Molecular cloning of a mouse submaxillary gland renin cDNA fragment

Approaches to cloning of pain-related ion channel genes

Molecular pain research is a relatively new and rapidly expanding field that represents advancement in conventional pain research. One of the fundamentals of molecular pain involves the cloning of genes and especially the ion channels specifically involved in nociceptive processing at the periphery and centrally. A variety of approaches were used to isolate these critically important genes. Cloning of these genes involved innovative strategies based on existing molecular approaches. This review will discuss well-utilized cloning approaches and their exploitation in molecular pain research.

Two isoforms of the kidney androgen-regulated protein are encoded by two alleles of a single gene in OFl mice

Two cDNA clones coding for two forms of the mouse kidney androgen-regulated protein (KAP) distinguished by their electrophoretic mobilities on SDS gel electrophoresis have been isolated from libraries prepared from strains of mice having one (BALB/c) or two (OFl) forms of the KAP protein. The corresponding mRNAs have identical sizes, as well as identical sequences in their 5' non-translated regions. The size difference observed between the two proteins is due to two point mutations in the coding region of the KAP mRNA, leading to two amino-acid changes one of which resulted in the substitution of a glycine for a glutamic acid. As shown byin vitrotranscription/translation experiments, these two amino-acid differences are responsible for the shift in the apparent molecular weight of the protein on SDS gels. Both forms of the protein are more abundant in males than in females.

In vitrotranslation of kidney RNAs isolated from six different strains and species of mice revealed the presence of other forms of the KAP protein, characterized by small variations of their molecular weights. Southern blot analysis data are consistent with the presence of only onekapgene in the mouse genome. A restriction fragment length polymorphism has been observed, which does not correlate with the protein polymorphism, indicating the presence of another allele in the OF1 mouse genome.

From the messenger RNA saga to the transcriptome era

This review attempts to provide an overview of the evolution of the ideas and techniques that prevailed at the beginning of research on ribonucleic acids, until the contemporary era of cellular transcript analysis using DNA biochips and microarrays. Certain applications derived from the use of microarrays and the corresponding analyses of transcriptomes are discussed, particularly concerning diagnosis and prevision of evolution of certain cancers.

Some physiological outcomes of renin gene studies

1. The cloning of the renin gene has permitted studies of its physiological regulation, extrarenal expression and role in disease. 2. Marked modulation of renin mRNA concentration is seen in adrenal, heart and hypothalamus in response to sodium depletion and inhibition of AII formation, as well as in models of renal and genetic hypertension in the rat. 3. One important outcome of studies of the promoter has been the discovery of a cyclic AMP-responsive sequence. 4. Sequence variations have been detected in or near the renin gene and have been used as markers in studies of its role in cardiovascular disease aetiology. 5. In conclusion, molecular biology has, in the past decade, made a significant contribution to the understanding of renin physiology and pathophysiology.

Enzymatic characterization of purified recombinant human renin

Renin is a highly specific aspartyl protease of the renin-angiotensin system initially synthesized as preprorenin. Recombinant human prorenin was produced in cell factories from stably transfected DAMP cells, a dog epithelial cell line. The equivalent of 10-15 mg of recombinant human renin was secreted in the supernatant from each cell factory. Following a single affinity chromatography step using a renin inhibitor as the ligand, a 181-fold purification was achieved with 81% recovery of the renin activity. This highly pure recombinant enzyme having a specific activity of 3.44 mg angiotensin I.mg protein-1.h-1 was used for kinetic analysis. The kinetic parameters were determined with the natural substrate angiotensinogen and a tetradecapeptide substrate corresponding to the amino terminus of angiotensinogen, Asp1-Asn14, at their respective optimum pH of 5.5 and 6.8. Although there was a six-fold increase in both Km and kcat values for the peptidic substrate (13.3 microM and 8.1 s-1, respectively), when compared with values for the natural substrate (2.04 microM and 1.41 s-1), the catalytic efficiency (0.69 microM-1.s-1) of the enzyme for both substrates was the same. However, the kcat/Km value with angiotensinogen at the physiological pH 7.4 was 30% lower than that observed at the optimum pH 5.5. The recombinant human renin displayed similar optimum pH and kinetic parameters with angiotensinogen and the tetradecapeptide substrate when compared with human kidney renin.

