Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0022716 (Menkes)
 1,057 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Copper is an essential trace element necessary for normal growth and development. During pregnancy, copper is transported from the maternal circulation to the fetus by mechanisms which have not been clearly elucidated. Two copper transporting ATPases, Menkes (ATP7A; MNK) and Wilson (ATP7B; WND) are known to be expressed in the placenta and are thought to have a role in copper transport to the fetus. In this study, the expression and localization of the MNK and WND proteins in the human placenta were investigated in detail using immunoperoxidase and double-label immunohistochemistry. MNK and WND are differentially localized within the placenta. MNK is present in the syncytiotrophoblast, the cytotrophoblast and the fetal vascular endothelial cells whereas WND is only in the syncytiotrophoblast. Placental levels of both proteins, measured by Western blot analysis, did not change across pregnancy. These data offer some insights into possible roles for MNK and WND within the placenta.
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PMID:Expression and localization of menkes and Wilson copper transporting ATPases in human placenta. 1513 34

The Menkes protein (MNK; ATP7A) functions as a transmembrane copper-translocating P-type ATPase and plays a vital role in systemic copper absorption in the gut and copper reabsorption in the kidney. Polarized epithelial cells such as Madin-Darby canine kidney (MDCK) cells are a physiologically relevant model for systemic copper absorption and reabsorption in vivo. In this study, cultured MDCK cells were used to characterize MNK trafficking and enabled the identification of signaling motifs required to target the protein to specific membranes. Using confocal laser scanning microscopy and surface biotinylation we demonstrate that MNK relocalizes from the Golgi to the basolateral (BL) membrane under elevated copper conditions. As previously shown in nonpolarized cells, the metal binding sites in the NH2-terminal domain of MNK were found to be required for copper-regulated trafficking from the Golgi to the plasma membrane. These data provide molecular evidence that is consistent with the presumed role of this protein in systemic copper absorption in the gut and reabsorption in the kidney. Using site-directed mutagenesis, we identified a dileucine motif proximal to the COOH terminus of MNK that was critical for correctly targeting the protein to the BL membrane and a putative PDZ target motif that was required for localization at the BL membrane in elevated copper.
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PMID:Signals regulating trafficking of Menkes (MNK; ATP7A) copper-translocating P-type ATPase in polarized MDCK cells. 1526 5

Chloroquine has been widely used for malaria treatment and prophylaxis for several decades, but its usefulness has now declined with the emergence of chloroquine resistance. Recent studies showed that the K76T mutation in the PfCRT protein, initially associated to chloroquine-resistant parasites, is sometimes also present in susceptible parasites, suggesting that other factors control the expression of the resistance phenotype. Here, we sought new mutations in the Pfcrt gene and used real-time PCR to investigate variations in the expression level of this gene with respect to the in vitro response to chloroquine. About 40 Cambodian isolates of Plasmodium falciparum were selected on the basis of their response to chloroquine in vitro. The Pfcrt gene was characterised by amplifying and sequencing the full-length cDNA. Twelve point mutations--M74I, N75D/E, K76T, A144F, L148I, I194T, A220S, Q271E, N326S, T333S, I356T and R371I--were detected. Mutations identified at positions 144, 148, 194 and 333 had never been described before. These mutations define six distinct haplotypes, distributed heterogeneously throughout Cambodia. Only the mutations at positions 74-76, 220 and 271 were significantly associated with the in vitro response to chloroquine. Three major haplotypes--MNK/A/Q, IDT/S/E and IET/S/E--accounted for all the isolates examined. The MNK/A/Q haplotype corresponded to susceptible isolates whereas parasites with the IDT/S/E haplotype displayed an intermediate response to chloroquine and those with the IET/S/E haplotype displayed the highest IC50 values. Phylogenic analysis suggested that the IDT and IET haplotypes (positions 74-76) arose independently from the wild-type MNK sequence. We found that the expression level of Pfcrt, evaluated by real-time PCR, had no effect on the response of the parasite to the drug in vitro. Similarly, in a CQ-resistant strain short-term cultured in the presence of CQ, no change was observed in the level of transcripts. These results are discussed in light of recent finding suggesting the possible involvement of other transporters in CQ-resistance.
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PMID:Variations in the sequence and expression of the Plasmodium falciparum chloroquine resistance transporter (Pfcrt) and their relationship to chloroquine resistance in vitro. 1547 6

