Increased ferritin gene expression is both promoted by cAMP and a marker of growth arrest in rabbit vascular smooth muscle cells

Genetic Characterization of Rat Hepatic Stellate Cell Line HSC-T6 for In Vitro Cell Line Authentication

Immortalized hepatic stellate cells (HSCs) established from mouse, rat, and humans are valuable in vitro models for the biomedical investigation of liver biology. These cell lines are homogenous, thereby providing consistent and reproducible results. They grow more robustly than primary HSCs and provide an unlimited supply of proteins or nucleic acids for biochemical studies. Moreover, they can overcome ethical concerns associated with the use of animal and human tissue and allow for fostering of the 3R principle of replacement, reduction, and refinement proposed in 1959 by William M. S. Russell and Rex L. Burch. Nevertheless, working with continuous cell lines also has some disadvantages. In particular, there are ample examples in which genetic drift and cell misidentification has led to invalid data. Therefore, many journals and granting agencies now recommend proper cell line authentication. We herein describe the genetic characterization of the rat HSC line HSC-T6, which was introduced as a new in vitro model for the study of retinoid metabolism. The consensus chromosome markers, outlined primarily through multicolor spectral karyotyping (SKY), demonstrate that apart from the large derivative chromosome 1 (RNO1), at least two additional chromosomes (RNO4 and RNO7) are found to be in three copies in all metaphases. Additionally, we have defined a short tandem repeat (STR) profile for HSC-T6, including 31 species-specific markers. The typical features of these cells have been further determined by electron microscopy, Western blotting, and Rhodamine-Phalloidin staining. Finally, we have analyzed the transcriptome of HSC-T6 cells by mRNA sequencing (mRNA-Seq) using next generation sequencing (NGS).

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.

Identification of H ferritin-dependent and independent genes in K562 differentiating cells by targeted gene silencing and expression profiling

Ferritin is best known as the key molecule in intracellular iron storage, and is involved in several metabolic processes such as cell proliferation, differentiation and neoplastic transformation. We have recently demonstrated that the shRNA silencing of the ferritin heavy subunit (FHC) in a melanoma cell line is accompanied by a consistent modification of gene expression pattern leading to a reduced potential in terms of proliferation, invasiveness, and adhesion ability of the silenced cells. In this study we sought to define the repertoire of genes whose expression might be affected by FHC during the hemin-induced differentiation of the erythromyeloid cell line K562. To this aim, gene expression profiling was performed in four different sets of cells: i) wild type K562; ii) sh-RNA FHC-silenced K562; iii) hemin-treated wild-type K562; and iv) hemin-treated FHC-silenced K562. Statistical analysis of the gene expression data, performed by two-factor ANOVA, identified three distinct classes of transcripts: a) Class 1, including 657 mRNAs whose expression is modified exclusively during hemin-induced differentiation of K562 cells, independently from the FHC relative amounts; b) Class 2, containing a set of 70 mRNAs which are consistently modified by hemin and FHC-silencing; and c) Class 3, including 128 transcripts modified by FHC-silencing but not by hemin. Our data indicate that FHC may function as a modulator of gene expression during erythroid differentiation and add new findings to the knowledge of the complex gene network modulated during erythroid differentiation.

Nuclear ferritin in corneal epithelial cells: tissue-specific nuclear transport and protection from UV-damage

