Deregulation of Genes Related to Iron and Mitochondrial Metabolism in Refractory Anemia with Ring Sideroblasts

The presence of SF3B1 gene mutations is a hallmark of refractory anemia with ring sideroblasts (RARS). However, the mechanisms responsible for iron accumulation that characterize the Myelodysplastic Syndrome with ring sideroblasts (MDS-RS) are not completely understood. In order to gain insight in the molecular basis of MDS-RS, an integrative study of the expression and mutational status of genes related to iron and mitochondrial metabolism was carried out. A total of 231 low-risk MDS patients and 81 controls were studied. Gene expression analysis revealed that iron metabolism and mitochondrial function had the highest number of genes deregulated in RARS patients compared to controls and the refractory cytopenias with unilineage dysplasia (RCUD). Thus mitochondrial transporters SLC25 (SLC25A37 and SLC25A38) and ALAD genes were over-expressed in RARS. Moreover, significant differences were observed between patients with SF3B1 mutations and patients without the mutations. The deregulation of genes involved in iron and mitochondrial metabolism provides new insights in our knowledge of MDS-RS. New variants that could be involved in the pathogenesis of these diseases have been identified.     

The ATP-Binding Cassette Transporter ABCB19 Regulates Postembryonic Organ Separation in Arabidopsis

The phytohormone auxin plays a critical role in plant development, including embryogenesis, organogenesis, tropism, apical dominance and in cell growth, division, and expansion. In these processes, the concentration gradient of auxin, which is established by polar auxin transport mediated by PIN-FORMED (PIN) proteins and several ATP-binding cassette/multi-drug resistance/P-glycoprotein (ABCB/MDR/PGP) transporters, is a crucial signal. Here, we characterized the function of ABCB19 in the control of Arabidopsis organ boundary development. We identified a new abcb19 allele, abcb19-5, which showed stem-cauline leaf and stem-pedicel fusion defects. By virtue of the DII-VENUS marker, the auxin level was found to be increased at the organ boundary region in the inflorescence apex. The expression of CUP-SHAPED COTYLEDON2 (CUC2) was decreased, while no obvious change in the expression of CUC3 was observed, in abcb19. In addition, the fusion defects were greatly enhanced in cuc3 abcb19-5, which was reminiscent of cuc2 cuc3. We also found that some other organ boundary genes, such as LOF1/2 were down-regulated in abcb19. Together, these results reveal a new aspect of auxin transporter ABCB19 function, which is largely dependent on the positive regulation of organ boundary genes CUC2 and LOFs at the postembryonic organ boundary.     

The Effect of Iron Treatment on Adhesion Molecules in Patients with Iron Deficiency Anemia

The present study was aimed to determine the effect of iron supplementation on levels of soluble intercellular adhesion molecule-1 (sICAM-1) and soluble vascular cell adhesion molecule-1 (sVCAM-1) in patients with iron deficiency anemia (IDA). In this study, 26 female patients diagnosed with iron deficiency were treated approximately 3 months of oral iron supplementation (99 ± 10 days; ferrous glycine sulfate; 100 mg/day of elemental iron). Levels of sICAM-1 and sVCAM-1 were assessed prior to treatment and after approximately 3 months of treatment and compared with 26 healthy female subjects. A significant increase in sVCAM levels was found in the patients with iron deficiency at the end of the treatment relative to pretreatment levels compared to controls, whereas no significant differences were determined in sICAM levels. In the posttreatment period, no significant change was observed in sICAM levels compared to the pretreatment levels, whereas sVCAM levels decreased. However, after the treatment period, the sVCAM, hemoglobin, mean corpuscular volume (MCV), and serum ferritin levels did not return to the normal range compared to the controls. Pretreatment sVCAM-1 levels were inversely correlated with levels of hemoglobin, hemotocrit, MCV, serum iron, and ferritin. After treatment, the sVCAM-1 levels were negatively correlated with ferritin levels. Levels of sVCAM were significantly higher in patients with IDA than controls. After the treatment period, the sVCAM levels were not completely normalized in patients with IDA compared to controls, regardless of the presence of inadequate levels of hemoglobin, MCV, and serum ferritin. Thus, iron supplementation not only ameliorates anemia, but may also reduce the inflammation markers in cases with IDA.     

