Biomedical subjects

J R Bundgaard

Publications and source records attributed to J R Bundgaard.

15 recordsLinked to original sources

PubMed1999

Identification and expression of gastrin and cholecystokinin mRNAs from the turtle, Pseudemys scripta: evidence of tissue-specific tyrosyl sulfation(1).

Gastrin and cholecystokinin (CCK) are related peptide hormones expressed in the brain and gut of vertebrates. In this study, complementary DNAs have been characterised from the red-eared slider turtle, Pseudemys scripta. The encoded preproCCK contains mono and dibasic endoproteolytic processing sites for formation of the previously identified CCK-70, CCK-40 and CCK-8 products, whereas preprogastrin contains two dibasic processing sites for the generation of gastrin-52. Alignment of the predicted preprohormone structures with those of other species, showed that preproCCK has been well conserved among all vertebrates, whereas progastrin is less conserved. Both gastrin and CCK mRNA display expression patterns similar to their mammalian counterparts, with CCK being expressed in the brain, duodenum and small intestine, and gastrin in the antrum. Heterologous expression of turtle preprogastrin in a mammalian endocrine cell line led to production of carboxyamidated gastrin-52 as observed in turtle antrum. However, in contrast to the non-sulfated endogenous peptide, the heterologously expressed gastrin was completely Tyr sulfated. Consequently, it appears that either gastrin producing cells in the turtle gut do not express tyrosylprotein sulfotransferases or the enzyme(s) present in turtle antrum is unable to sulfate turtle gastrin.

Amino Acid Sequence↗

PubMed1999

Composite action of three GC/GT boxes in the proximal promoter region is important for gastrin gene transcription.

The proximal region of the human gastrin gene promoter contains three GC/GT boxes at positions -140 to -134 bp, -108 to -102 bp and -67 to -61 bp. In this study we have examined the significance of the three elements, and their role in Sp1 and Sp3 mediated gastrin transcription. In AGS cells, mutation of each of the boxes caused a moderate decrease in promoter activity from 33 to 63%, whereas double or triple mutations reduced activity to 3-12%. In Drosophila cells Sp1 activated the promoter, mainly through the distal GC box. Similarly, co-transfection of heterologous promoter constructs revealed that only the distal GC box increased activation by Sp1. The effect of Sp3 was cell-line dependent, since Sp3 inhibited the gastrin promoter activity in AGS cells and caused a synergistic activation of the Sp1 stimulated gastrin promoter in Drosophila cells. Both effects were dependent on the C-terminal DNA binding domain of Sp3. The results indicates that the combined effect of the GC/GT boxes and the ratio between Sp1 and Sp3 are important for gastrin gene expression.

Adenocarcinoma↗

PubMed1999

A Kazal-type trypsin inhibitor from the protochordate Ciona intestinalis.

A trypsin inhibitor from Ciona intestinalis, present throughout the animal, was purified by ion-exchange chromatography followed by four HPLC steps. By MS the molecular mass of the native form was determined to be 6675 Da. The N-terminal amino acid sequence was determined by protein sequencing, but appeared to be partial because the theoretical molecular mass of the protein was 1101 Da too low. Thermolysin treatment gave rise to several fragments each containing a single disulphide bridge. By sequence analysis and MS intramolecular disulphide bridges could unequivocally be assigned to connect the pairs Cys4-Cys37, Cys8-Cys30 and Cys16-Cys51. The structure of the inhibitor is homologous to Kazal-type trypsin inhibitors. The inhibitor constant, KI, for trypsin inhibition was 0.05 nM whereas chymotrypsin and elastase were not inhibited. To reveal the complete sequence the cDNA encoding the trypsin inhibitor was isolated. This cDNA of 454 bp predicts a protein of 82 amino acid residues including a 20 amino acid signal peptide. Moreover, the cDNA predicts a C-terminal extension of 11 amino acids compared to the part identified by protein sequencing. The molecular mass calculated for this predicted protein is in accordance with the measured value. This C-terminal sequence is unusual for Kazal-type trypsin inhibitors and has apparently been lost early in evolution. The high degree of conservation around the active site strongly supports the importance of the Kazal-type inhibitors.

Amino Acid Sequence↗

PubMed1998

Unique progastrin processing in equine G-cells suggests marginal tyrosyl sulfotransferase activity.

