Membrane-bound transferrin-like protein (MTf): structure, evolution and selective expression during chondrogenic differentiation of mouse embryonic cells

Lactoferrin: from the structure to the functional orchestration of iron homeostasis

Iron is by far the most widespread and essential transition metal, possessing crucial biological functions for living systems. Despite chemical advantages, iron biology has forced organisms to face with some issues: ferric iron insolubility and ferrous-driven formation of toxic radicals. For these reasons, acquisition and transport of iron constitutes a formidable challenge for cells and organisms, which need to maintain adequate iron concentrations within a narrow range, allowing biological processes without triggering toxic effects. Higher organisms have evolved extracellular carrier proteins to acquire, transport and manage iron. In recent years, a renewed interest in iron biology has highlighted the role of iron-proteins dysregulation in the onset and/or exacerbation of different pathological conditions. However, to date, no resolutive therapy for iron disorders has been found. In this review, we outline the efficacy of Lactoferrin, a member of the transferrin family mainly secreted by exocrine glands and neutrophils, as a new emerging orchestrator of iron metabolism and homeostasis, able to counteract iron disorders associated to different pathologies, including iron deficiency and anemia of inflammation in blood, Parkinson and Alzheimer diseases in the brain and cystic fibrosis in the lung.

Two peptides targeting endothelial receptors are internalized into murine brain endothelial cells

The blood-brain barrier (BBB) is one of the main obstacles for therapies targeting brain diseases. Most macromolecules fail to pass the tight BBB, formed by brain endothelial cells interlinked by tight junctions. A wide range of small, lipid-soluble molecules can enter the brain parenchyma via diffusion, whereas macromolecules have to transcytose via vesicular transport. Vesicular transport can thus be utilized as a strategy to deliver brain therapies. By conjugating BBB targeting antibodies and peptides to therapeutic molecules or nanoparticles, it is possible to increase uptake into the brain. Previously, the synthetic peptide GYR and a peptide derived from melanotransferrin (MTfp) have been suggested as candidates for mediating transcytosis in brain endothelial cells (BECs). Here we study uptake, intracellular trafficking, and translocation of these two peptides in BECs. The peptides were synthesized, and binding studies to purified endocytic receptors were performed using surface plasmon resonance. Furthermore, the peptides were conjugated to a fluorophore allowing for live-cell imaging studies of their uptake into murine brain endothelial cells. Both peptides bound to low-density lipoprotein receptor-related protein 1 (LRP-1) and the human transferrin receptor, while lower affinity was observed against the murine transferrin receptor. The MTfp showed a higher binding affinity to all receptors when compared to the GYR peptide. The peptides were internalized by the bEnd.3 mouse endothelial cells within 30 min of incubation and frequently co-localized with endo-lysosomal vesicles. Moreover, our in vitro Transwell translocation experiments confirmed that GYR was able to cross the murine barrier and indicated the successful translocation of MTfp. Thus, despite binding to endocytic receptors with different affinities, both peptides are able to transcytose across the murine BECs.

Concanavalin A Enhanced Proliferation and Osteogenic Differentiation of Dental Pulp Stem Cells

Objective  Dental pulp stem cells (DPSCs) can be used as a component in the formation of regenerative dentine during direct pulp capping therapy. Concanavalin A (ConA) is a type of lectin with a molecular weight of 26 kDa derived from the Canavalia ensiformis plant. Lectins possess strong proliferation and differentiation abilities in various animal cells including lymphocytes, osteoblasts, and chondrocytes. The aim of study was to determine the effect of ConA on the proliferation and osteogenic differentiation of DPSCs in vitro .

Materials and Methods  In this in vitro study, DPSCs were isolated from third molars before ConA induction was performed at concentrations of 5 and 10 μg/mL. The proliferation assay was determined by 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay. Osteogenic differentiation was determined by means of mineralization.

Statistical Analysis  Data were analyzed using analysis of variance and a Student’s t -test. The p -value was set at 0.05.

Results  The addition of 5 and 10 µg/mL of ConA to DPSCs can significantly increase the proliferation and osteogenic differentiation of DPSCs ( p ≤0.05).

Conclusion  ConA can increase the proliferation and osteogenic differentiation of DPSCs.

