Transferrin receptor: its biological significance

Rapid increase in transferrin receptor recycling promotes adhesion during T cell activation

Background

T cell activation leads to increased expression of the receptor for the iron transporter transferrin (TfR) to provide iron required for the cell differentiation and clonal expansion that takes place during the days after encounter with a cognate antigen. However, T cells mobilise TfR to their surface within minutes after activation, although the reason and mechanism driving this process remain unclear.

Results

Here we show that T cells transiently increase endocytic uptake and recycling of TfR upon activation, thereby boosting their capacity to import iron. We demonstrate that increased TfR recycling is powered by a fast endocytic sorting pathway relying on the membrane proteins flotillins, Rab5- and Rab11a-positive endosomes. Our data further reveal that iron import is required for a non-canonical signalling pathway involving the kinases Zap70 and PAK, which controls adhesion of the integrin LFA-1 and eventually leads to conjugation with antigen-presenting cells.

Conclusions

Altogether, our data suggest that T cells boost their iron importing capacity immediately upon activation to promote adhesion to antigen-presenting cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01386-0.

Dihydroartemisinin Inhibits the Proliferation, Colony Formation and Induces Ferroptosis of Lung Cancer Cells by Inhibiting PRIM2/SLC7A11 Axis

Objective

Lung cancer is the first leading cause of cancer-related deaths both worldwide and in China and threatens human health and quality of life. New drugs and therapeutic methods are urgently needed. Our study evaluated the roles of dihydroartemisinin (DHA) in lung cancer and further explored its underlying mechanisms.

Methods

CCK-8, colony formation and trypan blue exclusion assays were used to detect the cell viability, colony formation ability and cell death. qRT-PCR and Western blotting assays were applied to analyze the expressions of key molecules.

Results

DHA inhibited the proliferation and colony formation abilities and enhanced the cell death and induced ferroptosis of lung NCI-H23 and XWLC-05 cancer cells. DHA reduced PRIM2 expression and silencing PRIM2 mimicked the inhibitory roles on proliferation and colony formation and promotive roles on cell death and ferroptosis of DHA in lung NCI-H23 and XWLC-05 cancer cells. We further found that DHA treatment and loss of PRIM2 reduced the GSH level and increased the cellular lipid ROS and mitochondrial MDA levels, and further downregulated the expressions of SLC7A11 and β-catenin in lung cancer cells, respectively. Exogenetic overexpression of PRIM2 recovered the inhibitory effects of DHA on proliferation and colony formation in lung NCI-H23 cancer cells, meanwhile loss of PRIM2 sensitizes NCI-H23 cells to DHA therapy. In vivo experiment further showed that DHA treatment significantly suppressed the tumor growth and downregulated PRIM2 and SLC7A11.

Conclusion

Our study suggested that DHA inhibited the proliferation, colony formation and enhanced cell death and induced ferroptosis of lung cancer cells by inactivating PRIM2/SLC7A11 axis. Loss of PRIM2 induced ferroptosis might developed to be a novel therapeutic method in lung cancer therapy.

Exposure to Static and Extremely-Low Frequency Electromagnetic Fields and Cellular Free Radicals

This paper summarizes studies on changes in cellular free radical activities from exposure to static and extremely-low frequency (ELF) electromagnetic fields (EMF), particularly magnetic fields. Changes in free radical activities, including levels of cellular reactive oxygen (ROS)/nitrogen (RNS) species and endogenous antioxidant enzymes and compounds that maintain physiological free radical concentrations in cells, is one of the most consistent effects of EMF exposure. These changes have been reported to affect many physiological functions such as DNA damage; immune response; inflammatory response; cell proliferation and differentiation; wound healing; neural electrical activities; and behavior. An important consideration is the effects of EMF-induced changes in free radicals on cell proliferation and differentiation. These cellular processes could affect cancer development and proper growth and development in organisms. On the other hand, they could cause selective killing of cancer cells, for instance, via the generation of the highly cytotoxic hydroxyl free radical by the Fenton Reaction. This provides a possibility of using these electromagnetic fields as a non-invasive and low side-effect cancer therapy. Static- and ELF-EMF probably play important roles in the evolution of living organisms. They are cues used in many critical survival functions, such as foraging, migration, and reproduction. Living organisms can detect and respond immediately to low environmental levels of these fields. Free radical processes are involved in some of these mechanisms. At this time, there is no credible hypothesis or mechanism that can adequately explain all the observed effects of static- and ELF-EMF on free radical processes. We are actually at the impasse that there are more questions than answers.

Free-Floating Mesothelial Cells in Pleural Fluid After Lung Surgery

OBJECTIVES

The mesothelium, the surface layer of the heart, lung, bowel, liver, and tunica vaginalis, is a complex tissue implicated in organ-specific diseases and regenerative biology; however, the mechanism of mesothelial repair after surgical injury is unknown. Previous observations indicated seeding of denuded mesothelium by free-floating mesothelial cells may contribute to mesothelial healing. In this study, we investigated the prevalence of mesothelial cells in pleural fluid during the 7 days following pulmonary surgery.

STUDY DESIGN

Flow cytometry was employed to study pleural fluid of 45 patients after lung resection or transplantation. We used histologically validated mesothelial markers (CD71 and WT1) to estimate the prevalence of mesothelial cells.

RESULTS

The viability of pleural fluid cells approached 100%. Leukocytes and mesothelial cells were identified in the pleural fluid within the first week after surgery. The leukocyte concentration was relatively stable at all time points. In contrast, mesothelial cells, identified by CD71 and WT1 peaked on POD3. The broad expression of CD71 molecule in postoperative pleural fluid suggests that many of the free-floating non-leukocyte cells were activated or proliferative mesothelial cells.

CONCLUSION

We demonstrated that pleural fluid post lung surgery is a source of mesothelial cells; most of these cells appear to be viable and, as shown by CD71 staining, activated mesothelial cells. The observed peak of mesothelial cells on POD3 is consistent with a potential reparative role of free-floating mesothelial cells after pulmonary surgery.

