A recombinant form of angiotensin converting enzyme expressed from baculovirus-infected insect cells

A secreted form of the C-domain of angiotensin converting enzyme has been expressed from the baculovirus-infected insect cell system. This soluble enzyme was purified by affinity chromatography and characterised in terms of its carbohydrate side chains and binding of substrates and inhibitors.

Mutation of Asp74 of the rat angiotensin II receptor confers changes in antagonist affinities and abolishes G-protein coupling

Aspartic acid in the second transmembrane domain is a highly conserved amino acid among the G protein-coupled receptors and is functionally important for agonist binding and G-protein coupling in beta 2-adrenergic and luteinizing hormone receptors. To determine whether this aspartic acid is also involved in the function of the rat vascular angiotensin II receptor subtype 1 (AT1a), Asp74 was replaced either by asparagine or by glutamic acid. When expressed in CHO cells, the two mutants and the wild-type receptor displayed similarly high affinities for the agonist [Sar1, Tyr(125I)4]angiotensin II [where Sar is sarcosine and Tyr(125I) is monoiodinated tyrosine] and the other agonists: ([Sar1]angiotensin II > angiotensin II > angiotensin III >> angiotensin I). However, the Asn74 mutant shows striking differences in its affinity for some antagonists when compared with the wild-type receptor: the affinity for DUP753 was decreased 10-fold, whereas it was increased 6-fold for [Sar1,Ala8]angiotensin II and 20-fold for CGP42112A. These pharmacological changes were associated with a major defect in transmembrane signaling, since angiotensin II was unable to stimulate inositol phosphate production and increase cytosolic Ca2+ concentration through the two mutated receptors, whereas a clear dose-dependent stimulation was observed in cells expressing the wild-type receptor. Angiotensin II was able to promote DNA synthesis through the wild type but not through the mutated receptors. These data indicate that the conserved Asp74 residue of the AT1a receptor is important for the binding of angiotensin II antagonists and is essential for the transmembrane signaling cascade.

Co-expression of type 1 angiotensin II receptor (AT1R) and renin mRNAs in juxtaglomerular cells of the rat kidney

Physiological and ligand binding studies have shown that Angiotensin II (AII) exerts various functions along different segments of the nephron, via the type-1 receptor (AT1R), resulting in the control of glomerular filtration rate (GFR) and water and salt homeostasis. We have used the recently cloned AT1R cDNA to localize, by in situ hybridization, the cells expressing AT1R mRNA in the rat kidney. On serial sections, juxtaglomerular (JG) renin secreting cells, identified by hybridization with a renin cRNA probe, also co-express AT1R mRNA. The co-expression of AT1R and renin mRNAs in the same cells documents visually the direct feedback control of AII on renin secretion. AT1R mRNA was also present in known target cells for AII: proximal convoluted tubule, mesangium and vasa recta.

A recombinant rat vascular AT1 receptor confers growth properties to angiotensin II in Chinese hamster ovary cells

A rat vascular AT1 receptor cDNA has been stably expressed into Chinese Hamster Ovary cells and the resulting recombinant AT1a receptor has been functionally characterized. This receptor binds 125I Sar1-angiotensin II with an affinity of 0.9 nM and the displacement of this ligand by a series of peptidic and nonpeptidic analogs is shown. Binding of angiotensin II to this receptor causes a rapid increase in inositol phosphate production, whereas this effect is not observed in nontransfected cells. Des-aspartyl1 angiotensin II and at a lesser extent angiotensin I are also able to produce an increase in inositol phosphates. More importantly, the actions of angiotensin II on cell division were clearly demonstrated in this model, since angiotensin II is able to stimulate DNA synthesis by 400% and double the cell population of the transfected cells in 36 hours in the absence of any other growth factor, whereas no effect is observed in nontransfected cells.

N-linked oligosaccharide chains of the insulin receptor beta subunit are essential for transmembrane signaling

Insulin receptor (IR) is a glycoprotein possessing N-linked oligosaccharide side chains on both alpha and beta subunits. The present study focuses for the first time on the potential contribution of N-linked oligosaccharides of the beta subunit in the processing, structure, and function of the insulin receptor. To investigate this point, a receptor mutant (IR beta N1234) was obtained by stable transfection into Chinese hamster ovary cells of an IR cDNA modified by site-directed mutagenesis on the four potential N-glycosylation sites (Asn-X-Ser/Thr) of the beta subunit. The mutated receptor presents an alpha subunit of 135 kDa, indistinguishable from the wild type alpha subunit, but the beta subunit has a reduced molecular mass (80 kDa instead of 95 kDa) most likely due to the absence of N-glycosylation. Metabolic labeling experiments indicate a normal processing and maturation of this mutated receptor which is normally expressed at the surface of the cells as demonstrated by indirect immunofluorescence. The affinity of the mutant for insulin (Kd = 0.12 nM) is similar to that of the wild type receptor (Kd = 0.12 nM). However, a major defect of the mutated IR tyrosine kinase was assessed both in vitro and in vivo by (i) the absence of insulin-stimulated phosphorylation of the poly(Glu-Tyr) substrate in vitro; (ii) the reduction of the insulin maximal stimulation of the mutated IR autophosphorylation in vitro (2-fold stimulation for the mutant receptor as compared to a 7-fold stimulation for the wild type); and (iii) a more complex alteration of the mutated receptor tyrosine autophosphorylation in vivo (3-fold increase of the basal phosphorylation and a 4-fold simulation of this phosphorylation as compared to the wild type receptor, the phosphorylation of which is stimulated 14-fold by insulin). The physiological consequences of this defect were tested on three classical insulin cellular actions; in Chinese hamster ovary IR beta N1234, glucose transport, glycogen synthesis, and DNA synthesis were all unable to be stimulated by insulin indicating the absence of insulin transduction through this mutated receptor. These data provide the first direct evidence for a critical role of oligosaccharide side chains of the beta subunit in the molecular events responsible for the IR enzymatic activation and signal transduction.