A PDZ-Like Motif in the Biliary Transporter ABCB4 Interacts with the Scaffold Protein EBP50 and Regulates ABCB4 Cell Surface Expression

ABCB4/MDR3, a member of the ABC superfamily, is an ATP-dependent phosphatidylcholine translocator expressed at the canalicular membrane of hepatocytes. Defects in the ABCB4 gene are associated with rare biliary diseases. It is essential to understand the mechanisms of its canalicular membrane expression in particular for the development of new therapies. The stability of several ABC transporters is regulated through their binding to PDZ (PSD95/DglA/ZO-1) domain-containing proteins. ABCB4 protein ends by the sequence glutamine-asparagine-leucine (QNL), which shows some similarity to PDZ-binding motifs. The aim of our study was to assess the potential role of the QNL motif on the surface expression of ABCB4 and to determine if PDZ domain-containing proteins are involved. We found that truncation of the QNL motif decreased the stability of ABCB4 in HepG2-transfected cells. The deleted mutant ABCB4-ΔQNL also displayed accelerated endocytosis. EBP50, a PDZ protein highly expressed in the liver, strongly colocalized and coimmunoprecipitated with ABCB4, and this interaction required the QNL motif. Down-regulation of EBP50 by siRNA or by expression of an EBP50 dominant-negative mutant caused a significant decrease in the level of ABCB4 protein expression, and in the amount of ABCB4 localized at the canalicular membrane. Interaction of ABCB4 with EBP50 through its PDZ-like motif plays a critical role in the regulation of ABCB4 expression and stability at the canalicular plasma membrane.     

The Bicarbonate Transporter SLC4A7 Plays a Key Role in Macrophage Phagosome Acidification

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The Role of the Membrane in Transporter Folding and Activity

The synthesis, folding, and function of membrane transport proteins are critical factors for defining cellular physiology. Since the stability of these proteins evolved amidst the lipid bilayer, it is no surprise that we are finding that many of these membrane proteins demonstrate coupling of their structure or activity in some way to the membrane. More and more transporter structures are being determined with some information about the surrounding membrane, and computational modeling is providing further molecular details about these solvation structures. Thus, the field is moving towards identifying which molecular mechanisms - lipid interactions, membrane perturbations, differential solvation, and bulk membrane effects - are involved in linking membrane energetics to transporter stability and function. In this review, we present an overview of these mechanisms and the growing evidence that the lipid bilayer is a major determinant of the fold, form, and function of membrane transport proteins in membranes.     

Role of transferrin receptor and the ABC transporters ABCB6 and ABCB7 for resistance and differentiation of tumor cells towards artesunate

The anti-malarial artesunate also exerts profound anti-cancer activity. The susceptibility of tumor cells to artesunate can be enhanced by ferrous iron. The transferrin receptor (TfR) is involved in iron uptake by internalization of transferrin and is over-expressed in rapidly growing tumors. The ATP-binding cassette (ABC) transporters ABCB6 and ABCB7 are also involved in iron homeostasis. To investigate whether these proteins play a role for sensitivity towards artesunate, Oncotest's 36 cell line panel was treated with artesunate or artesunate plus iron(II) glycine sulfate (Ferrosanol). The majority of cell lines showed increased inhibition rates, for the combination of artesunate plus iron(II) glycine sulfate compared to artesunate alone. However, in 11 out of the 36 cell lines the combination treatment was not superior. Cell lines with high TfR expression significantly correlated with high degrees of modulation indicating that high TfR expressing tumor cells would be more efficiently inhibited by this combination treatment than low TfR expressing ones. Furthermore, we found a significant relationship between cellular response to artesunate and TfR expression in 55 cell lines of the National Cancer Institute (NCI), USA. A significant correlation was also found for ABCB6, but not for ABCB7 in the NCI panel. Artesunate treatment of human CCRF-CEM leukemia and MCF7 breast cancer cells induced ABCB6 expression but repressed ABCB7 expression. Finally, artesunate inhibited proliferation and differentiation of mouse erythroleukemia (MEL) cells. Down-regulation of ABCB6 by antisense oligonucleotides inhibited differentiation of MEL cells indicating that artesunate and ABCB6 may cooperate. In conclusion, our results indicate that ferrous iron improves the activity of artesunate in some but not all tumor cell lines. Several factors involved in iron homeostasis such as TfR and ABCB6 may contribute to this effect.     