Increased frequency of GM-CSF secreting PBMC in patients with active systemic lupus erythematosus can be reduced by immunoadsorption

An objective was to determine the frequency of GM-CSF secreting peripheral blood mononuclear cells (PBMC) in patients with active systemic lupus erythematosus (SLE) and their relation to other cytokine secreting PBMC, activation markers on lymphocytes/monocytes, clinical manifestations and anti- dsDNA antibodies.A second objectivewas to further investigatethe influence of immunoadsorption(IA) therapy on these parameters.The number of GM-CSF, interleukin-1b (IL-1b), IL-6, interferon-g (INF-g) or tumour necrosis factor-a (TNF-a) secreting PBMC was assessed by ELISPOT assay in 10 patients with active SLE. Further, the expression of activation markers on lymphocytes and monocytes was determined by flow cytometry. Three courses of IA were performed in the patients. Seventeen healthy, age- and sex-matched volunteers served as controls. GM-CSF secreting PBMC were significantly increased whereas INF-g secreting cells were decreased in SLE patients. The expression of CD71 (transferrin receptor) on CD4 + T-cells and of the costimulatorymolecule CD86 on B-lymphocyteswas significantly increased in SLE patients. GM-CSF secreting PBMC and CD4 + /CD71 + T-cells correlated with anti-dsDNA antibody titres and decreased towards levels of controls during IA. Disease activity and anti-dsDNA autoantibody titres were significantly reduced after the treatment. Our results demonstrate significant alterations of cellular and humoral immunity in SLE patients. The impaired immunity can be modulated by IA. Thus IA may prove an immunomodulatory therapeutic option in addition to the mere depletion of anti-dsDNA autoantibodies.

Anticancer Effect of AntiMalarial Artemisinin Compounds

The anti-malarial drug artemisinin has shown anticancer activity in vitro and animal experiments, but experience in human cancer is scarce. However, the ability of artemisinins to kill cancer cells through a variety of molecular mechanisms has been explored. A PubMed search of about 127 papers on anti-cancer effects of antimalarials has revealed that this class of drug, including other antimalarials, have several biological characteristics that include anticancer properties. Experimental evidences suggest that artemisinin compounds may be a therapeutic alternative in highly aggressive cancers with rapid dissemination, without developing drug resistance. They also exhibit synergism with other anticancer drugs with no increased toxicity toward normal cells. It has been found that semisynthetic artemisinin derivatives have much higher antitumor activity than their monomeric counterparts via mechanisms like apoptosis, arrest of cell cycle at G₀/G₁, and oxidative stress. The exact mechanism of activation and molecular basis of these anticancer effects are not fully elucidated. Artemisinins seem to regulate key factors such as nuclear factor-kappa B, survivin, NOXA, hypoxia-inducible factor-1α, and BMI-1, involving multiple pathways that may affect drug response, drug interactions, drug resistance, and associated parameters upon normal cells. Newer synthetic artemisinins have been developed showing substantial antineoplastic activity, but there is still limited information regarding the mode of action of these synthetic compounds. In view of the emerging data, specific interactions with established chemotherapy need to be further investigated in different cancer cells and their phenotypes and validated further using different semisynthetic and synthetic artemisinin derivatives.

Regulation of RAB5C is important for the growth inhibitory effects of MiR-509 in human precursor-B acute lymphoblastic leukemia

MicroRNAs (miRs) regulate essentially all cellular processes, but few miRs are known to inhibit growth of precursor-B acute lymphoblastic leukemias (B-ALLs). We identified miR-509 via a human genome-wide gain-of-function screen for miRs that inhibit growth of the NALM6 human B-ALL cell line. MiR-509-mediated inhibition of NALM6 growth was confirmed by 3 independent assays. Enforced miR-509 expression inhibited 2 of 2 additional B-ALL cell lines tested, but not 3 non-B-ALL leukemia cell lines. MiR-509-transduced NALM6 cells had reduced numbers of actively proliferating cells and increased numbers of cells undergoing apoptosis. Using miR target prediction algorithms and a filtering strategy, RAB5C was predicted as a potentially relevant target of miR-509. Enforced miR-509 expression in NALM6 cells reduced RAB5C mRNA and protein levels, and RAB5C was demonstrated to be a direct target of miR-509. Knockdown of RAB5C in NALM6 cells recapitulated the growth inhibitory effects of miR-509. Co-expression of the RAB5C open reading frame without its 3' untranslated region (3'UTR) blocked the growth-inhibitory effect mediated by miR-509. These findings establish RAB5C as a target of miR-509 and an important regulator of B-ALL cell growth with potential as a therapeutic target.

Distinct activation phenotype of a highly conserved novel HLA-B57-restricted epitope during dengue virus infection

Variation in the sequence of T-cell epitopes between dengue virus (DENV) serotypes is believed to alter memory T-cell responses during second heterologous infections. We identified a highly conserved, novel, HLA-B57-restricted epitope on the DENV NS1 protein. We predicted higher frequencies of B57-NS1(26-34) -specific CD8(+) T cells in peripheral blood mononuclear cells from individuals undergoing secondary rather than primary DENV infection. However, high tetramer-positive T-cell frequencies during acute infection were seen in only one of nine subjects with secondary infection. B57-NS1(26-34) -specific and other DENV epitope-specific CD8(+) T cells, as well as total CD8(+) T cells, expressed an activated phenotype (CD69(+) and/or CD38(+)) during acute infection. In contrast, expression of CD71 was largely limited to DENV epitope-specific CD8(+) T cells. In vitro stimulation of cell lines indicated that CD71 expression was differentially sensitive to stimulation by homologous and heterologous variant peptides. CD71 may represent a useful marker of antigen-specific T-cell activation.

pH-responsive artemisinin derivatives and lipid nanoparticle formulations inhibit growth of breast cancer cells in vitro and induce down-regulation of HER family members

Artemisinin (ART) dimers show potent anti-proliferative activities against breast cancer cells. To facilitate their clinical development, novel pH-responsive artemisinin dimers were synthesized for liposomal nanoparticle formulations. A new ART dimer was designed to become increasingly water-soluble as pH declines. The new artemisinin dimer piperazine derivatives (ADPs) remained tightly associated with liposomal nanoparticles (NPs) at neutral pH but were efficiently released at acidic pH's that are known to exist within solid tumors and organelles such as endosomes and lysosomes. ADPs incorporated into nanoparticles down regulated the anti-apoptotic protein, survivin, and cyclin D1 when incubated at low concentrations with breast cancer cell lines. We demonstrate for the first time, for any ART derivative, that ADP NPs can down regulate the oncogenic protein HER2, and its counterpart, HER3 in a HER2+ cell line. We also show that the wild type epidermal growth factor receptor (EGFR or HER1) declines in a triple negative breast cancer (TNBC) cell line in response to ADP NPs. The declines in these proteins are achieved at concentrations of NP109 at or below 1 µM. Furthermore, the new artemisinin derivatives showed improved cell-proliferation inhibition effects compared to known dimer derivatives.

The long history of iron in the Universe and in health and disease

BACKGROUND

Not long after the Big Bang, iron began to play a central role in the Universe and soon became mired in the tangle of biochemistry that is the prima essentia of life. Since life's addiction to iron transcends the oxygenation of the Earth's atmosphere, living things must be protected from the potentially dangerous mix of iron and oxygen. The human being possesses grams of this potentially toxic transition metal, which is shuttling through his oxygen-rich humor. Since long before the birth of modern medicine, the blood-vibrant red from a massive abundance of hemoglobin iron-has been a focus for health experts.

