Cloning and characterization of a cDNA encoding the rat brain glucose-transporter protein.

Antibody raised against the human erythrocyte glucose transporter identified a recombinant lambda gt11 bacteriophage in a cDNA library prepared from immunoselected polysomal RNA from adult rat brain. The cDNA predicts a 492-amino acid protein that demonstrates 97.6% identity to the human hepatoma hexose carrier. The tissue distribution of the transporter mRNA is identical to that of immunologically identifiable protein and transport activity, except in liver in which high levels of transport are associated with little or no transporter mRNA or protein. As assayed by blot-hybridization analysis, mRNA from insulin-responsive and nonresponsive tissues are indistinguishable. These data suggest that a genetically unrelated protein is responsible for hexose transport in normal liver.     

Sequence, tissue distribution, and differential expression of mRNA for a putative insulin-responsive glucose transporter in mouse 3T3-L1 adipocytes.

The cDNAs for two putative glucose transporters from mouse 3T3-L1 adipocytes were isolated and sequenced. One of these cDNAs encodes the murine homolog of the human hepG2/erythrocyte glucose transporter, termed GT1. GT1 mRNA is most abundant in mouse brain and is expressed in both 3T3-L1 preadipocytes and adipocytes. The other cDNA encodes a glucose transporter-like protein, termed GT2, that has a unique amino acid sequence and tissue distribution. GT2 cDNA encodes a protein with 63% amino acid sequence identity and a similar structural organization to GT1. GT2 mRNA is found at high levels in mouse skeletal muscle, heart, and adipose tissue, all of which exhibit insulin-stimulated glucose uptake. GT2 mRNA is absent from 3T3-L1 preadipocytes but is induced dramatically during differentiation into adipocytes. This increase in mRNA content correlates closely with the acquisition of insulin-stimulated glucose uptake. We propose that GT2 is an insulin-regulated glucose transporter.     

Functional expression cloning and characterization of the hepatocyte Na+/bile acid cotransport system.

Liver parenchymal cells continuously extract high amounts of bile acids from portal blood plasma. This uptake process is mediated by a Na+/bile acid cotransport system. A cDNA encoding the rat liver bile acid uptake system has been isolated by expression cloning in Xenopus laevis oocytes. The cloned transporter is strictly sodium-dependent and can be inhibited by various non-bile-acid organic compounds. Sequence analysis of the cDNA revealed an open reading frame of 1086 nucleotides coding for a protein of 362 amino acids (calculated molecular mass 39 kDa) with five possible N-linked glycosylation sites and seven putative transmembrane domains. Translation experiments in vitro and in oocytes indicate that the transporter is indeed glycosylated and that its polypeptide backbone has an apparent molecular mass of 33-35 kDa. Northern blot analysis with the cloned probe revealed crossreactivity with mRNA species from rat kidney and intestine as well as from liver tissues of mouse, guinea pig, rabbit, and man.     

A glucose transport protein expressed predominately in insulin-responsive tissues.

Using low-stringency hybridization to the rat brain glucose transporter (GT), a 2489-base-pair cDNA clone was isolated from a rat soleus lambda gt10 cDNA library. It encodes a 509-amino acid protein whose sequence and predicted membrane structure is very similar to those of the rat brain and liver GTs. The muscle GT-like protein is 65% identical in amino acid sequence to the rat brain GT and 52% identical to the rat liver GT; the major differences are in the NH2- and COOH-terminal hydrophilic segments. This GT-like mRNA is expressed predominately in tissues where glucose transport is sensitive to insulin, including striated muscle, cardiac muscle, and adipose tissue; low-level expression is also detected in smooth muscle and kidney mRNA. This GT-like cDNA is the fourth member of the mammalian GT-related gene family identified to date. We propose that it encodes an insulin-sensitive GT.     

Expression of plasma glutathione peroxidase in human liver in addition to kidney, heart, lung, and breast in humans and rodents.

