Nonsense-mediated mRNA decay factor Upf2 exists in both the nucleoplasm and the cytoplasm

Upf2 protein predominantly localizes to the cytoplasmic fraction, and binds to the exon junction complex (EJC) on spliced mRNA. The present study aimed to determine the cellular site where the interaction between Upf2 and EJC occurs. First, the cell lysate was fractionated into the cytoplasm and nucleoplasm, and western blotting to detect levels of Upf2 protein was performed. Upf2 was clearly detected in the cytoplasm and in the nucleoplasm. Secondly, immunostaining was performed, and the majority of Upf2 was detected in the cytoplasmic perinuclear region; a small quantity of Upf2 was detected in the intranuclear region. RNase treatment of the cells reduced the Upf2 immunostained signal. The immune-purified fractions containing nuclear and cytoplasmic Upf2 also contained one of the EJC core factors, RBM8A. These results implied the existence of Upf2 in the nucleoplasm and the cytoplasm, and it appeared to be involved in the construction of the mRNA complex. In order to verify the construction of Upf2-binding EJC in the nucleoplasm, an in situ proximity ligation assay was performed with anti-Upf2 and anti-RBM8A antibodies. These results demonstrated that their interaction occurred not only in the cytoplasmic region, but also in the intranuclear region. Taken together, these results suggested that Upf2 combines with EJC in both the cytoplasmic and the intranuclear fractions, and that it is involved in mRNA metabolism in human cells.

Associations among Erythroferrone and Biomarkers of Erythropoiesis and Iron Metabolism, and Treatment with Long-Term Erythropoiesis-Stimulating Agents in Patients on Hemodialysis

BACKGROUND

We aimed to identify associations between erythroferrone (ERFE), a regulator of hepcidin 25, and biomarkers of erythropoiesis and iron metabolism. We also aimed to determine the effects of erythropoiesis-stimulating agents (ESA), continuous erythropoietin receptor activator (CERA) and darbepoetin-α (DA) on ERFE production in patients on hemodialysis (HD).

METHODS

Blood samples were obtained from 59 patients before HD sessions on day 0 (baseline). Twenty patients who were injected with either CERA (N = 10) or DA (N = 10) at the end of the dialysis week (day 0), who had ferritin ≥ 100 ng/mL and/or transferrin saturation ≥ 20%, and hemoglobin > 9 g/dL were selected from among the 59 patients. Blood was sampled serially before HD sessions on days 3, 5, 7 from patients on DA and on the same days plus day 14 from those on CERA.

RESULTS

Levels of ERFE correlated inversely with those of hepcidin 25 and ferritin, and positively with those of soluble transferrin receptor. The hepcidin 25: ERFE ratio and hepcidin 25 levels positively correlated with ferritin levels. Levels of ERFE significantly increased from day 3 of treatment with DA and CERA and decreased by days 7 and 14, respectively. Erythropoiesis-stimulating agents concomitantly decreased levels of hepcidin 25 as those of ERFE increased.

CONCLUSION

We identified a novel association between ESA and ERFE in patients on HD. Both DA and CERA increased levels of ERFE that regulated hepcidin 25 and led to iron mobilization from body stores during erythropoiesis.

A Novel Phenotype of a Hereditary Hemochromatosis Type 4 with Ferroportin-1 Mutation, Presenting with Juvenile Cataracts

Hereditary hemochromatosis (HH) is an inherited disorder usually seen in Northern Europeans, which results in iron overload syndrome. A few cases have also been reported in Japan. We herein report a Japanese man presenting with fever, arthritis, liver dysfunction, and hyperferritinemia who was diagnosed with type 4 HH. He was heterozygous for the 1520A>G (His507Arg) mutation in the ferroportin-1 gene (SLC40A1). He had a familial cataract as an infant, but hereditary hyperferritinemia cataract syndrome was excluded. This is the first report of type 4 HH with juvenile cataracts and suggests that there is an association between hyperferritinemia and early cataract formation.