SCOPE OF REVIEW

We describe the current understanding of iron metabolism, highlight the many important discoveries that accreted this knowledge, and describe the perils of dysfunctional iron handling.

GENERAL SIGNIFICANCE

Isaac Newton famously penned, "If I have seen further than others, it is by standing upon the shoulders of giants". We hope that this review will inspire future scientists to develop intellectual pursuits by understanding the research and ideas from many remarkable thinkers of the past.

MAJOR CONCLUSIONS

The history of iron research is a long, rich story with early beginnings, and is far from being finished. This article is part of a Special Issue entitled Transferrins: Molecular mechanisms of iron transport and disorders.

Iron chelating agents with clinical potential

Iron is a critically important metal for a wide variety of cellular events. The element holds this central position by virtue of its facile redox chemistry and the high affinity of both redox states (iron II and iron III) for oxygen. These same properties also render iron toxic when levels exceed the normal binding capacity of the cell. As a result of this potential toxicity, selective iron chelators are finding an important role in the treatment of iron overload associated with many forms of thalassaemia. In addition, they appear to have potential in treating situations where a local increase in iron concentration causes an unfavourable pathology, for instance, in reperfused tissue (heart disease and stroke) and in Parkinsonian brain. There is also evidence that iron chelators may minimise the toxicity of paraquat and the side effects of bleomycin and doxorubicin.

Non-haem iron enzymes can also be inhibited by iron chelators and consequently such enzymes as ribonucleotide reductase and lipoxygenase can be selectively inhibited. Such inhibitory action is being investigated for the treatment of malaria, neoplastic disease, psoriasis and asthma.

Recent developments in these areas are discussed in the present overview.

Antitumor activity of artemisinin and its derivatives: from a well-known antimalarial agent to a potential anticancer drug

Improvement of quality of life and survival of cancer patients will be greatly enhanced by the development of highly effective drugs to selectively kill malignant cells. Artemisinin and its analogs are naturally occurring antimalarials which have shown potent anticancer activity. In primary cancer cultures and cell lines, their antitumor actions were by inhibiting cancer proliferation, metastasis, and angiogenesis. In xenograft models, exposure to artemisinins substantially reduces tumor volume and progression. However, the rationale for the use of artemisinins in anticancer therapy must be addressed by a greater understanding of the underlying mechanisms involved in their cytotoxic effects. The primary targets for artemisinin and the chemical base for its preferential effects on heterologous tumor cells need yet to be elucidated. The aim of this paper is to provide an overview of the recent advances and new development of this class of drugs as potential anticancer agents.

Identification of the Schistosoma mansoni molecular target for the antimalarial drug artemether

Plasmodium falciparum and Schistosoma mansonii are the parasites responsible for most of the malaria and schistosomiasis cases in the world. Notwithstanding their many differences, the two agents have striking similarities in that they both are blood feeders and are targets of an overlapping set of drugs, including the well-known artemether molecule. Here we explore the possibility of using the known information about the mode of action of artemether in Plasmodium to identify the molecular target of the drug in Schistosoma and provide evidence that artemether binds to SmSERCA, a putative Ca²⁺-ATPase of Schistosoma . We also predict the putative binding mode of the molecule for both its Plasmodium and Schistosoma targets. Our analysis of the mode of binding of artemether to Ca²⁺-ATPases also provides an explanation for the apparent paradox that, although the molecule has no side effect in humans, it has been shown to possess antitumoral activity.

Biological activity of dihydroartemisinin in canine osteosarcoma cell lines

OBJECTIVE

To evaluate the biological activity of dihydroartemisinin on canine osteosarcoma cell lines in vitro.

SAMPLE POPULATION

4 canine osteosarcoma cell lines.

PROCEDURES

Cell viability assays were performed on canine osteosarcoma cell lines OSCA2, OSCA16, OSCA50, and D17 after 24, 48, and 72 hours of treatment with dihydroartemisinin at concentrations of 0.1 to 100 microM. Apoptosis was assessed by use of an ELISA for free nuclosomal DNA fragmentation and by western blot analysis for cleavage of caspase 3. Cell cycle analysis was performed by use of staining with propidium iodide and flow cytometry. Detection of reactive oxygen species (ROS) was conducted in the D17 cell line by use of 6-carboxy-2',7'-dihydrofluorescein diacetate and flow cytometry.

RESULTS

The concentration of dihydroartemisinin required for 50% inhibition of cell viability (IC50) was achieved in all 4 canine osteosarcoma cell lines and ranged from 8.7 to 43.6 microM. Induction of apoptosis was evident as an increase in nucleosomal DNA fragmentation, cleavage of caspase 3, and an increase in the population in the sub G0/G1 phase of the cell cycle detected by flow cytometry. Exposure to dihydroartemisinin also resulted in a decrease in the G0/G1 population. Iron-dependent generation of ROS was detected in dihydroartemisinin-treated D17 cells; ROS generation increased in a dose-dependent manner.

CONCLUSIONS AND CLINICAL RELEVANCE

Incubation with dihydroartemisinin resulted in biological activity against canine osteosarcoma cell lines, which included induction of apoptosis and arrest of the cell cycle. Clinical trials of dihydroartemisinin in dogs with osteosarcoma should be conducted.

Dihydroartemisinin induces apoptosis in human leukemia cells HL60 via downregulation of transferrin receptor expression

Dihydroartemisinin (DHA), a water-soluble active metabolite of artemisinin derivatives, is the safest and most effective antimalarial analog of artemisinin. In the present investigation, we assessed the apoptotic effect of DHA on leukemia HL60 cells and its regulation of transferrin receptor (TfR). Cell growth inhibition was assessed by Trypan blue exclusive staining; the expression of caspase-3, Bcl-2, and Bax in HL60 cells was evaluated by Western blotting; DHA-induced apoptosis was determined by AO/EB double staining, DNA fragmentation assay, and flow cytometric analysis; the expression of TfR in HL60 cells was examined by real-time PCR assays, Western blotting, and flow cytometric analysis. DHA could specifically reduce the mRNA and protein expression of TfR in HL60 cells, and the flow cytometric analysis presented the unity tendency that the TfR content decreased progressively in a dose-dependent manner. Consequently, DHA exhibited high anticancer activity in HL60 cells; MTT assay and growth inhibition assay showed that DHA could specifically inhibit the growth of HL60 cells in a dose-dependent (0.25-8 micromol/l) and time-dependent (12-72 h) manner. DHA-induced DNA fragmentation also induced the activation of caspase-3 and influenced the expression of Bcl-2 and Bax. Taken together, these data from our study show that DHA can induce HL60 cell apoptosis via the effect of downregulation TfR expression resulting in an induction of apoptosis through the mitochondrial pathway, and it might be a potential antileukemia strategy for leukemia therapy.

