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The amino-terminal sequences in the pro-alpha and -beta polypeptides of human lysosomal beta-hexosaminidase A and B are retained in the mature isozymes.

The alpha- and beta-subunits of beta-hexosaminidase (beta-N-acetylhexosaminidase, EC 3.2.1.52) are synthesized in the rough endoplasmic reticulum as prepropolypeptides. After the loss of the signal peptide and formation of enzymatically active dimers, the pro-isoenzymes are transported through the Golgi and into the lysosome for proteolytic and glycolytic processing to their stable mature forms. Maturation includes the hydrolysis, and previously presumed loss, of small N-terminal peptides from each propolypeptide. A recent report characterizing the processing of the beta-prepropolypeptide in beta-hexosaminidase from a human fibroblast cell line [(1989) J. Biol. Chem. 264, 3380-3384] reported that the small pro-beta peptide was retained through a disulfide bond in the mature subunit, and that it was glycosylated. We have confirmed this result in normal human tissue. However, we report a different N-terminal for the mature pro-beta peptide. Furthermore, we have found that the pro-alpha peptide is similarly retained in the mature alpha-subunit through its single cysteine residue and that each pro-peptide undergoes C-terminal processing.

Amino Acid Sequence↗

Production and characterization of antibody blocking epidermal growth factor:receptor interactions.

Membranes were prepared from the human epithelioid carcinoma cell line A-431 which has approx. 2 . 10(6) epidermal growth factor receptors per cell. This membrane preparation which retained a high epidermal growth factor binding specific activity was used as an antigen to produce antisera in rabbits. Double-immunodiffusion experiments demonstrated that the immune serum contained precipitating antibodies to several components of detergent solubilized A-431 membranes. The immunoglobulin G fraction of this immune sera inhibited 125I-labeled epidermal growth factor binding to receptors in: (1) intact human and mouse cells; (2) membrane preparations from A-431 cells and human placenta, and (3) solubilized A-431 membranes. Inhibition of 125I-labeled epidermal growth factor binding was observed with divalent and monovalent fragments of immunoglobulin G prepared from the immunoglobulin G fraction. Also, the immunoglobulin G fraction blocked growth factor binding to membranes at low temperature (5 degrees C). Anti-A-431 antibody blocked the induction of DNA synthesis in quiescent fibroblasts by epidermal growth factor in a manner similar to that of anti-epidermal growth factor antibody. Addition of either anti-A431 or anti-epidermal growth factor antibodies to fibroblasts at times up to 5 h after the addition of epidermal growth factor completely reversed the hormone's mitogenic potential. At later times (after 12 h) addition of either antibody was without effect on the stimulation of DNA synthesis by epidermal growth factor. Anti-A-431 antibody did not block the induction of DNA synthesis in fibroblasts by fibroblast growth factor or serum.

Animals↗

Developmental control and alternative splicing of the placentally expressed transcripts from the human growth hormone gene cluster.

Four of the five genes in the human growth hormone gene cluster are expressed in the villous layer of the placenta. We report that the expression of these genes, hCS-A, hCS-B, hCS-L, and hGH-V, are coordinately induced during fetal development, increasing between 12 and 20 weeks of gestation and then plateauing through term. Within the context of this coordinate activation, these genes are expressed at widely different levels and are alternatively spliced in different patterns. There is a developmentally regulated switch in the relative expression of the two chorionic somatomammotropin genes, hCS-A and hCS-B. Starting from approximately equal levels at 8 weeks of gestation, hCS-A is expressed 5-fold more abundantly than hCS-B by term. The proportion of alternatively spliced hGH-V transcripts that retain intron 4 is also developmentally regulated, increasing 3-fold during gestation to 15% at term. A small percentage of hCS transcripts stably retain intron 4 through gestation, the majority derived from the hCS-A gene. hCS-L transcripts undergo two distinct, developmentally stable, splicing pathways between exons 2 and 3. These result from the absence of the normal splice-donor site in intron 2 and the activation of two cryptic splice-acceptor sites. Despite high levels of sequence identity, the four placentally expressed genes in the growth hormone cluster generate a complex set of mRNAs based on alternative splicing and developmental regulation during gestation.

Amino Acid Sequence↗

Production of recombinant proteins in plant root exudates.