Ultra-fast stem cell labelling using cationised magnetoferritin

Magnetic cell labelling with superparamagnetic iron oxide nanoparticles (SPIONs) facilitates many important biotechnological applications, such as cell imaging and remote manipulation. However, to achieve adequate cellular loading of SPIONs, long incubation times (24 hours and more) or laborious surface functionalisation are often employed, which can adversely affect cell function. Here, we demonstrate that chemical cationisation of magnetoferritin produces a highly membrane-active nanoparticle that can magnetise human mesenchymal stem cells (hMSCs) using incubation times as short as one minute. Magnetisation persisted for several weeks in culture and provided significant T2* contrast enhancement during magnetic resonance imaging. Exposure to cationised magnetoferritin did not adversely affect the membrane integrity, proliferation and multi-lineage differentiation capacity of hMSCs, which provides the first detailed evidence for the biocompatibility of magnetoferritin. The combination of synthetic ease and flexibility, the rapidity of labelling and absence of cytotoxicity make this novel nanoparticle system an easily accessible and versatile platform for a range of cell-based therapies in regenerative medicine.

Roads to melanoma: Key pathways and emerging players in melanoma progression and oncogenic signaling

Melanoma has markedly increased worldwide during the past several decades in the Caucasian population and is responsible for 80% of skin cancer deaths. Considering that metastatic melanoma is almost completely resistant to most current therapies and is linked with a poor patient prognosis, it is crucial to further investigate potential molecular targets. Major cell-autonomous drivers in the pathogenesis of this disease include the classical MAPK (i.e., RAS-RAF-MEK-ERK), WNT, and PI3K signaling pathways. These pathways play a major role in defining the progression of melanoma, and some have been the subject of recent pharmacological strategies to treat this belligerent disease. This review describes the latest advances in the understanding of melanoma progression and the major molecular pathways involved. In addition, we discuss the roles of emerging molecular players that are involved in melanoma pathogenesis, including the functional role of the melanoma tumor antigen, p97/MFI2 (melanotransferrin).

Phylogenomic analysis of transferrin family from animals and plants

Transferrins have been identified in animals and green algae, and they consist of a family of evolutionarily related proteins that play a central role in iron transport, immunity, growth and differentiation. This study assessed the transferrin genes among 100 genomes from a wide range of animal and plant kingdoms. The results showed that putative transferrins were widespread in animals, but their gene quantity and type differ greatly between animal groups. Generally, Mammalia possess abundant transferrin genes, whereas Trematoda contain few ones. Melanotransferrin and serotransferrin are widely distributed in vertebrates, while melanotransferrin-like and transferrin-like 1 are frequent in invertebrates. However, only a few plant species detected putative transferrins, and a novel transferrin member was first uncovered in Angiospermae and Pteridophyta. The structural comparison among transferrin family members revealed seven very well-repeated and conserved characteristic motifs, despite a considerable variation in the overall sequences. The phylogenetic analysis suggested that gene duplication, gene loss and horizontal transfer contributed to the diversification of transferrin family members, and their inferred evolutionary scenario was proposed. These findings help to the understanding of transferrin distribution, characteristic motifs and residues, and evolutionary process.

Evolutionary diversification of the vertebrate transferrin multi-gene family

In a phylogenetic analysis of vertebrate transferrins (TFs), six major clades (subfamilies) were identified: (a) S, the mammalian serotransferrins; (b) ICA, the mammalian inhibitor of carbonic anhydrase (ICA) homologs; (c) L, the mammalian lactoferrins; (d) O, the ovotransferrins of birds and reptiles; (e) M, the melanotransferrins of bony fishes, amphibians, reptiles, birds, and mammals; and (f) M-like, a newly identified TF subfamily found in bony fishes, amphibians, reptiles, and birds. A phylogenetic tree based on the joint alignment of N-lobes and C-lobes supported the hypothesis that three separate events of internal duplication occurred in vertebrate TFs: (a) in the common ancestor of the M subfamily, (b) in the common ancestor of the M-like subfamily, and (c) in the common ancestor of other vertebrate TFs. The S, ICA, and L subfamilies were found only in placental mammals, and the phylogenetic analysis supported the hypothesis that these three subfamilies arose by gene duplication after the divergence of placental mammals from marsupials. The M-like subfamily was unusual in several respects, including the presence of a uniquely high proportion of clade-specific conserved residues, including distinctive but conserved residues in the sites homologous to those functioning in carbonate binding of human serotransferrin. The M-like family also showed an unusually high proportion of cationic residues in the positively charged region corresponding to human lactoferrampin, suggesting a distinctive role of this region in the M-like subfamily, perhaps in antimicrobial defense.

