Transgenic mice overexpressing human vasoactive intestinal peptide (VIP) gene in pancreatic beta cells. Evidence for improved glucose tolerance and enhanced insulin secretion by VIP and PHM-27 in vivo

Vasoactive intestinal peptide (VIP), a 28-amino acid peptide hormone, plays many physiological roles in the peripheral and central nervous systems. It has been proposed that endogenous VIP released from VIP-containing nerves is involved in the regulation of the secretory function of the endocrine pancreas. To test this hypothesis in vivo, we produced transgenic mice carrying the human VIP/peptide histidine methionine 27 (PHM-27) gene under the control of insulin promoter. In immunohistochemical analyses of islets, all the islet beta cells of transgenic mice were intensely stained for both VIP and PHM-27, consistent with the fact that these two peptides are encoded in a single mRNA (Itoh, N., Obata, K., Yanaihara, N., and Okamoto, H. (1983) Nature 304, 547-549). VIP was efficiently secreted from isolated transgenic islets in vitro. The blood glucose assays in free-fed mice indicated that the transgene lowered the blood glucose levels of transgenic mice (128 +/- 4 mg/dl) by about 20% below control levels (155 +/- 6 mg/dl). In the glucose tolerance test, at 60 min after glucose administration, the transgenic blood glucose levels (129 +/- 12 mg/dl) were much lower than control levels (175 +/- 13 mg/dl). The transgenic serum insulin levels at 15 min after glucose administration were 2.5-3.0-fold higher than control levels. The transgene was also effective in ameliorating glucose intolerance of 70% depancreatized mice. These results indicate that VIP and PHM-27 produced from the transgenic beta cells efficiently enhance glucose-induced insulin secretion from beta cells by an autocrine mechanism. These results also suggest that genetic manipulation of islet beta cells by the human VIP/PHM-27 gene or delivery of VIP to beta cells may ultimately provide a valuable approach to enhancing insulin secretion in clinical diabetes.

Cloning and characterization of cDNA encoding rat ADP-ribosyl cyclase/cyclic ADP-ribose hydrolase (homologue to human CD38) from islets of Langerhans

We report the cloning and cDNA sequence of rat CD38, ADP-ribosyl cyclase/cyclic ADP-ribose hydrolase. Rat CD38 is composed of 303 amino acids and shares a high degree of homology with human and mouse CD38. Rat CD38 mRNA is expressed in various tissues including pancreatic islets but not in RINm5F cells.

Cyclic ADP-ribose modulates Ca2+ release channels for activation by physiological Ca2+ entry in bullfrog sympathetic neurons

Although Ca(2+)-induced Ca2+ release (CICR) via ryanodine receptors has been found to occur in intact neurons, little is known about the physiological processes that regulate it. We studied the effects of cyclic ADP-ribose (cADPR) on CICR in cultured bullfrog sympathetic neurons by fura-2 fluorescence recording and patch-clamp techniques. cADPR applied through a patch pipette augmented action potential- or depolarizing pulse-induced rises in intracellular Ca2+ without a change in Ca2+ entry initiating the responses, but not in the presence of ryanodine. Likewise, cADPR enhanced a single or oscillatory rise(s) in intracellular Ca2+ induced by caffeine. These results strongly suggest that cADPR can be an endogenous modulator of ryanodine receptors in neurons.

Structural determination and characterization of a 40 kDa protein isolated from rat 40 S ribosomal subunit

We have purified a 40 kDa protein from the rat 40 S ribosomal subunit and determined its primary structure by amino acid and cDNA sequencing. The amino acid sequence of the 40 kDa protein shared 29-37% homology with prokaryotic ribosomal protein S2 of eubacteria and chloroplasts, indicating that the protein is a eukaryotic counterpart to prokaryotic S2. Moreover, the amino acid sequence shared 99% identity with those deduced from cDNAs for 68 kDa laminin binding proteins of human, murine and bovine origins. The cDNAs are capable of encoding polypeptides with predicted molecular mass of 33,000 which lacked typical signal sequences, N-linked glycosylation sites and putative transmembrane domains. These results indicate that the cDNAs for 68 kDa laminin binding proteins actually code for the 40 kDa ribosomal protein.