The large-scale production of recombinant proteins in plants is limited by relatively low yields and difficulties in extraction and purification. These problems were addressed by engineering tobacco plants to continuously secrete recombinant proteins from their roots into a simple hydroponic medium. Three heterologous proteins of diverse origins (green fluorescent protein of jellyfish, human placental alkaline phosphatase [SEAP], and bacterial xylanase) were produced using the root secretion method (rhizosecretion). Protein secretion was dependent on the presence of the endoplasmic reticulum signal peptide fused to the recombinant protein sequence. All three secreted proteins retained their biological activity and, as shown for SEAP, accumulated in much higher amounts in the medium than in the root tissue.

Alkaline Phosphatase↗

Selectivity of the cleavage/attachment site of phosphatidylinositol-glycan-anchored membrane proteins determined by site-specific mutagenesis at Asp-484 of placental alkaline phosphatase.

Many proteins are now known to be anchored to the plasma membrane by a phosphatidylinositol-glycan (PI-G) moiety that is attached to their COOH termini. Placental alkaline phosphatase (PLAP) has been used as a model for investigating mechanisms involved in the COOH-terminal processing of PI-G-tailed proteins. The COOH-terminal domain of pre-pro-PLAP provides a signal for processing during which a largely hydrophobic 29-residue COOH-terminal peptide is removed, and the PI-G moiety is added to the newly exposed Asp-484 terminus. This cleavage/attachment site was subjected to an almost saturation mutagenesis, and the enzymatic activities, COOH-terminal processing, and cellular localizations of the various mutant PLAP forms were determined. Substitution of Asp-484 by glycine, alanine, cysteine, asparagine, or serine (category I) resulted in PI-G-tailed and enzymatically active proteins. However, not all category I mutant proteins were PI-G tailed to the same extent. Pre-pro-PLAP with other substituents at position 484 (threonine, proline, methionine, valine, leucine, tyrosine, tryptophan, lysine, glutamic acid, and glutamine; category II) were expressed, as well as the category I amino acids, but there was little or no processing to the PI-G-tailed form, and this latter group exhibited very low enzyme activity. The bulk of the PLAP protein produced by category II mutants and some produced by category I mutants were sequestered within the cell, apparently in the endoplasmic reticulum (ER). Most likely, certain amino acids at residue 484 are preferred because they yield better substrates for the putative "transamidating" enzyme. In transfected COS cells, at least, posttranslational PI-G-tail processing does not go to completion even for preferred substrates. Apparently PI-G tailing is a requisite for transport from the ER and for PLAP enzyme activity. Proteins that are not transamidated are apparently retained in the ER in an inactive conformation.

Alkaline Phosphatase↗

Vitamin A nutrition in the human foetus. A comparison of Sweden and Ethiopia.

The accumulation of vitamin A during foetal development was investigated post mortem in foetuses and newborn infants of well-defined socio-economic groups of Swedish and Ethiopian women. The median vitamin A concentration in the liver was 37.0 micrograms/g in the Swedish foetuses (n = 39) and 9.1 micrograms/g in the Ethiopian ones (n = 49) (p less than 0.001). The liver vitamin A concentration in the Swedish foetuses increased exponentially during the second and third trimesters of pregnancy. This trend was not evident in the Ethiopian material. The mean serum concentration of retinol-binding protein was only slightly lower in the healthy Ethiopian newborns (18.6 mg/l; n = 70.) than in the Swedish newborns. This finding suggests that vitamin A is retained i the foetal circulation in preference to storage, much like the situation in a vitamin A deficiency state in the adult.

Adolescent↗

Differential properties of attachment of human fibroblasts to various extracellular matrix proteins.