Molecular cloning, characterization and expression analysis of melanotransferrin from the sea cucumber Apostichopus japonicus

Melanotransferrin (MTf), a member of the transferrin families, plays an important role in immune response. But the research about MTf in sea cucumber is limited till now. In this study, the Melanotransferrin (Aj-MTf) gene was firstly cloned and characterized from the sea cucumber Apostichoupus japonicus by reverse transcriptase polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends. The full-length cDNA of Aj-MTf is 2,840 bp in length and contains a 2,184 bp open reading frame that encodes a polypeptide of 727 amino acids. An iron-responsive element-like structure is located at the 5'-UTR of Aj-MTf cDNA. Sequence analysis shows that the Aj-MTf contains two conserved domains, and the binding-iron (III) sites, including eight amino acid residues (D81,Y109,Y215,H283,D425,Y454,Y565 and H634) and three N-linked glycosylation sites (N121V122S123,N173A174S175 and N673S674T675). Quantitative real-time polymerase chain reaction (qRT-PCR) analyses suggested that the Aj-MTf expressions in the coelomic fluid, body cavity wall and respiratory trees were significantly changed from 4 to 24 h post lipopolysaccharide (LPS) injection. The mRNA levels of Aj-MTf in coelomic fluid was significantly up-regulated at 12 and 24 h in treatment group, and Aj-MTf shared a similar expression pattern with C-type lectin in coelomic fluid, while both genes appears to gradually increase after 4 h of LPS injection. These results indicate that the Aj-MTf plays a pivotal role in immune responses to the LPS challenge in sea cucumber, and provide new information that it is complementary to the sea cucumber immune genes and initiate new researches concerning the genetic basis of the holothurian immune response.

The effects of iron oxide incorporation on the chondrogenic potential of three human cell types

Non-invasive monitoring of living cells in vivo provides an important tool in the development of cell-based therapies in cartilage tissue engineering. High-resolution magnetic resonance imaging (MRI) has been used to monitor target cell populations in vivo. However, the side-effects on cell function of the labelling reagents, such as superparamagnetic iron oxide (SPIO), are still unclear. This study investigated the effect of SPIO particles on the chondrogenic differentiation of human bone marrow stromal cells (HBMSCs), neonatal and adult chondrocytes in vitro. Cells were labelled with SPIO for 24 h and chondrogenesis induced in serum-free medium including TGFβ3. For labelled/unlabelled cells, viability, morphology and proliferation were determined using CellTracker™ Green and PicoGreen dsDNA assays. The expression of SOX9, COL2A1 and ACAN was investigated using qRT-PCR after 2, 7 and 14 days. The results showed that viability was unaffected in all of the cells but cell morphology changed towards a 'stretched' phenotype following SPIO uptake. Cell proliferation was reduced only for labelled neonatal chondrocytes. SOX9 and COL2A1 expression decreased at day 2 but not at days 7 and 14 for labelled HBMSCs and adult chondrocytes; ACAN expression was unaffected. In contrast, SOX9 and COL2A1 expression were unaffected in labelled neonatal chondrocytes but a decrease in ACAN expression was seen at day 14. The results suggest that downregulation of chondrogenic genes associated with SPIO labelling is temporary and target cell-dependent. Resovist® can be used to label HBMSCs or mature chondrocytes for MR imaging of cells for cartilage tissue engineering.

Phylogenetic analyses uncover a novel clade of transferrin in nonmammalian vertebrates

Transferrin is a protein super-family involved in iron transport, a central process in cellular homeostasis. Throughout the evolution of vertebrates, transferrin members have diversified into distinct subfamilies including serotransferrin, ovotransferrin, lactoferrin, melanotransferrin, the inhibitor of carbonic anhydrase, pacifastin, and the major yolk protein in sea urchin. Previous phylogenetic analyses have established the branching order of the diverse transferrin subfamilies but were mostly focused on the transferrin repertoire present in mammals. Here, we conduct a comprehensive phylogenetic analysis of transferrin protein sequences in sequenced vertebrates, placing a special focus on the less-studied nonmammalian vertebrates. Our analyses uncover a novel transferrin clade present across fish, sauropsid, and amphibian genomes but strikingly absent from mammals. Our reconstructed scenario implies that this novel class emerged through a duplication event at the vertebrate ancestor, and that it was subsequently lost in the lineage leading to mammals. We detect footprints of accelerated evolution following the duplication event, which suggest positive selection and early functional divergence of this novel clade. Interestingly, the loss of this novel class of transferrin in mammals coincided with the divergence by duplication of lactoferrin and serotransferrin in this lineage. Altogether, our results provide novel insights on the evolution of iron-binding proteins in the various vertebrate groups.