Synthesis and hydrolysis of cyclic ADP-ribose by human leukocyte antigen CD38 and inhibition of the hydrolysis by ATP

Cyclic ADP-ribose (cADPR) has been recently shown to be generated in pancreatic beta-cells by glucose stimulation, serving as a second messenger for Ca2+ mobilization in the endoplasmic reticulum in the process of insulin secretion (Takasawa, S., Nata, K., Yonekura, H., and Okamoto, H. (1993) Science 259, 370-373). In the present study, we isolated a cDNA for CD38, which has been reported to be a human leukocyte antigen, from a human insulinoma and expressed the cDNA in COS-7 cells. CD38 expression was observed in the plasma membrane and the microsome fractions of the COS-7 cells. When we incubated the plasma membrane fraction with NAD+ and analyzed the reaction products by high pressure liquid chromatography, the formation of cADPR was observed in addition to the ADP-ribose (ADPR) formation. When the plasma membrane fraction was incubated with cADPR, cADPR was converted to ADPR stoichiometrically. These results suggest that CD38 has both cADPR-forming and -hydrolyzing activities. Moreover, we found that ATP (2-10 mM), generated in the glucose metabolism in beta-cells, inhibited the cADPR-hydrolyzing activity, resulting in the increased formation of cADPR. These findings indicate a role for CD38 in the synthesis and hydrolysis of cADPR in the process of insulin secretion in pancreatic beta-cells.

Cyclic ADP-ribose in insulin secretion from pancreatic beta cells

Inositol 1,4,5-trisphosphate (IP3) is thought to be a second messenger for intracellular calcium mobilization. However, in a cell-free system of islet microsomes, cyclic adenosine diphosphate-ribose (cADP-ribose), a nicotinamide adenine dinucleotide (NAD+) metabolite, but not IP3, induced calcium release. In digitonin-permeabilized islets, cADP-ribose and calcium, but not IP3, induced insulin secretion. Islet microsomes released calcium when combined with the extract from intact islets that had been incubated with high concentrations of glucose. Sequential additions of cADP-ribose inhibited the calcium release response to extracts from islets treated with high concentrations of glucose. Conversely, repeated additions of the islet extract inhibited the calcium release response to a subsequent addition of cADP-ribose. These results suggest that cADP-ribose is a mediator of calcium release from islet microsomes and may be generated in islets by glucose stimulation, serving as a second messenger for calcium mobilization in the endoplasmic reticulum.

The primary structure of rat rig/ribosomal protein S15 gene

We have isolated rat rig/ribosomal protein S15 gene from a DNA library derived from a rat insulinoma and determined the complete nucleotide sequence. The rat rig/S15 gene is composed of four exons and three introns spanning 2 kbp and exhibits distinctive structural features unique for a ribosomal protein gene.

Structural determination of Saccharomyces cerevisiae rig gene and identification of its product as ribosomal protein S21

rig was originally isolated from a rat insulinoma-derived cDNA library. The 145 amino acid sequence of the rig protein is invariant in mammalian cDNAs. In this paper, we have isolated the cDNA and genomic clones for yeast (Saccharomyces cerevisiae) rig, determined their nucleotide sequences, and identified the gene product. The gene and the mRNA encode a basic protein of 142 amino acids which has 61.3% amino acid identity with mammalian rig protein. On two-dimensional gel electrophoresis, the in vitro transcription/translation product of yeast rig cDNA co-migrated with yeast ribosomal protein S21. These results led to the conclusion that yeast rig ribosomal protein S21 and to the determination of the previously unknown primary structure of yeast S21 protein. Unlike most ribosomal protein genes of S. cerevisiae, the gene exists as a single copy in a haploid set of the yeast genome and has no intron, locating at chromosome VII or XV.