Previous studies have indicated that equine G-cell processing of progastrin differs from that of other species. Since the difference may be due to structural features, we have identified equine gastrin-17 and -34 (<ELGLQGSPHLVADLSKKQGPWLEKEEAAYGWMDF-NH2), and cloned a corresponding 451-bp cDNA that encodes a 107-amino-acid preprogastrin. Comparison with other mammalian gastrins shows a high degree of conservation, but instead of four or five acidic residues preceding the bioactive carboxyamidated C-terminal heptapeptide, equine gastrin contains the remarkable substitution of Lys for Glu in this presumed invariant region. In contrast with known mammalian gastrins, which are all significantly Tyr-sulphated, the equine antral gastrins are virtually non-sulphated. Transfection of the equine preprogastrin cDNA into an endocrine cell line resulted in highly sulphated gastrins, indicating that the absence of in situ sulphation is not due to the structure of gastrin, but occurs rather because the equine antral G-cells are unique with respect to tyrosyl sulfotransferase activity. Furthermore, the marginal sulphation may explain the high proportion of gastrin-34 versus gastrin-17 in the equine antrum, since tyrosyl sulphation has been shown to promote the endoproteolytic processing of prohormones.

Amino Acid Sequence↗

PubMed1998

Structure and tissue-specific expression of genes encoding bovine copper amine oxidases.

A cDNA coding for an enzyme belonging to the family of copper amine oxidases was cloned from a bovine lung cDNA library using a PCR approach. The nucleotide sequence of this cDNA was found to be different from that of the previously published liver cDNA encoding bovine serum amine oxidase, another copper amine oxidase. Analyses using reverse transcription followed by PCR of RNA extracted from different bovine tissues confirmed that the copper amine oxidase gene expressed in bovine liver is closely related to, but different from, the copper amine oxidase gene expressed in bovine lung, kidney, spleen and heart. Northern blotting data showed that the level of copper amine oxidase expression in liver is considerably higher than in the other tissues tested. Southern blotting analyses of bovine chromosomal DNA suggested the existence of at least three copper amine oxidase genes. Two of these genes are apparently expressed in a tissue-specific manner as outlined above. A fragment of a third copper amine oxidase gene is identified. The exon-intron organization of the bovine copper amine oxidase genes analyzed is similar to that of the related human diamine oxidase gene, except that no intron in the position equivalent to that of the third intron in the human gene is found. In the third gene, a complete replacement of the third intron of the bovine copper amine oxidase gene (equivalent to the fourth intron of the human gene) has occurred.

Amine Oxidase (Copper-Containing)↗

PubMed1997

New consensus features for tyrosine O-sulfation determined by mutational analysis.

Tyrosine sulfation is an ubiquitous modification of proteins synthesized along the secretory pathway. It enhances protein-protein interactions and may be necessary for the bioactivity of secreted proteins and peptides. To predict tyrosine sulfation, a consensus has been proposed based on sequence comparisons of known substrates and on in vitro studies using synthetic peptides. This consensus predicts the presence of acidic residues on the amino-terminal side of the target tyrosine as the key feature. Using site-directed mutagenesis, we have examined the role of residues neighboring the sulfation site of an intact protein, human progastrin, in vivo. The results show that the charge of the residue in the amino-terminal position (-1) of the tyrosine is critical and can be neutral or acidic, whereas a basic residue abolishes sulfation. In addition, the degree of sulfation is influenced by the residues in positions -2 and -3. Hence, surprisingly a basic residue in position -2 enhances sulfation. Our data suggest a considerably broader range of substrates for the tyrosylprotein sulfotransferase than hitherto assumed and that the tyrosylprotein sulfotransferase is cell-specifically expressed.

Amino Acid Sequence↗

PubMed1996

Molecular structure and genetic mapping of the mouse gastrin gene.

The mouse gastrin gene has three exons totalling 460 bp and a deduced preprogastrin of 101 amino acids. The sequence of murine gastrin-34 is 94% identical to rat gastrin-34 and 76% identical to human gastrin-34. At Arg79, mouse progastrin has a unique cleavage site that might allow species-specific synthesis of gastrin-13. Northern analysis and RT-PCR demonstrated that gastrin gene transcripts are abundant in mouse stomach and duodenum and present at low levels in brain, ovary and pancreas, similar to the pattern described for other mammals. The gastrin gene was mapped to the distal region of mouse chromosome 11.

Amino Acid Sequence↗

PubMed1996

An efficient cellular system for mutational analysis of prohormone processing.