Melanotransferrin: search for a function

BACKGROUND

Melanotransferrin was discovered in the 1980s as one of the first melanoma tumour antigens. The molecule is a transferrin homologue that is found predominantly bound to the cell membrane by a glycosyl-phosphatidylinositol anchor. MTf was described as an oncofoetal antigen expressed in only small quantities in normal tissues, but in much larger amounts in neoplastic cells. Several diseases are associated with expression of melanotransferrin, including melanoma and Alzheimer's disease, although the significance of the protein to the pathogenesis of these conditions remains unclear.

SCOPE OF REVIEW

In this review, we discuss the roles of melanotransferrin in physiological and pathological processes and its potential use as an immunotherapy.

MAJOR CONCLUSIONS

Although the exact biological functions of melanotransferrin remain elusive, a growing number of roles have been attributed to the protein, including iron transport/metabolism, angiogenesis, proliferation, cellular migration and tumourigenesis.

GENERAL SIGNIFICANCE

The high expression of melanotransferrin in several disease states, particularly malignant melanoma, remains intriguing and may have clinical significance. Further studies on the biology of this protein may provide new insights as well as potential therapeutic avenues for cancer treatment. This article is part of a Special Issue entitled Transferrins: Molecular mechanisms of iron transport and disorders.

Polymorphism, selection and tandem duplication of transferrin genes in Atlantic cod (Gadus morhua)--conserved synteny between fish monolobal and tetrapod bilobal transferrin loci

BACKGROUND

The two homologous iron-binding lobes of transferrins are thought to have evolved by gene duplication of an ancestral monolobal form, but any conserved synteny between bilobal and monolobal transferrin loci remains unexplored. The important role played by transferrin in the resistance to invading pathogens makes this polymorphic gene a highly valuable candidate for studying adaptive divergence among local populations.

RESULTS

The Atlantic cod genome was shown to harbour two tandem duplicated serum transferrin genes (Tf1, Tf2), a melanotransferrin gene (MTf), and a monolobal transferrin gene (Omp). Whereas Tf1 and Tf2 were differentially expressed in liver and brain, the Omp transcript was restricted to the otoliths. Fish, chicken and mammals showed highly conserved syntenic regions in which monolobal and bilobal transferrins reside, but contrasting with tetrapods, the fish transferrin genes are positioned on three different linkage groups. Sequence alignment of cod Tf1 cDNAs from Northeast (NE) and Northwest (NW) Atlantic populations revealed 22 single nucleotide polymorphisms (SNP) causing the replacement of 16 amino acids, including eight surface residues revealed by the modelled 3D-structures, that might influence the binding of pathogens for removal of iron. SNP analysis of a total of 375 individuals from 14 trans-Atlantic populations showed that the Tf1-NE variant was almost fixed in the Baltic cod and predominated in the other NE Atlantic populations, whereas the NW Atlantic populations were more heterozygous and showed high frequencies of the Tf-NW SNP alleles.

CONCLUSIONS

The highly conserved synteny between fish and tetrapod transferrin loci infers that the fusion of tandem duplicated Omp-like genes gave rise to the modern transferrins. The multiple nonsynonymous substitutions in cod Tf1 with putative structural effects, together with highly divergent allele frequencies among different cod populations, strongly suggest evidence for positive selection and local adaptation in trans-Atlantic cod populations.

Differential regulation of transferrin 1 and 2 in Aedes aegypti

Available evidence has shown that transferrins are involved in iron metabolism, immunity and development in eukaryotic organisms including insects. Here we characterize the gene and message expression profile of Aedes aegypti transferrin 2 (AaTf2) in response to iron, bacterial challenge and life stage. We show that AaTf2 shares a low similarity with A. aegypti transferrin 1 (AaTf1), but higher similarity with mammalian transferrins and avian ovotransferrin. Iron-binding pocket analysis indicates that AaTf2 has residue substitutions of Y188F, T120S, and R124S in the N lobe, and Y517N, H585N, T452S, and R456T in the C lobe, which could alter or reduce iron-binding activity. In vivo studies of message expression reveal that AaTf2 message is expressed at higher levels in larva and pupa, as well as adult female ovaries 72h post blood meal (PBM) and support that AaTf2 could play a role in larval and pupal development and in late physiological events of the gonotrophic cycle. Bacterial challenge significantly increases AaTf1 expression in ovaries at 0 and 24h PBM, but decreases AaTf2 expression in ovaries at 72h PBM, suggesting that AaTf1 and AaTf2 play different roles in immunity of female adults during a gonotrophic cycle.