Human diploid fibroblasts (TIG-3) were shown to attach and spread onto substrata coated with collagen, fibronectin, laminin and vitronectin. The cell attachment to these proteins required divalent cations. Mg2+ stimulated the cell attachment to all the proteins, while Ca2+ alone was not effective for the attachment to collagen and laminin. A mild trypsin treatment had prevented cells from attaching to the laminin, while it had no effect on the attachment to the other proteins. The fibronectin fragment, which retained cell binding activity, inhibited the cells from attaching and spreading onto fibronectin, but it did not cause any inhibition on the other proteins. The synthetic peptide GRGDSP inhibited the cells from attaching and spreading onto fibronectin and vitronectin, while it did not cause any inhibition on collagen and laminin. In attempts to isolate distinct receptors for these proteins, we were able to purify proteins very similar to the fibronectin and vitronectin receptors of human placenta. Based on the differential properties of the attachment of TIG-3 cells to these proteins and biochemical data, we indicate that human diploid fibroblasts have distinctive binding sites (receptors) for collagen, fibronectin, laminin and vitronectin.

Cations, Divalent↗

Comparison of glycosylation patterns of placental proteins between normal pregnancy and missed abortion.

Contemporary understanding of missed abortion, as the case of spontaneous abortion where embryo is retained in uterus for four-weeks or more after its death, is very poor. Aiming to improve the level of knowledge about this process, we have compared glycosylation patterns of placental proteins in normal pregnancy and missed abortion. Oligosaccharide branches were detected by Western-blot using SNA, DBA and PHA-E lectins. The comparison of samples of the same gestational age enabled identification of changes in protein glycosylation between normal and pathological placentas. Lectin DBA detects in normal placenta the glycoprotein GP 105 during the eleventh week, which is absent in missed abortion. PHA-E identifies GP 71 during fourteenth week only in normal placenta. However GP 25 recognized by SNA in missed abortion was not found in normal pregnancy at tenth week. These results indicate that abnormal placental development is associated with changes in glycoprotein structures, and that glycoconjugates might have an important role in placental development.

Abortion, Missed↗

Molecular cloning of the alpha-subunit of human prolyl 4-hydroxylase: the complete cDNA-derived amino acid sequence and evidence for alternative splicing of RNA transcripts.

Prolyl 4-hydroxylase [procollagen-proline, 2-oxyglutarate 4-dioxygenase; procollagen-L-proline, 2-oxoglutarate:oxygen oxidoreductase (4-hydroxylating), EC 1.14.11.2], an alpha 2 beta 2 tetramer, catalyzes the formation of 4-hydroxyproline in collagens by the hydroxylation of proline residues in peptide linkages. We report here on the isolation of cDNA clones encoding the alpha-subunit of the enzyme from human tumor HT-1080, placenta, and fibroblast cDNA libraries. Eight overlapping clones covering almost all of the corresponding 3000-nucleotide mRNA, including all the coding sequences, were characterized. These clones encode a polypeptide of 517 amino acid residues and a signal peptide of 17 amino acids. Previous characterization of cDNA clones for the beta-subunit of prolyl 4-hydroxylase has indicated that its C terminus has the amino acid sequence Lys-Asp-Glu-Leu, which, it has been suggested, is necessary for the retention of a polypeptide within the lumen of the endoplasmic reticulum. The alpha-subunit does not have this C-terminal sequence, and thus one function of the beta-subunit in the prolyl 4-hydroxylase tetramer appears to be to retain the enzyme within this cell organelle. Interestingly, three of the cDNA clones for the alpha-subunit contained a 64-nucleotide sequence homologous but not identical to the corresponding 64-nucleotide sequence found in four other cDNA clones. Nuclease S1 mapping experiments demonstrated that this difference was due to the existence of two types of mRNA present in approximately equal amounts. Southern blot analyses of human genomic DNA with a cDNA probe for the alpha-subunit suggested the presence of only one gene encoding the two types of mRNA, which appear to result from mutually exclusive alternative splicing of primary transcripts of one gene.

Amino Acid Sequence↗

Induced abortion and ectopic pregnancy in subsequent pregnancies.

In a prospective study the rate of ectopic pregnancies of women with prior induced abortion was contrasted to two sets of comparison groups: a large set of unmatched observations and a smaller subset of matched and refined data. The crude rates of ectopic pregnancy among 4004 abortion and 98,316 control pregnancies, excluding repeat pregnancies of the same women, were 0.57% and 0.49%, respectively. No significant association was detected between history of induced abortion and ectopic pregnancy based on the chi 2 analysis on unmatched data stratified by maternal age and marital status (relative risk = 1.18, 95% confidence limits (CL) 0.57-1.79) or the multivariate logistic regression analysis on the smaller set of data (relative risk = 1.34, 95% CL 0.66-2.72). Within pregnancies of the induced abortion group the risk of ectopic pregnancy was not related to abortion procedure, use of laminaria, number of prior induced abortions, or length of gestation at time of abortion. However, there was a clear association between the presence of post-abortion infection or retained secundines and ectopic pregnancy with a fivefold increase for those pregnancies of women with a history of these complications over those without these complications within the induced abortion cohort.