Sequence of the chicken rig gene encoding ribosomal protein S15

The nucleotide sequence of the chicken rig gene encoding ribosomal protein S15 was determined. The 1.6-kb gene consists of four exons and three introns. The 5'-flanking region of the gene lacks TATA- or CAAT-box sequences. Several GC-box sequences were found around the transcription start point.

A mutated ARO4 gene for feedback-resistant DAHP synthase which causes both o-fluoro-DL-phenylalanine resistance and beta-phenethyl-alcohol overproduction in Saccharomyces cerevisiae

o-Fluoro-DL-phenylalanine (OFP)-resistant mutants which overproduce beta-phenethyl-alcohol were isolated from a laboratory strain of Saccharomyces cerevisiae. Cells of one of the mutants accumulated tyrosine and phenylalanine 1.5-3 fold more than did wild-type cells. Its 3-deoxy-D-arabino-hepturosonate-7-phosphate (DAHP) synthase (EC 4.1.2.15), encoded by ARO4, was free from feedback inhibition by tyrosine. Genetic analysis revealed that the mutation was controlled by a single dominant gene, ARO4-OFP, encoding feedback-resistant DAHP synthase by tyrosine, and that this gene caused both the OFP resistance and beta-phenethyl-alcohol overproduction. This was supported by molecular genetic studies using cloned ARO4 both from the wild-type and its mutant strain.

Isolation and genetic study of p-fluoro-DL-phenylalanine-resistant mutants overproducing beta-phenethyl-alcohol in Saccharomyces cerevisiae

p-Fluoro-DL-phenylalanine (PFP)-resistant mutants which produce a large amount of beta-phenethyl-alcohol, a rose-like flavor component, were isolated from the isogenic strains X2180-1A and X2180-1B of Saccharomyces cerevisiae. Cells of these mutants accumulated phenylalanine and tryptophan more than 3-fold times that of wild-type cells, while they accumulated less than half the tyrosine. The activity of prephenate dehydrogenase (PDG) (EC 1.3.1.12) was markedly decreased while that of 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase (EC 4.1.2.15) was increased. Genetic analysis revealed that the mutation occurred at the TYR1 locus, encoding PDG, and that the mutated TYR1 gene, try1-pfp, caused both PFP resistance and beta-phenethyl-alcohol overproduction. This was supported by molecular genetic studies with cloned tyr1-pfp DNA.

rig encodes ribosomal protein S15. The primary structure of mammalian ribosomal protein S15

rig, a gene originally isolated from a rat insulinoma cDNA library, codes for a basic 145 amino acid protein [( 1986) Diabetes 35, 1178-1180]. Here we show that the immunoreactivity to a monoclonal antibody against the deduced rig protein and the translation product of rig mRNA comigrated with ribosomal protein S15. The amino acid sequence of ribosomal protein S15 purified from rat liver coincided with that deduced from the nucleotide sequence of rig mRNA, but there were indications that the initiator methionine was removed and the succeeding alanyl residue was monoacetylated. From these results, we conclude that the product of rig is ribosomal protein S15.

Nucleotide sequence determination of mouse, chicken and Xenopus laevis rig cDNAs: the rig-encoded protein is extremely conserved during vertebrate evolution

Mouse, chicken and Xenopus laevis homologues to rig (rat insulinoma gene) cDNA were isolated and their nucleotide sequences were determined. Each homologue encoded a 145-amino acid protein; the amino acid sequence remained invariant in the murine and avian genes, and there were only 6 amino acid substitutions in the salientian gene. The evolutionary rate calculated for rig mRNA was sufficiently low to be viewed as evidence that rig is vital to vertebrate species. Southern blot analysis indicated that haploid sets of the mammalian genomes contain several copies of rig or rig-related sequences, whereas there appeared to be only one copy in the amphibian and bird genomes. The possibility that rig belongs to the class of housekeeping genes is discussed.