Selective processing of submandibular rat 1 protein at dibasic cleavage sites. Salivary and bloodstream secretion products

The amino acid sequence of submandibular rat 1 (SMR1) protein, deduced from its cDNA sequence, led to the prediction that the SMR1 gene encodes a hormone-like precursor [Rosinski-Chupin, I., Tronik, D. & Rougeon, F. (1988) Proc. Natl Acad. Sci. USA 85, 8553-8557]. SMR1 contains an N-terminal putative secretory signal sequence and a tetrapeptide (QHNP), located between dibasic amino acids which constitute the most common signal for prohormone processing. We have isolated and characterized from the male rat submandibular gland and its secretions three structurally related peptides, namely an undecapeptide (VRGPRRQHNPR), a hexapeptide (RQHNPR) and a pentapeptide (QHNPR) generated from SMR1 by selective proteolytic cleavages at pairs of arginine residues. The biosynthesis of these peptides is subjected to distinct regulatory pathways depending on the organ, sex and age of the rat. Furthermore, the peptides are differentially distributed in the submandibular gland and in resting or epinephrine-elicited submandibular salivary secretions, suggesting distinct proteolytic pathways for their maturation. The undecapeptide is generated in the gland of both male and female rats, but under basal conditions it is only released into the saliva in male animals. The hexapeptide is produced in large amounts in the gland of adult male rats and released into the saliva in both resting and stimulated conditions. The pentapeptide appears only in the male saliva and is present mostly under stimulated conditions. In addition, administration of epinephrine induces the release of the hexapeptide from the submandibular gland into the bloodstream. The evidence indicates that the rat submandibular gland can function as a dual exocrine and endocrine organ for the SMR1-derived hexapeptide, as has been reported for nerve growth factor, epidermal growth factor, renin and kallikrein. Although the biological activities of the SMR1-derived peptides are not yet known, their high production and adrenergic-induced release only into the saliva and bloodstream of adult male rats, suggest a physiological involvement in some male-specific processes.

Structure, expression, and regulation of the murine renin genes

It has long been known that the renin-angiotensin system plays an integral role in the regulation of blood pressure and electrolyte and fluid balance in mammals. The advent of molecular biologic techniques has afforded new insights into the genes regulating blood pressure. Laboratory mice and rats have been used as experimental models to examine the structural organization and expression of the renin gene. It is now well established that some mice, unlike rats and humans, contain a duplicated copy of the renin locus, which accounts for the high level of renin activity long known to be found in the submandibular gland of some mice. Indeed it is this fortuitous observation that facilitated the isolation of the first complementary DNA clones for renin and ultimately the many species-specific probes now available to analyze mammalian tissues for evidence of primary renin expression. The use of complementary DNAs as probes for primary renin expression helped confirm and further clarify earlier studies demonstrating the presence of renin activity in a number of extrarenal tissues. Although expression in some of these tissues is evolutionarily conserved, their significance has still been elusive. In this report we review the impact of molecular biology on our current understanding of renin gene structure and organization, tissue- and cell-specific expression and regulation, and the changes in renin expression throughout ontogeny. In addition, we describe how new developments in gene transfer technology have added important tools to our arsenal for examining renin gene regulation and how these technologies can be used to develop new tools for renin and hypertension research.