Abortion, Induced↗

Description of a human placental anti-insulin receptor polyclonal antibody that activates insulin binding to the receptor in vitro.

A polyclonal anti-human placental insulin receptor antibody has been developed, and its interaction with the receptor has been studied in vitro. This antibody enhances insulin binding to the receptor, both in the immunoprecipitate and also in in vitro binding assay. In the Scatchard analysis of the insulin-receptor interaction, in the presence of the antiserum, a marked increase in Bmax is observed, while Kd remains more or less unaffected. This antibody recognizes insulin receptor from all tissues of old world monkey but does not recognize new world monkey, rat or mouse receptor. Insulin receptor binds to this antibody very strongly on a immunoaffinity column and cannot be eluted by gentle means, but it retains insulin stimulated tyrosine kinase activity while immobilized to immunoaffinity column. This antibody also activates insulin receptor mediated histone phosphorylation in vitro. It has been proposed that this antireceptor antibody modulates receptor function by causing conformational perturbation in vitro.

Animals↗

Osmoregulation, the secretion of arginine vasopressin and its metabolism during pregnancy.

This review stresses changes in osmoregulation as well as the secretion and metabolism of arginine vasopressin during pregnancy, focusing on human gestation. Pregnant women experience a decrease in body tonicity, plasma osmolality decreasing immediately after conception to a nadir approximately 10 mosmol/kg below non-pregnant levels early in pregnancy, after which a new steady state is maintained until term. Data from both human and rodent gestation have led to a formation of how these changes occur. The osmotic thresholds for thirst and antidiuretic hormone release decrease in parallel. Lowering the threshold to drink stimulates increased water intake and dilution of body fluids. Because arginine vasopressin (AVP) release is not suppressed at the usual level of body tonicity, the hormone continues to circulate and the ingested water is retained. Plasma osmolality declines until it is below the osmotic thirst threshold, and a new steady state with little change in water turnover is established. Pregnancy is characterized by increments in intravascular volume, but volume-sensing AVP release mechanisms appear to adjust as gestation progresses so that each new volume status is "sensed" as normal. The metabolic clearance of AVP increases fourfold, the rise paralleling that of circulating cystine aminopeptidase (vasopressinase), and enzyme produced by the placenta. Furthermore, the disposal rate of 1-deamino-8-D-AVP, and AVP analogue resistant to inactivation by vasopressinase, is unaltered in pregnancy. Thus, the increase in AVP's metabolism and the high circulating aminopeptidase levels have been implicated in certain forms of transient diabetes insipidus that occur in late pregnancy. Finally, mechanisms responsible for the altered osmoregulation in pregnancy are obscure, but chorionic gonadotropin and relaxin may be implicated in the changes.

Animals↗

Renal and hormonal effects of water deprivation in late-term pregnant rats.

Water-retaining hormones are stimulated during pregnancy allowing normal volume expansion. Because pregnant rats actively retain water, we postulate that water deprivation (WD) would cause a greater reduction in plasma volume in pregnant than in nonpregnant rats. To test this hypothesis, Sprague-Dawley pregnant and nonpregnant rats were water-deprived for 48 hours. At day 19 of pregnancy, or in the corresponding day in nonpregnant rats, they were randomly assigned to either a WD or a control (C) pair-fed group (n=10 to 12 per group). WD significantly reduced body weight, food intake, and creatinine clearance, and increased urinary osmolality in nonpregnant and pregnant rats. WD reduced plasma volume in a similar proportion in nonpregnant and pregnant rats (nonpregnant rats C=13.1+/-0.4, WD=11.0+/-0.2; pregnant rats C=19.4+/-0.7, WD=16.8+/-0.5 mL, P<0.001). Both groups of pregnant rats had a similar reduction in blood pressure. Plasma renin activity (nonpregnant rats C=6.1+/-1.1, WD=20.5+/-2.0; pregnant rats C=49+/-9.7, WD=94+/-12 ng angiotensin I/mL per hour, P<0.001) and plasma aldosterone levels were increased by pregnancy and further increased by WD. WD significantly reduced urinary kallikrein. WD caused a significant reduction in fetal but not placental weights. Present data indicate that 48-hour WD reduced renal kallikrein and further stimulated water-retaining hormones. We speculate that these are compensatory changes contributing to the maintenance of pregnancy in response to WD.