We have identified the heavy chain of ferritin as a developmentally regulated nuclear protein of embryonic chicken corneal epithelial cells. The nuclear ferritin is assembled into a supramolecular form that is indistinguishable from the cytoplasmic form of ferritin found in other cell types. Thus it most likely has iron-sequestering capabilities. Free iron, via the Fenton reaction, is known to exacerbate UV-induced and other oxidative damage to cellular components, including DNA. Since corneal epithelial cells are constantly exposed to UV light, we hypothesized that the nuclear ferritin might protect the DNA of these cells from free radical damage. To test this possibility, primary cultures of cells from corneal epithelium and other tissues were UV irradiated, and damage to DNA was detected by an in situ 3'-end labeling assay. Consistent with the hypothesis, corneal epithelial cells with nuclear ferritin had significantly less DNA breakage than the other cells types examined. However, when the expression of nuclear ferritin was inhibited the cells now became much more susceptible to UV-induced DNA damage. Since ferritin is normally cytoplasmic, corneal epithelial cells must have a mechanism that effects its nuclear localization. We have determined that this involves a nuclear transport molecule which binds to ferritin and carries it into the nucleus. This transporter, which we have termed ferritoid for its similarity to ferritin, has at least two domains. One domain is ferritin-like and is responsible for binding the ferritin; the other domain contains a nuclear localization signal that is responsible for effecting the nuclear transport. Therefore, it seems that corneal epithelial cells have evolved a novel, nuclear ferritin-based mechanism for protecting their DNA against UV damage. In addition, since ferritoid is structurally similar to ferritin, it may represent an example of a nuclear transporter that evolved from the molecule it transports (i.e., ferritin).

Decreased serum ferritin is associated with alopecia in women

Alopecia in women is a common problem, and conflicting observational data have failed to determine whether an association exists between alopecia and iron deficiency in women. We therefore utilized an analytical cross-sectional methodology to evaluate whether common types of alopecia in women are associated with decreased tissue iron stores, as measured by serum ferritin. We studied patients with telogen effluvium (n = 30), androgenetic alopecia (n = 52), alopecia areata (n = 17), and alopecia areata totalis/universalis (n = 7). The normal group consisted of 11 subjects without hair loss from the same referral base and source population as those patients with alopecia. We analyzed the data utilizing the unpaired Student's t test assuming unequal variances with an alpha adjustment for multiple comparisons to assess whether the mean ages, ferritin levels, and hemoglobin levels of women without hair loss differed from the means in each alopecia group. The mean age of patients and normals did not differ significantly. We found that the mean ferritin level (ng per ml [95% confidence intervals]) in patients with androgenetic alopecia (37.3 128.4, 46.1]) and alopecia areata (24.9 [17.2, 32.6]) were statistically significantly lower than in normals without hair loss (59.5 [40.8, 78.1]). The mean ferritin levels in patients with telogen effluvium (50.1 [33.9, 66.33]) and alopecia areata totalis/universalis (52.3 [23.1, 81.5]) were not significantly lower than in normals. Our findings have implications regarding therapeutics, clinical trial design, and understanding the triggers for alopecia.

Cloning and sequence analysis of cDNA for heavy-chain ferritin from the Canis familiaris

Ferritin serves as a storage protein for iron in animals. Complementary DNA encoding a heavy chain ferritin was cloned from the brain of Canis familiaris. The dog ferritin cDNA encodes a 182 amino acid that shows high levels of amino acid identity with vertebrate ferritins (90-98%). Near the cap region of the 5'-untranslated region, the dog H-ferritin mRNA displays a 28-nucleotide sequence that is exactly conserved in the corresponding region of the human and pig H-ferritin mRNA, thus making this sequence a prime candidate for involvement in the known translational regulation of H-ferritin by iron.

Purification and properties of a folate-catabolizing enzyme

We have identified and purified to homogeneity an enzyme from rat liver that catalyzes the oxidative catabolism of 5-formyltetrahydrofolate to p-aminobenzoylglutamate and a pterin derivative. Purification of the enzyme utilized six column matrices, including a pterin-6-carboxylic acid affinity column. Treatment of crude rat liver extracts with EDTA or heat decreased the specific activity of the enzyme by up to 85%. Peptides generated from the purified protein were sequenced and found to be identical to primary sequences present within rat light chain or heavy chain ferritin. Commercial rat ferritin did not display catabolic activity, but activity could be acquired with iron loading. The purified enzyme contained 2000 atoms of iron/ferritin 24-mer and displayed similar electrophoretic properties as commercial rat liver ferritin. The ferritin-catalyzed reaction displayed burst kinetics, and the enzyme catalyzed only a single turnover in vitro. Expression of rat heavy chain ferritin cDNA resulted in increased rates of folate turnover in cultured Chinese hamster ovary cells and human mammary carcinoma cells and reduced intracellular folate concentrations in Chinese hamster ovary cells. These results indicate that ferritin catalyzes folate turnover in vitro and in vivo and may be an important factor in regulating intracellular folate concentrations.

