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Biomedical subjects

I Boime

Publications and source records attributed to I Boime.

At least 91 records · Page 5Linked to original sources
PubMed1985

Structural elucidation of the disulfated oligosaccharide from bovine lutropin.

The Asn-linked oligosaccharides of the pituitary hormone lutropin (LH) contain both sulfate and GalNAc. Bovine pituitary explants incorporate [3H]glucosamine, [3H]mannose, [3H]fucose, and [35S]sulfate into the Asn-linked oligosaccharides of LH. Endoglycosidase F or N-glycanase releases the [3H]glucosamine- and [3H]mannose-labeled oligosaccharides from the protein, which resolve on anion-exchange high pressure liquid chromatography as neutral (S-0), mono- (S-1), and disulfated (S-2) species. Based on sequential enzyme digestion, methylation, periodate oxidation, and nuclear magnetic resonance studies, the proposed structure for S-2 is as follows: formula see text. Sulfate is confined to position 3 or 4 of GalNAc based on periodate and methylation data and can be removed by methanolysis. The presence of beta-linked GalNAc at a position typically occupied by Gal has not previously been observed.

Animals↗
PubMed1985

Cell-free sulfation of human and bovine pituitary hormones. Comparison of the sulfated oligosaccharides of lutropin, follitropin, and thyrotropin.

Lutropin (LH), follitropin (FSH), and thyrotropin (TSH) from pituitary and human chorionic gonadotropin (hCG) from placenta are a family of glycoprotein hormones, each with an alpha and beta subunit. The alpha subunits of all four hormones have the same amino acid sequence, whereas biological specificity is determined by their unique beta subunits. The carbohydrate compositions of these hormones indicate the structures of their Asn-linked oligosaccharides are not identical. Sulfate is present on most, but not all, of these hormones, and for bovine LH is attached to GalNAc (Green, E.D., van Halbeek, H., Boime, I., and Baenziger, J.U. (1985) J. Biol. Chem. 260, 15623-15630). We used a reconstituted cell-free system to study sulfation of bovine (b) and human (h) glycoprotein hormones and its relationship to glycosylation. Exogenously added bLH, bTSH, bFSH, hLH, and hTSH are sulfated exclusively on the oligosaccharides of both alpha and beta subunits. The distribution of sulfated oligosaccharide structures varies among the hormones and appears to result from differences in the extent and/or pathway of oligosaccharide processing. Significant amounts of disulfated, dibranched complex oligosaccharides are present on all the sulfated hormones. Human FSH is not susceptible to sulfation unless first treated with neuraminidase. The sulfated oligosaccharides obtained from bovine FSH and desialylated human FSH are unlike those of the other hormones. Therefore, there is differential processing of the oligosaccharides on pituitary hormones. For FSH and LH, which are believed to be synthesized in the same cell, we would suggest that the unique beta subunits may regulate processing of all oligosaccharides present on the alpha-beta dimers.

Animals↗
PubMed1985

Structural requirements for sulfation of asparagine-linked oligosaccharides of lutropin.

Human and bovine pituitary glycoprotein hormones (lutropin, follitropin, and thyrotropin) contain varying amounts of N-acetylgalactosamine and sulfate. The sulfate on asparagine-linked oligosaccharides of bovine lutropin (bLH) is present exclusively on GalNAc in the sequence GalNAc(beta 1-4)GlcNAc(beta 1-2)Man alpha. We have examined the structural requirements for sulfation of bLH oligosaccharides by using a reconstituted cell-free system. After cleavage from the protein, oligosaccharides containing the sequence GalNAc(beta 1-4)Glc-NAc(beta 1-2)Man alpha were sulfated by enzymes in pituitary membranes. Addition of one or two sulfates was observed, depending upon the number of GalNAc acceptor sites on the oligosaccharide. Neither GalNAc alone nor oligosaccharides devoid of GalNAc were sulfated. Membranes from placenta or liver did not sulfate oligosaccharides released from bLH, indicating that the sulfating activity is pituitary-specific. The lack of peptide dependence for sulfation, in conjunction with the oligosaccharide specificity, suggests that the sequence GalNAc(beta 1-4)GlcNAc(beta 1-2)Man alpha contains the recognition signal for the sulfotransferase(s).

Adenine Nucleotides↗
PubMed1985

Differential expression of the human gonadotropin alpha gene in ectopic and eutopic cells.