The two homologous domains of human angiotensin I-converting enzyme interact differently with competitive inhibitors

The endothelial angiotensin I-converting enzyme (ACE; EC 3.4.15.1) has recently been shown to contain two large homologous domains (called here the N and C domains), each being a zinc-dependent dipeptidyl carboxypeptidase. To further characterize the two active sites of ACE, we have investigated their interaction with four competitive ACE inhibitors, which are all potent antihypertensive drugs. The binding of [3H] trandolaprilat to the two active sites was examined using the wild-type ACE and four ACE mutants each containing only one intact domain, the other domain being either deleted or inactivated by point mutation of the zinc-coordinating histidines. In contrast with all the previous studies, which suggested the presence of a single high affinity inhibitor binding site in ACE, the present study shows that both the N and C domains of ACE contain a high affinity inhibitor binding site (KD = 3 and 1 X 10(-10) M, respectively, at pH 7.5, 4 degrees C, and 100 mM NaCl). Chloride stabilizes the enzyme-inhibitor complex for each domain primarily by slowing its dissociation rate, as the k-1 values of the N and C domains are markedly decreased (about 30- and 1100-fold, respectively) by 300 mM NaCl. At high chloride concentrations, the chloride effect is much greater for the C domain than for the N domain resulting in a higher affinity of this inhibitor for the C domain. In addition, the inhibitory potency of captopril (C), enalaprilat (E), and lisinopril (L) for each domain was assayed by hydrolysis of Hip-His-Leu. Their Ki values for the two domains are all within the nanomolar range, indicating that they are all highly potent inhibitors for both domains. However, their relative potencies are different for the C domain (L greater than E greater than C) and the N domain (C greater than E greater than L). The different inhibitor binding properties of the two domains observed in the present study provide strong evidence for the presence of structural differences between the two active sites of ACE.

Similarity of HLA-DQ profiles in adult-onset type 1 insulin-dependent diabetic patients with and without extra-pancreatic auto-immune disease

Some insulin-dependent diabetic patients present with auto-immune diseases involving extra pancreatic tissues (type 1b diabetes mellitus). The genetic specificity of this syndrome, as opposed to insulin dependent diabetes mellitus (IDDM) free of such associations (Type 1a IDDM) is not clearly established. We have analyzed the HLA-DQB1 and DQA1, loci, after PCR amplification of genomic DNA, in 44 Type 1b IDDM patients, 78 Type 1a IDDM patients and 105 control subjects. No essential difference in HLA-DQ profiles appeared between Type 1b and Type 1a IDDM patients. Both diabetic groups displayed a significant enrichment in DQB1 alleles negative for aspartate at position 57 (Type 1b: 83%; Type 1a: 89%; controls 48%; p < 0.001 vs both patient groups) and in DQB1 Asp 57 negative homozygosity: 71% of Type 1b; 80% of Type 1a; 25% of controls (p < 0.01). This enrichment in DQB1 Asp 57 negative alleles was accounted for by DQB1* 0201 in the Type 1b group, and by DQB1 % 0201 and 0302 in the Type 1a patients. Conversely, alleles DQB1* 0602 and 0301 (DQB1 Asp 57 positive) were protective. Both diabetic groups also displayed a significant enrichment in DQA1 alleles positives for arginine at position 52 (65% of Type 1b; 76% of Type 1a; 50% of control subjects; p < 0.01 and 0.001, respectively, vs controls), and in DQA1 Arg 52 positive homozygotes (48% of Type 1b, 58% of Type 1a, 22% of control subjects; p < 0.01). All differences between diabetic groups and the control group were more pronounced in the case of Type 1a than of Type 1b patients. The HLA-DQ genes shared by Type 1a and Type 1b patients must therefore be closely associated with islet autoimmunity. Genetic differences between Type 1a and Type 1b syndromes, if any, must be investigated in other MHC and non-MHC regions of the genome.

Molecular basis of insulin resistance

The recent application of recombinant DNA technology to clinical investigation now allows the identification of the molecular alterations responsible for insulin resistance. In this review, the recent knowledge concerning these investigations is reported. Genetic mutations of the insulin gene as the source of insulin resistance have been reported for a long time. More recently a series of mutations of the insulin receptor gene have been identified as the cause of the extreme insulin resistance, observed in rare syndromes, such as type A insulin resistance or leprechaunism. However, it is probable that the majority of the molecular defects causing insulin resistance occur at the postreceptor level. The key proteins involved in the different intracellular signalling pathways of insulin are only partly identified. A better understanding of the mechanisms of insulin action is essential for the identification of corresponding genetic alterations. The investigations concerning the glucose transporter GLUT4 and glucokinase genes are good examples of complex but promising research, which has recently started. Elucidation of the genetic and molecular basis of diseases such as type II diabetes or other states associated with insulin resistance, is the long-term goal.

Cloning and functional characterization of a novel mas-related gene, modulating intracellular angiotensin II actions

The mas oncogene codes for a GTP binding protein-coupled receptor that determines a physiological response to angiotensin when expressed in Xenopus laevis oocytes or in the neuronal cell line NG115-401L. However, another gene, rat thoracic aorta gene, structurally related to mas, is devoid of any functional similarity with the angiotensin receptor(s). The relationships between the mas-related proteins and the angiotensin receptors were investigated by identifying and characterizing new members of the mas gene family. A new mas-related gene (mrg) was cloned in a human genomic library at low stringency using the mas cDNA as probe. Mrg codes for a seven-hydrophobic-segment receptor that is 35% identical to the mas product and 29% identical to the rat thoracic aorta gene product. Mrg mRNA was not detected in several rat and human adult tissues that normally express the angiotensin II (AII) receptor, and transfections of COS and CHO cells with the mrg gene did not modify the number of AII binding sites. These results indicate that mrg and the human AII receptor genes are not identical. However, injection of mrg mRNA into Xenopus oocytes markedly increased the electrophysiological response to angiotensin peptides, indicating some functional similarities with the mas product. The reduction of the response after defolliculation of the oocyte, together with the full agonist effect of Sar1IIe8AII and the partial agonist effect of Sar1Ala8AII, seem to indicate that mrg interacts with the signaling pathways of the endogenous Xenopus angiotensin receptor to potentiate the response to AII.

HLA-DQA1 and DQB1 alleles in French and Algerian type 1 diabetic subjects

Some alleles of the HLA-DQB1 and DQA1 loci are preferentially associated with susceptibility to type 1 (insulin-dependent) diabetes mellitus (IDDM). Analysis of the HLA-DQ genetic profile may therefore become important for the screening of subjects at risk of IDDM. However ethnic variations in the genetic profile can occur and require background knowledge of the HLA-DQ allelic distribution before screening campaigns. In the present work, HLA-DQA1 and DQB1 genes have been analyzed, after PCR amplification of the genomic DNA, in French and Algerian control subjects (a total of 148) and diabetic patients (a total of 107). Allelic distributions have been investigated in view of a) possible inter-ethnic differences; b) identification of risk and protective alleles and c) the prevalence of DQB1 aspartate 57 negative and DQA1 arginine 52 positive alleles in control and diabetic groups. The DQB1 allelic distribution was similar in both control groups; alleles negative for aspartate at position 57 were 48% in French and 50% in Algerian. In both diabetic groups, the prevalence of alleles negative for aspartate at position 57 was significantly higher: 91% (French) and 81% (Algerian) (p less than 0.001). A majority of patients were homozygote for DQB1 Asp 57 negativity: 83% (French) and 63% (Algerian). The highest relative risk was associated with HLA-DQB1 0201/0302 heterozygosity. The HLA-DQA1 allelic distribution was also similar in French and Algerian controls. Alleles positive for arginine (ARG+) at position 52 were 50% (French) and 57% (Algerian) of controls. In both diabetic groups the prevalence of alleles positive for arginine at position 52 was significantly higher: 78% (French) and 84% (Algerian).(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular basis for hereditary antithrombin III quantitative deficiencies: a stop codon in exon IIIa and a frameshift in exon VI