Isolation and identification of psoralen plus ultraviolet A (PUVA)-induced genes in human dermal fibroblasts by polymerase chain reaction-based subtractive hybridization

Premature aging of the skin is a prominent side-effect of psoralen photoactivation, a therapy used for a variety of skin disorders. Recently, we demonstrated that treatment of human dermal fibroblasts with 8-methoxypsoralen and ultraviolet A irradiation resulted in a permanent growth arrest with a switch of mitotic to postmitotic fibroblasts. Furthermore, an upregulation of matrix-degrading metalloproteinases and a high level of de novo expression of the senescence-associated beta-galactosidase was detected in the PUVA-treated postmitotic fibroblasts. The molecular basis for this PUVA-induced change in the functional and morphologic phenotype of fibroblasts resembling or mimicking replicative senescence is, however, unknown. Herein after, we have used a polymerase chain reaction-based subtractive hybridization protocol to identify human genes that are induced by PUVA treatment. Application of polymerase chain reaction-Select resulted in the cloning of four PUVA genes. Sequence analysis and homology searches identified three cDNA clones of known genes related to cell cycle regulation (p21waf1/cip1), stress response (ferritin H) and connective tissue metabolism (tissue inhibitor of metalloproteinases-3), whereas one cDNA clone represented a novel gene (no. 478). Northern blot analyses were performed to confirm a PUVA-dependent increase in specific mRNA levels in human dermal fibroblasts in vitro. This report on the identification of growth arrest related genes in PUVA-treated fibroblasts may stimulate further research addressing the causal role of these known and novel genes in extrinsic and intrinsic aging processes on a molecular and cellular level.

Increased expression of mRNA encoding ferritin heavy chain in brain structures of a rat model of absence epilepsy

Differential mRNA display was carried out to find genes that are differentially regulated in the brain of a rat strain with absence epilepsy, the genetic absence epilepsy rats from Strasbourg (GAERS). Among the 32 differentially displayed cDNA fragments actually cloned and sequenced, one shows 100% identity with the rat heavy chain ferritin (H-ferritin) mRNA. Northern blot analysis confirmed the up-regulation of the H-ferritin mRNA. Using dot blotting, a 40% increase in expression was reported in the subcortical forebrain of the adult GAERS, while cortex, brain stem, and cerebellum appeared unmodified. This change was not observed in the brain of 25-day-old rats, an age at which the epileptic phenotype is not present. By in situ hybridization, the enhanced expression was localized in the hippocampus. The increase in mRNA encoding H-ferritin was not immunodetected at the protein level by Western blotting. These results are not apparently related to the neural substrate of SWD or to the distribution of local increase in glucose metabolism previously described in the GAERS. It is hypothesized that the up-regulation of the H-ferritin mRNA is part of a mechanism protecting the hippocampus, a seizure-prone area, against a possible overactivation during absence seizures.

Selective treatment of neoplastic cells using ferritin-mediated electromagnetic hyperthermia

A new method of cancer treatment is proposed, based on the unique magnetic properties of ferritin iron core which, in alternating magnetic field of frequency approximately 100 kHz, is easily heated to temperatures sufficiently high to destroy neoplastic cells containing an excess of this protein, without damaging the normal cells.