We have analyzed the regulation of the alpha gonadotropin gene in eutopic placental cells and ectopic tumor cells by constructing a series of plasmid vectors containing alpha genomic 5' flanking DNA placed upstream of the gene encoding the bacterial enzyme chloramphenicol acetyltransferase (CAT). These plasmid DNAs were transfected into a eutopic (JAr) and an ectopic (HeLa) cell line. Both cell types expressed the CAT gene from plasmid constructs containing as much as 1,500 base pairs (bp) and as little as 140 bp of alpha 5' flanking DNA; JAr cells were considerably more efficient than HeLa cells. Ectopic and eutopic cells differed qualitatively in their expression from these alpha-CAT constructs when cells were treated with cAMP or butyrate. Butyrate induced alpha expression in HeLa cells but not in JAr cells, while cAMP induced expression in JAr cells. These results are consistent with and extend previous observations suggesting that there are cell-specific differences in the regulation of alpha gene expression in ectopic and eutopic cells. However, by using deletion constructs of the alpha-CAT gene, we found that the basal expression and cell-specific induction of the alpha gene in ectopic and eutopic cells were dependent on the same 140 bp of alpha 5' flanking DNA. These 140 bp were sequenced and found to contain a 9-bp stretch of DNA homologous with the consensus viral enhancer sequence. Such features of alpha expression common to both ectopic and eutopic cells may be involved in the coordinate expression of the alpha gene and the tumorigenic phenotype observed in each cell type.

Acetyltransferases↗
PubMed1985

Differential secretion of O-glycosylated gonadotropin alpha-subunit and luteinizing hormone (LH) in the presence of LH-releasing hormone.

The pituitary hormones LH, FSH, and TSH are secreted as dimers of two subunits, alpha and beta. The alpha-subunit, identical in all three hormones, is produced by the pituitary in excess of beta and secreted as free subunit. Bovine free alpha does not combine with purified beta-subunit and contains an extra O-linked oligosaccharide not found on dimer alpha. We have developed an assay to quantitate this modified form of alpha in the medium of incubated steer pituitary slices. The assay, based on reverse phase HPLC analysis of radiolabeled alpha-subunit tryptic peptides, shows that under basal conditions, 75% of secreted free alpha is O-glycosylated. When the secretagogue LHRH is added to the slices, a 14-fold increase in LH dimer release is observed, but secretion of the modified alpha is increased by only 2-fold. Our results indicate that the majority of free alpha-subunit secreted by the pituitary contains O-linked oligosaccharide, and that secretion of this form of alpha differs from that of LH dimer.

Animals↗
PubMed1985

[The expression of oncogene fms in human chorionic tissue].

The roles of oncogenes have been a subject of great interest not only concerning oncogenesis but also recently concerning physiological regulation in cell proliferation and cell differentiation. We here report the expression of oncogene fms in human chorionic tissue using a molecular hybridization method. RNAs extracted from human chorionic tissue of the first and third trimester were electrophoresed in horizontal agarose gel, blotted according to Northern's method and were hybridized to 32P labeled fms-cDNA (complementary DNA). Four kb RNA molecules homologous to fms-cDNA were detected in chorionic RNAs of the first and third trimester placental tissue with an increase toward term. We then observed the distribution of fms-mRNA in chorionic tissue with in situ hybridization. The signals for fms were observed over trophoblasts without specific localization to the proliferative cells. These results revealed that oncogene fms is expressed in human chorionic tissue of both the first and third trimester. Furthermore the results suggest that the role of fms c-onc may be related to cell differentiation and not to cell proliferation.

Cell Differentiation↗
PubMed1984

Posttranslational modification of the carboxy-terminal region of the beta subunit of human chorionic gonadotropin.

The beta subunit of human chorionic gonadotropin (hCG) contains at its carboxy terminus an extension of 29 amino acids not found in the beta subunits of the other glycoprotein hormones. This region provides the sites of attachment of four serine-linked oligosaccharide chains. We have examined the synthesis of this subunit in a cell-free translation system derived from Krebs II ascites tumor cells. The primary translation product was found to undergo a temperature-dependent posttranslational modification which resulted in an increase in apparent molecular weight of 2000 on sodium dodecyl sulfate gel electrophoresis. This modification was specific for the beta subunit of hCG, since no changes were observed for the beta subunit of bovine luteinizing hormone or for the alpha subunits of either hormone. The increase in molecular weight occurred in the absence of microsomal membranes and was not due to the addition of N-linked carbohydrate. An identical shift was observed when pre-hCG beta was incubated with extracts of human placenta. The site of modification was localized by fingerprint analysis to a carboxy-terminal tryptic peptide which contains two of the four O-glycosylated serine residues in the mature form of the subunit. The modified protein was resistant to oligosaccharidase digestion and beta-elimination, indicating that it does not contain O-linked oligosaccharides of the type found on mature hCG beta. These results demonstrate that a specific modification of the carboxy-terminal segment of hCG beta synthesized in vitro occurs in the absence of O-linked glycosylation.