Dihydroartemisinin induces apoptosis and sensitizes human ovarian cancer cells to carboplatin therapy

The present study was designed to determine the effects of artemisinin (ARS) and its derivatives on human ovarian cancer cells, to evaluate their potential as novel chemotherapeutic agents used alone or in combination with a conventional cancer chemotherapeutic agent, and to investigate their underlying mechanisms of action. Human ovarian cancer cells (A2780 and OVCAR-3), and immortalized non-tumourigenic human ovarian surface epithelial cells (IOSE144), were exposed to four ARS compounds for cytotoxicity testing. The in vitro and in vivo antitumour effects and possible underlying mechanisms of action of dihydroartemisinin (DHA), the most effective compound, were further determined in ovarian cancer cells. ARS compounds exerted potent cytotoxicity to human ovarian carcinoma cells, with minimal effects on non-tumourigenic ovarian surface epithelial (OSE) cells. DHA inhibited ovarian cancer cell growth when administered alone or in combination with carboplatin, presumably through the death receptor- and, mitochondrion-mediated caspase-dependent apoptotic pathway. These effects were also observed in in vivo ovarian A2780 and OVCAR-3 xenograft tumour models. In conclusion, ARS derivatives, particularly DHA, exhibit significant anticancer activity against ovarian cancer cells in vitro and in vivo, with minimal toxicity to non-tumourigenic human OSE cells, indicating that they may be promising therapeutic agents for ovarian cancer, either used alone or in combination with conventional chemotherapy.

Transferrin receptor in proliferation of T lymphocytes in infants with iron deficiency

The aim of this study was to contribute to clarify the mechanism of cellular immune insufficiency occurring during iron deficiency. We studied the expression of the transferrin receptor (TfR) which is called as CD71, on the surface of T lymphocytes in infants with iron deficiency (with and without anemia). A total of 33 infants, aged between 7 and 26 months were included in this study. These subjects were divided into three groups: (i) latent iron deficiency (LID) (group 1), (ii) iron deficiency anemia (IDA) (group 2), and (iii) healthy infants (group 3). Both CD3 levels and CD71 expression of T lymphocytes were analysed by flow cytometry before and after phytohaemagglutinin (PHA) stimulation. The percentage of CD3(+) lymphocytes in infants with IDA was lower than that in controls after PHA stimulation (mean +/- SD, 48.6 +/-10.5% vs. 70.7 +/-7.8%, P < 0.001). The TfR expression of T lymphocytes (CD3 + CD71%) increased in all three groups after PHA stimulation (P < 0.001). No significant difference was seen among the three groups with respect to CD3 + CD71%. Although there was a reduction in the proliferative capacity of T lymphocytes in infants with IDA, their ability to express transferrin receptor on T-lymphocyte cell surface was normal.

Targeted treatment of cancer with artemisinin and artemisinin-tagged iron-carrying compounds

Artemisinin is a chemical compound that reacts with iron to form free radicals which can kill cells. Cancer cells require and uptake a large amount of iron to proliferate. They are more susceptible to the cytotoxic effect of artemisinin than normal cells. Cancer cells express a large concentration of cell surface transferrin receptors that facilitate uptake of the plasma iron-carrying protein transferrin via endocytosis. By covalently tagging artemisinin to transferrin, artemisinin could be selectively picked up and concentrated by cancer cells. Futhermore, both artemisinin and iron would be transported into the cell in one package. Once an artemisinin-tagged transferrin molecule is endocytosed, iron is released and reacts with artemisinin moieties tagged to transferrin. Formation of free radicals kills the cancer cell. The authors have found that artemisinin-tagged transferrin is highly selective and potent in killing cancer cells. Thus, artemisinin and artemisinin-tagged iron-carrying compounds could be developed into powerful anticancer drugs.

Oral artemisinin prevents and delays the development of 7,12-dimethylbenz[a]anthracene (DMBA)-induced breast cancer in the rat

Artemisinin, a compound isolated from the sweet wormwood Artemisia annua L., has previously been shown to have selective toxicity towards cancer cells in vitro. In the present experiment, we studied the potential of artemisinin to prevent breast cancer development in rats treated with a single oral dose (50mg/kg) of 7,12-dimethylbenz[a]anthracene (DMBA), known to induce multiple breast tumors. Starting from the day immediately after DMBA treatment, one group of rats was provided with a powdered rat-chow containing 0.02% artemisinin, whereas a control group was provided with plain powdered food. For 40 weeks, both groups of rats were monitored for breast tumors. Oral artemisinin significantly delayed (P<.002) and in some animals prevented (57% of artemisinin-fed versus 96% of the controls developed tumors, P<.01) breast cancer development in the monitoring period. In addition, breast tumors in artemisinin-fed rats were significantly fewer (P<.002) and smaller in size (P<.05) when compared with controls. Since artemisinin is a relatively safe compound that causes no known side effects even at high oral doses, the present data indicate that artemisinin may be a potent cancer-chemoprevention agent.

Transferrin as a muscle trophic factor

Muscle cells grow by proliferation and protein accumulation. During the initial stages of development the participation of nerves is not always required. Myoblasts and satellite cells proliferate, fusing to form myotubes which further differentiate to muscle fibers. Myotubes and muscle fibers grow by protein accumulation and fusion with other myogenic cells. Muscle fibers finally reach a quasi-steady state which is then maintained for a long period. The mechanism of maintenance is not well understood. However, it is clear that protein metabolism plays a paramount role. The role played by satellite cells in the maintenance of muscle fibers is not known. Growth and maintenance of muscle cells are under the influence of various tissues and substances. Among them are Tf and the motor nerve, the former being the main object of this review and essential for both DNA and protein synthesis. Two sources of Tf have been proposed, i.e., the motor nerve and the tissue fluid. The first proposal is that the nervous trophic influence on muscle cells is mediated by Tf which is released from the nerve terminals. In this model, the sole source of Tf which is donated to muscle cells should be the nerve, and Tf should not be provided for muscle fiber at sites other than the synaptic region; otherwise, denervation atrophy would not occur, since Tf provided from TfR located at another site would cancel the effect of denervation. The second proposal is that Tf is provided from tissue fluid. This implies that an adequate amount of Tf is transferred from serum to tissue fluid; in this case TfR may be distributed over the entire surface of the cells. The trophic effects of the motor neuron have been studied in vivo, but its effects of myoblast proliferation have not been determined. There are few experiments on its effects on myotubes. Most work has been made on muscle fibers, where innervation is absolutely required for their maintenance. Without it, muscle fibers atrophy, although they do not degenerate. In contrast, almost all the work on Tf has been performed in vitro. Its effects on myoblast proliferation and myotube growth and maintenance have been established; myotubes degenerate following Tf removal. But its effects on mature muscle fibers in vivo are not well understood. Muscle fibers possess TfR all over on their cell surface and contain a variety of Fe-binding proteins, such as myoglobin. It is entirely plausible that muscle fibers require an amount of Tf, and that this is provided by TfR scattered on the cell surface.(ABSTRACT TRUNCATED AT 400 WORDS)

House keeping genes and gene expression analysis in transplant recipients: a note of caution

BACKGROUND

House keeping genes are often used as a means of standardising results obtained in gene expression investigations. This study was performed to investigate whether beta-actin, beta2-microglobulin (two genes frequently quoted as house keeping genes) and/or transferrin receptor would be suitable house keeping genes for use in gene expression analysis of renal transplant recipients.

