Biomedical subjects

L Friis-Hansen

Publications and source records attributed to L Friis-Hansen.

18 recordsLinked to original sources

PubMed2006

Achlorhydria is associated with gastric microbial overgrowth and development of cancer: lessons learned from the gastrin knockout mouse.

Gastrin and gastrin receptor-deficient mice have been used for genetic dissection of the role of gastrins in maintaining gastric homeostasis and control of acid secretion. The gastrin knockout mice are achlorhydric due to inactivation of the ECL and parietal cells. Moreover, this achlorhydria is associated with intestinal metaplasia and bacterial overgrowth, which ultimately leads to the development of gastric tumours. The association between progastrin, progastrin-derived processing intermediates and colorectal carcinogenesis has also been examined through genetic or chemical cancer induction in several mouse models, although the clinical relevance of these studies remains unproven. While others have focused on models of increased gastrin production, the present review describes the lessons learned from gastrin-deficient mice. Study of these mice helps our understanding of how dysregulation of gastrin secretion may be implicated in human disease.

Achlorhydria↗

PubMed2003

On the tissue-specific processing of procholecystokinin in the brain and gut--a short review.

Cholecystokinin (CCK) is a major peptide hormone in the gut and a major peptide transmitter in the brain. Its synthesis requires endoproteolytic cleavage of proCCK at several mono- and dibasic sites by prohormone convertases (PCs). Of these, PC1 and PC2 are expressed in cerebral neurons and intestinal endocrine cells. Characteristically, however, the processing of proCCK varies markedly between the brain and the gut. In neurons, CCK-8 is always the predominating form, whereas the endocrine gut cells (I-cells) contain a mixture of small and larger CCK-peptides of which CCK-33 or CCK-22 often predominate. The role of PC1 and PC2 in the processing of proCCK have now been examined by measuring the concentrations of prohormone, processing intermediates and amidated end-products in jejunal and cerebral extracts of PC1 and PC2 deficient mice and corresponding wild type controls. The PC1 null mice revealed a pattern opposite to that of the PC2 null mice, in whom only the cerebral processing of proCCK was affected. Thus PC1 knockouts reveal a severe block in the processing of intestinal proCCK. Accordingly, the intestinal concentration of proCCK was many fold increased, and also the concentrations of different processing intermediates were raised; but the concentration of bioactive, alpha-amidated and O-sulfated CCK was reduced to a few percent of normal. The only bioactive CCK peptide in the gut of PC1 deficient mice was CCK-22, and it was present only in trace amounts. The cerebral processing of proCCK was, however, not at all affected by the lack of PC1 - in sharp contrast to the effect of PC2. The results show that the tissue-specific processing of proCCK to a large extent can be explained by prohormone convertases, as PC1 plays a decisive role in the maturation of hormonal CCK in the gut, whereas PC2 governs the processing of brain proCCK.

Animals↗

PubMed2001

E2F repression by C/EBPalpha is required for adipogenesis and granulopoiesis in vivo.

The C/EBPalpha transcription factor is required for differentiation of adipocytes and neutrophil granulocytes, and controls cellular proliferation in vivo. To address the molecular mechanisms of C/EBPalpha action, we have identified C/EBPalpha mutants defective in repression of E2F-dependent transcription and found them to be impaired in their ability to suppress cellular proliferation, and to induce adipocyte differentiation in vitro. Using targeted mutagenesis of the mouse germline, we show that E2F repression-deficient C/EBPalpha alleles failed to support adipocyte and granulocyte differentiation in vivo. These results indicate that E2F repression by C/EBPalpha is critical for its ability to induce terminal differentiation, and thus provide genetic evidence that direct cell cycle control by a mammalian lineage-instructive transcription factor couples cellular growth arrest and differentiation.

3T3 Cells↗

PubMed2001

Lessons from the gastrin and gastrin receptor knockout mice.

The gastric hormone gastrin was first recognized for its ability to induce acid secretion. Following the purification and subsequent development of specific radioimmunoassays for gastrin, it was also shown to be a regulator of oxyntic mucosal growth. To examine the importance of gastrin or its receptors during development in general and for gastric physiology specifically both have been knocked out. Gastrin and gastrin receptor knockout mice are viable, develop without any gross abnormalities, and are fertile. Even though gastrin acts as a growth factor during hypergastrinemia there was no general atrophy of the gastric mucosa in the knockout mice. However, the maturation of both parietal and ECL cells was disturbed and the number of parietal cells was reduced. Basal acid secretion was impaired and rendered the parietal cells unresponsive to secretagogues. Outside the stomach the mice had no apparent phenotype. However, studies have suggested that progastrin and glycine-extended proforms of gastrin may have biological importance, but these results are still circumstantial and identification of the implicated receptors will be crucial for further studies.