Post-transcriptional regulation of H-ferritin mRNA. Identification of a pyrimidine-rich sequence in the 3'-untranslated region associated with message stability in human monocytic THP-1 cells

We have previously demonstrated that phorbol myristate acetate (PMA) up-regulates H-ferritin gene expression in myeloid cells by stabilization of its message. In the present report, we showed that insertion of the 3'-untranslated region (3'-UTR) of H-ferritin mRNA at the 3'-end of luciferase coding sequence significantly reduced the stability of luciferase mRNA in human monocytic THP-1 cells. However, the half-life of the chimeric transcript was markedly prolonged after PMA treatment. A cytosolic protein factor from THP-1 cells was found to specifically bind to H-ferritin 3'-UTR. PMA treatment of THP-1 cells resulted in the reduction of the RNA binding activity in a time-dependent manner. Deletion analysis and RNase T1 mapping revealed a pyrimidine-rich sequence within the 3'-UTR which interacts with the protein factor. Competition experiments with homoribopolymers further demonstrated the importance of uridines for the binding activity. Point mutations in uridines of the pyrimidine-rich sequence reduced the protein binding to 3'-UTR, while increasing the stability of the chimeric luciferase transcript. Together, these results demonstrate that the pyrimidine-rich sequence in the 3'-UTR is involved in post-transcriptional regulation of H-ferritin gene expression in myeloid cells.

Coordinated regulation of iron-controlling genes, H-ferritin and IRP2, by c-MYC

The protein encoded by the c-MYC proto-oncogene is a transcription factor that can both activate and repress the expression of target genes, but few of its transcriptional targets have been identified. Here, c-MYC is shown to repress the expression of the heavy subunit of the protein ferritin (H-ferritin), which sequesters intracellular iron, and to stimulate the expression of the iron regulatory protein-2 (IRP2), which increases the intracellular iron pool. Down-regulation of the expression of H-ferritin gene was required for cell transformation by c-MYC. These results indicate that c-MYC coordinately regulates genes controlling intracellular iron concentrations and that this function is essential for the control of cell proliferation and transformation by c-MYC.

Activation of the ferritin H enhancer, FER-1, by the cooperative action of members of the AP1 and Sp1 transcription factor families

We have previously reported that the adenovirus E1A oncogene represses the transcription of the H subunit of the mouse ferritin gene. Subsequent analyses defined FER-1, a 37-nucleotide sequence located 4.1 kilobases proximal to the start site of transcription, as the target of E1A-mediated transcriptional repression and as an enhancer of the ferritin H gene. FER-1 is composed of an AP1-like sequence followed by an element with dyad symmetry. To achieve maximal enhancer activity and transcriptional repression by E1A, both elements were essential. Using gel retardation assays, we now demonstrate that the binding complex for the AP1-like sequence of FER-1 contains JunD, FosB, and ATF1. Furthermore, JunD and FosB were able to activate FER-1 enhancer activity by transient cotransfection with ferritin H-chloramphenicol acetyltransferase reporter constructs. This augmented enhancer activity was inhibited by E1A. In addition, we have defined the minimal sequence in the dyad element of FER-1 required for protein interaction. This was determined to be a C-rich sequence to which Sp1 and Sp3 bind. Experiments with recombinant proteins indicate that members of both transcription factor families simultaneously bind FER-1. Taken together, these results elucidate molecular mechanisms involved in the transcriptional regulation of a pivotal gene in iron metabolism and provide insights into the contribution of the Sp1 family to the activation of AP1-dependent enhancers.

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.