Expression of the insulinoma gene rig during liver regeneration and in primary cultured hepatocytes

We have isolated a novel gene, rig (rat insulinoma gene) from rat insulinomas. In the present study, rig was found to be expressed in rat regenerating liver and in primary cultured rat hepatocytes. The level of rig mRNA was increased at the proliferative phase of liver regeneration. In synchronously cultured hepatocytes, the rig mRNA level was elevated at the G1 phase of the cell cycle and the rig-protein was accumulated in the nuclei during the S phase. These results indicated that rig could be involved in a more general way in growth or cell replication.

A novel gene activated in regenerating islets

Administration of poly(ADP-ribose) synthetase inhibitors such as nicotinamide to 90% depancreatized rats induces regeneration of pancreatic islets, thereby ameliorating the surgical diabetes (Yonemura, Y., Takashima, T., Miwa, K., Miyazaki, I., Yamamoto, H., and Okamoto, H. (1984) Diabetes 33, 401-404). In screening the regenerating islet-derived cDNA library, we came across a novel gene encoding a 165-amino acid protein. The gene was expressed in regenerating islets but not in normal pancreatic islets, insulinomas, or regenerating liver. In 90% depancreatized and nicotinamide-injected rats, the expression of the gene was increased 1 month after the partial pancreatectomy and reached a peak 3 months after the operation. The increase in expression of the gene was temporally correlated with the increase in size of regenerating islets and the decrease in urinary glucose level. The gene was also found to be activated in hyperplastic islets of aurothioglucose-treated mice. Thus, the expression of the gene in both regenerating and hyperplastic islets suggests possible roles for this gene in replication, growth, and maturation of islet beta-cells. We also found that a human pancreas-derived cDNA library contained a homologue to the gene.

Evolutionary conservation of the insulinoma gene rig and its possible function

We have identified a gene, rig (rat insulinoma gene), that is activated in chemically induced rat insulinomas but not in normal pancreatic islets or in regenerating islets. In the present study, we have found that the insulinoma gene was activated in a BK virus-induced hamster insulinoma cell line and in a spontaneously occurring human insulinoma. From the hamster and human insulinoma cDNA libraries, rig homologues were isolated, and their nucleotide sequences were determined. In the same manner as the rat gene, both hamster and human homologues contained one open reading frame of 435 nucleotides, differing by 32- and 41-base substitutions, respectively. All the base substitutions were same-sense mutations. Accordingly, the deduced 145-amino acid sequence remained invariant in hamster, human, and rat insulinomas, suggesting that rig has evolved under extraordinarily strong selective constraints. Computerized structure analysis indicated that rig-encoded protein is a possible DNA-binding protein. The antisense oligodeoxyribonucleotide complementary to hamster rig mRNA was synthesized and injected into the hamster insulinoma cells. The antisense rig oligodeoxyribonucleotide inhibited DNA synthesis in the insulinoma cells, whereas the sense rig oligodeoxyribonucleotide or antisense insulin oligodeoxyribonucleotide had no inhibitory effect. These results strongly suggest that the activation of rig is both common and potentially significant in the oncogenic growth of pancreatic B cells of islets of Langerhans.

Novel gene activated in rat insulinomas

Insulinomas can be induced in experimental animals by the combined administration of diabetogenic agents with polyadenosine diphosphate (polyADP)-ribose synthetase inhibitors. A complementary DNA (cDNA) library that was constructed from streptozocin-nicotinamide-induced rat insulinomas has been found to contain a novel gene encoding a basic protein of 145 amino acids. The gene was expressed in alloxan-nicotinamide-induced insulinomas as well as in streptozocin-nicotinamide-induced insulinomas but not in normal pancreatic islets or in regenerating islets. This indicates that the activation of the gene designated rig, i.e., rat insulinoma gene, may be a general feature of pancreatic beta-cell transformation.