The melanoma tumor antigen, melanotransferrin (p97): a 25-year hallmark – from iron metabolism to tumorigenesis

Melanotransferrin (MTf) or melanoma tumor antigen p97 is a transferrin (Tf) homolog that is found predominantly bound to the cell membrane via a glycosyl phosphatidylinositol anchor. The molecule is a member of the Tf superfamily and binds iron through a single high-affinity iron(III)-binding site. Since its discovery on the plasma membrane of melanoma cells, the function of MTf has remained intriguing, particularly in relation to its role in cancer cell iron transport. In fact, considering the crucial role of iron in many metabolic pathways, e.g., DNA synthesis, it was important to understand the function of MTf in the transport of this vital nutrient. MTf has also been implicated in diverse physiological processes, such as plasminogen activation, angiogenesis and cell migration. However, recent studies using a knockout mouse and post-transcriptional gene silencing have demonstrated that MTf is not involved in iron metabolism, but plays a vital role in melanoma cell proliferation and tumorigenesis. In this review, we discuss the possible biological functions of MTf, particularly in relation to cancer.

Stimulation of tPA-dependent provisional extracellular fibrin matrix degradation by human recombinant soluble melanotransferrin

Tissue-type plasminogen activator (tPA) and its substrate plasminogen (Plg) are key components in the fibrinolytic system. We have recently demonstrated, that truncated human recombinant soluble melanotransferrin (sMTf) could stimulate the activation of Plg by urokinase plasminogen activator and inhibit angiogenesis. Since various angiogenesis inhibitors were shown to stimulate tPA-mediated plasminogen activation, we examined the effects of sMTf on tPA-dependent fibrinolysis. This study demonstrated that sMTf enhanced tPA-activation of Plg by 6-fold. sMTf also increased the release of [125I]-fibrin fragments by tPA-activated plasmin. Moreover, we observed that the interaction of sMTf with Plg provoked a change in the fibrin clot structure by cleaving the fibrin alpha and beta chains. Overall, the present study shows that sMTf modulates tPA-dependent fibrinolysis by modifying the clot structure. These results also suggest that sMTf properties could involve enhanced dissolution of the provisional extracellular fibrin matrix.

Role of melanotransferrin in iron metabolism: studies using targeted gene disruption in vivo

Melanotransferrin (MTf) or tumor antigen p97 is a transferrin homolog that binds one iron (Fe) atom and has been suggested to play roles in a variety of processes, including Fe metabolism, eosinophil differentiation, and plasminogen activation. Considering the vital role of Fe in many metabolic pathways, such as DNA and heme synthesis, it is important to understand the function of MTf. To define this, a MTf knockout (MTf–/–) mouse was generated through targeted disruption of the MTf gene. The MTf–/– mice were viable and fertile and developed normally, with no morphologic or histologic abnormalities. Assessment of Fe indices, tissue Fe levels, hematology, and serum chemistry parameters demonstrated no differences between MTf–/– and wild-type (MTf+/+) mice, suggesting MTf was not essential for Fe metabolism.

Otolith matrix proteins OMP-1 and Otolin-1 are necessary for normal otolith growth and their correct anchoring onto the sensory maculae

Fish otoliths are highly calcified concretions deposited in the inner ear and serve as a part of the hearing and balance systems. They consist mainly of calcium carbonate and a small amount of organic matrix. The latter component is considered to play important roles in otolith formation. Previously, we identified two major otolith matrix proteins, OMP-1 (otolith matrix protein-1) and Otolin-1, from salmonid species. To assess the function of these proteins in otolith formation, we performed antisense morpholino oligonucleotide (MO)-mediated knockdown of omp-1 and otolin-1 in zebrafish embryos. We first identified zebrafish cDNA homologs of omp-1 (zomp-1) and otolin-1 (zotolin-1). Whole-mount in situ hybridization then revealed that the expression of both zomp-1 and zotolin-1 mRNAs is restricted to the otic vesicles. zomp-1 mRNA was expressed from the 14-somite stage in the otic placode, but the zOMP-1 protein was detected only from 26-somite stage onwards. In contrast, zotolin-1 mRNA expression became clear around 72 hpf. MOs designed to inhibit zomp-1 and zotolin-1 mRNA translation, respectively, were injected into 1-2 cell stage embryos. zomp-1 MO caused a reduction in otolith size and an absence of zOtolin-1 deposition, while zotolin-1 MO caused a fusion of the two otoliths, and an increased instability of otoliths after fixation. We conclude that zOMP-1 is required for normal otolith growth and deposition of zOtolin-1 in the otolith, while zOtolin-1, a collagenous protein, is involved in the correct arrangement of the otoliths onto the sensory epithelium of the inner ear and probably in stabilization of the otolith matrix.