Molecular biology of human renin and its gene

This article describes investigations of several aspects of the molecular biology of the human renin gene and the three-dimensional structure of renin and its precursor, prorenin. Because of the importance of the RAS in hypertension, heart failure, renal failure, and possibly other disorders such as atherosclerosis, it is critical to understand the detailed control of this system. This control involves regulation at the transcriptional level, folding of prorenin, sorting of prorenin to a regulated pathway where it is proteolytically cleaved to renin and released in response to secretogogues, constitutive release of uncleaved prorenin, and nonproteolytic activation of prorenin. Currently there is great interest not only in the control of renin in the kidney, the sole source of circulating renin, but also at extrarenal sites where RAS activity may regulate cardiovascular functions. The renin gene was found to be expressed significantly in the renal juxtaglomerular cells and several other cell types. Most tissue culture cells did not express the gene; exceptions were cultured SK-LMS-1 cells and cAMP-stimulated human lung fibroblasts. Cultured human uterine-placental cells expressed the human renin gene at levels higher than in other cell types assessed. Renin mRNA had the same start site in the placental cells as the kidney and was regulated by calcium ionophores and cAMP. Thus, these cells provide primary nontransformed human cells to study the homologous human promoter. Transfected renin promoters showed cell type-specific expression and cAMP responsiveness in these cells in constructs containing as few as 102 bp of 5'-flanking DNA. DNA upstream from this appears to contain an inhibitory element(s) that may have some tissue specificity in its distribution. The cAMP response is not due to cAMP induction of a transcription factor that secondarily affects the renin promoter. A novel element may be involved, since the promoter does not contain a CRE element that mediates many cAMP responses, and the cells do not appear to respond to another known cAMP-responsive transcription factor, AP-2. Studies with transfected vectors expressing a mutant cAMP-responsive protein kinase A regulatory subunit suggest that cAMP is not responsible for basal renin promoter activity in the placental cells. By contrast, cAMP induces in essence gene activation in WI26VA4 transformed human lung fibroblasts in which renin mRNA levels increase by up to 150-fold in response to forskolin. Thus, cAMP may activate renin gene expression under certain circumstances and tissue-specific renin gene expression may be directed by more than one mechanism.(ABSTRACT TRUNCATED AT 400 WORDS)

Biochemistry and pharmacology of the renin-angiotensin system

Knowledge of the structure, function and distribution of the components of the renin-angiotensin-aldosterone system (RAS) and the integrated physiological role of this hormonal system is rapidly increasing, although many questions remain unanswered. The primary structure and localisation of RAS such as renin, prorenin, angiotensinogen, angiotensin-converting enzyme (ACE) and the angiotensins have now been described. Moreover, the genes for the production of renin and ACE have been cloned and their nucleotide sequences determined. In addition to its well-established role as a circulating endocrine system, the renin-angiotensin system has more recently been ascribed a local autocrine or paracrine function. Physiologically active levels of components such as renin and angiotensin, or their messenger RNAs, have been identified in several extrarenal tissues, notably the central nervous system. The components of such tissue renin-angiotensin systems may be derived from de novo tissue synthesis and/or from the circulation by endocytosis. Angiotensin has pharmacological actions on a wide range of body tissues, including the kidney, heart, brain, gastrointestinal tract and reproductive organs. In many of these locations, angiotensin receptors have been isolated and characterised. The most firmly established roles of angiotensin are the control of blood pressure and local blood flow, and in salt and water homeostasis; the physiological significance of many of angiotensin's tissue effects is unknown. In some areas of clinical interest, such as the pathophysiology of left ventricular hypertrophy, ACE inhibitors are very useful for elucidating the possible influences of the renin-angiotensin system.

Differential extra-renal expression of the mouse renin genes

We have used RNase-protection analyses to study renin gene expression in one- and two-gene mouse strains. The RNase-protection assay is capable of discriminating between the transcripts from the different renin genes. In a two-gene strain containing Ren-1D and Ren-2, we demonstrate transcriptional activity from Ren-1D in kidney, submandibular gland (SMG), testes, liver, brain and heart. Ren-2 is clearly expressed in kidney, SMG and testes. Similar analyses of one gene strains (containing Ren-1C only) show expression in kidney, SMG, testes, brain and heart. We cannot detect renin mRNA in the liver of these mice. Ren-1C and Ren-1D thus display quite different tissue-specificities. In order to determine whether the different tissue-specificities of the highly homologous Ren-1C and Ren-1D genes are due to different trans-acting factors in the different mouse strains or to different cis-acting DNA elements inherent to the genes, we introduced a Ren-1D transgene (Ren-1*) into a background strain containing only the Ren-1C gene. The transgene exhibits the same tissue-specificity as the Ren-1D gene of two-gene strains suggesting the presence of different cis-acting DNA elements in Ren-1C and Ren-1D.