The interaction between the human copper(I) chaperone, HAH1, and one of its two physiological partners, the Menkes disease protein (ATP7A), was investigated in solution using heteronuclear NMR. The study was carried out through titrations involving HAH1 and either the second or the fifth soluble domains of ATP7A (MNK2 and MNK5, respectively), in the presence of copper(I). The copper-transfer properties of MNK2 and MNK5 are similar, and differ significantly from those previously observed for the yeast homologous system. In particular, no stable adduct is formed between either of the MNK domains and HAH1. The copper(I) transfer reaction is slow on the time scale of the NMR chemical shift, and the equilibrium is significantly shifted towards the formation of copper(I)-MNK2/MNK5. The solution structures of both apo- and copper(I)-MNK5, which were not available, are also reported. The results are discussed in comparison with the data available in the literature for the interaction between HAH1 and its partners from other spectroscopic techniques.
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PMID:An NMR study of the interaction between the human copper(I) chaperone and the second and fifth metal-binding domains of the Menkes protein. 1567 Jan 66

Deficiencies of different proteins involved in copper metabolism have been reported to cause human diseases. Well-known syndromes, for example, are Menkes and Wilson diseases. Here we report a patient presenting with congenital cataract, severe muscular hypotonia, developmental delay, sensorineural hearing loss and cytochrome-c oxidase deficiency with repeatedly low copper and ceruloplasmin levels. These findings were suggestive of a copper metabolism disorder. In support of this, the patient's fibroblasts showed an increased copper uptake with normal retention. Detailed follow-up examinations were performed. Immunoblotting for several proteins including ATP7A (MNK or Menkes protein), ATP7B (Wilson protein) and SOD1 showed normal results, implying a copper metabolism defect other than Wilson or Menkes disease. Sequence analysis of ATOX1 and genes coding for proteins that are known to play a role in the mitochondrial copper metabolism (COI-III, SCO1, SCO2, COX11, COX17, COX19) revealed no mutations. Additional disease genes that have been associated with cytochrome-c oxidase deficiency were negative for mutations as well. As beneficial effects of copper histidinate supplementation have been reported in selected disorders of copper metabolism presenting with low serum copper and ceruloplasmin levels, we initiated a copper histidinate supplementation. Remarkable improvement of clinical symptoms was observed, with complete restoration of cytochrome-c oxidase activity in skeletal muscle.
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PMID:Congenital cataract, muscular hypotonia, developmental delay and sensorineural hearing loss associated with a defect in copper metabolism. 1590 51

Hereditary inclusion body myopathy (HIBM) is an autosomal recessive neuromuscular disorder associated with mutations in uridine diphosphate (UDP)-N-acetylglucosamine (GlcNAc) 2-epimerase (GNE)/N-acetylmannosamine (ManNAc) kinase (MNK), the bifunctional and rate-limiting enzyme of sialic acid biosynthesis. We developed individual GNE and MNK enzymatic assays and determined reduced activities in cultured fibroblasts of patients, with HIBM harboring missense mutations in either or both the GNE and MNK enzymatic domains. To assess the effects of individual mutations on enzyme activity, normal and mutated GNE/MNK enzymatic domains were synthesized in a cell-free in vitro transcription-translation system and subjected to the GNE and MNK enzymatic assays. This cell-free system was validated for both GNE and MNK activities, and it revealed that mutations in one enzymatic domain (in GNE, G135V, V216A, and R246W; in MNK, A631V, M712T) affected not only that domain's enzyme activity, but also the activity of the other domain. Moreover, studies of the residual enzyme activity associated with specific mutations revealed a discrepancy between the fibroblasts and the cell-free systems. Fibroblasts exhibited higher residual activities of both GNE and MNK than the cell-free system. These findings add complexity to the tightly regulated system of sialic acid biosynthesis. This cell-free approach can be applied to other glycosylation pathway enzymes that are difficult to evaluate in whole cells because their substrate specificities overlap with those of ancillary enzymes.
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PMID:Use of a cell-free system to determine UDP-N-acetylglucosamine 2-epimerase and N-acetylmannosamine kinase activities in human hereditary inclusion body myopathy. 1598 57

The aim was to study the subcellular localization of the Menkes protein (MNK; ATP7A) in the rat parotid acinar cell. MNK protein is a copper transporting P-type ATPase whose absence or dysfunction causes a fatal neurodegenerative disorder, MNK disease. Rat parotid glands were fixed and low-temperature embedded in Lowicryl K4M resin, and ultrathin sections were prepared for immunocytochemical analysis. Immunolocalization of MNK was demonstrated mainly over the trans Golgi network (TGN) area. Immature and mature secretory granules were also labelled, indicating that MNK protein could be involved here in copper secretion from acinar cells into saliva, consistent with a proposed cariostatic role for copper.
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PMID:Menkes protein localization in rat parotid acinar cells. 1618 50