We analyzed the expression of plasma glutathione peroxidase (GSHPx-P) messenger RNA (mRNA) in mouse, rat, and human tissues, using a human GSHPx-P cDNA clone as the probe. Unlike the classical cellular glutathione peroxidase (GSHPx-1), GSHPx-P expression appears to be tissue-specific. In the mouse and rat, kidney expresses an mRNA at a high level detected with the human probe. A signal is also detected in mRNA isolated from mouse and rat heart, rat cardiac myocytes, mouse lung, epididymis, and the mammary gland of midpregnant mice. No signal is detected in mRNA isolated from mouse and rat liver, mouse brain, uterus, and testis. In human tissues, an mRNA hybridizing to GSHPx-P cDNA is present in liver, as well as kidney, heart, lung, breast, and placenta. We have shown that human kidney expresses a GSHPx-P mRNA, and not a GSHPx-P-like message, by isolating a cDNA clone from a human kidney library in lambda gt11. From the 412-nucleotide partial sequence of the kidney cDNA, which codes for the 40-170 amino acids of GSHPx-P including the TGA codon for selenocysteine, we found complete sequence identity of the kidney cDNA with GSHPx-P isolated from placenta. The expression of GSHPx-P mRNA in cell lines was also studied. There is some correlation of the expression of GSHPx-P in these cell lines with that in normal tissues. Cell lines that expressed GSHPx-P mRNA or protein included the human hepatocarcinoma HepG2, Hep3B cells, human kidney carcinoma A498 cells, and the human breast cancer SK-BR-3, T47D, MDA-MB-231, and AdrrMCF-7 cells. Cell lines that did not express GSHPx-P included human choriocarcinoma BeWo cells, human breast cancer MCF-7, ZR-75-1, and Hs578T cells, and mouse hepatoma Hepa-1 cells.     

Cloning of glycoprotein D cDNA, which encodes the major subunit of the Duffy blood group system and the receptor for the Plasmodium vivax malaria parasite.

cDNA clones encoding the major subunit of the Duffy blood group were isolated from a human bone marrow cDNA library using a PCR-amplified DNA fragment encoding an internal peptide sequence of glycoprotein D (gpD) protein. The open reading frame of the 1267-bp cDNA clone indicated that gpD protein was composed of 338 amino acids, predicting a M(r) of 35,733, which was the same as a deglycosylated gpD protein. Portions of the predicted amino acid sequence, matched with six CNBr/pepsin peptides obtained from affinity-purified gpD protein. In ELISA analysis, an anti-Duffy murine monoclonal antibody reacted with a synthetic peptide deduced from the cDNA clone. Hydropathy analysis suggested the presence of 9 membrane-spanning alpha-helices. In bone marrow RNA blot analysis, the gpD cDNA detected a 1.27-kb mRNA in Duffy-positive but not in Duffy-negative individuals. It also identified the same size mRNA in adult kidney, adult spleen, and fetal liver; in brain, it detected a prominent 8.5-kb and a minor 2.2-kb mRNA. In Southern blot analysis, gpD cDNA identified a single gene in Duffy-positive and -negative individuals. Duffy-negative individuals, therefore, have the gpD gene, but it is not expressed in bone marrow. The same or a similar gene is active in adult kidney, adult spleen, and fetal liver of Duffy-positive individuals. Whether this is true in Duffy-negative individuals remains to be demonstrated. A GenBank sequence search yielded a significant protein sequence homology to human and rabbit interleukin-8 receptors.     

Altered expression of glucose transporter isoforms with aging in rats — selective decrease in GluT4 in the fat tissue and skeletal muscle