Immunohistochemical study of peripolar cells of the sheep

The proposal that the cytoplasmic granules of glomerular peripolar cells (PPCs) of the adult sheep and lamb contain a kallikrein-like substance has been re-examined. After extensive characterisation and purification of anti-kallikrein antibodies, it was concluded that PPCs do not contain immunohistochemically detectable amounts of urinary kallikrein; nor do such cells appear to synthesise kallikrein as shown by hybridisation histochemistry studies. They are also not renin-immunopositive. On the other hand, a proportion of them exhibit neuron-specific enolase (NSE) immunoreactivity, unlike the apparently closely related visceral and parietal epithelial cells.

The molecular biology of human renin and its gene

The molecular biology of renin, prorenin, and the renin gene have been studied. A tissue-specific pattern of expression was found in rat and human tissues. In the human placenta, the transfected and endogenous renin promoters are active, and renin mRNA levels and transfected promoter activity are increased by a calcium ionophore plus cAMP. Cultured pituitary AtT-20 cells transfected with a preprorenin expression vector mimick renal renin release by converting prorenin to renin and releasing renin in response to 8Br-cAMP. Studies with mutant renin genes suggest that the body of renin directs renin to the regulated secretory pathway, and renin glycosylation affects its trafficking. Chinese hamster ovary cells were used to produce recombinant prorenin. Infused prorenin was not converted to renin in monkeys. Renin crystals were used to determine its three-dimensional structure. Renin resembles other aspartyl proteases in the active site and core, but it differs in other regions that probably explain renin's unique substrate specificity. Based on structural and mutational analysis, a model for human prorenin was built that suggests lysine -2 of the prosegment interacts with active site aspartate residues, and that the prosegment inactivation of renin is stabilized by binding of an amino terminal beta strand into a groove on renin.

High level of accumulation of a mRNA coding for a precursor-like protein in the submaxillary gland of male rats

NaDodSO4/PAGE analysis of in vitro translation products of rat submaxillary gland (SMG) mRNAs has revealed an important sexual dimorphism. Moreover, most of the rat male-specific major translation products differ in size from those translated from male mouse SMG mRNAs. To characterize proteins accumulated in the rat SMG under androgen control, a cDNA library was constructed. Here we report the nucleotide sequence of a 0.7-kilobase mRNA that is 1000-3000 times more abundant in male rats than in female rats. The predicted corresponding protein, SMR1, has a molecular weight of 16,000 and contains a signal peptide for secretion and potential signals for glycosylation. An interesting feature of SMR1 is the presence, in a hydrophilic region, of the tetrapeptide Gln-His-Asn-Pro surrounded by two pairs of basic residues that represent potential cleavage sites for maturation enzymes. In rats, the tissue distribution of the SMR1 mRNA is restricted to the SMG and the prostate. Only very low amounts of SMR1 mRNA can be detected in the SMG of male or female mice. Southern blot analysis indicates the presence of three genes in rats but only one in mice. Hypotheses on the physiological role of SMR1-derived peptides in male rats are discussed.

Earliest renin containing cell differentiation during ontogenesis in the rat. An immunocytochemical study

The differentiation of renin containing cells was studied by immunocytochemistry in normal rat fetuses by the use of highly specific renin, angiotensin I and II antisera. Renin synthesizing cells were detectable as early as the 15th day of gestation outside the nephrogen territories within the walls of mesonephrotic-gonadic and renal arteries. Intrarenal differentiation began at the 17th day and progressed along the intrarenal arterial tree. AII immunostaining appeared concomitantly in the renin containing cells and developed considerably during ontogenesis, suggesting intracellular biosynthesis. It can be suggested that in the fetus newly synthesized AII may contribute to the early systemic and renal blood pressure regulation.