METHODS

Sequential expression of all three genes was measured in the peripheral blood mononuclear cells of 13 living donors and 45 renal transplant recipients, pre-operatively and then daily for up to 2 weeks. Fifteen of the recipients experienced an episode of biopsy proven acute rejection. Gene expression measurement was performed using quantitative real time 'TaqMan' PCR technology.

RESULTS

Gene expression of all three genes was unchanged in the living donor cohort. However, in the transplant recipients there were significant increases in expression following transplantation in the non-rejectors, and preceding the diagnosis of acute rejection. In the latter group, levels returned to pre-transplant values after the commencement of anti-rejection therapy.

CONCLUSIONS

Beta-actin, beta2-microglobulin and transferrin receptor gene expression, although not influenced by surgery, is influenced by transplantation, acute rejection and anti-rejection therapy making these genes unsuitable as house keeping genes following renal transplantation. These findings may cast doubt on the results of some studies that used these genes for the purposes of standardisation when looking at cDNA measurement. We suggest that any group wishing to use a house keeping gene ensure that its expression is independent of study parameters prior to the start of the study.

Serum-derived protein S binds to phosphatidylserine and stimulates the phagocytosis of apoptotic cells

Rapid phagocytosis of apoptotic cells is thought to limit the development of inflammation and autoimmune disease. Serum enhances macrophage phagocytosis of apoptotic cells. Here we identified protein S as the factor responsible for serum-stimulated phagocytosis of apoptotic cells. Protein S is best known for its anti-thrombotic activity, serving as a cofactor for protein C. Purified protein S was equivalent to serum in its ability to stimulate macrophage phagocytosis of apoptotic lymphoma cells, and immunodepletion of protein S eliminated the prophagocytic activity of serum. Protein S acted by binding to phosphatidylserine expressed on the apoptotic cell surface. Protein S is thus a multifunctional protein that can facilitate clearance of early apoptotic cells in addition to regulating blood coagulation.

The roles of iron in health and disease

Iron is vital for almost all living organisms by participating in a wide variety of metabolic processes, including oxygen transport, DNA synthesis, and electron transport. However, iron concentrations in body tissues must be tightly regulated because excessive iron leads to tissue damage, as a result of formation of free radicals. Disorders of iron metabolism are among the most common diseases of humans and encompass a broad spectrum of diseases with diverse clinical manifestations, ranging from anemia to iron overload and, possibly, to neurodegenerative diseases. The molecular understanding of iron regulation in the body is critical in identifying the underlying causes for each disease and in providing proper diagnosis and treatments. Recent advances in genetics, molecular biology and biochemistry of iron metabolism have assisted in elucidating the molecular mechanisms of iron homeostasis. The coordinate control of iron uptake and storage is tightly regulated by the feedback system of iron responsive element-containing gene products and iron regulatory proteins that modulate the expression levels of the genes involved in iron metabolism. Recent identification and characterization of the hemochromatosis protein HFE, the iron importer Nramp2, the iron exporter ferroportin1, and the second transferrin-binding and -transport protein transferrin receptor 2, have demonstrated their important roles in maintaining body's iron homeostasis. Functional studies of these gene products have expanded our knowledge at the molecular level about the pathways of iron metabolism and have provided valuable insight into the defects of iron metabolism disorders. In addition, a variety of animal models have implemented the identification of many genetic defects that lead to abnormal iron homeostasis and have provided crucial clinical information about the pathophysiology of iron disorders. In this review, we discuss the latest progress in studies of iron metabolism and our current understanding of the molecular mechanisms of iron absorption, transport, utilization, and storage. Finally, we will discuss the clinical presentations of iron metabolism disorders, including secondary iron disorders that are either associated with or the result of abnormal iron accumulation.

NMR studies on novel antitumor drug candidates, deoxoartemisinin and carboxypropyldeoxoartemisinin

Artemisinin and its derivatives, which have been known as antimalarial drugs, have also demonstrated their cytotoxicity against tumor cells. It has been proposed that antitumor activity depends on the lipophilicity of functional group on artemisinin derivatives. Solution structures of two artemisinin derivatives as antitumor drug candidates, deoxoartemisinin and carboxypropyldeoxoartemisinin, were determined by NMR spectroscopy to elucidate structure-activity relationship. According to biological assay, antitumor efficiencies are not dependent upon lipophilicity. Instead, these compounds demonstrated their distinctive structural features of boat/chair conformation and capability to interact with receptors, as they have different efficiencies on antitumor activity. Especially, carboxypropyl moiety or carbonyl moiety in artemisinin derivatives influences the conformation and stability of ring structure. Although the detailed mechanism of antitumor activity by artemisinin derivatives has not been addressed, we suggest that antitumor activity is not determined only with lipophilicity and that artemisinin derivatives have specific target proteins in each type of cancer.

Enhanced allograft survival via simultaneous blockade of transferrin receptor and interleukin-2 receptor

BACKGROUND

Transferrin receptor (TfR) expression follows the induction of interleukin 2 receptor (IL-2R) expression in a sequence that is necessary to initiate cell proliferation in quiescent T lymphocytes. Therefore, we tested the hypothesis that simultaneous blockade of TfR and IL-2R would be more effective in prolonging allograft survival and suppressing T-cell responses to alloantigen than single receptor blockade by modifying T-cell effectors to alloantigen.

METHODS

Neonatal C57BL/6 hearts were transplanted to CBA/J recipients in a heterotopic, nonvascularized cardiac allograft model. Anti-TfR and/or anti-IL-2R or isotype-matched control monoclonal antibodies (mAbs) were administered at 100 microg intravenously on days 0 and 1 of transplantation.

RESULTS

Anti-TfR mAb (25.7+/-0.9 days) significantly (P<0.01) prolonged cardiac allograft survival compared with anti-IL-2R mAb (12.5+/-0.9 days) or the isotype control (15.7+/-1.2 days, P<0.01, Wilcoxon rank-sum). Anti-TfR plus anti-IL-2R mAbs significantly (P<0.01) prolonged cardiac allograft survival to 50.7+/-2.0 days compared with the isotype control or either agent alone. These agents in combination down-regulated the intragraft T helper (Th)-1 cytokines, IL-2, interferon-gamma, and IL-15, while up-regulating the Th2 cytokine, IL-4, and completely abrogating the antigen-presenting cell IL-12p40 mRNA expression.