Low Serum Neutrophil Gelatinase-associated Lipocalin Level as a Marker of Malnutrition in Maintenance Hemodialysis Patients

Background

Neutrophil gelatinase-associated lipocalin (NGAL or LCN2) is an iron-transporting factor which possesses various activities such as amelioration of kidney injury and host defense against pathogens. Its circulating concentrations are elevated in acute and chronic kidney diseases and show a positive correlation with poor renal outcome and mortality, but its clinical significance in maintenance hemodialysis (HD) patients remains elusive.

Methods

Serum NGAL levels were determined by enzyme-linked immunosorbent assay in out-patient, Japanese HD subjects. Their correlation to laboratory findings and morbidity (as development of severe infection or serum albumin reduction) was investigated using linear regression analysis and χ² test.

Results

Pre-dialysis serum NGAL levels in HD patients were elevated by 13-fold compared to healthy subjects (n=8, P<0.001). In a cross-sectional study of 139 cases, serum NGAL concentrations were determined independently by % creatinine generation rate (an indicator of muscle mass, standardized coefficient β=0.40, P<0.001), peripheral blood neutrophil count (β=0.38, P<0.001) and anion gap (which likely reflects dietary protein intake, β=0.16, P<0.05). Iron administration to anemic HD patients caused marked elevation of peripheral blood hemoglobin, serum ferritin and iron-regulatory hormone hepcidin-25 levels, but NGAL levels were not affected. In a prospective study of 87 cases, increase in serum albumin levels a year later was positively associated to baseline NGAL levels by univariate analysis (r=0.36, P<0.01). Furthermore, within a year, patients with the lowest NGAL tertile showed significantly increased risk for marked decline in serum albumin levels (≥0.4 g/dl; odds ratio 5.5, 95% confidence interval 1.5–20.3, P<0.05) and tendency of increased occurrence of severe infection requiring admission (odds ratio 3.1, not significant) compared to the middle and highest tertiles.

Conclusion

Low serum NGAL levels appear to be associated with current malnutrition and also its progressive worsening in maintenance HD patients.

Effect of Saikokeishito, a Kampo medicine, on hydrogen peroxide-induced premature senescence of normal human dermal fibroblasts

OBJECTIVE

Saikokeishito (TJ-10) is a Kampo (traditional Japanese herbal) medicine, clinically used for hundreds of years in East Asia. Among its various mechanisms elucidated so far, TJ-10 inhibits the production of transforming growth factor-β1 (TGF-β1) and development of pancreatic fibrosis in vivo. Oxidative damage of normal human dermal fibroblasts (NHDFs) in the corium is a cause of human dermal senescence. Our aim was to determine whether TJ-10 protects NHDFs from premature senescence by hydrogen peroxide (H₂O₂).

METHODS

Premature senescence was induced in NHDFs by 200 μmol/L H₂O₂ for 4 h. Cell viability and the expressions of p53, AMP-activated protein kinase α1 (AMPKα1), AMPKα2, and 14-3-3 protein sigma (14-3-3 σ) were measured in NHDFs treated with TJ-10 for 48 h before exposure to H₂O₂for 4 h.

RESULTS

Cell viability after treatment with 200 μmol/L H₂O₂ for 4 h was similar (about 80%) to after pre-treatment with TJ-10. Ascorbic acid as a control did not protect NHDFs from damage by 200 μmol/L H₂O₂. Treatment with 200 μmol/L H₂O₂tended to up-regulate p53 and to down-regulate SIRT1 and AMPKα1, but had no effect on AMPKα2 and 14-3-3 σ expression. Pretreatment with TJ-10 inhibited H₂O₂-induced up-regulation of p53 and enhanced AMPKα1 expression.

CONCLUSION

It is suggested that Saikokeishito has a protective effect on oxidative stress-induced senescence of NHDFs.