Summary To elucidate the cellular mechanisms of glucose intolerance associated with aging, both the protein and mRNA levels of glucose transporter isoforms were studied in the various tissues of young (7-week-old) and aged (20-monthold) rats. GluT4 (adipose/muscle-type glucose transporter) protein, which is specifically expressed in insulin-responsive tissues, was selectively decreased per milligramme of cellular membrane protein in both the epididymal fat tissues and the gastrocnemius muscle of the aged rats compared with the young rats. When the changes in total cellular membranes per gramme of tissue are taken into account, a further decrease in GluT4 protein per gramme of tissue was observed in the tissues of the aged rats compared with the young rats. The decreased amount of GluT4 protein in the fat tissues of the aged rats is probably due to the decreased protein synthesis rather than the stability, since GluT4 mRNA/g of cellular total RNA was also decreased. In contrast, GluT4 mRNA in the gastrocnemius muscle was rather increased and a ratio of GluT4 protein/GluT4 mRNA was decreased by 70% in the aged rats, suggesting that the translational efficiency and/or stability of GluT4 protein is decreased in the skeletal muscle of the aged rats compared with the young rats. GluT2 (livertype glucose transporter) protein and mRNA in the liver were also decreased in the aged rats, while no apparent decrease in GluT1 (HepG2/brain-type glucose transporter) protein/mg of cellular membrane protein was observed in the skeletal muscle and fat tissues of the aged rats compared with the young rats. Thus, the tissue and isoform-specific alterations of glucose transporter expression are associated with aging and may contribute to glucose intolerance observed with aging.     

Broiler chickens (Ross strain) lack insulin-responsive glucose transporter GLUT4 and have GLUT8 cDNA

Identification of insulin-responsive glucose transporter proteins, GLUT4 and GLUT8, was attempted in chickens that characteristically are hyperglycemic and insulin resistant. Northern blot analysis using rat GLUT4 cDNA probe and RT-PCR using primers designed against the conserved regions in mammalian GLUT4 cDNA were not successful in identifying GLUT4 homologue(s) in various chicken tissues. Furthermore, GLUT4 homologues could not be detected in chicken tissues by genomic Southern blot analyses using a rat GLUT4 cDNA probe. These data, therefore, suggest that the GLUT4 homologous gene is deficient in chicken tissues. However, GLUT8, another insulin-responsive glucose transporter in the blastocyst, was identified with the aid of RACE (rapid amplification of cDNA ends) reactions in the chicken testis. Chicken GLUT8 was composed of 1449 bp with a coding region for a 482 amino acid protein. The deduced amino acid sequence was 58.8, 56.3, and 56.8% identical with human, rat, and mouse GLUT8, respectively. By RT-PCR, GLUT8 mRNA expressions were detected in chicken brain, kidney, adrenal, spleen, lung, testis, and pancreas; and barely detectable in skeletal muscle, liver, adipose tissue, and heart. Here we firstly report that GLUT8 was identified in chickens, while GLUT4, a major insulin-responsive transporter in mammals, is deficient in these animals. We propose the hypothesis that the hyperglycemia and insulin resistance observable in chickens is associated with their possible deficiency of GLUT4.     

Molecular cloning and protein structure of a human blood group Rh polypeptide.

cDNA clones encoding a human blood group Rh polypeptide were isolated from a human bone marrow cDNA library by using a polymerase chain reaction-amplified DNA fragment encoding the known common N-terminal region of the Rh proteins. The entire primary structure of the Rh polypeptide has been deduced from the nucleotide sequence of a 1384-base-pair-long cDNA clone. Translation of the open reading frame indicates that the Rh protein is composed of 417 amino acids, including the initiator methionine, which is removed in the mature protein, lacks a cleavable N-terminal sequence, and has no consensus site for potential N-glycosylation. The predicted molecular mass of the protein is 45,500, while that estimated for the Rh protein analyzed in NaDodSO4/polyacrylamide gels is in the range of 30,000-32,000. These findings suggest either that the hydrophobic Rh protein behaves abnormally on NaDodSO4 gels or that the Rh mRNA may encode a precursor protein, which is further matured by a proteolytic cleavage of the C-terminal region of the polypeptide. Hydropathy analysis and secondary structure predictions suggest the presence of 13 membrane-spanning domains, indicating that the Rh polypeptide is highly hydrophobic and deeply buried within the phospholipid bilayer. In RNA blot-hybridization (Northern) analysis, the Rh cDNA probe detects a major 1.7-kilobase and a minor 3.5-kilobase mRNA species in adult erythroblasts, fetal liver, and erythroid (K562, HEL) and megakaryocytic (MEG01) leukemic cell lines, but not in adult liver and kidney tissues or lymphoid (Jurkat) and promyelocytic (HL60) cell lines. These results suggest that the expression of the Rh gene(s) might be restricted to tissues or cell lines expressing erythroid characters.     