Antithrombin III (AT III) is an inhibitor of serine protease (serpin) comprising 432 amino acids. Quantitative AT III deficiencies are associated with a high risk of thrombotic disease. Although this risk is smaller in patients with qualitative AT III deficiencies, the molecular defects characterizing the latter have been the subject of many studies. However, in quantitative AT III deficiencies, only three mutations have been described: Pro 407 to Leu and A1a404 to Thr (both located in the C-terminal part of the AT III molecule) and also a frameshift in exon IIIa. Using the asymmetric polymerase chain reaction (PCR) and genomic DNA analysis by direct sequencing, we detected two mutations in three unrelated families: (i) a C----T transition in exon IIIa in two families, leading to the replacement of the codon corresponding to Arg 129 by a stop codon, and (ii) in the third family, insertion of an adenine in the codon corresponding to Phe 408, a highly conserved serpin amino acid. This insertion altered the reading frame and led to the appearance of a premature stop signal. Patients of all three families were heterozygous for their abnormality. These results show that asymmetric PCR and genomic DNA analysis by direct sequencing permit fast identification of the molecular basis of quantitative AT III deficiencies. It is concluded that in many cases the absence of AT III gene product probably results from point mutation, as previously observed for another serpin, alpha-1-antitrypsin.

The two homologous domains of human angiotensin I-converting enzyme are both catalytically active

Molecular cloning of human endothelial angiotensin I-converting enzyme (kininase II; EC 3.4.15.1) (ACE) has recently shown that the enzyme contains two large homologous domains (called here the N and C domains), each bearing a putative active site, identified by sequence comparisons with the active sites of other zinc metallopeptidases. However, the previous experiments with zinc or competitive ACE inhibitors suggested a single active site in ACE. To establish whether both domains of ACE are enzymatically active, a series of ACE mutants, each containing only one intact domain, were constructed by deletion or point mutations of putative critical residues of the other domain, and expressed in heterologous Chinese hamster ovary cells. Both domains are enzymatically active and cleave the C-terminal dipeptide of hippuryl-His-Leu or angiotensin I. Moreover, both domains have an absolute zinc requirement for activity, are activated by chloride and are sensitive to competitive ACE inhibitors, and appear to function independently. However, the two domains display different catalytic constants and different patterns of chloride activation. At high chloride concentrations, the C domain hydrolyzes the two substrates tested faster than does the N domain. His-361,365 and His-959,963 are established as essential residues in the N and C domains, respectively, most likely involved in zinc binding, and Glu-362 in the N domain and Glu-960 in the C domain are essential catalytic residues. These observations provide strong evidence that ACE possesses two independent catalytic domains and suggest that they may have different functions.

Expression and characterization of recombinant human angiotensin I-converting enzyme. Evidence for a C-terminal transmembrane anchor and for a proteolytic processing of the secreted recombinant and plasma enzymes

Chinese hamster ovary (CHO) cells have been transfected with either a full-length cDNA encoding human angiotensin I-converting enzyme (kininase II; EC 3.4.15.1) (ACE) or a mutated cDNA, in which the last C-terminal 47 amino acids, including the putative transmembrane domain, are not translated. Cell lines expressing high levels of the wild-type ACE or the mutant were established. The cells transfected with the wild-type cDNA (CHO-ACE) express a membrane-bound ectoenzyme with an intracellular C terminus, as shown by indirect immunofluorescence using an antiserum (28A7) raised against a synthetic peptide corresponding to the deduced C terminus of ACE. This enzyme is structurally, immunologically, and enzymatically identical to human kidney ACE. In addition, CHO-ACE cells also produce a secreted form of the enzyme. Neither this secreted form nor the enzyme purified from human plasma is recognized by the antiserum 28A7, indicating that they undergo a truncation in the C-terminal region. On the other hand, the transfected cells expressing the C-terminally truncated mutant (CHO-ACE delta COOH) do not retain ACE in the plasma membrane, but secrete it into the medium. These results indicate that ACE is anchored to the plasma membrane by the predicted C-terminal transmembrane domain, and the secreted form is derived from the membrane-bound form by a post-translational proteolytic cleavage of the C-terminal region.

Insulin receptor tyrosine residues 1162 and 1163 control insulin stimulation of myristoyl-diacylglycerol generation and subsequent activation of glucose transport

Chinese hamster ovary (CHO) transfectants expressing human insulin receptors that were mutated at tyrosines 1162 and 1163 (CHO-Y2 cells) exhibit decreased insulin stimulation of both receptor tyrosine kinase and 2-deoxyglucose uptake compared with transfectants expressing wild-type human insulin receptors (CHO-R cells). We now provide evidence that insulin stimulation of myristoyl-diacylglycerol (DAG) production is also markedly impaired in CHO-Y2 cells; this is manifested as a decreased responsiveness and sensitivity to insulin as compared with CHO-R and parental CHO cells. Further, we report that (i) the concentration-response curves of insulin-stimulated myristoyl-DAG production and 2-deoxyglucose uptake were superimposable within each of the three cell lines. (ii) The insulin-induced increase in myristoyl-DAG production preceded that in 2-deoxyglucose uptake, and the time course was altered for both responses in CHO-Y2 cells. (iii) Insulin also increased the phosphorylation of a 40-kDa protein known to be a substrate for protein kinase C, but to a much lesser extent in CHO-Y2 cells than in CHO-R cells. (iv) Exogenously added 1,2-dimyristoyl-glycerol and 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA) again stimulated both the phosphorylation of the 40-kDa protein and 2-deoxyglucose uptake, but in contrast to insulin, they elicited the same level of response in both CHO-R and CHO-Y2 cells. (v) Finally, in protein kinase C-depleted CHO-R cells, insulin and PMA stimulation of 40-kDa protein phosphorylation as well as PMA stimulation of 2-deoxyglucose uptake were completely abolished whereas insulin-stimulated 2-deoxyglucose uptake was only partially decreased. Taken together, these results suggest that insulin stimulation of 2-deoxyglucose uptake involves myristoyl-DAG production and, at least in part, protein kinase C activation, all three of these processes being controlled by receptor tyrosines 1162 and 1163.