Isolation and characterization of native human renin derived from Chinese hamster ovary cells

Transfection of Chinese hamster ovary (CHO) cells with a plasmid containing the cDNA for human preprorenin has provided cell lines that secrete 15 mg of native prorenin per liter of culture medium. Tryptic activation of the prorenin occurs by selective cleavage of the Arg66-Leu67 bond (numbering as in preprorenin). The renin product, purified in a single step and in high yield by affinity chromatography, is fully stable for as long as 8 months when stored in solution at 4 degrees C and pH 6.5. Purity of the renin was judged to be greater than 95% by gel electrophoresis, compositional and N-terminal sequence analyses, and specific enzyme activity. An important aspect of the present work is the development of a direct assay for renin which permits accurate and reproducible evaluation of enzyme units and kinetic parameters. Application of methods described herein, combined with appropriate scale-up fermentation capabilities, provides the means for generating gram quantities of human renin and its zymogen.

Effects of antihypertensive treatment in one-clip, two kidney hypertension in rats

In order to investigate the consequences of antihypertensive therapy on hormonal and renal parameters in one-clip, two kidney renovascular hypertension, we compared the effects of converting enzyme inhibition (CEI) with those of tripletherapy (clonidine, dihydralazine and furosemide) in this experimental model in rats. The treatment period was initiated four weeks after application of the clip and was continued for five weeks. In plasma, renin was increased and renin substrate was negatively correlated to plasma renin. Hypertension was associated with activation of the renin angiotensin system in both plasma and kidney. The degree of activation of the renin-angiotensin system in the clipped kidney and its suppression in the unclipped kidney was evaluated by two methods, renal renin content and semi-quantification of juxtaglomerular hyperplasia by immunofluorescent renin. These two methods were correlated. During the treatment period, average systolic blood pressure was 144 +/- 13 mmHg in the CEI treated group (HT1) which was not significantly different from the value found in the sham-operated group (139 +/- 4 mmHg; C2). Blood pressure, however, was lowered only to 173 +/- 18 mmHg in the group treated with tripletherapy (HT2). In control hypertensive animals, the wt of the clipped kidney did not decrease whereas significant hypertrophy was present in the unclipped kidney. Tripletherapy did not alter this relationship, whereas converting enzyme inhibition decreased kidney wt in the clipped kidney and increased further the hypertrophy of the contralateral unclipped kidney. A histological examination revealed that hypertensive microangiopathy was a predominant feature in the unclipped kidney of the untreated hypertensive group and of the group treated with tripletherapy, these lesions were completely absent in the CEI treated group. In the CEI treated group, however, ischemic lesions during this treatment were found to be decreased in the contralateral unclipped kidney and increased in the clipped kidney by comparison with untreated hypertensive rats. These renal lesions observed in the clipped kidney were most likely related to the normalization of blood pressure or to a disturbance of intrarenal mechanisms normally mediated by the renin-angiotensin system during stenosis of a renal artery.

Serum and thyroid hormones T3 and T4 regulate nerve growth factor mRNA levels in mouse L cells

Mouse L cells synthesize and secrete a neurotrophic factor related to the beta subunit of the submaxillary gland nerve growth factor (NGF) of male mice. Use of a cDNA probe which encodes the beta-NGF mRNA demonstrated that L cells produce a transcript identical in size to that of the submaxillary gland. Moreover, target sites of restriction enzymes EcoRI, PstI and BamHI were not significantly rearranged in the beta-NGF gene locus of these cells. The abundance of the beta-NGF transcript was found to depend on culture conditions. Removal of serum depressed the cellular content of polyadenylated RNA by a factor of 1.7, and decreased specifically the pool of beta-NGF transcript by an additional factor of 4. The presence of 10(-7) M testosterone in the serum-free medium did not modify the level of beta-NGF mRNA, while addition of 10(-7) M T3 (or T4) increased this level by a factor of 1.5. These data provide the first evidence that the beta-NGF mRNA of L cells is subjected to regulation, but in a way apparently different from that described for the submaxillary gland.