Amino Acid Sequence↗
PubMed1984

The role of trophoblast differentiation in the control of the hCG and hPL genes.

Normal trophoblast of the human placenta elaborates at least two major protein hormones, hCG and hPL. Molar and choriocarcinoma tissues characteristically synthesize large amounts of hCG and small quantities of hPL. To examine the role of trophoblast differentiation in the expression of the hCG and hPL genes, we studied the cytological distribution of their mRNAs in tissue sections of human hydatidiform mole and choriocarcinoma by in situ hybridization. Histologically, these tissues are in different stages of cellular differentiation. In normal placenta, hCG alpha and hCG beta mRNAs can be localized to some cytotrophoblasts and primarily to the syncytium, whereas hPL mRNA appears only in the syncytial layer. In hydatidiform mole, which still retains placental villous morphology, the hPL gene and hCG alpha and hCG beta genes are expressed but are poorly localized because of the admixture of cyto- and syncytiotrophoblasts. By contrast, choriocarcinoma, which is devoid of placental villous pattern but in which the cyto- and syncytiotrophoblast-like components are distinguishable, expresses hCG alpha and hCG beta in the syncytial-like areas but little, if any, hPL. These results suggest that a certain level of trophoblast differentiation, such as villus formation, is associated with hPL expression, while the hCG alpha gene and the hCG beta gene can be expressed in more disorganized tissues which contain cytotrophoblastic elements.

Cell Differentiation↗
PubMed1984

Sulfation of lutropin oligosaccharides with a cell-free system.

Sulfate is covalently linked to the oligosaccharides on the alpha and beta subunits of bovine lutropin (luteinizing hormone; LH) but not to those on human chorionic gonadotropin (hCG). Since the amino acid sequences of the pituitary and placental alpha subunits are homologous, comparison of their asparagine-linked sugars can provide information regarding tissue specificity of oligosaccharide maturation. To characterize this post-translational modification, we have developed a reconstituted cell-free sulfation system. Sulfate is incorporated into exogenously added glycoproteins by sulfotransferases from Triton X-100-lysed Golgi membranes in the presence of 3'-phosphoadenosine 5'-phospho[35S]sulfate, which is generated from [35S]sulfate by a ribosome-free supernate from Krebs ascites tumor cells. LH is sulfated by pituitary and liver membranes but not by those from placenta. Desialylated hCG (AshCG) is sulfated by membranes from placenta and pituitary, but not liver, while hCG is not sulfated by any of these membranes. Endoglycosidase F releases all the incorporated sulfate from LH in the form of a heterogeneous mixture of mono- and disulfated oligosaccharides. In contrast, the sulfate added to AshCG is apparently attached to peptide rather than oligosaccharide. As found with the cell-free system, sulfate metabolically incorporated into LH by pituitary cells is present on a heterogeneous population of mono- and disulfated oligosaccharides. Thus the cell-free sulfation system accurately duplicates the in vivo process.

Animals↗
PubMed1984

Segregation patterns of polymorphic restriction sites of the gene encoding the alpha subunit of human chorionic gonadotropin in trophoblastic disease.

The gene encoding the alpha subunit of human chorionic gonadotropin contains at least two polymorphic sites in its 3' flanking region detected by restriction enzymes HindIII and EcoRI. We used these polymorphic sites as markers of tissue genotype in normal placenta, hydatidiform mole, choriocarcinoma, and peripheral leukocytes. As expected, inheritance patterns of most hydatidiform moles showed only a paternal genetic contribution. However, one uncommon DNA polymorphism pattern, homozygosity for the absence of the EcoRI site and the presence of the HindIII site, predominated in choriocarcinoma. Thus, our results suggest that moles which have this uncommon polymorphism pattern appear particularly likely to develop into choriocarcinoma.

Choriocarcinoma↗
PubMed1984

[Molecular biological analysis of the DNA in trophoblastic disease--with special reference to genetic information of hPL and hCG(alpha, beta)].