Important role of arginine 129 in heparin-binding site of antithrombin III. Identification of a novel mutation arginine 129 to glutamine

An hereditary abnormal antithrombin III (ATIII Geneva) with defective heparin cofactor activity was characterized by DNA single strand amplification and subsequent direct sequencing. ATIII Geneva was found to have a G to A transition in Exon IIIa leading to an Arg-129 to Gln mutation. This amino acid is part of the ATIII region comprising residues 114-154, which contains the highest proportion of basic residues (Arg or Lys), and is known from chemical modification studies to be involved in heparin binding. The variant protein did not bind heparin-Sepharose and was isolated from the propositus plasma by immunoaffinity chromatography. High affinity (for ATIII) heparin had only a minimal effect on thrombin and activated factor X inhibition by the purified abnormal ATIII. Taken together, these results demonstrate an important role for Arg-129 in the binding and interaction of ATIII with heparin of high affinity. We propose that a cooperation between Lys-125, Arg-129, Lys-136, and Arg-47 exposed at the surface of the inhibitor allows the binding of the essential pentasaccharide domain of heparin which is specific for the ATIII interaction.

[Tissue renin-angiotensin system. Physiology and physiopathological value of their inhibition by ramipril]

The existence of tissue renin angiotensin system (RAS) has been widely suggested in the recent literature by 2 main approaches: first, a dissociation between antihypertensive effects of angiotensin converting enzyme (ACE) inhibitors and the levels of stimulation of the circulating RAS; secondly, by the demonstration of the presence of the 3 key-proteins of the system (angiotensinogen, creatinine, and converting enzyme) within the 3 main target-organs of hypertension (i.e. kidney, heart and vessels). Those organs are capable to synthetize locally angiotensin II. Ramipril, a new ACE inhibitor (Triatec), which possesses a high affinity for tissue CE of those organs, according to previous publications by Unger, has been used as a tool for the investigations of the inhibition of those systems in human hypertension: a decrease of micro proteinuria has been without antihypertensive effects. In binephrectomized patients, ramipril has been shown to possess an antihypertensive effect. Finally, an important improvement of myocardial hypertrophy has been shown in hypertensive patients. Furthermore, this effect has been observed in animals (rats with aortic stenosis) even with low doses without antihypertensive effects. Further studies with new methodological approaches are still necessary.

Successful detection by in situ cDNA hybridization of three members of the serpin family: angiotensinogen, alpha 1 protease inhibitor, and antithrombin III in human hepatocytes

In situ hybridization was used to investigate the presence of mRNAs of three members of the serine protease inhibitor (serpin) superfamily, angiotensinogen (AG), alpha 1 protease inhibitor (alpha 1PI), and antithrombin III (ATIII) in normal human liver. The probes were full length 35S radiolabeled complementary DNAs of human AG, alpha 1PI, and ATIII. The three mRNAs were found to be uniformly distributed in all hepatocytes, with no evidence of any special distribution, but the signal was more intense for alpha 1PI than for AG and ATIII. Kupffer cells, biliary epithelial cells, and vascular cells were all negative. The same tissue was studied by peroxidase-antiperoxidase immunohistochemistry using specific antibodies against AG, alpha 1PI, and ATIII. No significant amounts of any of the proteins, alpha 1PI, AG, or ATIII were detected in frozen or fixed sections of normal liver. This study indicates that these proteins are not stored in the normal human hepatocyte, but that their genes are actively expressed and that in situ hybridization is the only technique presently available to detect their presence.

Mutation of tyrosine residues 1162 and 1163 of the insulin receptor affects hormone and receptor internalization

Insulin internalization and degradation, insulin receptor internalization and recycling, as well as long term receptor down-regulation were comparatively studied in Chinese hamster ovary (CHO) cell lines, either parental or expressing the wild-type human insulin receptor (CHO.R) or a mutated receptor in which the tyrosine residues in positions 1162 and 1163 were replaced by phenylalanines (CHO.Y2). The two transfected cell lines presented very similar binding characteristics, and their pulse labeling with [35S]methionine revealed that the receptors were processed normally. As expected, the mutation of these twin tyrosines resulted in a defective insulin stimulation of both receptor kinase activity and glycogen synthesis. We now present evidence that compared to CHO.R cells, which efficiently internalized and degraded insulin, CHO.Y2 cells exhibited a marked defect in hormone internalization, leading to impaired insulin degradation. Moreover, the mutated receptors were found to be less effective than the wild-type receptors in transducing the hormone signal for receptor internalization, whereas the process of receptor recycling after internalization seemed not to be altered. In parental CHO cells, insulin induced long term receptor down-regulation, but was totally ineffective in both transfected cell lines. These results reveal that the tyrosines 1162 and 1163 in the kinase regulatory domain of the receptor beta-subunit play a pivotal role in insulin and receptor internalization.

The difficult challenge of cloning the angiotensin II receptor

The vasopressor peptide angiotensin II exerts its cellular effects through a membrane-bound receptor coupled to a G protein. Biochemical and pharmacological analyses of this receptor already identify two different membrane-bound receptors and one cytosoluble angiotensin-II-binding protein. Nevertheless, the purification of the membrane-bound form(s) appears to be difficult. In the absence of purified protein, two cloning strategies of the gene have been explored: (1) expression cloning, identifying the functions of the protein expressed from a cDNA library in COS cells or Xenopus oocytes, has been unsuccessful until now; (2) analogical cloning, trying to identify related members of the seven transmembrane segment receptor family, which could be related to angiotensin receptors, identifies the mas oncogene and two related genes. However, there are accumulating data to exclude their involvement in angiotensin binding.

Molecular characterization of antithrombin III (ATIII) variants using polymerase chain reaction. Identification of the ATIII Charleville as an Ala 384 Pro mutation

The genes of seven structural mutants of antithrombin III (ATIII), presenting either defective serine protease reactivity or abnormal heparin binding, were analyzed. The polymerase chain reaction (PCR) was used to amplify the corresponding gene exon and the mutation was identified by either dot blot analysis using a battery of allele-specific oligonucleotide probes or sequencing. Variants Paris and Paris 2 were identified as Arg 47 Cys mutations, and Clichy, Clichy 2, and Franconville were found to be Pro 41 Leu mutations. All five are heparin binding-site variants. ATIII Avranches is an Arg 393 His mutation and ATIII Charleville is an Ala 384 Pro mutation. These two mutations impair the reactive site of the molecule. ATIII Charleville is a new mutation of the reactive center, as predicted by previous biochemical data. The position of this new mutation, together with the other previously described mutations of the reactive center, sheds light on the molecular function of this site in inhibiting thrombin. Finally, genomic amplification by PCR is a powerful technique for the fast identification of antithrombin III mutations and their homozygous/heterozygous status, and should be useful for predicting thrombotic risk.