The Role of Cysteines and Histidins of the Norepinephrine Transporter

The thiol reagent N-ethylmaleimide (NEM) is known to inhibit irreversibly ligand binding by the norepinephrine transporter (NET), while the simultaneous presence of NET substrates or ligands protects from this inhibition. Therefore, cysteine residues located within the substrate binding pocket of the NET were assumed to play an important role in ligand binding. To examine which (if any) of the 10 cysteines (Cys) of the human (h) NET might be involved in transport and/or binding function, we mutated all hNET cysteines to alanine. Using transfected HEK293 cells we studied NEM effects on the hNET with respect to [³H]nisoxetine binding. Two cysteines (Cys176 and Cys185) within the extracellular loop of the NET have been proposed to form a disulfide bond. We could demonstrate that this is of crucial importance as corresponding hNET mutants, in which these cysteines have been replaced, showed a lack of plasma membrane expression. However, due to their oxidized state in the native NET protein, Cys176 and Cys185 may not be targets for NEM. All other Cys-to-Ala hNET mutants were fully active and showed no change in inhibition of [³H]nisoxetine binding by NEM. These observations clearly exclude cysteines as being involved in hNET ligand binding. Since NEM also interacts with histidin (His), we mutated all 13 histidins of the hNET to alanine and examined the NET mutants in functional and binding assays. His222 within the large extracellular loop of the transporter was identified as an interaction partner of NEM since in the corresponding hNET mutant NEM exhibited a significantly reduced inhibitory potency. Furthermore, we could show that histidins in position 296, 370 and 372 are important for nisoxetine binding, while His220, 441, 598 and 599 are crucial for plasma membrane expression of the hNET.     

通过农杆菌介导将番茄铁转运蛋白基因导入八棱海棠

用农杆菌介导法,成功地将番茄铁转运蛋白基因导入了苹果砧木八棱海棠.获得了19个卡那霉素抗性株系,其中有11个株系经PCR鉴定为阳性.Southern杂交结果显示:有9个转基因株系基因组中整合了完整的目的基因.选择其中含有单拷贝和3个拷贝目的基因的各一个株系进行水培试验,结果表明整合了单拷贝目的基因的转基因株系表现出较强的抗缺铁胁迫能力,5周后其植株的鲜重比对照高21%～34%.     

Transgenic Petunia with the Iron(III)-Phytosiderophore Transporter Gene Acquires Tolerance to Iron Deficiency in Alkaline Environments

Iron is an essential nutrient for all plants. However, terrestrial plants often suffer from iron deficiency in alkaline soil due to its extremely low solubility. Alkaline soil accounts for about 30% of all cultivated ground in the world. Plants have evolved two distinct strategies, I and II, for iron uptake from the soil. Dicots and non-graminaceous monocots use Strategy I, which is primarily based on the reduction of iron(III) to iron(II) and the uptake of iron(II) by the iron-regulated transporter, IRT1. In contrast, graminaceous plants use Strategy II to efficiently acquire insoluble iron(III). Strategy II comprises the synthesis and secretion of iron-chelating phytosiderophores, such as mugineic acids and the Yellow Stripe 1 transporter proteins of the iron(III)-phytosiderophore complex. Barley, which exhibits the highest tolerance to iron deficiency in alkaline soil among graminaceous plants, utilizes mugineic acids and the specific iron(III)-mugineic acids transporter, HvYS1. In this study, we established the transgenic plant Petunia hybrida, which originally had only Strategy I, by introducing the HvYS1 transporter gene derived from barley. When the transgenic plants were grown hydroponically in media containing the iron(III)-2′-deoxymugineic acid complex, free 2′-deoxymugineic acid and its iron(III) complex were detected in the root extract of the transgenic plant by electrospray ionization-Fourier transform-ion cyclotron resonance mass spectrometry. The growth of the transgenic petunia was significantly better than that of the control host in alkaline conditions. Consequently, the transgenic plant acquired a significantly enhanced tolerance to alkaline hydroponic media in the presence of the iron(III)-2′-deoxymugineic acid complex. Furthermore, the flower color of the transgenic plant deepened. The results showed that iron-phytosiderophore complexes and their transporters can potentially be utilized to overcome the worldwide iron uptake problems to diverse plant species that are found in areas with alkaline conditions.     