CONCLUSIONS

Anti-TfR and anti-IL-2R mAbs are potent immunosuppressants. Combined blockade of TfR and IL-2R at the time of antigen presentation seems to be the most effective by shifting the intragraft Th cytokine paradigm.

The transferrin receptor: role in health and disease

The transferrin receptor is a membrane glycoprotein whose only clearly defined function is to mediate cellular uptake of iron from a plasma glycoprotein, transferrin. Iron uptake from transferrin involves the binding of transferrin to the transferrin receptor, internalization of transferrin within an endocytic vesicle by receptor-mediated endocytosis and the release of iron from the protein by a decrease in endosomal pH. With the exception of highly differentiated cells, transferrin receptors are probably expressed on all cells but their levels vary greatly. Transferrin receptors are highly expressed on immature erythroid cells, placental tissue, and rapidly dividing cells, both normal and malignant. In proliferating nonerythroid cells the expression of transferrin receptors is negatively regulated post-transcriptionally by intracellular iron through iron responsive elements (IREs) in the 3' untranslated region of transferrin receptor mRNA. IREs are recognized by specific cytoplasmic proteins (IRPs; iron regulatory proteins) that, in the absence of iron in the labile pool, bind to the IREs of transferrin receptor mRNA, preventing its degradation. On the other hand, the expansion of the labile iron pool leads to a rapid degradation of transferrin receptor mRNA that is not protected since IRPs are not bound to it. However, some cells and tissues with specific requirements for iron probably evolved mechanisms that can override the IRE/IRP-dependent control of transferrin receptor expression. Erythroid cells, which are the most avid consumers of iron in the organism, use a transcriptional mechanism to maintain very high transferrin receptor levels. Transcriptional regulation is also involved in the receptor expression during T and B lymphocyte activation. Macrophages are another example of a cell type that shows 'unorthodox' responses in terms of IRE/IRP paradigm since in these cells elevated iron levels increase (rather than decrease) transferrin receptor mRNA and protein levels. Erythroid cells contain the highest mass of the total organismal transferrin receptors which are released from reticulocytes during their maturation to erythrocytes. Hence, plasma contains small amounts of transferrin receptors which represent a soluble fragment of the extracellular receptor domain. Measurements of serum transferrin receptor concentrations are clinically useful since their levels correlate with the total mass of immature erythroid cells.

Endosomal/lysosomal retention and degradation of major histocompatibility complex class I molecules is induced by myxoma virus

The highly immunosuppressive leporipoxvirus myxoma, previously was shown to promote the loss of cell surface class I major histocompatibility complex (MHC I) molecules. Here, we show that myxoma virus induces the loss of both cell surface and intracellular post-Golgi, beta(2)-microglobulin-associated MHC I. Myxoma-induced loss of these MHC I molecules is abrogated by vacuolar ATPase inhibitors, NH(4)Cl, and leupeptin. Furthermore, immunofluorescence microscopic studies reveal that in myxoma-infected cells, beta(2)-microglobulin-associated MHC I accumulates in Lamp-1(+) vesicular structures, suggesting that myxoma virus targets MHC I for degradation in late endosomes and/or lysosomes. These events are regulated by early gene product or products because they occur unabated in cells infected with myxoma virus in the presence of cytosine arabinoside, an inhibitor of DNA synthesis. Studies with baby green monkey kidney cells transfected with wild-type and tail-less forms of a mouse MHC I molecule, H-2L(d), indicate that the MHC I cytoplasmic tail is required for myxoma-induced localization in Lamp-1(+) organelles. Myxoma-induced endocytosis and degradation of MHC I may provide the virus with a means of dispensing with cell surface MHC I molecules that were loaded with peptides derived from viral proteins synthesized early in infection.

Differential effects of transferrin receptor blockade on the cellular mechanisms involved in graft rejection

Since transferrin receptor (TfR) appears on activated T cells following the interaction of the antigen-major histocompatibility complex (MHC) with the T cell receptor (TCR) and the appearance of interleukin (IL)-2R, we therefore hypothesize that in vivo blockade of TfR prolongs allograft survival by altering the cellular mechanisms involved in graft rejection. Previous results in our laboratory have demonstrated that anti-TfR monoclonal antibody (mAb) at 100 microg on days 0 and 1 of transplantation significantly prolonged allograft survival to 25.7 +/- 0.9 days in a murine heterotopic, nonvascularized cardiac allograft model. In the current studies, administration of anti-TfR mAb at the time of maximal TfR expression, on days 2 and 3 post-transplantation, failed to prolong allograft survival (13.0 +/- 0.0 days) compared to the isotype controls (10.5 +/- 0.5 and 10.7 +/- 0.4 days) (p < 0.01, Wilcoxon rank sum). A 4-day course of anti-TfR mAb significantly prolonged allograft survival compared to the isotype controls, but was no more effective than a 2-day course of the mAb. Anti-TfR mAb suppressed the mixed lymphocyte response to donor-specific and third-party alloantigen by 78.7% (p < 0.05) and 80.8% (p < 0.05), respectively, while stimulating the CTL response to donor-specific (16.3%, p < 0.05) and third party (49.3%, p < 0.01) alloantigen. Anti-TfR mAb suppressed IL-15 and increased IL-4 intragraft mRNA expression when compared to the isotype controls. Examination of cell surface receptors important during T cell activation revealed alterations in expression following anti-TfR mAb treatment. Anti-TfR mAb is an effective immunosuppressant prolonging allograft survival by altering cell-mediated immune responses and the intragraft cytokine micro-environment.