A novel system for heterologous expression of prohormones based on transient transfection of the HIT beta-cell line was established using human progastrin as a model. Progastrin was expressed at high levels compared to other gene transfer systems in endocrine cells, and the processing pattern was similar to that of normal antral gastrin cells. Thus, gastrin was partially tyrosine O-sulfated and carboxyamidated. Cell extracts contained mainly gastrin-17 and gastrin-34 and the corresponding glycine-extended forms. In contrast, the media contained more incompletely processed gastrin forms. This suggests that gastrin was directed to the regulated secretory pathway but that some progastrin products were constitutively secreted. Glucose increased both the level of gastrin gene expression and maturation to carboxyamidated peptides, indicating that glucose influences the activity of the amidation enzyme complex, peptidylglycine alpha-amidating mono-oxygenase (PAM), in insulin cells. Mutational analysis of tyrosine sulfation of gastrin demonstrated that substitution of the uncharged residue carboxy-terminal to the tyrosine with an acidic residue does not increase sulfation in contrast to previous results, where the amino-terminal residue was replaced with an acidic residue. The mutant peptides displayed sulfation-dependent processing, supporting our recent suggestion that tyrosine sulfation increases the proteolytic processing of prohormones.

Amino Acid Sequence↗

PubMed1996

Induction of NGAL synthesis in epithelial cells of human colorectal neoplasia and inflammatory bowel diseases.

In inflammatory and neoplastic disorders of the colon a defect barrier function of the mucosa may result in absorption of bacterial products from the intestinal lumen. These products may further recruit inflammatory cells and thus augment the inflammatory response. A novel lipocalin in neutrophils, neutrophil gelatinase associated lipocalin (NGAL), with the ability to bind bacterial formylpeptides, has been described and therefore it is of interest to investigate the expression of this protein in diseases of the colon. Expression of NGAL was investigated by immunohistochemistry and by mRNA in situ hybridisation in normal colon and in neoplastic and inflammatory colorectal diseases. A very high expression of NGAL was seen in colonic epithelium in areas of inflammation, both in non-malignant epithelium (diverticulitis, inflammatory bowel disease, and appendicitis) as well as in premalignant and malignant neoplastic lesions of the colon. In adenocarcinoma, the NGAL expression was especially abundant in the transitional mucosa and in the superficial ulcerated area. On the other hand, no NGAL expression could be detected in lymph node metastases from these adenocarcinomas. A weak expression of NGAL in some epithelial cells was only occasionally seen in normal colon. In conclusion, NGAL synthesis is induced in epithelial cells in inflammatory and neoplastic, colorectal diseases. NGAL may serve an important anti-inflammatory function as a scavenger of bacterial products.

Acute-Phase Proteins↗

PubMed1995

An ELISA for grancalcin, a novel cytosolic calcium-binding protein present in leukocytes.

Grancalcin is a newly discovered cytosolic calcium-binding protein, belonging to the group of EF-hand proteins. Grancalcin is specifically associated with cells originating in the bone marrow. Grancalcin binds reversibly to secretory vesicles and plasma membranes in human neutrophils and might therefore play a role in the regulation of vesicle/granule exocytosis. We describe here the production of recombinant grancalcin, the generation of antibodies to the protein and the development of a specific, accurate and sensitive ELISA for the detection of human leukocytic grancalcin. This ELISA may be useful for monitoring leukocyte infiltration into tissues.

Antibody Specificity↗

PubMed1995

A distal Sp1-element is necessary for maximal activity of the human gastrin gene promoter.

Studies of transgenic mice have shown that transcriptional control of the gastrin gene exhibits significant species differences. Transfection of the human gastrin promoter in murine cells have depicted proximal Sp1, E-box and CACC elements as the major determinants of transcription. We have examined cis-regulatory elements of the human promoter on a human gastrin expressing cell line and find that a distal -135 to -142 Sp1 element is necessary for maximal activity. Alignment of the mouse and human promoters shows that the proximal human Sp1 and CACC elements are not conserved, whereas the E-box element is retained. The distal Sp1 element is present in mouse but exhibits a C to T transition in the core that is likely to reduce binding affinity of Sp1. We conclude that gastrin gene transcription is regulated by distinct elements in man and rodents.

Adenocarcinoma↗

PubMed1995

Tyrosine O-sulfation promotes proteolytic processing of progastrin.