Regulation of angiotensinogen gene

The development of recombinant DNA technology has introduced new directions for the study of the angiotensinogen molecule. The cloning and sequencing of the human and rat cDNAs demonstrate the similarity of angiotensinogen to various serine protease inhibitors produced by the liver and was the beginning of studies looking for new physiological roles of angiotensinogen, in addition to the substrate for renin. The determination of the nucleotide sequence of these cDNAs also allowed the identification of angiotensinogen mRNA in many tissues in addition to the liver that is the major site of synthesis. This multilocalization of angiotensinogen is one of the arguments for the presence and the function of local renin-angiotensin systems. Finally, the hepatic biosynthesis of angiotensinogen is regulated by many different hormonal factors including glucocorticoid, estrogen, thyroid hormone, insulin, and angiotensin II. The cloning of the angiotensinogen gene offers the opportunity to study this regulation at the transcriptional level. We present in this paper a review of the literature concerning the new aspects of angiotensinogen using molecular biological tools and its regulation together with the characterization of the human angiotensinogen gene.

Structure of human angiotensinogen gene

A cDNA clone encoding human angiotensinogen was isolated from a cDNA library prepared from human liver mRNA and used to isolate the angiotensinogen gene. The complete exon sequence of this gene together with extensive intron and flanking sequences are reported. The human angiotensinogen gene contains five exons interrupted by four intervening sequences. We compared the intron-exon structure of this human gene with that of the rat gene or the genes coding for proteins such as alpha 1-antitrypsin and antithrombin III, whose primary amino acid sequences show similarities. The human angiotensinogen gene shows identical organization with the alpha 1-antitrypsin gene, but is different from the antithrombin III gene. The 5'-flanking sequence (-500 to -1 bp) of the human angiotensinogen gene was examined for hormone regulatory elements (HRE), which may be implicated in the interaction with the hormone receptor complexes.

Receptor cross-linking restores an insulin metabolic effect altered by mutation on tyrosine 1162 and tyrosine 1163

The pivotal role that the tyrosine residues in positions 1162 and 1163 play in the control of the insulin action has been clearly established by substitution of these tyrosine residues for phenylalanine [Ellis, L. (1986) Cell 45, 721-732]. We have recently found that this type of mutation, which abolishes the effects of insulin on glucose metabolism, was without any effect on the mitogenic effect of the hormone [Debant, A. (1988) Proc. Natl. Acad. Sci. U.S.A. (in press)]. Here, we provide evidence that a polyclonal antibody, raised against the human insulin receptor, can restore the receptor-mediated stimulation of glycogen synthesis that was abolished by the mutation. Stimulation of the biological effect by the anti-receptor antibody did not necessitate, whatsoever, the activation of the tyrosine kinase activity and/or receptor autophosphorylation. Furthermore, the antibody-induced reversal of the mutation was not observed when we used Fab fragments alone, but addition of anti-(Fab')2 IgG in a second step resulted in a similar effect as that observed with intact IgG. We propose that Tyr 1162 and Tyr 1163 exert their control on the metabolic effects of insulin through the modulation of receptor aggregation.

A novel rat carboxypeptidase, CPA2: characterization, molecular cloning, and evolutionary implications on substrate specificity in the carboxypeptidase gene family

A new member of the carboxypeptidase gene family, carboxypeptidase A2 (CPA2), has been identified from the predicted amino acid sequence of a rat pancreatic cDNA clone. In vivo recombination and in situ hybridization techniques employing the CPA2 cDNA resulted in the isolation of two genomic clones spanning the 25-kilobase pair rat CPA2 gene. Evolutionary trees built from the amino acid sequences of the known pancreatic carboxypeptidases show that CPA2 and carboxypeptidase A1 (CPA1) are the products of genes which duplicated before the mammalian radiation, and that bovine CPA is of the A1 type. The substrate specificities of CPA1 and CPA2 isolated from rat pancreas are similar to bovine CPA in that carboxyl-terminal amino acids with aromatic or branched aliphatic side chains are preferred. However, the substrate preference of rat CPA1 is skewed toward smaller amino acids, while that of rat CPA2 is skewed toward bulkier amino acids as compared to bovine CPA. The differences in the substrate specificities of these three carboxypeptidases are compatible with the nature of the amino acid replacements in their binding pockets for the carboxylterminal amino acid of the substrate.

Structural characterization of the rat carboxypeptidase A1 and B genes. Comparative analysis of the rat carboxypeptidase gene family

Nucleotide sequencing of a rat carboxypeptidase B (CPB) cDNA and direct sequencing of the CPB mRNA via primer extension on pancreatic polyadenylated RNA has yielded the complete amino acid sequence of rat CPB. The rat enzyme is synthesized as a precursor species containing a large amino-terminal fragment (108 amino acids) that contributes a putative signal sequence and an activation peptide. The mature form of rat CPB is homologous to bovine CPB (77% identity); the amino acids in bovine CPB which have been previously implicated in catalysis or ligand binding are invariant in the rat orthologue. The rat CPB cDNA was used as a probe for the isolation of the rat CPB gene. Detailed characterization of three overlapping rat genomic clones demonstrated that the coding region for the rat CPB precursor is sequestered in 11 exons which are dispersed throughout 34 kilobase pairs of genomic DNA. The nucleotide sequence of a large part of the gene has been determined including that of the exons, the exon/intron boundaries, and the 5' flanking region. We also report the partial nucleotide sequence of the rat CPA1 gene. Comparative analysis of the structural organization of the rat CPB, rat CPA1, and rat CPA2 genes (Gardell, S. J., Craik, C. S., Clauser, E., Goldsmith, E. J., Stewart, C.-B., Graf, M., and Rutter, W. J. (1988) J. Biol. Chem. 263, 17828-17836) reveals that, with one exception, the number, position, and sequence composition of the exons in these three carboxypeptidase genes are conserved in spite of considerable divergence with respect to the lengths of their corresponding intervening sequences. Conserved sequences in the 5' flanking regions of the rat CPA1, CPA2, CPB, and other pancreas-specific genes have been identified.