Aldosterone↗

Implication of inhibin and related proteins in fetal development.

Initial studies on inhibin, activin and follistatin focussed on their role as regulators of adult gonadal function via feedback regulation of anterior pituitary hormones and via intragonadal control of steroid hormones. The discovery of isoforms of follistatin which are either secreted or retained on the cell surface and which bind activin and, to a lesser extent, inhibin adds a further dimension to the regulation of these peptides. More recently, the cloning of inhibin and activin, and the observation of their close homology to the transforming growth factor-beta family of peptides, has led to an interest in their possible role as growth and differentiation factors. Activin, inhibin and follistatin are expressed in embryonic and fetal tissues, as well as in the placenta. However, although activin is a potent regulator of growth and differentiation in a number of cell types, their role in embryonic and fetal development has yet to be established. High concentrations of inhibin have been observed in the fetal gonads, particularly the testes, and in the fetal adrenals of a number of species and a sex difference in fetal plasma concentrations has also been observed. Although the stimulus for high concentrations of inhibin in the fetus is not know, they are associated with decreased testicular testosterone and a decrease in the concentration of circulating follicle-stimulating hormone (FSH); this suggests that, as in the adult, inhibin may be involved in the regulation of fetal testicular androgen and pituitary FSH secretion during late gestation. The recent reports of elevated concentrations of inhibin and, particularly, activin in amniotic fluid during late gestation and its ability to stimulate the production of prostaglandin E2 by fetal membranes provides yet another potential role for this hormone in the regulation of events leading to parturition.

Activins↗

The proportion of symmetric and asymmetric IgG antibody molecules synthesized by a cellular clone (hybridoma) can be regulated by placental culture supernatants.

The purpose of the present work was to establish whether the placenta is producing factors favoring an increased synthesis of asymmetric IgG antibodies which are known to assume a protective effect upon paternal antigens to which they largely are specific. In this way they can contribute to fetal survival in the maternal uterine environment. The hybridoma cell lines OKT8 (anti-CD8) and 112B4 (anti-DNP) were used in this respect since they synthesized both symmetric and asymmetric molecules of the IgG2a and IgG1 subclasses, respectively, murine isotypes in which anti-paternal antibodies have been detected. The cells were cultured in RPMI 1640 medium supplemented with 10% BCS and different amounts (5, 10, and 20%) of human placental supernatant. After incubation for 3 days at 37 degrees C in a humid chamber containing 5% CO2 the cells were centrifuged and the antibodies were obtained from the culture medium by a purification procedure involving precipitation at 50% ammonium sulfate saturation followed by DEAE-cellulose chromatography. Symmetric and asymmetric antibodies were separated by Con A-Sepharose affinity chromatography, the latter lectin retaining selectively only asymmetric IgG molecules. Both OKT8 and 112B4 hybridomas presenting a stable background synthesis of 15-17% of asymmetric antibodies have shown an increased level reaching 27-28% of these molecules in the presence of 5-10% placental supernatant added to the RPMI 1640 culture medium. These results clearly show that placental factors can up-regulate efficiently the synthesis of asymmetric IgG molecules of different isotypes secreted by plasma cells.

Animals↗

Rabbit placental-conditioned medium stimulates progesterone accumulation by granulosa-lutein cells in culture: preliminary characterization of a placental luteotropic hormone.