Genomic DNAs extracted from normal placenta, while blood cells, hydatidiform mole and choriocarcinoma were examined to see if they had the same coding structure for hPL, hCG alpha and hCG beta using each of the complementary DNAs. The restriction analysis of these genomic DNAs showed the same pattern even for the DNA of choriocarcinoma that transcribed no hPL mRNA but a relatively high level of hCG(alpha,beta)mRNA. We considered that during trophoblastic malignant transformation, neither the gene deletion for hPL nor the gene amplification for hCG occurred. Moreover, the genomic DNA sequence in hCG alpha gene has polymorphic restriction sites designated as R+/- and H+/-. Using these polymorphisms, we confirmed the hypothesis that a hydatidiform mole develops from an androgenetic origin. We also observed that it is possible that a hydatidiform mole having R- and H+ homozygous DNA may develop into a choriocarcinoma. These observation suggested that some intervening sequence between these polymorphic sites is related to the tumorigenesis of choriocarcinoma.

Chorionic Gonadotropin↗
PubMed1984

[Cytological localization of hPL, hCG, and mRNA in chorionic tissue using in situ hybridization].

The human trophoblast elaborates at least two major hormones, hPL and hCG(alpha, beta). To clarify the mechanism of biosynthesis and the gene expression of hPL and hCG(alpha, beta), the specific mRNA should be examined. We here studied the cytological distribution of these mRNAs in trophoblastic tissue of normal placenta, hydatidiform mole and choriocarcinoma by in situ hybridization using complementary DNAs(cDNA) corresponding to hPL and hCG alpha, beta-subunit. mRNAs for hPL and hCG alpha, beta were primarily observed on syncytiorophoblasts excepting some cytotrophoblasts which contain the signals for hCG alpha mRNA and probably beta mRNA. Therefore, we came to the conclusion that hPL and hCG were synthesized mainly in syncytiotrophoblasts. AT the same time, we believe that the gene expression of hCG alpha and probably hCG beta begins before transformation from cyto- to syncytiotrophoblast, while that of hPL appears later in well differentiated syncytiotrophoblasts. On the other hand, in choriocarcinoma hPL mRNA was not observed while many signals for hCG alpha, beta mRNA were localized in syncytiotrophoblastic cells. In other words, the hPL gene was not expressed in choriocarcinoma because of the blocking of trophoblastic differentiation. The data presented here show that the gene expression of hPL and hCG alpha, beta is closely related to trophoblastic differentiation and/or dedifferentiation (tumoregenesis).

Choriocarcinoma↗
PubMed1983

The beta subunit of human chorionic gonadotropin is encoded by multiple genes.

Two recombinant phage clones bearing sequences corresponding to the beta subunit of human chorionic gonadotropin (hCG beta) were isolated from a human genomic library. The beta sequences were mapped by blot hybridization of restriction digests of these phage DNAs and the nonoverlapping inserts were subcloned in pBR322 and sequenced. The nucleotide-sequencing data show that the hCG beta subunit is encoded by at least three nonallelic genes. Moreover, based on restriction analyses of human placental DNA, these genes may be linked in a single cluster with four other hCG beta-like genes. The sequenced genes all differ in their 5' flanking regions, and none of them is completely homologous in sequence to either of two hCG beta cDNA clones used here. In the translated region of one of these genes, three base substitutions result in two changes from the reported amino acid sequence. In the family of beta-containing glycoprotein hormones, the hCG beta subunit is unique in that it contains an extension of 29 amino acids at its COOH end. The DNA sequence corresponding to this region in the sequenced genes is part of a larger exon. These data show that the COOH-terminal extension does not result from splicing of the primary RNA transcript.

Amino Acid Sequence↗
PubMed1983

Imbalanced synthesis of human choriogonadotropin alpha and beta subunits reflects the steady state levels of the corresponding mRNAs.