Expression and characterization of recombinant human angiotensinogen in a heterologous eukaryotic cell line

Transfection of Chinese hamster ovary cells with an expression plasmid containing a full length human angiotensinogen cDNA has provided cell lines that secrete recombinant angiotensinogen in large quantities. This angiotensinogen is immunologically identical to plasma angiotensinogen and can be cleaved by human kidney renin (EC 3.4.23.15.). The peptide liberated by renin cleavage is immunologically identical to standard angiotensin I and shows a retention time on isocratic reversed-phase high-pressure liquid chromatography identical to that of standard angiotensin I. The heterogeneity of recombinant angiotensinogen on sodium dodecyl sulfate-polyacrylamide gel electrophoresis differs from that of plasma angiotensinogen. Treatment with endoglycosidases demonstrated that this difference is restricted to that of N-glycans and that N-glycans correspond to the quasi-totality of the carbohydrate content of both recombinant and plasma angiotensinogens. The development of a system capable of expressing human angiotensinogen cDNA in mammalian cells and the ability to obtain the corresponding angiotensinogen in large quantities will allow new studies on structure-function relationships of this protein.

Replacement of insulin receptor tyrosine residues 1162 and 1163 does not alter the mitogenic effect of the hormone

Chinese hamster ovary transfectants that express insulin receptors in which tyrosine residues 1162 and 1163 were replaced by phenylalanine exhibit a total inhibition of the insulin-mediated tyrosine kinase activity toward exogenous substrates [histone, casein, and poly(Glu/Tyr)]; this latter activity is associated with total inhibition of the hypersensitivity reported for insulin in promoting 2-deoxyglucose uptake. We now present evidence that the twin tyrosines also control the insulin-mediated stimulation of glycogen synthesis. Surprisingly, this type of Chinese hamster ovary transfectant is as hypersensitive to insulin for its mitogenic effect as are Chinese hamster ovary cells expressing many intact insulin receptors. Such data suggest that (i) the insulin mitogenic effect routes through a different pathway than insulin uses to activate the transport and metabolism of glucose and (ii) the mitogenic effect of insulin is not controlled by the twin tyrosines. At the molecular level, the solubilized mutated receptor has no insulin-dependent tyrosine kinase activity, whereas this receptor displays measurable insulin-stimulated phosphorylation of its beta subunit in 32P-labeled cells. We therefore propose that the autocatalytic phosphorylating activity of the receptor reports a cryptic tyrosine kinase activity that cannot be visualized by the use of classical exogenous substrates.

A simple strategy to amplify specifically the HLA-DQ beta gene region with genomic DNA as template

The nature of codon 57 in the HLA-DQ beta gene was recently reported as a potential marker of genetic susceptibility to insulin-dependent diabetes mellitus. When exploring the relevance of this marker by using genomic DNA amplification, we encountered difficulties resulting from the coamplification of the homologous DX beta region. A simple strategy is proposed to amplify the DQ beta region exclusively. It involves the preliminary digestion of genomic DNA with a restriction enzyme which cleaves DX beta specifically, leaving intact the DQ beta sequence. The amplified material is suitable for dot blot analysis and restriction enzyme digestion. This strategy is of general interest when homologous sequences impair the specificity of enzymatic DNA amplification.

[Diabetogenic tropical pancreatitis]

The tropical calcifying pancreatitis and/or fibrous pancreatitis are responsible for a number of cases of juvenile insulin-dependent diabetes in the Third World countries. World wide distributed in the tropical areas of Asia, Africa and South America, they can also be observed in Europe, in migrants from these countries. Intensive epidemiological and biochemical studies are currently developed in order to shed light on the many obscure points. Classification of the typical calcifying pancreatitis and the related syndromes is a matter of debate. The pathological basis is calcification of the pancreas and echography of the gland may become a cheap convenient relatively specific tool for epidemiology. The clinical syndrome consists of chronic painful pancreatic episodes since childhood, associated with pancreatic exocrine insufficiency, followed by the onset, during adolescence, of diabetes mellitus, which is most of the times insulin dependent. Patients' history is free of chronic alcoholism, but includes constantly chronic caloric and proteic malnutrition. Although insulin dependent this diabetes in not prone to ketosis, due presumably to carnitine deficiency and relative glucagon deficiency (or suppressibility). Insulin resistance is traditionally noted, the pathophysiology of which is unknown. The mechanism of calcification appearance is also undetermined. Either a deficiency in pancreatic stone protein, or the toxic effect of cyanogen glucosides present in cassava and other tropical foodstuffs, or the malnutrition-related deficiency in sulphur-containing aminoacids may be causal factors. No valid experimental model of the disease is available.

The renin-angiotensin system in the rat brain. Immunocytochemical localization of angiotensinogen in glial cells and neurons

The distribution of angiotensinogen containing cells was determined in the brain of rats using immunocytochemistry. Specific angiotensinogen immunoreactivity is demonstrated both in glial cells and neurons throughout the brain, except the neocortical and cerebellar territories. Positive neurons are easily and invariably detected in female brains, and haphazardly in male brain (sex hormone dependent). Angiotensinogen immunoreactivity in male brain neurons can be induced by water deprivation or binephrectomy in some areas and particularly in paraventricular nuclei. Finally, the highest concentrations of positive neurons are found in the anterior and lateral hypothalamus, preoptic area, amygdala and some well known nuclei of the mesencephalon and the brainstem. Our results confirm the wide distribution of angiotensinogen mRNA in the brain reported recently by Lynch et al. (1987). Thus the demonstration of angiotensinogen in neurons and glial cells allows a greater understanding of the biochemical and physiological data in accordance with multiple brain renin angiotensin systems.

A membrane-anchored cytoplasmic domain of the human insulin receptor mediates a constitutively elevated insulin-independent uptake of 2-deoxyglucose

Insulin stimulates the autophosphorylation of the beta-subunit of the insulin receptor (IR) on tyrosine residues. Mutations which compromise IR autophosphorylation in vivo result in a decrease of the insulin-activated uptake of 2-deoxyglucose. These results are consistent with previous results which implicate IR autophosphorylation in the generation of the insulin response by cells. To further explore the specificity of the IR tyrosine phosphokinase (TPK) domain in IR function, we have altered the human IR (hIR) cDNA to encode truncated insulin-independent TPKs, which are expressed in chinese hamster ovary (CHO) cells as either membrane-anchored or cytosolic proteins. Both mutant hIRs exhibit TPK activity in vitro, although the cytosolic form is approximately 20 times more active. The carbohydrate moiety of the membrane-anchored form is of the high mannose type, consistent with an intracellular localization for this mutant hIR. The two mutant hIRs mediate very different physiological responses in transfected cells: the membrane-anchored, but not the cytosolic, hIR TPK mediates a constitutively elevated (135% the maximum insulin-stimulated response in CHO cells) insulin-independent uptake of 2-deoxyglucose. These results thus suggest that the hIR TPK is in fact specific for this aspect of IR function and, when membrane-associated, can mediate the insulin-independent uptake of 2-deoxyglucose. Neither of these mutant hIRs appears to transform CHO cells.

