (Dps, DNA-protecting protein during starvation) ferritin protein DpsA from the halophile Halobacterium salinarum was determined with low endogenous iron content at 1.6-A resolution. The mechanism of iron uptake and storage was analyzed in this noncanonical ferritin by three high-resolution structures at successively increasing iron contents. In the high-iron state of the DpsA protein, up to 110 iron atoms were localized in the dodecameric protein complex. For ultimate iron storage, the archaeal ferritin shell comprises iron-binding sites for iron translocation, oxidation, and nucleation. Initial iron-protein interactions occur through acidic residues exposed along the outer surface in proximity to the iron entry pore. This narrow pore permits translocation of ions toward the ferroxidase centers via two discrete steps. Iron oxidation proceeds by transient formation of tri-iron ferroxidase centers. Iron storage by biomineralization inside the ferritin shell occurs at two iron nucleation centers. Here, a single iron atom provides a structural seed for iron-oxide cluster formation. The clusters with up to five iron atoms adopt a geometry that is different from natural biominerals like magnetite but resembles iron clusters so far known only from bioinorganic model compounds.

Intracellular ferritin accumulation in neural and extraneural tissue characterizes a neurodegenerative disease associated with a mutation in the ferritin light polypeptide gene

Abnormal accumulation of ferritin was found to be associated with an autosomal dominant slowly progressing neurodegenerative disease clinically characterized by tremor, cerebellar ataxia, parkinsonism and pyramidal signs, behavioral disturbances, and cognitive decline. These symptoms may appear sequentially over a period of 4 decades. Pathologically, intranuclear and intracytoplasmic bodies were found in glia and subsets of neurons in the central nervous system as well as in extraneural tissue. Biochemical analyses of these bodies isolated from the striatum and cerebellar cortex revealed that ferritin light polypeptide (FTL) and ferritin heavy polypeptide (FTH1) were the main constituents. Molecular genetic studies revealed a 2-bp insertion mutation in exon 4 of the FTL gene. The resulting mutant polypeptide is predicted to have a carboxy terminus that is altered in amino-acid sequence and length. In tissue sections, the bodies were immunolabeled by anti-ferritin and anti-ubiquitin antibodies and were stained by Perls' method for ferric iron. Synthetic peptides homologous to the altered and wild-type carboxy termini were used to raise polyclonal antibodies. These novel antibodies as well as an antibody recognizing FTH1 immunolabeled the bodies. This study of this disorder has provided additional knowledge and insights in the growing area of ferritin-related neurodegeneration.