Induction of rat pancreatic B-cell tumors by the combined administration of streptozotocin or alloxan and poly(adenosine diphosphate ribose) synthetase inhibitors

Streptozotocin and alloxan were administered to Wistar rats in combination with poly(adenosine diphosphate ribose) synthetase inhibitors. Ten to 16 months after the injection of streptozotocin (50 mg/kg body weight i.v.) and 3-aminobenzamide (345 mg/kg i.v.), streptozotocin (50 mg/kg) and nicotinamide (350 mg/kg i.p.), streptozotocin (50 mg/kg) and picolinamide (250 mg/kg i.p.), alloxan (40 mg/kg i.v.) and nicotinamide (350 mg/kg), alloxan (40 mg/kg) and 3-aminobenzamide (345 mg/kg), and alloxan (40 mg/kg) and picolinamide (250 mg/kg), pancreatic islet cell tumors developed in 100, 98, 60, 26, 22, and 20% of surviving rats, respectively. However, after the single injection of streptozotocin and alloxan, islet cell tumors developed in 42 and 11% of surviving rats, respectively. The tumors were rich in B-granules on electron micrographs and contained as large amounts of proinsulin messenger RNA as normal pancreatic islets. The results indicate that poly(adenosine diphosphate ribose) synthetase inhibitors enhance the tumorigenic effect of streptozotocin and alloxan on islet B-cells.

Biosynthesis of astromicin and related antibiotics. II. Biosynthetic studies with blocked mutants of Micromonospora olivasterospora

An inosamine-idiotrophic mutant, KY11559, which produced no astromicin unless scyllo-inosamine was added to the fermentation medium, was isolated from Micromonospora olivasterospora. Biotransformation studies were performed with resting cells of this mutant and compounds assumed to be precursors of 1,4-diaminocyclitol (fortamine). Scyllo-inosose, scyllo-inosamine and FU-10 were converted to astromicin. A number of mutants blocked in the biosynthesis of astromicin were developed from M. olivasterospora, and the intermediates accumulated by these mutants were isolated and identified. Twenty-five blocked mutants were classified into 10 groups, based on their complementation patterns by cosynthesis experiments. Further, utilizing these blocked mutants and the isolated compounds, biotransformation analyses were performed. The results showed that the amination at position 4 in fortamine occurred after formation of the pseudodisaccharide. Subsequently, the aminosugar and aminocyclitol moieties were aminated, methylated, dehydroxylated, epimerized and acylated to produce astromicin. Thus it was demonstrated that the astromicin biosynthetic pathway has a unique feature which is not found in the biosynthesis of other aminoglycoside antibiotics.

Fortimicins A and B, new aminoglycoside antibiotics. I. Producing organism, fermentation and biological properties of fortimicins

A culture of Micromonospora species MK-70 was found to produce two new antibiotics, fortimicins A and B. Antibacterial and paper chromatographic data on an eluate from IRC-50 treatment of fermentation beers indicated that fortimicins A and B are new antibiotics with broad-spectrum, basic and water-soluble properties. Fortimicin A exhibited potent, unique, broad-spectrum antibacterial activity against Gram-positive and negative bacteria both in vitro and in vivo, while fortimicin B was only weakly active.

Fortimicins A and B, new aminoglycoside antibiotics. II. Isolation, physico-chemical and chromatographic properties

The aminoglycoside antibiotics fortimicins A and B produced by a naturally occurring strain Micromonospora sp. MK-70 were isolated from its fermentation beer. Fortimicins A and B were isolated as water-soluble, basic, white amorphous powders having molecular formula C17H35N5O6 and C15H32N4O5, respectively. Acid hydrolysis of fortimicin A indicated that it has one mole of glycine in its molecule while fortimicin B has not. Paper chromatography, silica-gel and carbon thin-layer chromatography revealed that fortimicins A and B are novel aminoglycoside antibiotics.