Evolution of the transferrin family: Conservation of residues associated with iron and anion binding

The transferrin family spans both vertebrates and invertebrates. It includes serum transferrin, ovotransferrin, lactoferrin, melanotransferrin, inhibitor of carbonic anhydrase, saxiphilin, the major yolk protein in sea urchins, the crayfish protein, pacifastin, and a protein from green algae. Most (but not all) contain two domains of around 340 residues, thought to have evolved from an ancient duplication event. For serum transferrin, ovotransferrin and lactoferrin each of the duplicated lobes binds one atom of Fe (III) and one carbonate anion. With a few notable exceptions each iron atom is coordinated to four conserved amino acid residues: an aspartic acid, two tyrosines, and a histidine, while anion binding is associated with an arginine and a threonine in close proximity. These six residues in each lobe were examined for their evolutionary conservation in the homologous N- and C-lobes of 82 complete transferrin sequences from 61 different species. Of the ligands in the N-lobe, the histidine ligand shows the most variability in sequence. Also, of note, four of the twelve insect transferrins have glutamic acid substituted for aspartic acid in the N-lobe (as seen in the bacterial ferric binding proteins). In addition, there is a wide spread substitution of lysine for the anion binding arginine in the N-lobe in many organisms including all of the fish, the sea squirt and many of the unusual family members i.e., saxiphilin and the green alga protein. It is hoped that this short analysis will provide the impetus to establish the true function of some of the TF family members that clearly lack the ability to bind iron in one or both lobes and additionally clarify the evolutionary history of this important family of proteins.

Evolution of duplications in the transferrin family of proteins

The transferrin family is a group of proteins, defined by conserved amino acid motifs and putative function, found in both vertebrates and invertebrates. Included in this group are molecules known to bind iron, including serum transferrin, ovotransferrin, lactotransferrin, and melanotransferrin (MTF). Additional members of this family include inhibitor of carbonic anhydrase (ICA; mammals), major yolk protein (sea urchins), saxiphilin (frog), pacifastin (crayfish), and TTF-1 (algae). Most family members contain two lobes (N and C) of around 340 amino acids, the result of an ancient duplication event. In this article, we review the known functions of these proteins and speculate as to when the different homologs arose. From multiple-sequence alignments and neighbor-joining trees using 71 transferrin family sequences from 51 different species, including several novel sequences found in the Takifugu and Ciona genome databases, we conclude that melanotransferrins are much older (>670 MY) and more pervasive than previously thought, and the serum transferrin/melanotransferrin split may have occurred not long after lobe duplication. All subsequent duplication events diverged from the serum transferrin gene. The creation of such a large multiple-sequence alignment provides important information and could, in the future, highlight the role of specific residues in protein function.

Feridex labeling of mesenchymal stem cells inhibits chondrogenesis but not adipogenesis or osteogenesis

Magnetic resonance (MR) tracking of superparamagnetic iron oxide (SPIO)-labeled cells is a relatively new technique to non-invasively determine the biodistribution and migration of transplanted stem cells. A number of studies have recently reported encouraging results in the use of bone marrow-derived mesenchymal stem cells (MSCs) for repair of a variety of tissues. For MR tracking of SPIO-labeled MSCs, it is important to determine the effect that the magnetic labeling procedure may have on the differentiation capacity of labeled MSCs. Human MSCs were labeled with poly-L-lysine (PLL)-coated Feridex, with Feridex being an FDA-approved SPIO formulation in an off-label application, and assayed for cellular differentiation using five different assays. As compared with unlabeled controls, labeled MSCs exhibited an unaltered viability, proliferated similarly, and underwent normal adipogenic and osteogenic differentiation. However, there was a marked inhibition of chondrogenesis. The blocking of chondrogenic activity was mediated by the Feridex, rather than by the transfection agent (PLL). This is the first report showing Feridex blocking of cellular differentiation down a specific pathway (while not affecting viability and proliferation), and caution should thus be exercised when using Feridex-labeled MSCs for chondrogenic MR tracking studies. On the other hand, no detrimental effects of Feridex-labeling are anticipated for MR-guided osteogenic or adipogenic transplantation studies.