Animals↗

PubMed2001

Attenuated processing of proglucagon and glucagon-like peptide-1 in carboxypeptidase E-deficient mice.

The maturation of many peptide hormones is attenuated in carboxypeptidase E (CPE)-deficient fat/fat mice, leading to a slowly developing, adult-onset obesity with mild diabetes. To determine the contribution of the hormones generated from the proglucagon precursor to this phenotype, we studied the tissue-specific processing of glucagon and glucagon-like peptide-1 (GLP-1) in these mice. In all tissues examined there was a great reduction in mature amidated GLP-1. Furthermore, a lack of CPE attenuates prohormone convertase processing of proglucagon in both the pancreas and the intestine. These findings suggest that defects in proglucagon processing together with other endocrine malfunctions could contribute to the diabetic and obesity phenotype in fat/fat mice.

Animals↗

PubMed2000

Structure and developmental expression of the mouse CCK-B receptor gene.

Cholecystokinin (CCK) and gastrin exert their effects through two receptors, the CCK-A and CCK-B receptors. We have cloned the mouse CCK-B receptor gene (Cckbr) and determined its complete genomic structure, nucleotide sequence, and tissue-specific expression pattern. Cckbr is divided into five exons spanning 11 kb. A primer extension assay was used to map the transcription initiation site to 199 bp upstream of the translational start site. Rapid amplification of cDNA ends was used to localize the 3' end downstream of an atypical polyadenylation site (GATAAA). Mouse Cckbr transcripts were most abundant in brain and stomach, but were also detected in colon, kidney, ovary, and pancreas. Prenatal expression of both CCK-A and CCK-B receptors in various tissues was analyzed by RT-PCR. The expression pattern was similar to the adult pattern, suggesting that receptor transcription is an early event in gastrointestinal development.

Aging↗

PubMed2000

Impaired feedback of gastric functions in carboxypeptidase E-deficient mice.

Carboxypeptidase E deficiency as seen in the fat/fat mice is associated with reduced antral somatostatin content but tripling of the progastrin product. Thus, fat/fat mice are able to maintain normal tissue concentrations of bioactive alpha-amidated gastrin in spite of grossly attenuated progastrin processing. After induction of achlorhydria, however, neither the amount of alpha-amidated gastrin nor the total progastrin product increased in the fat/fat mice. This is contrary to what is seen in wild-type mice. Furthermore, the synthesis of antral somatostatin and fundic chromogranin A is also abnormal. Hence the results suggest a breakdown in the feedback loop that regulates gastric acid secretion.

Achlorhydria↗

PubMed1998

Altered processing of procholecystokinin in carboxypeptidase E-deficient fat mice: differential synthesis in neurons and endocrine cells.

The fat mouse strain exhibits a late-onset obesity syndrome associated with a mutation in the gene encoding carboxypeptidase E (CPE). CPE plays a central role in the biosynthesis of many regulatory peptides. Therefore, we examined the processing of procholecystokinin (proCCK) in the brain (neurons) and small intestine (endocrine cells) of fat/fat mice. In the brain, bioactive CCK was markedly reduced (7.9+/-1.0 pmol/g in fat/fat mice vs. 82.5+/-11.2 pmol/g in controls), but the concentration of the CPE substrate, glycylarginine-extended CCK, was elevated 105-fold. In contrast, the concentration of bioactive CCK in intestinal endocrine cells was unaffected. Endocrine cell processing was, nevertheless, altered with a 33-fold increase in glycyl-arginine-extended CCK. Interestingly, although total proCCK products were normal in the brain they were elevated 3-fold in the intestine, indicating that biosynthesis is upregulated in endocrine cells but not neurons to compensate for the processing defect. These results demonstrate that the CPE mutation differentially affects CCK processing in these two cell types. Intestinal CCK synthesis more closely resembles progastrin processing, suggesting the presence of an endocrine-specific biosynthetic regulatory mechanism not present in neurons.

Animals↗

PubMed1998

Rapid confirmation of gene targeting in embryonic stem cells using two long-range PCR techniques.