ICA69 is expressed equally in the human endocrine and exocrine pancreas

Summary Islet cell autoantigen 69 kDa (ICA69) has been reported as a polypeptide antigen expressed in pancreatic beta cells, and autoimmunity against this antigen has been associated with insulin-dependent diabetes mellitus. We have studied the cell type specificity and ontogeny of ICA69 gene expression in man. The ICA69 gene was expressed in all adult human tissues. The level of expression was three-to five-times higher in the pancreas than in the brain, liver, intestine, kidney, spleen, lung or adrenal glands. Pancreatic ICA69 expression increased with age, adult levels being five times higher than the levels present at 13 weeks of gestation. Total RNA from four separate preparations of isolated human islets revealed levels of ICA69 mRNA similar to those found in the pancreas as a whole, although another islet antigen, glutamic acid decarboxylase 65, was highly enriched in the islets. In situ hybridization and immunohistochemical staining of sections of the fetal and adult pancreas revealed expression of the ICA69 gene and protein throughout the acinar, ductal, and islet tissue, but not in the mesenchyme. Analysis of ICA69 mRNA levels in human cell lines indicated expression in neural, endothelial and epithelial cells, but not in fibroblasts. In conclusion, ICA69, although highest in the pancreas, is widely distributed in other human tissues, excluding connective tissue. Within the human pancreas, ICA69 is not enriched in the islets or in the beta cells.Abbreviations GAD Glutamic acid decarboxylase - BSA bovine serum albumin - GLUT2 glucose transporter 2 - bp base pair - PBS phosphate buffered saline - IDDM insulin-dependent diabetes mellitus - HAEC human aortic endothelial cells - ICA islet cell autoantibodies     

3β-Hydroxysteroid dehydrogenase/Δ-isomerase expression in rat and characterization of the testis isoform

The isolation, cloning and expression of a DNA insert complementary to mRNA encoding rat testis 3β-hydroxysteroid dehydrogenase/Δ^5→4-isomerase (3β-HSD) is reported. The insert contains an open reading frame encoding a protein of 373 amino acids, which exhibits 73% and 78% identity to the cDNA encoding the human placental form at the amino acid and nucleotide levels respectively. Northern blot analysis of total RNA of rat tissues using as probe a specific radiolabeled cDNA insert encoding rat testis 3β-HSD demonstrated high levels of 1.6 kb mRNA species in ovary, adrenal and Leydig tumor, with lower but detectable message in testis and adult male liver, while the probe also hybridized to a 2.1 kb mRNA species in liver. The cDNA was inserted into a modified pCMV vector and expressed in COS-1 monkey kidney tumor cells. The expressed protein was similar in size to 3β-HSD present in H540 Leydig tumor cell homogenate and human placental microsomal 3β-HSD, as detected by immunoblot analysis, and catalyzed the conversion of pregnenolone to progesterone, 17-hydroxypregnenolone to 17-hydroxyprogesterone, and dehydroepiandrosterone to androstenedione. Transfected COS cell homogenates, supplemented with NAD⁺, but not NADP⁺, converted pregnenolone to progesterone and dehydroepiandrosterone to androstenedione with apparent K_m values of 0.13 and 0.09 μM, respectively. Immunoblot analysis of various rat tissues using a polyclonal antibody directed against human placental 3β-HSD, in addition to immunoreactivity in the adrenal and testis, demonstrated immunoreactive 3β-HSD protein in adult male liver, but not in adult female or fetal liver. We conclude that while one gene product is highly expressed in testicular Leydig cells, and probably adrenal and ovary, accounting for their 3β-HSD content, a 3β-HSD is also expressed in liver in a sex-specific manner.     

Molecular cloning of protein 4.1, a major structural element of the human erythrocyte membrane skeleton.

Protein 4.1 is an important structural protein that is expressed in erythroid and in a variety of non-erythroid tissues. In mammalian erythrocytes, it plays a key role in regulating membrane physical properties of mechanical stability and deformability by stabilizing spectrin-actin interaction. We report here the molecular cloning and characterization of human erythrocyte protein 4.1 cDNA and the complete amino acid sequence of the protein derived from the nucleotide sequence. Probes prepared from the cloned erythrocyte protein 4.1 cDNA hybridized with distinct mRNA species from a wide variety of non-erythroid tissues, including brain, liver, placenta, pancreas, and intestine, implying substantial homology between erythroid and non-erythroid protein 4.1. The availability of cloned erythrocyte protein 4.1 cDNA should facilitate the study of the functional characteristics of this protein in erythroid as well as non-erythroid cells.     

