Gastrina: hormona de múltiples funciones / Gastrin: multifunctional hormone

Gastrin is a polypeptide hormone secreted primarily by G cells of the gastric antrum. Its main function is the regulation of gastric acidity, through the release of histamine, which ultimately acts on the parietal cell. There are a number of pathological conditions characterized by persistent hypergastrinemia will cause various effects, from peptic disease to cancer. Most research points to clarify their involvement in processes of proliferation of different cell types and thus to find a treatment for cancer. Intermediates molecules have been described for the metabolism of gastrin, which also possess the property of stimulating the proliferation of various cell lines and participated in processes of cell migration and invasion. Using molecular bioengineering has been able to modify the original molecule to create receptor antagonist and thus able to address some of the associated diseases. Much of this hormone, described over a century ago, is still unknown (AU)

Evolutionary conservation of the cholecystokinin/gastrin signaling system in nematodes.

Members of the cholecystokinin (CCK)/gastrin family of peptides, including the arthropod sulfakinins and their cognate receptors, play an important role in the regulation of feeding behavior and energy homeostasis. By using the potential Caenorhabditis elegans CCK receptors as bait, we have isolated and identified two CCK-like neuropeptides as the endogenous ligands of these nematode receptors. Both receptors and ligands share a high degree of sequence similarity with their vertebrate and arthropod counterparts and also display similar biological activities with respect to digestive enzyme secretion and fat storage. Our data indicate that the CCK/gastrin signaling system was already well established prior to the divergence of protostomes and deuterostomes.

The endoproteolytic maturation of progastrin and procholecystokinin.

The homologous brain-gut propeptides, procholecystokinin (proCCK) and progastrin, both undergo extensive posttranslational maturation in specific neuroendocrine cells. The process comprises multiple endoproteolytic cleavages at mono- and dibasic sites, in addition to exoproteolytic trimmings and amino acid derivatizations. Knockout of prohormone convertases (PCs) in mice and studies in cell lines indicate that PC1, PC2 and, to a minor extent, PC5, are responsible for most of the endoproteolytic cleavages of both prohormones. Progastrin in antral G-cells is cleaved by PC1 at two di-Arg sites, R36R37 and R73R74, whereas, PC2 only cleaves at the single di-Lys site, K53K54. Pituitary corticotrophs and intestinal TG-cells, both of which express gastrin, do not cleave K53K54 due to lack of PC2. In proCCK five monobasic (R25, R44, R50, K61 and R75) as well as a single dibasic site (R85R86) can all be cleaved by both PC1 and PC2. But the cleavage differs in a cell-specific manner in that PC1 is responsible for the entire endoproteolytic cleavage in intestinal endocrine I-cells, except for perhaps the K61 site. In contrast PC2 is responsible for most endoproteolysis of proCCK in the cerebral CCK-neurons, which do not express PC1 in significant amounts. Moreover, PC5 appears to contribute to a minor extent to the neuronal proCCK and to the antral progastrin processing. This review emphasizes that prohormone convertases play a decisive but substrate and cell-specific role in the biosynthetic maturation of gastrin and CCK.

Naming progastrin-derived peptides.

The antral hormone gastrin continues to be in focus, because its hormonal and growth promoting effects are essential both for the function of the normal stomach and for the pathogenesis of major dyspeptic and neoplastic diseases. Deduction of the progastrin structure has improved the insight in the cellular synthesis of gastrin, but has also revealed that the biosynthetic machinery is complex, and, accordingly, that progastrin is processed to a multitude of more or less bioactive fragments. The naming of these fragments has, however, become inconsistent and confusing. Therefore, we propose a systematic nomenclature for progastrin-derived peptides of which there are three classes: (I) The gastrins with the evolutionary preserved tetrapeptide amide (Trp-Met-Asp-PheNH2) at the C-terminus, which ensures high-affinity binding to the gastrin (CCK-B) receptor. Among the gastrins, gastrin-34 and gastrin-17 constitute the primary forms. (II) Processing intermediates, which are early products of progastrin that contain the structure of the primary gastrins within their sequence, but still cannot bind the gastrin receptor due to insufficient processing at their C-terminus. (III) Flanking fragments from the N- and C-termini of progastrin that do not contain any primary gastrin in their sequence, but nevertheless may undergo posttranslational processing. Each fragment can be specified with suffixes corresponding to the derived sequence in progastrin.

Abnormally processed gastrins in active duodenal ulcer disease.

In contrast to healthy subjects, duodenal ulcer patients in the active phase contain large amounts of a peptide in serum and antrum which react with antiserum specific for the N-terminus, but not the C-terminus of gastrin-17. The immunochemical and chromatographic properties were similar to that of the N-terminal tridecapeptide sequence of gastrin-17. The peptide follows the clinical course of duodenal ulcer disease, as it disappears when the ulcer heals. The N-terminal tridecapeptide - lacking the bioactive tetrapeptide of gastrin-17 - is a potent inhibitor of gastric acid secretion, presumably by way of competitive antagonism to gastrin. It is suggested to participate in the regulation of gastric acid secretion in patients with active duodenal ulcer disease. To confirm the chemical structure of the peptide, antral and gastrinoma extracts were used for isolation, purification and amino acid analysis. We found two different peptides with the same N-terminus as gastrin-17, namely the previously known N-terminal tridecapeptide fragment of gastrin-17 and a new gastrin component, identical with a C-terminal glycine extended gastrin-17. Furthermore, a C-terminal glycine extended component, corresponding to each of the other molecular forms of gastrin were present. Thus, a variety of abnormally processed gastrins are synthesized and released to the circulation during the active period of duodenal ulcer disease.

[A method for the extraction of high serum-gastrin concentrations for the quantitative differentiation of human gastrin types]. / Eine Methode zur Gewinnung hoher Serumgastrinkonzentrationen für die quantitative Differenzierung der menschlichen Gastrinformen

By selective investigation of human antral venous blood, concentrations of gastrin are sufficiently elevated for the quantitative differentiation of the various forms. The results of comparative determinations of gastrin from antral and peripheral venous blood are shown.

Relative abundance of big and little gastrins in the tumours and blood of patients with the Zollinger Ellison syndrome.

The relative concentrations of big gastrin (G-34) and little gastrin (G-17) were compared in the sera and tumours (gastrinomas) of Zollinger-Ellison syndrome patients. Big and little gastrins were identified in all 10 serum samples and in all 10 tumour biopsies examined. In serum, G-34 (range of concentrations 58-220 000 fmol/ml) was the major form of gastrin and G-17 (22-78 000 fmol/ml) was a minor component; the mean relative abundance of G-17/[G17 + G34]) in serum was 0-18 and the mean relative abundance of G-34 was 0-82. In tumour, however, the opposite was true: G-17 (49-869 000 pmol/g) was the major component and G-34 (45-464 pmol/g) a minor component, and the relative proportions of G-17 and G-34 were 0-73 and 0-27 respectively. Following an intravenous injection of porcine secretin (2-0 U/kg) there was a rapid increase in concentration of all forms of gastrin in the blood, but the increase in G-17 was proportionately greater than that of G-34 (relative abundance of G-17 in basal serum was 0-21 compared with 0-37, five minutes after secretin). Differences in the half lives of G-17 and G-34 may partly explain their relative abundancies in serum and tumour tissue.