Gastrin

Gastrin
Identifiers
Symbols	GAST ; GAS
External IDs	OMIM: 137250 MGI: 1098667 HomoloGene: 628 GeneCards: GAST Gene
Gene ontology Molecular function • hormone activity • protein binding Cellular component • extracellular region • extracellular space Biological process • signal transduction • G-protein coupled receptor signaling pathway • response to food Sources: Amigo / QuickGO
RNA expression pattern
More reference expression data
Orthologs
Species	Human	Mouse
Entrez	2520	14459
Ensembl	ENSG00000184502	ENSMUSG00000017165
UniProt	P01350	P48757
RefSeq (mRNA)	NM_000805	NM_010257
RefSeq (protein)	NP_000796	NP_034387
Location (UCSC)	Chr 17: 41.71 – 41.72 Mb	Chr 11: 100.33 – 100.34 Mb
PubMed search

Gastrin
Identifiers
Symbol	Gastrin
Pfam	PF00918
InterPro	IPR001651
PROSITE	PDOC00232
Available protein structures: Pfam structures PDB RCSB PDB; PDBe; PDBj PDBsum structure summary

Gastrin is a peptide hormone that stimulates secretion of gastric acid (HCl) by the parietal cells of the stomach and aids in gastric motility. It is released by G cells in the pyloric antrum of the stomach, duodenum, and the pancreas.

Gastrin binds to cholecystokinin B receptors to stimulate the release of histamines in enterochromaffin-like cells, and it induces the insertion of K⁺/H⁺ ATPase pumps into the apical membrane of parietal cells (which in turn increases H⁺ release into the stomach cavity). Its release is stimulated by peptides in the lumen of the stomach.

Physiology

Genetics

The GAS gene is located on the long arm of the eighteenth chromosome (17q21).^[1]

Synthesis

Gastrin is a linear peptide hormone produced by G cells of the duodenum and in the pyloric antrum of the stomach. It is secreted into the bloodstream. Gastrin is found primarily in three forms:

• gastrin-34 ("big gastrin")
• gastrin-17 ("little gastrin")
• gastrin-14 ("minigastrin")

Also, pentagastrin is an artificially synthesized, five amino acid sequence identical to the last five amino acid sequence at the C-terminus end of gastrin. The numbers refer to the amino acid count.

Release

Gastrin is released in response to certain stimuli. These include:

• Stomach antrum distension
• vagal stimulation (mediated by the neurocrine bombesin, or GRP in humans)
• the presence of partially digested proteins, especially amino acids, in the stomach
• hypercalcemia (via Calcium-sensing receptors^[2])

Gastrin release is inhibited by:^[3][4]

• The presence of acid (primarily the secreted HCl) in the stomach (a case of negative feedback).
• Somatostatin also inhibits the release of gastrin, along with secretin, GIP (gastroinhibitory peptide), VIP (vasoactive intestinal peptide), glucagon and calcitonin.

Function

G cell is visible near bottom left, and gastrin is labeled as the two black arrows leading from it. Note: this diagram does not illustrate gastrin's stimulatory effect on ECL cells.

The presence of gastrin stimulates parietal cells of the stomach to secrete hydrochloric acid (HCl)/gastric acid. This is done both directly on the parietal cell and indirectly via binding onto CCK2/gastrin receptors on ECL cells in the stomach, which then responds by releasing histamine, which in turn acts in a paracrine manner on parietal cells stimulating them to secrete H+ ions. This is the major stimulus for acid secretion by parietal cells.

Along with the above-mentioned function, gastrin has been shown to have additional functions as well:

• Stimulates parietal cell maturation and fundal growth.
• Causes chief cells to secrete pepsinogen, the zymogen (inactive) form of the digestive enzyme pepsin.
• Increases antral muscle mobility and promotes stomach contractions.
• Strengthens antral contractions against the pylorus, and constricts the pyloric sphincter, which diminishes the rate of gastric emptying.
• Plays a role in the relaxation of the ileocecal valve.^[5]
• Induces pancreatic secretions and gallbladder emptying.^[6]
• May impact lower esophageal sphincter (LES) tone, causing it to contract,^[7] - although pentagastrin, rather than endogenous gastrin, may be the cause.^[8]

Factors influencing secretion

Gastric lumen

• Stimulatory factors: dietary protein and amino acids (meat), hypercalcemia. (i.e. during the gastric phase)
• Inhibitory factor: acidity (pH below 3) - a negative feedback mechanism, exerted via the release of somatostatin from δ cells in the stomach, which inhibits gastrin and histamine release.

Paracrine

• Stimulatory factor: bombesin
• Inhibitory factor: somatostatin - acts on somatostatin-2 receptors on G cells. in a paracrine manner via local diffusion in the intercellular spaces, but also systemically through its release into the local mucosal blood circulation; it inhibits acid secretion by acting on parietal cells.