Precursors of the nerve growth factor gamma subunit and renin bind to microtubules

Translation products of a reticulocyte lysate reaction, programmed with poly(A)-rich RNAs from the male mouse submaxillary gland, were subjected to affinity chromatography on a tubulin-Sepharose column. Analysis of the bound proteins in sodium dodecylsulfate/polyacrylamide gels revealed two polypeptides of Mr 27 000 and 45 000, that were shown to bind to tubulin in a specific manner. These polypeptides were absent from the translation products coded by poly(A)-rich RNAs from the female mouse. They were eluted from the tubulin-Sepharose resin under conditions similar to those employed for the dissociation of immune complexes. The Mr-27 000 and Mr-45 000 proteins were identified by immunoprecipitation with specific antisera as the precursors of the gamma subunit of the nerve growth factor (NGF) and renin respectively. These two precursors as well as a third, unidentified polypeptide of Mr 38 000, probably unrelated to the beta subunit of NGF, bound also to microtubules. The mature form of renin, purified from the submaximillary gland, also displayed an affinity for the microtubules. In contrast, the mature form of the gamma subunit of NGF did not bind to the microtubules. The possible involvement of the microtubules (tubulin) in the biosynthesis of these two secretory proteins is discussed.

Mouse kidney and submaxillary gland renin genes differ in their 5' putative regulatory sequences

The genomic DNAs that specify the renin mRNAs found in the submaxillary gland and in the kidney of Swiss mice have been isolated by molecular cloning in phage lambda. The Ren1 and Ren2 genes, encoding the kidney and submaxillary renins, respectively, span about 9.5 kilobases each. Restriction maps of both renin genes and their flanking sequences are presented. To correlate the differential expression of the renin genes with their structures, a sequence analysis of the putative 5' regulatory sequences of both genes was conducted. The results show that the leader sequences and promoter regions of both genes are highly homologous to a point located 179 nucleotides upstream from the transcription start point; the sequences diverge beyond this position.

Influence of androgen on translatable renin mRNA in the mouse submandibular gland

In mature outbred Swiss male mice, submandibular gland renin enzyme activity is 4- and 10-fold higher than in glands of prepubescent males and mature females, respectively. Levels of translatable renin mRNA have been studied in mouse submandibular gland during postnatal development and following administration of testosterone. The [35S]methionine-labeled cell-free translation products directed by male glandular mRNA contain a 47 +/- 2kd renin precursor that is not detected in products coded by prepubescent male or female gland mRNA. This cell-free synthesized precursor is detected immunochemically only in the translation products of gland mRNA from males of 33 days or older and from females receiving testosterone administration, a pattern consistent with the measurements of renin enzyme activity. This increase in biologically active renin mRNA is a selective one, since unfractionated male and female mRNAs have similar overall nucleotide sequence complexity corresponding to 1% of mouse single copy DNA. The cDNA transcribed from male gland mRNA reacts 5- and 10-fold faster with the template mRNA than with female or prepubescent male gland mRNA, respectively, which indicates that the male gland contains abundant nucleotide sequences that exist at low concentration in the female or prepubescent male. Selective hybrid arrested translation confirms that the levels of renin mRNA are lower in the glands of prepubescent males than in those of the mature males. These data indicate that the regulation of renin enzymatic activity by androgens is mediated by an increase in the levels of translatable renin mRNA both during postnatal development and after testosterone administration.

Ultrastructural immunocytochemical localization of renin and angiotensin II in the juxtaglomerular cells of the ischemic kidney in experimental renal hypertension

Partial ligation of the rat aorta between the renal arteries induces acute hypertension with atrophy of the left (ischemic) kidney, intense stimulation of juxtaglomerular cell (JGC) secretory activity, and significant increases in renal cortical renin activity, in plasma renin activity, and in the plasma levels of angiotensin I (AI) and angiotensin II (AII). With the unlabeled antibody technique at the light-microscopic level and various dilutions of renin antiserum, immunoreactive renin can be visualized in the JGC of sham-operated controls with high dilutions of antiserum that do not reveal renin in the JGC of ischemic kidney. The reverse is true with AII antisera; ie, high dilutions of AII antisera immunostain the JGCs of ischemic kidney but not those of control kidney. With the protein A-gold technique at the electron-microscopic level, using gold particles of small and large size and immunoreacting the two faces of a fine section, renin and AII can be localized in the same JGC secretory granules. With the same technique (immunoreacting only one face of a fine section with small gold particles), quantitative analysis reveals a lower concentration of renin and a higher concentration of AII in the secretory granules of the ischemic kidney JGCs; these granules are also of smaller size than those of control kidney JGCs. AI cannot be visualized in these cells at either the light- or electron-microscopic level. These results indicate that AII co-localized with renin in JGC secretory granules and probably co-secreted, is not synthetized by these cells but is internalized following receptor binding.