Ferritin is a developmentally regulated nuclear protein of avian corneal epithelial cells

Previously, we generated monoclonal antibodies against chicken corneal cells (Zak, N. B., and Linsenmayer, T. F. (1983) Dev. Biol. 99, 373). We have now observed that one group of these antibodies reacts with a developmentally regulated component of corneal epithelial cell nuclei. This component is the heavy chain of ferritin, as determined by analyses of immunoisolated cDNA clones and immunoblotting of the protein. Immunoblotting also suggests that the nuclear ferritin may be in a supramolecular form that is similar to the iron-binding ferritin complex found in the cytoplasm of many cells. In vitro cultures and transfection studies show that the nuclear localization depends predominantly on cell type but can be altered by the in vitro environment. The appearance of nuclear ferritin is at least partially under translational regulation, as is known to be true for the cytoplasmic form of the molecule. The tissue and developmental distributions of the mRNA for the molecule are much more extensive than the protein itself, and the removal of iron from cultures of corneal epithelial cells with the iron chelator deferoxamine prevents the appearance of nuclear ferritin. At present the functional role(s) of nuclear ferritin remain unknown, but previous studies on cytoplasmic ferritin raise the possibility that it prevents damage due to free radical generation ("oxidative stress") by sequestering iron. Although it remains to be tested whether nuclear ferritin prevents oxidative damage, we find this an attractive possibility. Since the corneal epithelium is transparent and is constantly exposed to free radical-generating UV light, it is possible that the cells of this tissue have evolved a specialized mechanism to prevent oxidative damage to their nuclear components.

Inhibitory effect of prostaglandin E1 on intimal thickening following photochemically induced endothelial injury in the rat femoral artery

The inhibitory effect of prostaglandin E1, which has an anti-platelet action and a vasodilating action via intracellular cyclic AMP elevation, was studied on intimal thickening in the rat femoral artery. A segment of the femoral artery was occluded by a platelet and fibrin-rich thrombus due to photochemical reaction between systemically administered Rose Bengal and transluminal green light which causes endothelial injury followed by platelet adhesion and aggregation at the site of photochemical reaction. Three weeks after endothelial injury, intimal thickening occurred at the irradiated site. Prostaglandin E1 (0.3 microgram/kg per min), administered as a continuous infusion 10 min before photochemical reaction significantly (P < 0.05) prolonged the time to occlusion of the femoral artery. In a separate experiment, prostaglandin E1 (0.3 microgram/kg per min) administered as a continuous infusion for 7 days just after endothelial injury significantly (P < 0.05) inhibited intimal thickening compared with a control group. In cultured rat-derived vascular smooth muscle cells, prostaglandin E1 produced concentration-dependent inhibition of migration and proliferation, stimulated by platelet-derived growth factor. These results suggest that prostaglandin E1 may be effective in preventing vascular restenosis after vascular surgery and angioplasty.

Differential expression of ferritin heavy chain in a rat transitional cell carcinoma progression model

To identify molecular markers with predictive value for the progression of superficial bladder cancer we used the differential hybridization analysis approach. Since primary tumor material is heterogeneously composed of subpopulations that are poorly characterized, we used in this study a rat progression model system that phenotypically and cytogenetically resembles human superficial bladder cancer. In the differential hybridization analysis we compared the mRNA populations of low and high metastatic tumor lines. We observed an overexpression of ferritin Heavy chain (ferritin H) in the tumor line with the lower metastatic capacity and better differentiated phenotype. The exact clinical relevance for the differential expression of ferritin H in human bladder cancer remains to be determined.

Interaction between iron-regulatory proteins and their RNA target sequences, iron-responsive elements

In this chapter, we have focused on the biochemistry of IRP-1 and the features which distinguish it from the related RNA-binding protein, IRP-2. IRP-1 is the cytoplasmic isoform of the enzyme aconitase, and, depending on iron status, may switch between enzymatic and RNA-binding activities. IRP-1 and IRP-2 are trans-acting regulators of mRNAs involved in iron uptake, storage and utilisation. The finding of an IRE in the citric acid cycle enzymes, mitochondrial aconitase and succinate dehydrogenase, suggests that the IRPs may also influence cellular energy production. These two proteins appear to bind RNAs with different but overlapping specificity, suggesting that they may regulate the stability or translation of as yet undefined mRNA targets, possibly extending their regulatory function beyond that of iron homeostasis. The interaction between the IRPs and the IRE represents one of the best characterised model systems for posttranscriptional gene control, and given that each IRP can also recognise its own unique set of RNAs, the search for new in vivo mRNA targets is expected to provide yet more surprises and insights into the fate of cytoplasmic mRNAs.