血清Hepcidin 水平在老年缺铁性贫血和慢性病贫血诊断中的临床应用

目的:探讨血清铁调素(Hepcidin)在老年人群缺铁性贫血(IDA)和慢性病贫血(ACD)中的应用价值。方法:选择老年IDA患者32例,老年ACD患者34例,健康对照组28例。检测对比三组血清Hepcidin、血清铁(SI)、血清铁蛋白(SF)、C-反应蛋白(CRP)、红细胞数(RBC)、血红蛋白(Hb)、红细胞比容(HCT)、红细胞平均体积(MCV)、白细胞数(WBC)水平。结果:ACD组中WBC明显高于IDA组(P0.05)。血清Hepcidin在IDA组、ACD组及对照组之间具有显著性差异(P0.05),IDA组中Hepcidin含量比对照组低,而ACD组中Hepcidin含量比对照组高(P0.05)。IDA组、ACD组中SI明显低于对照组(P0.05),而两组间无显著性差异(P0.05)。ACD组中SF、CRP均明显高于IDA组与对照组(P0.05)。Hepcidin诊断IDA组的ROC曲线下面积(AUC)值大于诊断ACD组,IDA组的诊断指数高于ACD组。结论:血清Hepcidin含量的检测对于鉴别IDA和ACD具有重要的意义。     

Role of FAAH-Like Anandamide Transporter in Anandamide Inactivation

The endocannabinoid system modulates numerous physiological processes including nociception and reproduction. Anandamide (AEA) is an endocannabinoid that is inactivated by cellular uptake followed by intracellular hydrolysis by fatty acid amide hydrolase (FAAH). Recently, FAAH-like anandamide transporter (FLAT), a truncated and catalytically-inactive variant of FAAH, was proposed to function as an intracellular AEA carrier and mediate its delivery to FAAH for hydrolysis. Pharmacological inhibition of FLAT potentiated AEA signaling and produced antinociceptive effects. Given that endocannabinoids produce analgesia through central and peripheral mechanisms, the goal of the current work was to examine the expression of FLAT in the central and peripheral nervous systems. In contrast to the original report characterizing FLAT, expression of FLAT was not observed in any of the tissues examined. To investigate the role of FLAT as a putative AEA binding protein, FLAT was generated from FAAH using polymerase chain reaction and further analyzed. Despite its low cellular expression, FLAT displayed residual catalytic activity that was sensitive to FAAH inhibitors and abolished following mutation of its catalytic serine. Overexpression of FLAT potentiated AEA cellular uptake and this appeared to be dependent upon its catalytic activity. Immunofluorescence revealed that FLAT localizes primarily to intracellular membranes and does not contact the plasma membrane, suggesting that its capability to potentiate AEA uptake may stem from its enzymatic rather than transport activity. Collectively, our data demonstrate that FLAT does not serve as a global intracellular AEA carrier, although a role in mediating localized AEA inactivation in mammalian tissues cannot be ruled out.     