A HAMP promoter bioassay system for identifying chemical compounds that modulate hepcidin expression

Hepcidin is the central regulator of systemic iron homeostasis; dysregulation of hepcidin expression causes various iron metabolic disorders, including hereditary hemochromatosis and anemia of inflammation. To identify molecules that modulate hepcidin expression, we developed a bioassay system for hepcidin gene (HAMP) promoter activity by stable transfection of Hep3B hepatoma cells with an expression plasmid in which EGFP was linked to a 2.5-kb human HAMP promoter. Interleukin 6, bone morphogenetic protein 6 (BMP-6), and oncostatin M, well-characterized stimulators of the HAMP promoter, strongly enhanced the green fluorescence intensity of these cells. Dorsomorphin, heparin, and cobalt chloride, known inhibitors of hepcidin expression, significantly suppressed green fluorescence intensity, and these inhibitory effects were more prominent when the cells were stimulated with BMP-6. Employing this system, we screened 1,280 biologically active small molecules and found several candidate inhibitors of hepcidin expression. Apomorphine, benzamil, etoposide, CGS-15943, kenpaullone, and rutaecarpine (all at 10 μmol/L) significantly inhibited hepcidin mRNA expression by Hep3B cells without affecting cell viability. CGS-15943 was the strongest suppressor of BMP-6-induced hepcidin-25 secretion in these cells. We conclude that our newly developed hepcidin promoter bioassay system is useful for identifying and evaluating compounds that modulate hepcidin expression.

Phosphorylation status of human RNA-binding protein 8A in cells and its inhibitory regulation by Magoh

The RNA-binding protein 8A (RBM8A)-mago-nashi homolog, proliferation-associated (Magoh) complex is a component of the exon junction complex (EJC) required for mRNA metabolism involving nonsense-mediated mRNA decay (NMD). RBM8A is a phosphorylated protein that plays some roles in NMD. However, the detailed status and mechanism of the phosphorylation of RBM8A is not completely understood. Therefore, in this study, we analyzed in detail RBM8A phosphorylation in human cells. Accordingly, analysis of the phosphorylation status of RBM8A protein in whole-cell lysates by using Phos-tag gels revealed that the majority of endogenous RBM8A was phosphorylated throughout the cell-cycle progression. Nuclear and cytoplasmic RBM8A and RBM8A in the EJC were also found to be mostly phosphorylated. We also screened the phosphorylated serine by mutational analysis using Phos-tag gels to reveal modifications of serine residues 166 and 168. A single substitution at position 168 that concomitantly abolished the phosphorylation of serine 166 suggested the priority of kinase reaction between these sites. Furthermore, analysis of the role of the binding protein Magoh in RBM8A phosphorylation revealed its inhibitory effect in vitro and in vivo. Thus, we conclude that almost all synthesized RBM8A proteins are rapidly phosphorylated in cells and that phosphorylation occurs before the complex formation with Magoh.

Regulation of Hepcidin-25 by Short- and Long-Acting rhEPO May Be Dependent on Ferritin and Predict the Response to rhEPO in Hemodialysis Patients

Background/Aims

We examined whether regulation of hepcidin-25 by short- or long-acting recombinant human erythropoietin (rhEPO) is dependent on ferritin and predicts the response to rhEPO in hemodialysis (HD) patients.

Methods

Two studies with rhEPO were performed in 9 HD patients with a 2-year interval. Serum hepcidin-25 was measured at 0-18 h after intravenous epoetin-β (EPO) or methoxy polyethylene glycol-epoetin-β (PEG-EPO) administration and on days 3-7 after PEG-EPO. Hemoglobin (Hb), serum ferritin, transferrin, C-reactive protein (CRP), and interleukin (IL)-6 were analyzed before hepcidin measurement and 6 months after rhEPO. Based on the serum ferritin levels before hepcidin measurement, the patients in the two studies with EPO or PEG-EPO were combined into low (11; serum ferritin of <15.0 ng/ml) and high ferritin groups (7; serum ferritin of ≥15.0 ng/ml). The response of hepcidin-25 to rhEPO and the effect of rhEPO on anemia were compared between the groups.