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.

Induction of ferritin synthesis in cells infected with Mengo virus

We have recently identified ferritin as a cellular protein particle whose synthesis is stimulated in mouse or human cells infected by the picornavirus Mengo. Immunoprecipitation of the particle from infected murine L929 cells showed a 4- and 6-fold increase in the intracellular concentrations of H and L apoferritin subunits, respectively. This differential expression altered the H/L subunit ratio from 3.0 in uninfected cells to 2.2 in Mengo virus-infected cells. The induction is not due to an increase in transcription of the apoferritin L and H genes, nor is it due to an increase in stability of the apoferritin mRNAs. At the level of translation, the iron regulatory protein (IRP) remained intact, with similar amounts being detected in uninfected and infected cells. The Mengo virus RNA genome does not compete with the iron regulatory element (IRE) for the binding of IRP, and sequence analysis confirmed that there are no IREs in the virus RNA. The IRE binding activity of IRP in infected cells decreased approximately 30% compared with uninfected cells. The decrease in binding activity could be overcome by the addition of Desferal (deferoxamine mesylate; CIBA) an intracellular iron chelator, which suggests that virus infection causes an increase in intracellular free iron. Electron paramagnetic resonance (EPR) studies have confirmed the increase in free iron in Mengo virus infected cells. The permeability of cells for iron does not change in virus infected cells, suggesting that the induction of ferritin by Mengo virus is due to a change in the form of intracellular iron from a bound to a free state.

Human cDNA clones that modify radiomimetic sensitivity of ataxia-telangiectasia (group A) cells

Genes responsible for genetic diseases with increased sensitivity to DNA-damaging agents can be identified using complementation cloning. This strategy is based on in vitro complementation of the cellular sensitivity by gene transfer. Ataxia-telangiectasia (A-T) is a multisystem autosomal recessive disorder involving cellular sensitivity to ionizing radiation and radiomimetic drugs. A-T is genetically heterogeneous, with four complementation groups. We attempted to identify cDNA clones that modify the radiomimetic sensitivity of A-T cells assigned to complementation group [A-T(A)]. The cells were transfected with human cDNA libraries cloned in episomal vectors, and various protocols of radiomimetic selection were applied. Thirteen cDNAs rescued from survivor cells were found to confer various degrees of radiomimetic resistance to A-T(A) cells upon repeated introduction, and one of them also partially influenced another feature of the A-T phenotype, radioresistant DNA synthesis. None of the clones mapped to the A-T locus on chromosome 11q22-23. Nine of the clones were derived from known genes, some of which are involved in cellular stress responses. We concluded that a number of different genes, not necessarily associated with A-T, can influence the response of A-T cells to radiomimetic drugs, and hence the complementation cloning approach may be less applicable to A-T than to other diseases involving abnormal processing of DNA damage.

Isolation of a cDNA encoding a growth-arrest associated gene and characterization of its regulation