The human insulin receptor cDNA: a new tool to study the function of this receptor

The human insulin receptor (hIR) is an integral transmembrane glycoprotein comprised of two alpha and two beta subunits. An immediate consequence of insulin binding to the extracellular alpha subunit is the autophosphorylation of tyrosine residues on the intracellular domain of the beta subunit. The placental hIR cDNA has been cloned and sequenced, providing the primary structural features of the protein. In order to investigate the functions of the beta subunit and particularly the role of autophosphorylation and tyrosine phosphokinase (TPK) activity (a feature shared by other receptors and oncogene proteins) in transmembrane signalling, we designed an expression system of the hIR cDNA in eucaryotic cells. Superexpressing CHO cell lines that contain about 10(6) functional hIR/cell have been developed. In these cells half maximum stimulation of glucose uptake occurs at 5 X 10(-10)M insulin, whereas normal CHO cells require 5 X 10(-12)M insulin. In this expression system we have carried out site-directed mutagenesis experiments in which domains of the molecule have been deleted or particular amino acids have been replaced by others. The replacement of either or both the tyrosine residues 1162 and 1163 compromise an autophosphorylated site that is important for kinase function and the insulin response. Expression of an isolated membrane-bound form of the beta-subunit produces a 6 fold increase in glucose uptake. This insulin-independent effect disappears if the twin tyrosines are mutated or if the beta subunit is expressed in the cytoplasm. These studies also show that the C terminal 112 amino acid portion of the beta subunit is important for the stability of this protein.

Linking functional domains of the human insulin receptor with the bacterial aspartate receptor

A hybrid receptor has been constructed that is composed of the extracellular domain of the human insulin receptor fused to the transmembrane and cytoplasmic domains of the bacterial aspartate chemoreceptor. This hybrid protein can be expressed in rodent (CHO) cells and displays several functional features comparable to wild-type insulin receptor. It is localized to the cell surface, binds insulin with high affinity, forms oligomers, and is recognized by conformation-specific monoclonal antibodies. Although most of the expressed protein accumulates as a 180-kDa proreceptor, some processed 135-kDa receptor can be detected on the cell surface by covalent cross-linking. Expression of the hybrid receptor inhibits the insulin-activated uptake of 2-deoxyglucose by CHO cells. Thus, this hybrid is partially functional and can be processed; however, it is incapable of native transmembrane signaling. The results indicate that the intact domains of different types of receptors can retain some of the native features in a hybrid molecule but specific requirements will need to be satisfied for transmembrane signaling.

Replacement of insulin receptor tyrosine residues 1162 and 1163 compromises insulin-stimulated kinase activity and uptake of 2-deoxyglucose

Insulin stimulates the autophosphorylation of tyrosine residues of the beta subunit of the insulin receptor (IR); this modified insulin-independent kinase has increased activity toward exogenous substrates in vitro. We show here that replacement of one or both of the twin tyrosines (residues 1162 and 1163) with phenylalanine results in a dramatic reduction in or loss of insulin-activated autophosphorylation and kinase activity in vitro. In vivo, these mutations not only result in a substantial decrease in insulin-stimulated IR autophosphorylation but also in a parallel decrease in the insulin-activated uptake of 2-deoxyglucose. Furthermore, a truncated IR protein (lacking the last 112 amino acids) has an unstable beta subunit; this mutant has no kinase activity in vitro or in vivo and does not mediate insulin-stimulated uptake of 2-deoxyglucose. IR autophosphorylation is thus implicated in the regulation of IR activities, with tyrosines 1162 and 1163 as major sites of this regulation.

Generation of angiotensinogen by cultured neuroblastoma and glioma cells

Cultured neuroblastoma cells and neuroblastoma-glioma cells have been shown to contain renin activity, angiotensin-converting enzyme activity, and angiotensins. It has been assumed that these cells also produce angiotensinogen as the substrate of an intracellular renin-angiotensin system. However, measurements of angiotensinogen have not been reported in the neuroblastoma or neuroblastoma-glioma cells, and the possibility that the cells generate angiotensins from fetal bovine angiotensinogen has not been eliminated. In this work angiotensinogen was shown to accumulate in the serum-free medium of thoroughly washed neuroblastoma cells (mouse Neuro-2A and rat B103) and glioma cells (rat C6). Separate experiments demonstrated that mouse Neuro-2A cells continue to produce angiotensinogen even after two passages in a defined serum-free culture medium. Further evidence that the angiotensinogen was not a contaminant from fetal bovine serum was obtained by the use of a monoclonal antibody raised against angiotensinogen of rat plasma. The angiotensinogen of Neuro-2A and C6-glioma cells is bound by the monoclonal antibody, whereas fetal bovine angiotensinogen is not bound. These results are consistent with the hypothesis that angiotensinogen is produced locally in the brain and in neuroblastoma cells as a substrate for an intracellular renin-angiotensin system.

Mechanisms of receptor-mediated transmembrane communication

Our experiments with the hIR protein have been designed to address a very general question of transmembrane receptor structure and function: What are the roles and interactions of the various deduced structural domains of such molecules in the initiation of the response of cells to extracellular signals? All of the evidence to date supports the previous hypothesis based on biochemical data that the IR requires ligand-activated TPK functions to initiate the insulin response by cells (for review, see Kahn 1985). Thus, mutations that compromise hIR TPK activity (site-directed point mutations or deletions) result in a concomitant decrease in at least one aspect of insulin action (glucose uptake; Ellis et al. 1986a). Other studies utilizing microinjection of antibodies to inhibit the receptor kinase have extended this conclusion to include a critical role for the receptor kinase in insulin's ability to stimulate ribosomal protein S6 phosphorylation in CHO cells, glycogen synthetase in hepatoma cells, glucose uptake in adipocytes (Morgan and Roth 1987), and frog oocyte maturation (Morgan et al. 1986). Second, analyses of cell lines that express experimentally truncated hIR TPKs demonstrate that, when membrane-anchored, this TPK domain is in fact capable of autonomous hormone-independent IR function: Such cells exhibit a constitutively elevated, insulin-independent uptake of 2-deoxyglucose (Ellis et al. 1987). Finally, by substitution of a homologous TPK for that of hIR, we find that although such a hybrid is capable of insulin-dependent transmembrane signaling (phosphorylation of the hybrid beta-subunit on tyrosine residues), the hybrid IR.ros molecule does not function as an IR in such cells: It mediates neither short-term (uptake of 2-deoxyglucose) nor long-term (incorporation of [3H]thymidine) effects of insulin (L. Ellis et al., in prep.). Together, these results suggest that (1) the hIR TPK domain conveys a substrate specificity for the insulin response and (2) that a functional hIR extracellular domain alone is not sufficient for generation of the insulin response (e.g., ligand-induced aggregation, or simple delivery of insulin into the cell). With the linking of the extracellular and cytoplasmic domains of the hIR molecule has evolved a cellular mechanism for the control of hIR TPK activity; the result is that cells which express the IR are now insulin responsive, and the physiological responses associated with the hormone are ligand-activated. Thus, the uncontrolled state of autonomous TPK activity, with the associated constitutive physiological response (e.g., as exhibited by the spBam hIR mutant), is circumvented.(ABSTRACT TRUNCATED AT 400 WORDS)