Gene targeting in mouse embryonic stem (ES) cells generally includes the analysis of numerous colonies to identify a few with mutations resulting from homologous recombination with a targeting vector. Thus, simple and efficient screening methods are needed to identify targeted clones. Optimal screening approaches require probes from outside of the region included in the targeting vector to avoid detection of the more common random insertions. However, the use of large genomic fragments in targeting vectors can limit the availability of cloned DNA, thus necessitating a strategy to obtain unique flanking sequences. We describe a rapid method to identify sequences adjacent to cloned DNA using long-range polymerase chain reaction (PCR) amplification from a genomic DNA library, followed by direct nucleotide sequencing of the amplified fragment. We have used this technique in two independent gene targeting experiments to obtain genomic DNA sequences flanking the mouse cholecystokinin (CCK) and gastrin genes. The sequences were then used to design primers to characterize ES cell lines with CCK or gastrin targeted gene mutations, employing a second long-range PCR approach. Our results show that these two long-range PCR methods are generally useful to rapidly and accurately characterize allele structures in ES cells.

Alleles↗

PubMed1998

Impaired gastric acid secretion in gastrin-deficient mice.

To further understand the role of the peptide hormone gastrin in the development and function of the stomach, we have generated gastrin-deficient mice by gene targeting in embryonic stem cells. Mutant mice were viable and fertile, without obvious visible abnormalities. However, gastric function was severely affected by the loss of gastrin. Basal gastric acid secretion was abolished and could not be induced by histamine, carbachol, or gastrin. Histological analysis revealed alterations in the two cell types primarily involved in acid secretion, parietal and enterochromaffin-like (ECL) cells. Parietal cells were reduced in number with an accumulation of immature cells lacking H(+)-K(+)-adenosinetriphosphatase (H(+)-K(+)-ATPase). ECL cells were positioned closer to the base of the gastric glands, with markedly lower expression of histidine decarboxylase. Gastrin administration for 6 days reversed the effects of the gastrin deficiency, leading to an increase in the number of mature, H(+)-K(+)-ATPase-positive parietal cells and a partial restoration of acid secretion. The results show that gastrin is critically important for the function of the acid secretory system.

Animals↗

PubMed1997

Disturbed progastrin processing in carboxypeptidase E-deficient fat mice.

The fat mouse strain exhibits a late-onset obesity syndrome associated with a mutation in the gene encoding carboxypeptidase E (CPE). Since CPE plays a central role in the biosynthesis of a number of regulatory peptides, including gastrin, we examined the biogenesis and processing of progastrin in fat/fat mice by measuring gastrin mRNA, carboxyamidated gastrin and its processing intermediates in the stomach. The tissue concentration of carboxyamidated (i.e. bioactive) gastrin was only slightly reduced (601 +/- 28 pmol/g in fat/fat mice vs. 715 +/- 43 pmol/g in wild-type controls). However, progastrin processing intermediates accumulated excessively with an 86-fold increase in the concentration of the CPE substrate, glycyl-arginine extended gastrin, and a seven-fold increase in the concentration of glycine-extended gastrin. Accordingly, the total progastrin product was doubled, as was the concentration of gastrin mRNA. Plasma concentrations of carboxyamidated gastrin were, however slightly reduced both in fasted fat/fat mice and postprandially. The results show that the CPE mutation diminishes the efficiency of progastrin processing, but gastrin synthesis is nevertheless increased to maintain an almost normal production of bioactive gastrins. By comparison with other neuroendocrine prohormones, progastrin processing in CPE-deficient mice is unique. Hence, the increase of glycine-extended gastrin in combination with normal levels of carboxyamidated gastrin suggests that G-cells may have another biosynthetic pathway for gastrin.

Animals↗

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↗

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↗

PubMed1994

Ileal expression of gastrin and cholecystokinin. In search of a related hormone.

Antibodies against the common active site of cholecystokinin (CCK) and gastrin stain three endocrine cell-types in the gut: G-cells (that synthesize gastrin) I-cells (that synthesize CCK), and TG-cells (whose product is unknown). In order to examine whether TG-cells either process progastrin or proCCK in a specific manner, or express a novel gastrin-CCK related hormone, we studied the distal porcine ileum, which have far more TG- than G- and I-cells. Ileal CCK and gastrin mRNA corresponded to those of the antroduodenal mucosa. Gel, ion-exchange and reversed-phase chromatography monitored with sequence-specific immunoassays showed that the ileal mucosa on average contain 0.3 and 7.6 pmol/g progastrin and proCCK, respectively; 1.1 and 13.5 pmol/g glycine-extended intermediates; and 1.1 and 24.8 pmol/g of bioactive carboxyamidated gastrin and CCK, respectively. Gastrin was present only as non-sulfated gastrin-34, whereas CCK occurred in forms similar to those of the proximal intestine. Although ileal progastrin processing is tissue specific, the amounts of gastrin and CCK are too small to explain the TG-cells. Moreover, since the ileal extracts were without traces of other peptides having the C-terminus common to gastrin and CCK, the results suggest that TG-cells produce a peptide, which is only weakly related to gastrin and CCK.