Regulation of glucose transporter synthesis in cultured human skin fibroblasts

The present study was designed to see the effects of glucose on glucose transporter expression and glucose transport activity using cultured human skin fibroblasts. When the cells were incubated with various concentrations of glucose (11.1-44.4 mM), no differences were found in the HepG2 glucose transporter mRNA, protein levels and basal and insulin-stimulated 2-deoxyglucose uptake. Glucose deprivation, however, resulted in approximately 4-fold increases in the mRNA and 3-fold increases in the protein and the basal 2-deoxyglucose uptake. Chronic exposure to insulin increased the glucose transporter protein levels to similar degrees in the cells incubated with 11.1, 22.2 and 44.4 mM glucose accompanied by increases in the glucose transport activity. Effects of insulin on the glucose transporter mRNA and protein levels, however, were not evident in the glucose-deprived cells. It is concluded that glucose transport activity correlates closely with HepG2 glucose transporter expression in cultured human fibroblasts and that glucose (11.1-44.4 mM) does not affect the glucose transporter expression and glucose transport activity.     

Sequence of a second human asialoglycoprotein receptor: conservation of two receptor genes during evolution.

The asialoglycoprotein (ASGP) receptor isolated from human liver and from the human hepatoma cell line HepG2 migrates on NaDodSO4 gel electrophoresis as a single species of 45,000 daltons. Recently, we isolated a cDNA clone encoding this receptor (H1) from a HepG2 lambda gt11 library. From the same library, we have isolated and sequenced a clone encoding a second ASGP receptor, H2, with a protein sequence homology of 58% to H1. There are two subspecies of H2 that differ only by the presence of a five-amino acid insertion in the COOH-terminal extracytoplasmic domain. Comparison with the available sequences of the two rat ASGP receptors R1 and R2 indicates that H1 is more homologous to R1 than to H2, and H2 is more similar to R2 than to H1. Thus, the two receptor genes evolved before the separation of rat and man. As judged by RNA blot hybridization of HepG2 RNA using RNA transcribed in vitro from cDNA clones of the human receptors as standards, H1 and H2 mRNA are present in equimolar amounts, each 0.005-0.01% of the total mRNA. This finding raises the question of whether the three ASGP receptor proteins are functional as heterodimers or whether they might serve different functions in the cell.     

树鼠句膜转运蛋白ATP结合盒转运体A1cDNA和蛋白质结构分析及其组织表达

目的获得不易感动脉粥样硬化动物树鼠句的膜转运蛋白ATP结合盒转运体A1的cDNA和蛋白质序列,鉴定其组织分布,探讨其是否参与树鼠句独特的高密度脂蛋白代谢。方法以树鼠句肝脏mRNA反转录获得的cDNA一链为模板,应用SMART-RACE技术,获得树鼠句ATP结合盒转运体A1 cDNA序列并推导出其氨基酸序列,应用实时聚合酶链反应技术分析树鼠句ATP结合盒转运体A1 mRNA在各组织中的分布情况。结果获得的树鼠句ATP结合盒转运体A1 cDNA序列全长为7 762 bp,其中开放阅读框架6 786 bp,编码2 261个氨基酸的蛋白。该蛋白与人ATP结合盒转运体A1的长度相同,二者在氨基酸水平上高度同源(95%)。多组织表达谱显示树鼠句ATP结合盒转运体A1在多种组织中广泛表达,其中表达量最高的依次为肺脏、肝脏、肾脏和脾脏,这与人和小鼠ATP结合盒转运体A1在肝中高表达而在肺和脾中低表达的分布有很大差异。结论树鼠句ATP结合盒转运体A1组织表达谱的特点有可能增加其在体内的浓度和数量,从而可能间接增加高密度脂蛋白的合成。