Cloning, sequencing, and chromosomal localization of human term placental alkaline phosphatase cDNA

A human term (third trimester) placental alkaline phosphatase (PLAP; EC 3.1.3.1) cDNA was isolated from a human placental lambda gt11 cDNA library. The expression library was screened by using rabbit antibodies against PLAP and oligonucleotide probes. DNA sequence analysis of a positive clone with an insert of 2.7 kilobase pairs allowed us to predict the complete amino acid sequence of PLAP (530 residues), which coincided with the reported 42 N-terminal amino acid sequence of PLAP except at position 3. Contrary to the previous supposition that there was no amino acid sequence homology between PLAP and Escherichia coli alkaline phosphatase (471 residues), we found 30% overall homology, with regions of strong homology including the putative active site and the metal-binding sites. The 44-residue C-terminal extension of PLAP has a stretch of 17 hydrophobic amino acids, which presumably anchors the protein to the plasma membrane, a change perhaps necessary for the transition from a bacterial periplasmic enzyme to a mammalian membrane-associated enzyme. We have also localized PLAP-related DNA sequences mainly on chromosome 2 and to a lesser degree on chromosome 17. It seems likely therefore that the PLAP gene resides on chromosome 2 and other member(s) of the alkaline phosphatase family may exist (on this chromosome and) on chromosome 17.

The human insulin receptor cDNA: the structural basis for hormone-activated transmembrane signalling

A cloned approximately 5 kb cDNA (human placenta) contains the coding sequences for the insulin receptor. The nucleotide sequence predicts a 1382 amino acid precursor. The alpha subunit comprises the N-terminal portion of the precursor and contains a striking cysteine-rich "cross-linking" domain. The beta-subunit (the C-terminal portion of the precursor) contains a transmembrane domain and, in the intracellular region, the elements of a tyrosine phosphokinase: an ATP-binding site and a possible tyrosine autophosphorylation site or sites. The overall structure is reminiscent of the EGF receptor; the cross-linking domain of the alpha subunit and several regions of the beta subunit exhibit sequence homology with the EGF receptor. The phosphokinase domain also exhibits homology with some oncogenic proteins that have tyrosine phosphokinase activity, in particular, a striking homology with v-ros. Southern blotting experiments suggest that the coding region spans more than 45 kb. The insulin receptor gene is located on chromosome 19.

Angiotensinogen production and consumption in the adrenalectomized rat

The aim of this study was to investigate the mechanisms by which angiotensinogen decreases after adrenalectomy. Plasma angiotensinogen was measured by two different methods: an indirect assay, which measures angiotensin I liberated from the plasma by an excess of renin, and a direct RIA, which measures both angiotensinogen and des-angiotensin I-angiotensinogen. In the normal rat angiotensinogen concentrations were found to be slightly, but not significantly, higher using the direct assay. After adrenalectomy a large discrepancy was observed between the indirect assay, which showed a considerable drop in plasma angiotensinogen levels, and the direct assay, which revealed a small but significant decrease. This discrepancy arose from the presence of a molecule that cross-reacts with angiotensinogen antibodies, and has a more acidic pI in isoelectric focusing than angiotensinogen: des-angiotensin I-angiotensinogen. This molecule accumulates in adrenalectomized rat plasma. The decrease in plasma angiotensinogen levels, measured by the indirect assay, could not be explained by a decrease in angiotensinogen production, as this was unchanged in the in vitro liver slice system, but was caused by an increase in angiotensinogen consumption, due to a rise in the plasma concentration of renin. Renin concentration shows a negative correlation with angiotensinogen (as measured by the indirect assay), and a positive correlation with des-angiotensin I-angiotensinogen level. Moreover, mineralocorticoids were shown to correct both renin and angiotensinogen concentrations, whereas a replacement dose of glucocorticoids (dexamethasone) had no effect on the level of renin or angiotensinogen, as measured by the indirect assay. We conclude that after adrenalectomy, plasma angiotensinogen decreases, due to an increase in renin production. A parallel accumulation of des-angiotensin I-angiotensinogen is observed.

Production and characterization of monoclonal antibodies to rat angiotensinogen

Three stable monoclonal antibodies to rat angiotensinogen were obtained by fusing myeloma cells with spleen cells from Balb/c mice injected with pure rat angiotensinogen. They were screened by their binding to pure iodinated angiotensinogen and to insolubilized angiotensinogen in a solid phase assay. The titers of the three antibodies varied from 1/3500 to 1/35000, their dissociation constants from 2.5 X 10(-8) M to 3.8 X 10(-10) M, and the sensitivity of the assay ranged from 200 to 10 pmol of pure angiotensinogen. These monoclonal antibodies did not recognize either angiotensin peptides or angiotensinogen from other species, except for mouse angiotensinogen, which cross-reacted with the different antibodies from 0 to 25%. Rat cerebrospinal fluid angiotensinogen, plasma des-angiotensin I-angiotensinogen, and plasma angiotensinogen were equally recognized by these monoclonal antibodies. Contrary to what was observed for a polyclonal antiserum, the monoclonal antibodies failed to inhibit the renin-angiotensinogen reaction in vitro.

Effects of glucocorticoids and antiglucocorticoid on angiotensinogen production by hepatoma cells in culture

Angiotensinogen is synthesized in large amounts by Fao cells derived from the Reuber H35 rat hepatoma in a medium enriched with 5% fetal bovine serum (FBS). Treatment of FBS with dextran-coated charcoal removed endogenous steroids without modifying angiotensinogen production. This treatment allowed the study of the effects of steroids on angiotensinogen production. Hydrocortisone increased the angiotensinogen synthesis in a dose-dependent manner. The antiglucocorticoid RU 38486 did not change the basal rate of angiotensinogen production but inhibited the stimulation by hydrocortisone. Similar results were obtained with dexamethasone. Angiotensinogen biosynthesis seems to be regulated by two distinct mechanisms: (a) glucocorticoid independent, controlling the basal rate of angiotensinogen production and (b) glucocorticoid dependent, mediating the increased rate of angiotensinogen production upon glucocorticoid treatment.