Transferrin receptor on peripheral blood lymphocytes in iron deficiency anaemia

The effect of iron deficiency anaemia (IDA) on CD71 expression by peripheral blood lymphocytes was studied in 43 children with iron deficiency anaemia. 18 healthy age-matched children were selected as the control group. 11 children with beta-thalassaemia trait were also studied. Lymphocytes bearing CD71 were enumerated by flow cytometric analysis of peripheral blood. At diagnosis, CD71+ peripheral lymphocytes (mean+/-SE) was 5.90+/-0-76% in patients with IDA and 12.60+/-0.98% in healthy controls (P=0.000). In beta-thalassaemia trait patients the peripheral blood CD71+ lymphocytes were 7.80+/-1.20%. In IDA patients there was a statistically significant correlation between the levels of CD71+ peripheral lymphocytes and haemoglobin value (P = 0.000). In 19 patients studied at days 0 and 30 of oral iron therapy, the number of peripheral blood CD71+ lymphocytes was shown to be increased from 5.90+/-0.76% to 12.11+/-1.21%. In severe IDA presence of a limited number of CD71+ peripheral blood lymphocytes indicated that severe IDA should be borne in mind when considering conditions responsible for the suppression of lymphocyte proliferation.

mRNA differential display of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine-induced rat mammary gland tumors

The mRNA differential display technique was used to compare mRNAs between normal mammary gland and tumor-derived epithelial cells from female Sprague-Dawley rat mammary gland tumors induced by the heterocyclic amine 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and promoted by a high-fat diet (23.5% corn oil). Two genes, beta-casein and transferrin, were identified as differentially expressed. The expression of these genes was examined across a bank of rat mammary gland tumors derived from animals on a low-fat diet (5% corn oil) or the high-fat diet. Carcinomas had over a 10- and 50-fold lower expression of beta-casein and transferrin, respectively, than normal mammary gland. In addition, carcinomas from animals on the high-fat diet showed on average a 5-fold higher expression of beta-casein and transferrin than carcinomas from animals on the low-fat diet. The results indicate the process of mammary gland tumorigenesis alters the expression of certain genes in the mammary gland, and that the level of dietary fat further modulates the expression of these genes.

Localization of transferrin binding protein in relation to iron, ferritin, and transferrin receptors in the chicken cerebellum

We have demonstrated that transferrin binding protein (TfBP), ferritin, and iron, are specifically localized in Bergmann glia, while the transferrin receptor is confined to Purkinje cells in the chicken cerebellum. The results of this study suggest that Bergmann glia have previously undescribed functions related to iron regulation such as sequestration of iron and the maintenance of iron homeostasis in the cerebellum.

Anti-transferrin receptor monoclonal antibody: a novel immunosuppressant

BACKGROUND

Transferrin receptor is a widely distributed cell surface receptor present on most proliferating and highly specialized quiescent cells. Expression of transferrin receptor on the surface of immune cells is up-regulated during T-cell activation after the interaction of the antigen-MHC with the T cell receptor. The role of transferrin receptor in T-cell activation has not been well-established. Since transferrin receptor is physically associated with the CD3 zeta-chain, blockade of transferrin receptor has the potential to interfere with the T-cell signals important in transplant rejection.

METHODS

Anti-transferrin receptor monoclonal antibody (mAb) was administered in vivo and in vitro to determine whether this agent was effective in prolonging allograft survival and altering cell-mediated immunity.

RESULTS

Using donor C57BL/6J (H2b) hearts transplanted to CBA/J (H2k) recipients, anti-transferrin receptor mAb at the time of transplantation prolonged cardiac allograft mean survival time to 25.7+/-0.9 days compared with untreated (13.3+/-0.6 days, P < 0.05) or isotype-matched (10.7+/-0.4 days, P < 0.05) controls. Anti-transferrin receptor mAb administered in vivo failed to suppress the subsequent allogeneic responses. However, when added to culture, anti-transferrin receptor mAb suppressed the allogeneic cytotoxic T lymphocyte response by 79-100% but not the mixed lymphocyte response.

CONCLUSIONS

These studies are the first to suggest that transferrin receptor is a potential therapeutic target for clinical transplantation. Future studies will determine the most efficacious dose and time for maximal immunosuppression and the mechanisms responsible for the immunosuppression exhibited by antitransferrin receptor mAb.

The inability of cells to grow in low iron correlates with increasing activity of their iron regulatory protein (IRP)

We studied the factors that determine the differing growth requirements of low-iron-tolerant (LIT) versus high-iron-dependent (HID) cells for extracellular nontransferrin iron. The growth of LIT cells HeLa and THP-1, when transferred from transferrin (5 micrograms/ml) medium into low-iron (5 microM ferric citrate) medium, was not significantly affected while HID cells Jiyoye and K562 showed nearly no growth. HeLa and THP-1 cells, as well as Jiyoye and K562 cells, do not produce transferrin in sufficient amounts to support their growth in low-iron medium. Surprisingly, similar rates of iron uptake in low-iron medium (0.033 and 0.032 nmol Fe/min and 10(6) cells) were found for LIT cells HeLa and HID cells K562. Furthermore, the intracellular iron level (4.64 nmol/10(6) cells) of HeLa cells grown in low-iron medium was much higher than iron levels (0.15 or 0.20 nmol/10(6) cells) of HeLa or K562 cells grown in transferrin medium. We demonstrated that the activity (ratio activated/total) of the iron regulatory protein (IRP) in HID cells Jiyoye and K562 increased more than twofold (from 0.32 to 0.79 and from 0.47 to 1.12, respectively) within 48 h after their transfer into low-iron medium. In the case of LIT cells HeLa and THP-1, IRP activity stayed at similar or slightly decreased levels (0.86-0.73 and 0.58-0.55, respectively). Addition of iron chelator deferoxamine (50 microM, i.e., about half-maximal growth-inhibitory dose) resulted in significantly increased activity of IRP also in HeLa and THP-1 cells. We hypothesize that the relatively higher bioavailability of nontransferrin iron in LIT cells, over that in HID cells, determines the differing responses observed under low-iron conditions.

Immunohistochemical demonstration of transferrin and transferrin receptor in mammalian integument

The present study demonstrates the distribution of transferrin and the transferrin receptor in the integument of eleven wild mammalian species using immunohistochemical methods. Both substances were regularly found in or near the peripheral cells of the sebaceous glands, especially of dense-haired animals. The transferrin receptor was also detectable in the epidermis, the secretory portion of tubular apocrine glands, and the outer epithelium of primary hair follicles. Transferrin as well as the transferrin receptor reacted strongly in macrophages of the papillary dermis only in the common seal. The results obtained are discussed with regard to possible biological functions in the skin of the substances demonstrated.

The molecular mechanisms of the metabolism and transport of iron in normal and neoplastic cells