We are interested in understanding the molecular events associated with the growth-arrest of vascular SMCs. We constructed a subtracted cDNA library enriched in nucleotide sequences associated with quiescent SMCs. This library was screened with similarly subtracted 32P-labeled cDNAs to identify growth-arrest associated cDNA clones. Characterization of 19 of these cDNA clones revealed that 9 hybridized to mRNAs that exhibited a 2-3-fold increase in growth-arrested SMCs. In addition, two other cDNAs hybridized to a 5 Kb mRNA that was elevated approximately 10-fold in high density growth-arrested SMCs. Genomic Southern blot hybridization and DNA sequencing analysis indicated that these cDNAs encoded the same gene (LG7) and that this gene may be a member of a multigene family or that it may contain a sequence shared by other unrelated genes. Augmented expression of LG7 was associated with both high cell density and serum deprivation induced growth-arrest. LG7 mRNA expression was down-regulated when SMCs were incubated with FBS or with reagents that arrest cells in early S-phase. Additional analysis with cell cycle specific inhibitors indicated that LG7 mRNA levels were also low when cells were blocked at the G2 phase of the cell cycle but blockage at mitosis resulted in an elevated level of LG7 mRNA. We further demonstrated that the expression of LG7 was dependent on the presence of a relatively labile protein since protein synthesis inhibitors specifically blocked the expression of this mRNA but not the mRNA expression of alpha 1(III) collagen or ferritin H-chain. Finally, we demonstrated that Bt2cAMP was able to induce mRNA expression of LG7 within 2 h, suggesting that this gene may be directly regulated via the cyclic-AMP-dependent protein kinase pathway.

The ferritin genes: their response to iron status

Iron is a required nutrient which, at high concentrations, can peroxidize cell lipids and other cellular components. To prevent excess iron from damaging cells, it is stored in ferritin, which consists of a shell of protein subunits of two related types, H (heavy) and L (light), surrounding a cavity in which the iron can be deposited. In order to prepare for a rapid increase in ferritin in response to a rise in cellular iron, a large number of dormant ferritin mRNAs are accumulated in the cytoplasm. These can be rapidly activated to yield a large population of ferritin subunits. Regulation is achieved through a 28-nucleotide "stem-and-loop" structure near the beginning of the H- and L-ferritin mRNAs. When this structure is associated with a binding protein (iron regulatory element binding protein, IRE-BP), translation of the ferritin mRNA cannot proceed. However, when intracellular iron accumulates, IRE-BP releases its hold and translation of the mRNA then takes place. IRE-BP has been identified as a cytosolic form of aconitase, containing several fourfold iron-sulfur clusters. Within each cluster one iron atom is labile; this may be the mechanism by which IRE-BP responds to intracellular iron levels. Finally, transcription of the L- and H-genes shows that L is preferentially transcribed in response to increased iron intake, whereas H responds to cell differentiation and other factors. More work is needed to define independent transcription of the individual genes, including regulation of components other than the 28-nucleotide segment.

Identification and characterization of developmentally regulated genes in vascular smooth muscle cells

We wish to understand the process of smooth muscle cell (SMC) proliferation and maturation during late fetal development and have examined some of the molecular changes associated with blood vessel maturation in late gestational and early neonatal life. By differential screening of a fetal aortic smooth muscle cDNA library, we identified a gene (F-31) that was developmentally regulated in aortic smooth muscle. The F-31 gene encodes a 2.3-kb RNA that was highly expressed in fetal aortic smooth muscle (25-day gestation), was lower in newborns, and was undetectable in the aortic smooth muscle of 4-week-old animals. F-31 was also highly expressed in fetal muscle, esophagus, heart, liver, lung, and placenta; its expression was lower in skin, kidney, and brain. By contrast, the expression of F-31 was low or undetectable in the corresponding tissue of adult animals. DNA sequence analysis of cDNAs encoding F-31 and data base comparison revealed a 73% homology with a previously identified, developmentally regulated gene called H19. We also found that insulin-like growth factor II (IGF-II) expression was developmentally regulated in smooth muscle. However, unlike F-31, expression of IGF-II was undetectable in the aortic smooth muscle of newborn animals. Analysis of the mRNA level of several genes that encode cytoskeletal proteins in neonatal, newborn, and adult smooth muscle indicates that total actin mRNA level, alpha-smooth muscle actin, and alpha-tropomyosin mRNA levels were similar between the late gestational period and 4 weeks after birth.(ABSTRACT TRUNCATED AT 250 WORDS)