The MNK (Menkes disease protein; ATP7A) is a major copper- transporting P-type ATPase involved in the delivery of copper to cuproenzymes in the secretory pathway and the efflux of excess copper from extrahepatic tissues. Mutations in the MNK (ATP7A) gene result in Menkes disease, a fatal neurodegenerative copper deficiency disorder. Currently, detailed biochemical and biophysical analyses of MNK to better understand its mechanisms of copper transport are not possible due to the lack of purified MNK in an active form. To address this issue, we expressed human MNK with an N-terminal Glu-Glu tag in Sf9 [Spodoptera frugiperda (fall armyworm) 9] insect cells and purified it by antibody affinity chromatography followed by size-exclusion chromatography in the presence of the non-ionic detergent DDM (n-dodecyl beta-D-maltopyranoside). Formation of the classical vanadate-sensitive phosphoenzyme by purified MNK was activated by Cu(I) [EC50=0.7 microM; h (Hill coefficient) was 4.6]. Furthermore, we report the first measurement of Cu(I)-dependent ATPase activity of MNK (K0.5=0.6 microM; h=5.0). The purified MNK demonstrated active ATP-dependent vectorial 64Cu transport when reconstituted into soya-bean asolectin liposomes. Together, these data demonstrated that Cu(I) interacts with MNK in a co-operative manner and with high affinity in the sub-micromolar range. The present study provides the first biochemical characterization of a purified full-length mammalian copper-transporting P-type ATPase associated with a human disease.
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PMID:Purification and membrane reconstitution of catalytically active Menkes copper-transporting P-type ATPase (MNK; ATP7A). 1700 61

Copper deficiency during pregnancy results in early embryonic death and foetal structural abnormalities including skeletal, pulmonary and cardiovascular defects. During pregnancy, copper is transported from the maternal circulation to the foetus by mechanisms which have not been clearly elucidated. Two copper-transporting ATPases, Menkes (ATP7A; MNK) and Wilson (ATP7B; WND), are expressed in the placenta and both are involved in placental copper transport, as copper accumulates in the placenta in both Menkes and Wilson disease. The regulatory mechanisms of MNK and WND and their exact role in the placenta are unknown. Using a differentiated polarized Jeg-3 cell culture model of placental trophoblasts, MNK and WND were shown to be expressed within these cells. Distinct roles for MNK and WND are suggested on the basis of their opposing responses to insulin. Insulin and oestrogen increased both MNK mRNA and protein levels, altered the localization of MNK towards the basolateral membrane in a copper-independent manner, and increased the transport of copper across this membrane. In contrast, levels of WND were decreased in response to insulin, and the protein was located in a tight perinuclear region, with a corresponding decrease in copper efflux across the apical membrane. These results are consistent with a model of copper transport in the placenta in which MNK delivers copper to the foetus and WND returns excess copper to the maternal circulation. Insulin and oestrogen stimulate copper transport to the foetus by increasing the expression of MNK and reducing the expression of WND. These data show for the first time that MNK and WND are differentially regulated by the hormones insulin and oestrogen in human placental cells.
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PMID:Hormonal regulation of the Menkes and Wilson copper-transporting ATPases in human placental Jeg-3 cells. 1730 Feb 24

Copper (Cu) plays a critical role in the developing foetus, but virtually nothing is known concerning the regulation of its uptake and metabolism in the placenta. In this issue of the Biochemical Journal, Hardman and colleagues, using a model of placental trophoblasts in culture, identify differential hormonal regulation of two copper-transporting ATPases; namely, those responsible for Menkes disease (ATP7A; MNK) and Wilson disease (ATP7B; WND). Insulin and oestrogen, which are essential during gestation, up-regulate MNK and this leads to trafficking of the MNK protein from the Golgi to the basolateral membrane, resulting in increased Cu efflux. At the same time, insulin decreased WND levels, and this leads to intracellular sequestration of the protein to a perinuclear region that reduces apical Cu release. As such, this results in a concerted flux of Cu from the basolateral surface of the trophoblast that would potentially be used by the developing foetus. An integrated model of vectorized Cu transport is proposed, which involves co-ordinated expression of transporters, organelle interactions and probable protein-protein interactions. The findings have wider implications for considering general models of intracellular metal transport.
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PMID:Differential regulation of the Menkes and Wilson disease copper transporters by hormones: an integrated model of metal transport in the placenta. 1710 27


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