Anti-membrane-bound transferrin-like protein antibodies induce cell-shape change and chondrocyte differentiation in the presence or absence of concanavalin A

Membrane-bound transferrin-like protein (MTf), a glycosylphosphatidylinositol-anchored protein, is expressed at high levels in many tumors and in several fetal and adult tissues including cartilage and the intestine, as well as in the amyloid plaques of Alzheimer's disease, although its role remains unknown. MTf is one of the major concanavalin A-binding proteins of the cell surface. In this study, we examined the effects of anti-MTf antibodies and concanavalin A on cell shape and gene expression, using cultures of chondrocytes and MTf-overexpressing ATDC5 and C3H10T1/2 cells. In cultures expressing MTf at high levels, concanavalin A induced cell-shape changes from fibroblastic to spherical cells, whereas no cell-shape changes were observed with wild-type ATDC5 or C3H10T1/2 cells expressing MTf at very low levels. The cell-shape changes were associated with enhanced proteoglycan synthesis and expression of cartilage-characteristic genes, including aggrecan and type II collagen. Some anti-MTf antibodies mimicked this action of concanavalin A, whereas other antibodies blocked the lectin action. The findings suggest that the crosslinking of MTf changes the cell shape and induces chondrogenic differentiation. MTf represents the first identification of a plant lectin receptor involved in cell-shape changes and the differentiation of animal cells.

Basic helix-loop-helix protein DEC1 promotes chondrocyte differentiation at the early and terminal stages

The mRNA level of basic helix-loop-helix transcription factor DEC1 (BHLHB2)/Stra13/Sharp2 was up-regulated during chondrocyte differentiation in cultures of ATDC5 cells and growth plate chondrocytes, and in growth plate cartilage in vivo. Forced expression of DEC1 in ATDC5 cells induced chondrogenic differentiation, and insulin increased this effect of DEC1 overexpression. Parathyroid hormone (PTH) and PTH-related peptide (PTHrP) suppressed DEC1 expression and the differentiation of ATDC5 cells, but DEC1 overexpression antagonized this inhibitory action of PTH/PTHrP. Transforming growth factor-beta or bone morphogenetic protein-2, as well as insulin, induced DEC1 expression in ATDC5 cultures where it induced chondrogenic differentiation. In pellet cultures of bone marrow mesenchymal stem cells exposed to transforming growth factor-beta and insulin, DEC1 was induced at the earliest stage of chondrocyte differentiation and also at the hypertrophic stage. Overexpression of DEC1 in the mesenchymal cells induced the mRNA expressions of type II collagen, Indian hedgehog, and Runx2, as well as cartilage matrix accumulation; overexpression of DEC1 in growth plate chondrocytes at the prehypertrophic stage increased the mRNA levels of Indian hedgehog, Runx2, and type X collagen, and also increased alkaline phosphatase activity and mineralization. To our knowledge, DEC1 is the first transcription factor that can promote both chondrogenic differentiation and terminal differentiation.

Effects of overexpression of membrane-bound transferrin-like protein (MTf) on chondrogenic differentiation in Vitro

Membrane-bound transferrin-like protein (MTf) is expressed in parallel with the expression of cartilage-characteristic genes during differentiation of chondrocytes, and the MTf level is much higher in cartilage than in other tissues. To investigate the role of MTf in cartilage, we examined the effects of growth factors on MTf expression in mouse prechondrogenic ATDC5 cells and the effect of MTf overexpression on differentiation of ATDC5 and mouse pluripotent mesenchymal C3H10T1/2 cells. In ATDC5 cultures, bone morphogenetic protein-2 and transforming growth factor-beta as well as insulin induced MTf mRNA expression when these peptides induced chondrogenic differentiation. Forced expression of rabbit MTf in ATDC5 cells induced aggrecan, type II collagen, matrilin-1, type X collagen mRNAs, and cell-shape changes from fibroblastic cells to spherical chondrocytes. Accordingly, the synthesis and accumulation of proteoglycans were higher in MTf-expressing cultures than in control cultures. These effects of MTf overexpression correlated with the MTf protein level on the cell surface and decreased in the presence of anti-MTf antibody. However, the aggrecan mRNA level in the ATDC5 cells overexpressing MTf was lower than that in wild type ATDC5 cells exposed to 10 microg/ml insulin. MTf overexpression in C3H10T1/2 cells also induced aggrecan and/or type II collagen mRNA but not the spherical phenotype. These findings suggest that the expression of MTf on the cell surface facilitates the differentiation of prechondrogenic cells, although MTf overexpression alone seems to be insufficient to commit pluripotent mesenchymal cells to the chondrocyte lineage.