Molecular cloning of cDNAs from androgen-independent mRNA species of DBA/2 mouse sub-maxillary glands

cDNA libraries have been constructed from mRNAs isolated from mature male DBA/2 mouse submaxillary glands. Several recombinant plasmids have been assigned to particular mRNA species and their in vitro translation products by HART and hybrid selection. Clones containing copies of two abundant mRNA species that showed no sexual dimorphism were selected for detailed characterisation. Nucleotide sequences determined from one series of clones define an 850 nucleotide mRNA encoding a polypeptide of 16.5 kd having an N-terminal signal sequence, an acidic core and four glycosylation sites. A second family of clones correspond to an mRNA of 800 nucleotides, the sequence of which can be interpreted as coding for an intracellular protein of 14.7 kd. Computer searches of protein and nucleic acid sequences have not revealed the identity of either of these submaxillary gland products.

Synthesis and partial maturation of the alpha- and gamma-subunits of the mouse submaxillary gland nerve growth factor in Xenopus laevis oocytes

Sera raised against the alpha-, beta- and gamma-subunits of the mouse 7 S NGF were used to characterize translation products coded by submaxillary gland mRNAs microinjected into Xenopus oocytes. Anti-beta NGF sera did not cross-react with any material. In contrast, the precursors of the alpha- and gamma-subunits, as well as that of renin were identified. Use of tunicamycin, and a comparison of the translation products obtained in oocytes or in the reticulocyte lysate indicated that oocytes achieved the cleavage of signal sequences, the glycosylation of the alpha- and gamma-precursors, and the subsequent secretion of the 3 proteins. In the submaxillary gland, however, the mature forms of alpha NGF, gamma NGF and renin are composed of peptides of smaller size than those produced by the oocytes. These latter appear to lack specific proteases involved in the terminal processing of the submaxillary gland proteins.

Molecular cloning and nucleotide sequence of a human renin cDNA fragment

We have studied human renin messenger RNA by hybridization with the mouse submaxillary gland (SMG) renin cDNA probe. The human kidney messenger RNA is about 1.6 kilobase (kb) long, similarly to the mouse SMG renin mRNA. A kidney renin cDNA clone of 1.1 kb length was obtained. A comparison of nucleotide sequences of mouse and human cDNA clones reveals conservation of residues involved in catalytic mechanisms and a potential glycosylation site. The human renin molecular probe allowed us to study renin expression in human chorionic tissue. The chorionic and kidney renin messenger RNAs are similar in length. The Southern blot analysis reveals the presence of a single renin gene in human DNA.

Synthesis of mouse renin as a 2-5-33-5 kilodalton pre-pro-two-chain molecule and use of its cDNA to identify the human gene

A DNA coding for mouse submandibular gland (MSG) renin was used in studies of the biosynthesis and processing of MSG renin and precursors and as a probe for identification of the human renin gene. A 2 kilodalton signal peptide was demonstrated by cleavage of preprorenin (45 kilodaltons) in the presence of microsomal membranes from dog pancreas. Prior selection of renin mRNA by hybridization with its cDNA obviated the possibility that a protease translated from total MSG mRNA could be activated by the microsomal membranes and then act on the primary translation product. In vitro labelling experiments with female MSG demonstrated that prorenin (43 kilodaltons) is rapidly converted to renin (38 kilodaltons) and that testosterone stimulated synthesis by increasing transcription of renin mRNA. Electrophoresis under non-reducing conditions demonstrated 38 kilodalton renin which when reduced ran as two bands of 33 and 5 kilodaltons. Thus, native MSG renin has two chains linked by disulphide bonding. Hydrolysis of the 38 kilodalton single chain occurred only slowly during in vitro labelling. Prorenin bound only weakly to a pepstatin affinity column and could be activated by adding trypsin to column fractions. Both 38 kilodalton single and two chain renin bound strongly however, suggesting that both are active. Base sequencing of MSG renin cDNA indicated an Arg-Arg residue additional to the published amino acid sequence of the heavy chain. This may account for the two forms seen on isoelectric focusing. Mouse renin cDNA was used as a hybridization probe in screening a human genomic library in order to identify the human renin gene. The DNA in positive colonies had overlapping restriction maps and the coding region was found.