The rabbit fetal placenta plays an important physiological role in luteal maintenance in pregnancy, probably via the secretion of an unidentified placental "luteotropin." The objective of these studies was to examine conditioned medium from fetal placental-tissue incubations (FPI) for the presence of placental luteotropic hormones/factors, using the stimulation of progesterone accumulation by rabbit granulosa-lutein cells in culture, as an in vitro luteotropic bioassay. Progesterone accumulation by rabbit granulosa-lutein cells (during 5 days of culture) was increased (compared with controls), 1.5-fold by 10(-8) M estradiol-17 beta (E2) and 11.5-fold by 100 ng/ml luteinizing hormone (oLH). FPI stimulated progesterone accumulation (approximately 3-fold) and this was further increased in the presence of E2 (FPI + E2; approximately 6-fold). Luteotropic bioactivity in FPI (+ E2) was retained after dialysis (6000-8000 MW cutoff; 7.8-fold) and heating (90-95 degrees C for 1 h; 7.5-fold), but was destroyed after incubation with trypsin (1 mg/ml, 1 h at 37 degrees C; 0.9-fold). Media conditioned with skeletal muscle (1.2-fold), heart (1.6-fold), liver (1.5-fold), and uterus (0.5-fold) and 5-10% serum (less than 1-fold), from pseudopregnant rabbits, had little or no luteotropic bioactivity. These data indicate that FPI contains a luteotropic hormone/factor that is probably a heat-stable, trypsin-sensitive, protein/peptide of greater than 6000-8000 MW that acts in synergy with E2 to promote granulosa-lutein cell steroidogenesis. This placental hormone/factor is a good candidate for the elusive rabbit placental luteotropin.

Animals↗

Factors affecting the ability of glycosylphosphatidylinositol-specific phospholipase D to degrade the membrane anchors of cell surface proteins.

Mammalian serum and plasma contain high levels of glycosylphosphatidylinositol-specific phospholipase D (GPI-PLD). Previous studies with crude serum or partially purified GPI-PLD have shown that this enzyme is capable of degrading the GPI anchor of several purified detergent-solubilized cell surface proteins yet is unable to act on GPI-anchored proteins located in intact cells. Treatment of intact ROS17/2.8, WISH or HeLa cells (or membrane fractions prepared from them) with GPI-PLD purified from bovine serum by immunoaffinity chromatography gave no detectable release of alkaline phosphatase into the medium. However, when membranes were treated with GPI-PLD in the presence of 0.1% Nonidet P-40 substantial GPI anchor degradation (as measured by Triton X-114 phase separation) was observed. The mechanism of this stimulatory effect of detergent was further investigated using [3H]myristate-labelled variant surface glycoprotein and human placental alkaline phosphatase reconstituted into phospholipid vesicles. As with the cell membranes the reconstituted substrates exhibited marked resistance to the action of purified GPI-PLD which could be overcome by the inclusion of Nonidet P-40. Similar results were obtained when crude bovine serum was used as the source of GPI-PLD. These data indicate that the resistance of cell membranes to the action of GPI-PLD is not entirely due to the action of serum or membrane-associated inhibitory factors. A more likely explanation is that, in common with many other eukaryotic phospholipases, the action of GPI-PLD is restricted by the physical state of the phospholipid bilayer in which the substrates are embedded. These data may account for the ability of endothelial and blood cells to retain GPI-anchored proteins on their surfaces in spite of the high levels of GPI-PLD present in plasma.

Alkaline Phosphatase↗

MR imaging of maternal diseases of the abdomen and pelvis during pregnancy and the immediate postpartum period.

Magnetic resonance (MR) imaging provides multiplanar large field-of-view images of the body with excellent soft-tissue contrast and without ionizing radiation. As a result, MR imaging is increasingly being used to image the maternal abdomen and pelvis during and immediately after pregnancy. Results of rapid T1- and T2-weighted imaging are often diagnostic, and blood vessels, ductal structures, and the urinary tract can frequently be visualized without intravenous administration of contrast material. Until more conclusive safety data become available, MR imaging should be reserved for cases in which results of ultrasonography are inconclusive and patient care depends on further imaging. In the setting of acute abdomen during pregnancy, MR imaging allows identification of areas of inflammation, abscess formation, hemorrhage, and bowel obstruction. MR imaging also helps determine the organ of origin, extent, and composition of maternal neoplasms and is useful in evaluation of müllerian duct anomalies and abnormalities of placental formation, position, and implantation. Many postpartum complications such as retained products of conception and uterine dehiscence may be diagnosed with MR imaging when results of other modalities are indeterminate.

Abdomen↗