Identification of functional hypoxia response elements in the promoter region of the DEC1 and DEC2 genes

Adaptation to hypoxia is a crucial process both physiologically (i.e. in chondrocytes) and pathologically (i.e. in tumor cells). Previous studies have shown that DEC1, a basic helix-loop-helix transcription factor, is induced by hypoxia in glioma cells (Ivanova, A. V., Ivanov, S. V., Danilkovitch-Miagkova, A., and Lerman, M. I. (2001) J. Biol. Chem. 276, 15306-15315). In the present study, we found that hypoxia or CoCl(2) enhanced the mRNA expression of DEC2, as well as DEC1, within 24 h in chondrogenic ATDC5, 293T, and HeLa cells. In luciferase assays, the regions between -524 and -401 in the DEC1 promoter, and between -863 and -258 in the DEC2 promoter, were responsible for the hypoxia- or hypoxia-inducible factor-1alpha (HIF-1alpha)-induced transcription. In these regions, we identified functional hypoxia response elements (HREs) that bound to HIF-1alpha and HIF-1beta. In addition to an HIF-1 binding site consensus sequence, the DEC1 HRE had cAMP response element-like and CACAG sequences, which were also involved in the transcription activation in response to HIF-1alpha. Although the DEC2 HRE did not have a cAMP response element-like or CACAG sequence, it showed a higher affinity for HIF-1 than did the DEC1 HRE. Because DEC1 and DEC2 are directly inducible by HIF-1, these transcription factors may be crucial for the adaptation to hypoxia.

Structure and promoter analysis of the mouse membrane-bound transferrin-like protein (MTf) gene

Recently, we purified membrane-bound transferrin-like protein (MTf) from the plasma membrane of rabbit chondrocytes and showed that the expression levels of MTf protein and mRNA were much higher in cartilage than in other tissues [Kawamoto T, Pan, H., Yan, W., Ishida, H., Usui, E., Oda, R., Nakamasu, K., Noshiro, M., Kawashima-Ohya, Y., Fujii, M., Shintani, H., Okada, Y. & Kato, Y. (1998) Eur. J. Biochem. 256, 503--509]. In this study, we isolated the MTf gene from a constructed mouse genomic library. The mouse MTf gene was encoded by a single-copy gene spanning approximately 26 kb and consisting of 16 exons. The transcription-initiation site was located 157 bp upstream from the translation-start codon, and a TATA box was not found in the 5' flanking region. The mouse MTf gene was mapped on the B3 band of chromosome 16 by fluorescence in situ hybridization. Using primary chondrocytes, SK-MEL-28 (melanoma cell line), ATDC5 (chondrogenic cell line) and NIH3T3 (fibroblast cell line) cells, we carried out transient expression studies on various lengths of the 5' flanking region of the MTf gene fused to the luciferase reporter gene. Luciferase activity in SK-MEL-28 cells was higher than in primary chondrocytes. Although no luciferase activity was detectable in NIH3T3 cells, it was higher in chondrocytes than in ATDC5 chondrogenic cells. These findings were consistent with the levels of expression of MTf mRNA in these cells cultured under similar conditions. The patterns of increase and decrease in the luciferase activity in chondrocytes transfected with various 5' deleted constructs of the MTf promoter were similar to that in ATDC5 cells, but differed from that in SK-MEL-28 cells. The findings obtained with primary chondrocytes suggest that the regions between -693 and -444 and between -1635 and -1213 contain positive and negative cis-acting elements, respectively. The chondrocyte-specific expression of the MTf gene could be regulated via these regulatory elements in the promoter region.

The membrane-bound transferrin homologue melanotransferrin: roles other than iron transport?

Melanotransferrin (MTf) is a membrane-bound transferrin (Tf) homologue that is found at high levels in melanoma cells. MTf has many characteristics in common with serum Tf and previous studies have shown that it can bind Fe. This has led to speculation that MTf may be involved in Fe transport. Because Fe is required for a variety of metabolic reactions including ATP and DNA synthesis, MTf could play a role in proliferation. However, recently it has been shown that MTf plays very little role in Fe uptake by melanoma cells, and unlike other Fe transport molecules (e.g. the transferrin receptor), its expression is not controlled by Fe. In the present review the function of MTf is discussed in relation to data suggesting other roles apart from Fe uptake.