Previous studies have demonstrated an imbalance in placental levels of the human choriogonadotropin (hCG) alpha and beta subunits. Free alpha subunit was present in first trimester placentae, and the imbalance was accentuated as gestation approached parturition. Two sets of experiments were performed to assess the control on production levels of each subunit. Synthesis of the alpha and beta subunits was assessed by labeling the nascent chains of polysomes derived from first trimester placenta. The products of these reactions were immunoprecipitated with subunit-specific antisera and the labeled subunits were quantitated; the ratio of alpha to beta subunit synthesized was 1.7. To examine whether this imbalanced synthesis reflected differences in the amount of subunit mRNAs, or differing mRNA translational efficiencies, the ratio of the steady state levels of these mRNAs was also determined. Total first trimester placental RNA was hydrolyzed with alkali, 5'-end-labeled with 32P, and hybridized in DNA excess to cloned alpha and beta cDNAs. These experiments demonstrated the presence of twice as much hCG-alpha mRNA as hCG-beta mRNA. In term placenta, the amounts of excess alpha subunit are greater than at first trimester; the ratio of alpha to beta mRNAs in term RNA was about 12:1. Thus, the subunit mRNA levels are independently regulated and their imbalance accounts for differences in the quantities of alpha and beta subunits seen in placental tissue.

Base Sequence↗
PubMed1983

DL-threo-beta-fluoroasparagine inhibits asparagine-linked glycosylation in cell-free lysates.

The effect of beta-fluoroasparagine on N-linked glycosylation was examined in a cell-free translation system in which glycosylation is coupled to protein synthesis. The threo-isomer markedly inhibited glycosylation at a concentration of 1 mM, and this effect was blocked by L-asparagine, indicating that glycosylation was inhibited secondary to incorporation of the asparagine analog into protein. The erythro-isomer, at similar concentrations, was not incorporated into protein and had no effect on glycosylation. threo-beta-Fluoroasparagine is highly toxic to some mammalian cells in culture. Our observations suggest that its toxicity may be due in part to the failure of the fluoroasparagine-containing protein to become glycosylated. The data suggest that this analog will be useful for examining the structural determinants for glycosylation.

Animals↗
PubMed1983

Cytological distribution of chorionic gonadotropin subunit and placental lactogen messenger RNA in neoplasms derived from human placenta.

Normal trophoblast of the human placenta elaborates at least two major protein hormones, chorionic gonadotropin (hCG), and placental lactogen (hPL). There are several gestational trophoblastic diseases of the placenta called hydatidiform mole, invasive mole, and choriocarcinoma. Molar and choriocarcinoma tissues characteristically synthesize large amounts of hCG and small quantities of hPL. To examine the role of trophoblast differentiation in the expression of the hCG and hPL genes, we studied the cytological distribution of their messenger RNA (mRNA) in tissue sections of human hydatidiform mole and choriocarcinoma by in situ hybridization. Histologically, these tissues are in different stages of cellular differentiation. In normal placenta, hCG alpha and -beta mRNA can be localized to some cytotrophoblasts and primarily to the syncytium, whereas hPL mRNA appears only in the syncytial layer. In hydatidiform mole, which still retains placental villous morphology, the hPL gene and hCG alpha and -beta genes are expressed but are poorly localized because of the admixture of cyto- and syncytiotrophoblasts. By contrast, choriocarcinoma, which is devoid of placental villous pattern but in which the cyto- and syncytiotrophoblast-like components are distinguishable, expresses hCG alpha and -beta in the syncytial-like areas but little, if any, hPL. These results suggest that a certain level of trophoblast differentiation, such as villous formation, is associated with hPL expression, while the hCG alpha gene and the hCG beta gene can be expressed in more disorganized tissues that contain cytotrophoblastic elements.

Cell Differentiation↗
PubMed1982

Synthesis of bovine lutropin in cell-free lysates containing pituitary microsomes.

Bovine pituitary rough microsomes were used to determine the ratio of newly synthesized lutropin (LH) alpha and beta subunits in different physiological states of animals. Proteins synthesized by microsomal runoff are derived from preinitiated mRNAs and thus, in the present case, should reflect the initial intracellular steady state levels of the subunits. The products were identified by immunoprecipitation using bovine LH subunit specific antisera and analyzed by electrophoresis on sodium dodecyl sulfate-polyacrylamide gels. Microsomes isolated from castrated animals (steers) synthesized comparable amounts of LH alpha- and LH beta-subunits as determined by quantitation of the immunoprecipitated products. However, microsomes from intact animals (bulls) directed the synthesis of 3-5 times more alpha than LH beta. A comparison of the levels of alpha- and LH beta-subunits synthesized by an equivalent concentration of bull and steer pituitary microsomes indicates that the increased ratio of alpha to LH beta in bull pituitary microsomes is the result of a preferential decrease in the synthesis of the LH beta subunit. The results suggest that the rate of beta subunit synthesis determines the level of intact LH produced.

Animals↗