Functional Role of the Intracellular Loop Linking Transmembrane Domains 6 and 7 of the Human Dipeptide Transporter hPEPT1

The human intestinal di-/tripeptide transporter (hPEPT1) is a 12-transmembrane protein that facilitates transport of peptides from the intestine into the circulation. hPEPT1 is also an important target in oral delivery of drugs, but mechanistic and structural data for the protein are limited. In particular, there is little information on the function of the loops of the transporter. In this study, we show that mutation of several charged residues in the largest intracellular loop of hPEPT1 (loop 6-7, amino acids 224-278) significantly reduces hPEPT1 function. This loop has an asymmetric distribution of charged residues, with only positive charges in the N-terminal half and all five negative charges in the loop located in a small part of the C-terminal half. Point mutagenesis to alanine of three positive residues in the N-terminal half of loop 6-7 and four negative residues in the C-terminal half of the loop significantly reduced glycylsarcosine uptake. E267 was particularly sensitive to mutation, and kinetic analyses of E267A- and E267K-hPEPT1 gave V (max) values 10-fold lower than that for the wild-type protein. Secondary structure prediction suggested that loop 6-7 includes two amphipathic α-helices, with net positive and negative charges, respectively. We interpret the mutagenesis data in terms of interactions of the charged residues in loop 6-7 that may influence conformational changes of hPEPT1 during and after substrate transport.     

Abcb10 Role in Heme Biosynthesis In Vivo: Abcb10 Knockout in Mice Causes Anemia with Protoporphyrin IX and Iron Accumulation

Abcb10, member 10 of the ABC transporter family, is reportedly a part of a complex in the mitochondrial inner membrane with mitoferrin-1 (Slc25a37) and ferrochelatase (Fech) and is responsible for heme biosynthesis in utero. However, it is unclear whether loss of Abcb10 causes pathological changes in adult mice. Here, we show that Abcb10^−/− mice lack heme biosynthesis and erythropoiesis abilities and die in midgestation. Moreover, we generated Abcb10^F/−; Mx1-Cre mice, with Abcb10 in hematopoietic cells deleted, which showed accumulation of protoporphyrin IX and maturation arrest in reticulocytes. Electron microscopy images of Abcb10^−/− hematopoietic cells showed a marked increase of iron deposits at the mitochondria. These results suggest a critical role for Abcb10 in heme biosynthesis and provide new insights into the pathogenesis of erythropoietic protoporphyria and sideroblastic anemia.     

The Expression of Iron-repressible Outer Membrane Proteins in Helicobacter pylori and Its Association with Iron Deficiency Anemia

Background: Helicobacter pylori infection is known to be a cause of iron deficiency anemia (IDA) that is unresponsive to iron supplements. H. pylori bind iron to a specific receptor by iron-repressible outer membrane proteins (IROMPs) under conditions of restricted iron.
Materials and Methods: We compared the expression of IROMPs from strains of H. pylori under both iron-restricted and iron-supplemented conditions to determine the difference between strains with and without IDA. One standard strain, two clinical strains, and three IDA strains were cultured; and then the IROMPs were extracted under iron-restricted and iron-supplemented conditions. We used SDS-PAGE to compare the expression of the IROMPs from each strain.
Results:  IROMPs were found in IDA strains under iron-restricted conditions and their molecular sizes were estimated to be 56, 48, 41, and 37 kDa. In the iron-repleted media, the IROMPs were no longer present.
Conclusion: In the iron-depleted state, specific H. pylori strains associated with IDA demonstrated an advantage in iron acquisition due to a higher expression of IROMPs. Our results can explain in part why some patients with H. pylori infection are more prone to develop clinical IDA under restricted iron conditions in the host.     

三磷酸腺苷结合盒转运体A1在脑疾病发生发展中的作用

三磷酸腺苷结合盒转运体A1(ATP binding cassette transporter A1,ABCA1)在脑组织中广泛表达,它将脑细胞内胆固醇转运给载脂蛋白E(apolipoprotein E,apoE)及载脂蛋白A1(apolipoprotein A1,apoA-Ⅰ)形成高密度脂蛋白(high density lipoprotein,HDL),从而调控脑内胆固醇平衡.研究表明,ABCA1与胆固醇代谢相关脑疾病存在密切联系,包括阿尔茨海默病(Alzheimer's disease,AD)、创伤性脑损伤(traumatic brain injury,TBI)及脑梗死.虽然近来在ABCA1与相关脑疾病的研究取得了一些进展,但仍存在许多问题尚未阐明.本文对ABCA1在各种相关脑疾病发生发展中的作用做一综述,期望为相关脑疾病的治疗寻找新的靶点和方法.