Iron uptake by mammalian cells is mediated by the binding of serum Tf to the TfR. Transferrin is then internalized within an endocytotic vesicle by receptor-mediated endocytosis and the Fe released from the protein by a decrease in endosomal pH. Apart from this process, several cell types also have other efficient mechanisms of Fe uptake from Tf that includes a process consistent with non-specific adsorptive pinocytosis and a mechanism that is stimulated by small-Mr Fe complexes. This latter mechanism appears to be initiated by hydroxyl radicals generated by the Fe complexes, and may play a role in Fe overload disease where a significant amount of serum non-Tf-bound Fe exists. Apart from Tf-bound Fe uptake, mammalian cells also possess a number of mechanisms that can transport Fe from small-Mr Fe complexes into the cell. In fact, recent studies have demonstrated that the membrane-bound Tf homologue, MTf, can bind and internalize Fe from 59Fe-citrate. However, the significance of this Fe uptake process and its pathophysiological relevance remain uncertain. Iron derived from Tf or small-Mr complexes is probably transported into mammalian cells in the Fe(II) state. Once Fe passes through the membrane, it then becomes part of the poorly characterized intracellular labile Fe pool. Iron in the labile Fe pool that is not used for immediate requirements is stored within the Fe-storage protein, ferritin. Cellular Fe uptake and storage are coordinately regulated through a feedback control mechanism mediated at the post-transcriptional level by cytoplasmic factors known as IRP1 and IRP2. These proteins bind to stem-loop structures known as IREs on the 3 UTR of the TfR mRNA and 5 UTR of ferritin and erythroid delta-aminolevulinic acid synthase mRNAs. Interestingly, recent work has suggested that the short-lived messenger molecule, NO (or its by-product, peroxynitrite), can affect cellular Fe metabolism via its interaction with IRP1. Moreover, NO can decrease Fe uptake from Tf by a mechanism separate to its effects on IRP1, and NO may also be responsible for activated macrophage-mediated Fe release from target cells. On the other hand, the expression of inducible NOS which produces NO, can be stimulated by Fe chelators and decreased by the addition of Fe salts, suggesting that Fe is involved in the control of NOS expression.

Purification of a factor from CSF in patient after SAH which induces the cytosolic free calcium elevation in vascular smooth muscle cells

Cerebrospinal fluid from patients with aneurysmal subarachnoid hemorrhage induces the elevation of cytosolic free calcium [Ca2+]i in cultured vascular smooth muscle cells. We have purified a [Ca2+]i elevating factor from cerebrospinal fluid of a patient with subarachnoid hemorrhage due to aneurysm rupture. The calcium-elevating protein factor was purified to homogeneity by ammonium sulfate precipitation and a combination of Mono Q, Superose 12, and Mono S columns using liquid chromatography. Fifteen microgram of the purified protein was obtained from 340 mg of cerebrospinal fluid proteins and the molecular mass of the protein was estimated to be 81 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis. It was also shown that the purified protein was cross-reactive with anti-human transferrin antibody. These results suggested that transferrin may be involved with the cerebral vasospasm after subarachnoid hemorrhage.

Autocrine growth induced by transferrin-like substance in bladder carcinoma cells

Ample evidence confirms that certain cancer cells have the capacity to produce multiple peptides as growth factors and that expression of their receptor may act in tumour cell paracrine and/or autocrine loop mechanisms, either by extracellular release of the growth factor or by the tumour itself. To study the possibility of an autocrine growth mechanism in bladder carcinoma, we investigated the ability of various bladder carcinoma cell lines to proliferate in serum-free medium. A rat bladder carcinoma cell line, BC47, demonstrated exponential and density-dependent growth in serum-free medium. Furthermore, conditioned medium from BC47 cells induced growth-stimulating activity for BC47 cells themselves. Purification and further characterization of this activity was performed by chromatographic methods, SDS-PAGE and N-terminal amino acid analysis. Finally, we have identified that a transferrin-like 70-kDa protein is found to be the main growth-promoting factor in this conditioned medium. In addition, specific antibodies against transferrin and the transferrin-receptor inhibit the in vitro growth of this cell line. Our data suggest that this transferrin-like factor possibly acts as an autocrine growth factor for cancer cells.

Two-dimensional electrophoretic studies on down-regulated intracellular transferrin in human fibroblasts immortalized by treatment with either 4-nitroquinoline 1-oxide or 60Co gamma rays

The immortalization of human cells is an important early step of carcinogenesis. To investigate the mechanisms of immortalization, we established three immortalized human fibroblast cell lines by treatment with either 4-nitroquinoline 1-oxide (4NQO) or 60Co gama rays. Using two-dimensional gel electrophoresis (2-D PAGE), we identified proteins which are down-regulated in these immortalization cell lines. Their isoelectric points ranged between 5.5 and 6.3, and their molecular masses were approximately 80 kDa. The proteins were also decreased in another human fibroblast cell line immortalized with simian virus 40 (SV40) and two human cervical cell lines. The proteins were present in a cytoskeletal fraction, reacted with anti-transferrin antibody and some of them were phosphorylated. The proteins were identified as transferrin. Although the 2-D PAGE patterns of our proteins and serum transferrin of different origin were distinct from each other, their isoelectric points and molecular weights were similar. We implicate some functions of intracellular transferrin, other than an iron transporter, in immortalization of human cells and discuss a new aspect of transferrin metabolism in the cells.

Growth of human tumor cell lines in transferrin-free, low-iron medium

Iron is essential for tumor cell growth. Previous studies have demonstrated that apart from transferrin-bound iron uptake, mammalian cells also possess a transport system capable of efficiently obtaining iron from small molecular weight iron chelates (Sturrock et al., 1990). In the present study, we have examined the ability of tumor cells to grow in the presence of low molecular weight iron chelates of citrate. In chemically defined serum-free medium, most human tumor cell lines required either transferrin (5 micrograms/ml) or a higher concentration of ferric citrate (500 microM) as an iron source. However, we have also found that from 13 human cell lines tested, 4 were capable of long-term growth in transferrin-free medium with a substantially lower concentration of ferric citrate (5 microM). When grown in medium containing transferrin, both regular and low-iron dependent cell lines use transferrin-bound iron. Growth of both cell types in transferrin medium was inhibited to a certain degree by monoclonal antibody 42/6, which specifically blocks the binding of transferrin to the transferrin receptor. On the contrary, growth of low-iron dependent cell lines in transferrin-free, low-iron medium (5 microM ferric citrate) could not be inhibited by monoclonal antibody 42/6. Furthermore, no autocrine production of transferrin was observed. Low-iron dependent cell lines still remain sensitive to iron depletion as the iron(III) chelator, desferrioxamine, inhibited their growth. We conclude that low-iron dependent tumor cells in transferrin-free, low-iron medium may employ a previously unknown mechanism for uptake of non-transferrin-bound iron that allows them to efficiently use low concentrations of ferric citrate as an iron source. The results are discussed in the context of alternative iron uptake mechanisms to the well-characterized receptor-mediated endocytosis process.

Selective cancer cell cytotoxicity from exposure to dihydroartemisinin and holotransferrin

Rapid cell death, as evidenced by a decrease in cell counts, was observed when molt-4-lymphoblastoid cells, a human leukemia cell line, were exposed to holotransferrin (12 microM) and dihydroartemisinin (1-200 microM). Incubation with either compound alone was significantly less effective. Significantly less cell death was observed when normal human lymphocytes were exposed to a combination of these 2 drugs. Probit analysis of dose-response functions shows that the drug combination is approximately 100 times more effective on molt-4 cells than lymphocytes (LD50s for molt-4 and lymphocytes were 2.59 microM and 230 microM, respectively). This drug combination may provide a novel approach for cancer treatment.