Cell-free translation of human renin mRNA

The molecular weight of human renin precursor (preprorenin) was determined to be 43,000 by cell-free translation of its mRNA. Poly(A)+-containing RNA from human infarcted kidney was translated in a cell-free reticulocyte lysate system containing [35S] methionine. Immunoprecipitation with anti-renin antibody gave one major band with an apparent Mr = 43,000, as determined by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis and fluorography. The specific band, which represents the prepro-form of human renal renin, was very similar to mouse submandibular gland preprorenin in its electrophoretic mobility.

Distribution of exogenously administered renin in mouse kidney

Purified mouse submaxillary gland renin was labelled with iodine(125I) by the chloramine-T method and this 125I labelled renin was given to male ICR mice (6-7 wks. old), intravenously in a dose of 20 ng(2 microCi)/40 g body weight. At a specified time, the kidneys of these treated mice were excised, the radioactivity determined and the tissues immediately prepared for microscope and electron microscope autoradiography(micro-ARG and EM-ARG). Silver grains accumulated mainly at the apical site of the proximal convoluted tubules but were not identified in other areas of the nephron, including macula densa or in the arterial wall, glomeruli, and juxtaglomerular cells (micro-ARG). Silver grains were seen in the pinocytotic vesicles, vacuoles and lysosomal granules(EM-ARG). This is the first demonstration that exogenous renin is ultrafiltered through glomerular capillaries and is reabsorbed by pinocytosis in the one-third upper area of the proximal convoluted tubule.

In vitro studies on the conversion of the biosynthetic precursor of renin

The initial translation product of mouse submaxillary gland mRNA has a molecular weight of about 50,000. We have now translated renin mRNA in frog oocytes which are known to be able to remove the so-called "pre"- or "signal"- sequence from products of injected mRNAs. From these injected oocytes, we could precipitate with antirenin a 48,000 dalton polypeptide. Treatment with kallikrein or trypsin of the oocyte product resulted in a decrease in amount of this 48,000 dalton protein and a corresponding increase in a 45,000 dalton protein, precipitable with antirenin. We conclude that the initial translation product of renin mRNA is a preprorenin of molecular weight 50,000, which in oocytes is enzymatically cleaved to render 48,000 dalton prorenin. Although kallikrein may be a physiological activator of renin, it appears to be not the only one since no mature, 40,000 dalton renin was formed.

Biosynthesis of preprorenin. Studies using whole tissue, a cell-free system, and E. coli containing cDNA inserted at the PstI site of plasmid pBR322

The biosynthesis of renin as a higher molecular weight 'prorenin' was demonstrated by in vitro incorporation of [35S] methionine into nascent polypeptides of submandibular gland tissue from adult male mice. Immunoprecipitation with anti-renin and electrophoresis identified a Mr 44,500, pI 6.4 prorenin which normally represented 5% of renin-immunoreactive protein in tissue extracts and which was rapidly converted during in vitro labeling into a Mr 40,000, pI 6.2 species. The latter was subsequently processed slowly to forms of Mr 35,500, pI 5.6 and Mr 34,000, pI 5.4. The influence of processing enzymes was then eliminated by synthesizing renin in a cell-free translation system containing rabbit reticulocyte lysate and mRNA isolated from submandibular glands. This yielded an even larger species of Mr 46,000 likely to be 'preprorenin'. A clone bank of mouse submandibular gland cDNA was prepared. This consisted of E. coli RRI transformed with plasmid pBR322 in which cDNA had been inserted at the PstI site so that the bacteria could express the encoded polypeptide. Renin-immunoreactive colonies were identified suggesting the expression of renin-like proteins by a prokaryote. The cDNA which was 700-1000 base pairs big was excised for sequencing.