Results

The serum hepcidin-25 levels rose at 6-9 h and returned to the baseline at 18 h after EPO. They rose at 6-9 h, returned to the baseline at 18 h, and decreased on day 5-7 after PEG-EPO. Serum hepcidin-25 levels were low (<5.0 ng/ml) in the low ferritin group, but rose at 6-9 h after rhEPO in the high ferritin group. Serum transferrin levels were similar, and CRP and IL-6 were normal in both groups. Hb tended to increase in the low ferritin group, but it significantly decreased in the high ferritin group after rhEPO.

Conclusion

Regulation of hepcidin-25 by rhEPO may be dependent on ferritin, affecting the response to rhEPO in HD patients.

Long-term administration and efficacy of oxaliplatin with no neurotoxicity in a patient with rectal cancer: Association between neurotoxicity and the GSTP1 polymorphism

Neurotoxicity is one of the most frequent side-effects of oxaliplatin. Oxaliplatin-induced cumulative and dose-limiting neurotoxicity either results in dose reduction or decreases the patients’ quality of life. However, the symptoms of neurotoxicity often vary among patients. The current study presents the case of a male with rectal cancer, who was administered a cumulative oxaliplatin dose of >5,000 mg/m² without developing neurotoxicity or allergic reactions. Consequently, this patient continued therapy with modified 5-fluorouracil, leucovorin and oxaliplatin treatment for four years, with stabilization of the disease. This case indicates that if oxaliplatin-containing chemotherapy shows efficacy with no toxicity, the long-term administration of oxaliplatin would be effective and tolerable. Previously, the analysis of genomic polymorphisms in drug target genes has been important for explaining interindividual variations in the efficacy and toxicity of anti-cancer drugs. In the present patient, the glutathione S-transferase P1 (GSTP1) gene polymorphism, which is involved in the detoxification of platinum drugs, was analyzed. The genotype of the present case has been revealed as wild type (Ile/Ile) genotype. In addition, the associations between oxaliplatin-induced neurotoxicity and the GSTP1 polymorphism were also assessed. Certain studies have demonstrated that oxaliplatin-induced neurotoxicity occurs more frequently in patients with the Ile/Ile genotype, while others have demonstrated that those patients with the Val/Val or Ile/Val genotypes are more likely to develop neurotoxicity. Therefore, correlation between the GSTP1 polymorphism and oxaliplatin-induced neurotoxicity remains controversial. Overall, further development of individualized chemotherapy with an analysis of genomic polymorphisms in the drug target genes is required for the prophylaxis oxaliplatin-induced neurotoxicity.

Depletion of RNA-binding protein RBM8A (Y14) causes cell cycle deficiency and apoptosis in human cells

RBM8A (Y14) contains an RNA-binding motif and forms a tight heterodimer with Magoh. The heterodimer is known to be a member of the exon junction complex that forms on mRNA before export and it is required for mRNA metabolism processes such as splicing, mRNA export and nonsense-mediated mRNA decay. Recently, deficient cellular proliferation has been observed in RBM8A- or Magoh-depleted cells. These results prompted us to study the role of RBM8A in cell cycle progression of human tumour cells. The depletion of RBM8A in A549 cells resulted in poor cell survival and the accumulation of mitotic cells. After release from G1/S arrest induced by a double thymidine block, the RBM8A-silenced cells could not proceed to the next G1 phase beyond G2/M phase. Finally, the sub-G1 population increased and the apoptosis markers caspases 3/7 were activated. Silenced cells exhibited an increased frequency of multipolar or monopolar centrosomes, which may have caused the observed deficiency in cell cycle progression. Finally, silencing of either RBM8A or Magoh resulted in mutual downregulation of the other protein. These results illustrate that the RBM8A-Magoh mRNA binding complex is required for M phase progression and both proteins may be novel targets for anticancer therapy.