Amino Acid Sequence↗

PubMed1993

Expression but incomplete maturation of progastrin in colorectal carcinomas.

BACKGROUND: To evaluate the hypothesis that gastrin is a local growth factor in colonic carcinomas, the expression of gastrin messenger RNA (mRNA) and peptides were examined in five human colon carcinoma cell lines, 12 solid colon carcinomas, and normal colonic tissue. METHODS: Northern analysis, reverse-transcription PCR, and a library of sequence-specific radioimmunoassays were the principal methods. RESULTS: Cell lines, tumors, and normal tissue all expressed a gastrin mRNA of 0.7 kilobases, and all cell lines contained incompletely processed progastrin (range, 17-54 fmol/10(6) cells). Two cell lines secreted progastrin into the media (LoVo, 25 +/- 3 pmol/L; HCT116; 12 +/- 2 pmol/L). Normal colonic tissue and all the solid tumors also contained progastrin, the concentration being higher in tumors (range, 0.4-2 pmol/g) than in normal tissue (range, 0.1-0.2 pmol/g). Only one tumor contained carboxyamidated gastrins. CONCLUSIONS: Normal and neoplastic colonic mucosa both express the gastrin gene, but the posttranslational phase of expression is attenuated. The incomplete processing and low level of expression suggest that autocrine gastrin secretion has only minor significance for normal adult and most neoplastic colonic tissue.

Actins↗

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↗

PubMed1991

The expression of peptide hormones in normal cells and tumour cells.

Insight in the mechanisms of peptide hormone expression has grown explosively by elucidation of gene, mRNA and preprohormone structures for most hormone systems during the 1980s. In addition, information about the structure and substrate specificity of many prohormone processing enzymes is rapidly accumulating in these years. The preprohormones vary considerably in size and organization from poly- to monoprotein structures. According to the structural organization and sequence homology the hormones are grouped in families. The prohormones are processed to bioactive peptides by multiple enzymatic modifications during the intracellular transport from the rough endoplasmatic reticulum to the mature secretory granules. The modifications comprise different proteolytic cleavages and amino acid derivatizations. The same prohormone may be expressed in several different cell types that process the precursor in entirely different ways. Awareness of such cell-specific processing patterns is important for the understanding of ectopic synthesis in neuroendocrine tumours.

Gene Expression Regulation↗

PubMedDate not supplied

Effect of interleukin 1beta on the HPA axis in H1-receptor knockout mice.

OBJECTIVES AND METHODS: Circulating cytokines such as interleukin-1 (IL-1), and tumor necrosis factor-alpha as well as lipopolysaccharide (LPS) are potent ACTH secretagogues, acting via stimulation of corticotropin-releasing hormone (CRH) and vasopressinergic neurons in the paraventricular nucleus of the hypothalamus (PVN). Histamine (HA) has been shown to stimulate ACTH secretion in rats, an effect in part mediated by CRH and arginine vasopressin (AVP). We have previously shown that inhibition of neuronal HA synthesis or central blockade of H(1) receptors (H(1)R) decreased the ACTH response to LPS in male rats. To further elucidate the role of neuronal HA in cytokine-induced activation of the HPA axis, we compared the effect of H(1)R knockout on IL-1beta-induced ACTH secretion in adult male mice. RESULTS: In H(1)R knockout mice, ACTH secretion increased from basal levels of 261 to 492 pmol/l in response to IL-1beta whereas the cytokine-induced ACTH secretion increased from 140 to 406 pmol/l in wild-type mice. Plasma corticosterone (CORT) rose from basal levels of 99 to 831 nmol/l in knockout mice upon IL-1beta stimulation, whereas in wild-type mice CORT levels rose from 112 to 841 nmol/l. There was no significant difference in IL-1beta-stimulated plasma ACTH or CORT levels between wild-type and knockout mice. Furthermore, there was no significant difference in basal or IL-1beta-stimulated hypothalamic levels of histamine and tele-methyl-histamine between wild-type and knockout mice. HDC gene expression was significantly lower in knockout mice than in wild-type mice both under basal and IL-1beta-stimulated conditions, while there were no significant differences in CRH gene expression in the PVN in knockout mice under basal and IL-1beta-stimulated conditions. Increased basal expression of AVP in the PVN of knockout mice was observed in this study compared to wild-type mice. CONCLUSION: We conclude that the lack of the gene for histamine H(1)R does not seem to be crucial for the ACTH and CORT response to IL-1beta, either due to possible functional compensation in the H(1)R knockout mouse or due to activation of pathways other than the neuronal histaminergic system.

Adrenocorticotropic Hormone↗