Tyrosine O-sulfation is a common post-translational modification of secretory and membrane proteins. The biological function of sulfation is known in only a few proteins, where it appears to enhance protein-protein interactions. Based on known sequences around sulfated tyrosines, a consensus sequence for prediction of target tyrosines has been proposed. However, some proteins are tyrosine sulfated at sites that deviate from the proposed consensus. Among these is progastrin. It is possible that the deviation explains the incomplete sulfation characteristic for bioactive gastrin peptides. In order to test this hypothesis, we have performed site-directed mutagenesis of the gastrin gene followed by heterologous expression in an endocrine cell line. The results show that substitution of the alanyl residue immediately N-terminal to the sulfated tyrosine with an acidic amino acid promotes the sulfation of gastrin peptides. Hence, the study supports the proposed consensus sequence for tyrosine sulfation. Importantly, however, the results also reveal that complete sulfation increases the endoproteolytic maturation of progastrin. Thus, our study suggests an additional function for tyrosine sulfation of possible general significance.

Amino Acid Sequence↗

PubMed1995

Vitamin D3 effects on basal and cAMP modulated expression of cholecystokinin and somatostatin genes in a rat medullary thyroid carcinoma cell line [CA-77].

The regulation of cholecystokinin and somatostatin expression by vitamin D and cyclic AMP in the rat medullary thyroid carcinoma cell line CA-77 was investigated. Treatment with 100 nmol/l vitamin D did not affect cholecystokinin mRNA and peptide concentrations significantly; somatostatin mRNA level increased 6 times and the somatostatin peptide concentration increased 2-fold after 5 days of drug treatment. Under the same experimental conditions cyclic AMP increased cholecystokinin mRNA level 4.5 times and the cellular cholecystokinin-peptide concentration 2-fold; somatostatin mRNA and peptide concentrations were not significantly changed. Cyclic AMP stimulated peptide secretion from the cells were not affected by vitamin D, but cyclic AMP mediated increase in CCK peptide concentration was significantly inhibited by vitamin D (p < 0.05).

Amino Acid Sequence↗

PubMed1994

Molecular cloning and expression of a cDNA encoding NGAL: a lipocalin expressed in human neutrophils.

NGAL, a protein recently isolated from human neutrophils, is a novel member of the lipocalins. NGAL binds a derivative of the bacterial chemotactic peptide formylmethionyl-leucyl-phenylalanine and may have important immunomodulatory functions. We here report the cloning of a cDNA for NGAL covering a 63 bp 5' untranslated region and the coding region of 591 bp. The cDNA encodes a protein of 197 amino acids, with a 19 amino acid leader sequence and a mature protein of 178 amino acids. Alignment of the cDNA sequence of NGAL to the rat analogue, alpha 2-microglobulin related protein, demonstrates a very high degree of conservation of this lipocalin. Northern blotting of a variety of tissues revealed that NGAL is mainly expressed in myeloid cells, where a signal of approximately 850 bp is observed. A faint signal was observed in fetal and adult human lung tissue. The molecular cloning of the NGAL cDNA allowed the recombinant production of NGAL in E. coli.

Acute-Phase Proteins↗

PubMed1993

Peptide hormone processing in tumours: biogenetic and diagnostic implications.

Insight into the biogenesis of peptide hormones has grown explosively by elucidation of gene, mRNA and prohormone structures. In addition, information about prohormone processing enzymes is rapidly accumulating. Prohormones vary in size and organization from poly- to monoprotein structures. According to their structural organization and sequence homology, hormones are grouped in families. Prohormones are processed to bioactive peptides by multiple modifications during the transport from the endoplasmic reticulum to secretory granules. The modifications comprise different proteolytic cleavages and amino acid derivatizations. By constitutive secretion, the processing is less pronounced. The same prohormone may be expressed in several cell types that process the precursor in different ways. Awareness of cell-specific processing patterns is important for understanding the tumour synthesis of peptides and for appropriate diagnosis of peptide-producing tumours. These tumours comprise not only well-known neuroendocrine neoplasias. An increasing number of common carcinomas also expresses peptide hormone genes. However, the translation and post-translational processing in tumours are generally attenuated. Consequently, the expression is often functionally and clinically silent. A new diagnostic tool, processing-independent analysis (PIA), seems promising in quantitation of hormone gene expression at peptide level irrespective of the degree of processing. Studies of progastrin expression and processing in tumours illustrate the diagnostic superiority of PIA.

DNA, Complementary↗