Comparative evaluation of the effects of treatment with tocilizumab and TNF-α inhibitors on serum hepcidin, anemia response and disease activity in rheumatoid arthritis patients

Introduction

Anemia of inflammation (AI) is a common complication of rheumatoid arthritis (RA) and has a negative impact on RA symptoms and quality of life. Upregulation of hepcidin by inflammatory cytokines has been implicated in AI. In this study, we evaluated and compared the effects of IL-6 and TNF-α blocking therapies on anemia, disease activity, and iron-related parameters including serum hepcidin in RA patients.

Methods

Patients (n = 93) were treated with an anti-IL-6 receptor antibody (tocilizumab) or TNF-α inhibitors for 16 weeks. Major disease activity indicators and iron-related parameters including serum hepcidin-25 were monitored before and 2, 4, 8, and 16 weeks after the initiation of treatment. Effects of tocilizumab and infliximab (anti-TNF-α antibody) on cytokine-induced hepcidin expression in hepatoma cells were analyzed by quantitative real-time PCR.

Results

Anemia at base line was present in 66% of patients. Baseline serum hepcidin-25 levels were correlated positively with serum ferritin, C-reactive protein (CRP), vascular endothelial growth factor (VEGF) levels and Disease Activity Score 28 (DAS28). Significant improvements in anemia and disease activity, and reductions in serum hepcidin-25 levels were observed within 2 weeks in both groups, and these effects were more pronounced in the tocilizumab group than in the TNF-α inhibitors group. Serum hepcidin-25 reduction by the TNF-α inhibitor therapy was accompanied by a decrease in serum IL-6, suggesting that the effect of TNF-α on the induction of hepcidin-25 was indirect. In in vitro experiments, stimulation with the cytokine combination of IL-6+TNF-α induced weaker hepcidin expression than did with IL-6 alone, and this induction was completely suppressed by tocilizumab but not by infliximab.

Conclusions

Hepcidin-mediated iron metabolism may contribute to the pathogenesis of RA-related anemia. In our cohort, tocilizumab was more effective than TNF-α inhibitors for improving anemia and normalizing iron metabolism in RA patients by inhibiting hepcidin production.

A low-molecular-weight compound K7174 represses hepcidin: possible therapeutic strategy against anemia of chronic disease

Hepcidin is the principal iron regulatory hormone, controlling the systemic absorption and remobilization of iron from intracellular stores. The expression of the hepcidin gene, HAMP, is increased in patients with anemia of chronic disease. Previously, the synthetic compound K7174 was identified through chemical screening as a novel inhibitor of the adhesion of monocytes to cytokine-stimulated endothelial cells. K7174 also ameliorated anemia induced by inflammatory cytokines in mice, which suggests a possible involvement of hepcidin regulation. The present study was performed to assess the impact of K7174 on hepcidin expression in a human hematoma cell line and in mice in vivo. We first demonstrated that K7174 treatment in HepG2 cells significantly decreased HAMP expression. Then, we conducted microarray analysis to determine the molecular mechanism by which K7174 inhibits HAMP expression. Transcriptional profiling confirmed the downregulation of HAMP. Surprisingly, we found that K7174 strongly induced GDF15, known as a negative regulator of HAMP expression. Western blotting analysis as well as ELISA confirmed the induction of GDF15 by K7174 treatment. Furthermore, K7174-mediated HAMP suppression was rescued by the silencing of GDF15 expression. Interestingly, we found that K7174 also upregulates CEBPB. Promoter analysis and chromatin immunoprecipitation analysis revealed that CEBPB could contribute to K7174-mediated transcriptional activation of GDF15. Subsequently, we also examined whether K7174 inhibits hepcidin expression in mice. Quantitative RT-PCR analysis with liver samples from K7174-treated mice demonstrated significant upregulation of Gdf15 and downregulation of Hamp expression, as compared to control mice. Furthermore, serum hepcidin concentration was also significantly decreased in K7174-treated mice. In conclusion, K7174 inhibits hepcidin expression partly by inducing GDF15. K-7174 may be a potential therapeutic option to treat anemia of chronic disease.

RNA-binding protein RBM8A (Y14) and MAGOH localize to centrosome in human A549 cells

RBM8A (Y14) is carrying RNA-binding motif and forms the tight heterodimer with MAGOH. The heterodimer is known to be a member of exon junction complex on exporting mRNA and is required for mRNA metabolisms such as splicing, mRNA export and nonsense-mediated mRNA decay. Almost all RBM8A-MAGOH complexes localize in nucleoplasm and shuttle between nuclei and cytoplasm for RNA metabolism. Recently, the abnormality of G2/M transition and aberrant centrosome regulation in RBM8A- or MAGOH-deficient cells has been reported. These results prompt us to the reevaluation of the localization of RBM8A-MAGOH in human cells. Interestingly, our immunostaining experiments showed the localization of these proteins in centrosome in addition to nuclei. Furthermore, the transiently expressed eYFP-tagged RBM8A and Flag-tagged MAGOH also co-localized with centrosome signals. In addition, the proximity ligation in situ assay was performed to detect the complex formation in centrosome. Our experiments clearly showed that Myc-tagged RBM8A and Flag-tagged MAGOH formed a complex in centrosome. GFP-tagged PLK1 also co-localized with Myc-RBM8A. Our results show that RBM8A-MAGOH complex is required for M-phase progression via direct localization to centrosome rather than indirect effect.

Clinicopathological study of Japanese patients with genetic iron overload syndromes

In addition to hemochromatosis, aceruloplasminemia and ferroportin disease may be complicated by iron-induced multiple organ damage. Therefore, clinicopathological features should be evaluated in a wider range of genetic iron disorders. This study included 16 Japanese patients with genetic iron overload syndromes. The responsible genes were CP in four, HAMP in one, HJV in three, TFR2 in five, and SLC40A1 in three patients. No phenotype dissociation was observed in patients with the CP, TFR2, or HAMP genotypes. Two of the three patients with the HJV genotype displayed classic hemochromatosis instead of the juvenile type. Patients with the SLC40A1 genotype were affected by mild iron overload (ferroportin A) or severe iron overload (ferroportin B). Transferrin saturation was unusually low in aceruloplasminemia patients. All patients, except those with ferroportin disease, displayed low serum hepcidin-25 levels. Liver pathology showed phenotype-specific changes; isolated parenchymal iron loading in aceruloplasminemia, periportal fibrosis associated with heavy iron overload in both parenchymal and Kupffer cells of ferroportin B, and parenchyma-dominant iron-loading cirrhosis in hemochromatosis. In contrast, diabetes occurred in all phenotypes of aceruloplasminemia, hemochromatosis, and ferroportin disease B. In conclusion, clinicopathological features were partially characterized in Japanese patients with genetic iron overload syndromes.

Protein profiling of blood samples from patients with hereditary leiomyomatosis and renal cell cancer by surface-enhanced laser desorption/ionization time-of-flight mass spectrometry

Hereditary leiomyomatosis and renal cell cancer (HLRCC) is an extremely rare syndrome with autosomal dominant inheritance. HLRCC is characterized by a predisposition to leiomyomas of the skin and the uterus as well as renal cell carcinoma. The disease-related gene has been identified as fumarate hydratase (fumarase, FH), which encodes an enzyme involved in the mitochondrial tricarboxylic acid cycle. Protein profiling may give some insight into the molecular pathways of HLRCC. Therefore, we performed protein profiling of blood samples from HLRCC patients, their family members, and healthy volunteers, using surface-enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF MS) coupled with IMAC-Cu chips. For hierarchical clustering analysis, we used the 45 peaks that revealed significant differences in single-marker analysis over the range from 1500 to 15,000 m/z. Heat map analysis based on the results of clustering distinguished the HLRCC kindred from non-HLRCC subjects with a sensitivity of 94% and a specificity of 90%. SELDI-TOF MS profiling of blood samples can be applied to identify patients with HLRCC and to assess specific molecular mechanisms involved in this condition.