Nervous

• Stimulatory factors: Beta-adrenergic agents, cholinergic agents, gastrin-releasing peptide (GRP)
• Inhibitory factor: Enterogastric reflex

Circulation

• Stimulatory factor: epinephrine
• Inhibitory factors:gastric inhibitory peptide (GIP), secretin, somatostatin, glucagon, calcitonin

Role in disease

In the Zollinger-Ellison syndrome, gastrin is produced at excessive levels, often by a gastrinoma (gastrin-producing tumor, mostly benign) of the duodenum or the pancreas. To investigate for hypergastrinemia (high blood levels of gastrin), a "pentagastrin test" can be performed.

In autoimmune gastritis, the immune system attacks the parietal cells leading to hypochlorhydria (low stomach acidity). This results in an elevated gastrin level in an attempt to compensate for increased pH in the stomach. Eventually, all the parietal cells are lost and achlorhydria results leading to a loss of negative feedback on gastrin secretion. Plasma gastrin concentration is elevated in virtually all individuals with mucolipidosis type IV (mean 1507 pg/mL; range 400-4100 pg/mL) (normal 0-200 pg/mL) secondary to a constitutive achlorhydria. This finding facilitates the diagnosis of patients with this neurogenetic disorder.^[9]

History

Its existence was first suggested in 1905 by the British physiologist John Sydney Edkins,^[10][11] and gastrins were isolated in 1964 by Roderic Alfred Gregory at the University of Liverpool.^[12] In 1964 the structure of Gastrin was determined.^[13]

References

1. Lund T, Geurts van Kessel AH, Haun S, Dixon JE (1986). "The genes for human gastrin and cholecystokinin are located on different chromosomes". Hum. Genet. 73 (1): 77–80. doi:10.1007/BF00292669. PMID 3011648.
2. Feng J, Petersen CD, Coy DH, Jiang JK, Thomas CJ, Pollak MR, Wank SA (2010). "Calcium-sensing receptor is a physiologic multimodal chemosensor regulating gastric G-cell growth and gastrin secretion". Proc. Natl. Acad. Sci. U.S.A. 107 (41): 17791–17796. doi:10.1073/pnas.1009078107. PMID 20876097.
3. Holst JJ, Orskov C, Seier-Poulsen S (1992). "Somatostatin is an essential paracrine link in acid inhibition of gastrin secretion". Digestion 51 (2): 95–102. doi:10.1159/000200882. PMID 1354190.
4. Johnson LR (1984). "Effects of somatostatin and acid on inhibition of gastrin release in newborn rats". Endocrinology 114 (3): 743–746. doi:10.1210/endo-114-3-743. PMID 6141932.
5. Vadokas B, Lüdtke FE, Lepsien G, Golenhofen K, Mandrek K (1997). "Effects of gastrin-releasing peptide (GRP) on the mechanical activity of the human ileocaecal region in vitro". Neurogastroenterol. Motil. 9 (4): 265–270. doi:10.1046/j.1365-2982.1997.d01-59.x. PMID 9430795.
6. Valenzuela JE, Walsh JH, Isenberg JI (1976). "Effect of gastrin on pancreatic enzyme secretion and gallbladder emptying in man". Gastroenterology 71 (3): 409–411. PMID 950091.
7. Castell DO (1978). "Gastrin and lower esophageal sphincter tone". Arch. Intern. Med. 138 (2): 196. doi:10.1001/archinte.138.2.196. PMID 626547.
8. Henderson JM, Lidgard G, Osborne DH, Carter DC, Heading RC (1978). "Lower oesophageal sphincter response to gastrin--pharmacological or physiological?". Gut 19 (2): 99–102. doi:10.1136/gut.19.2.99. PMC 1411818. PMID 631634.
9. Schiffmann R, Dwyer NK, Lubensky IA, Tsokos M, Sutliff VE, Latimer JS, Frei KP, Brady RO, Barton NW, Blanchette-Mackie EJ, Goldin E (1998). "Constitutive achlorhydria in mucolipidosis type IV". Proc. Natl. Acad. Sci. U.S.A. 95 (3): 1207–12. doi:10.1073/pnas.95.3.1207. PMC 18720. PMID 9448310.
10. Edkins JS (1906). "The chemical mechanism of gastric secretion". J. Physiol. (Lond.) 34 (1-2): 133–44. PMC 1465807. PMID 16992839.
11. Modlin IM, Kidd M, Marks IN, Tang LH (1997). "The pivotal role of John S. Edkins in the discovery of gastrin". World J Surg 21 (2): 226–34. doi:10.1007/s002689900221. PMID 8995084.
12. Gregory RA, Tracy HJ (1964). "The constitution and properties of two gastrins extracted from hog antral mucosa: Part I the isolation of two gastrins from hog antral mucosa". Gut 5 (2): 103–107. doi:10.1136/gut.5.2.103.
13. Gregory H, Hardy PM, Jones DS, Kenner GW, Sheppard RC (1964). "THE ANTRAL HORMONE GASTRIN. STRUCTURE OF GASTRIN". Nature 204: 931–3. doi:10.1038/204931a0. PMID 14248711.

Further reading

• Rozengurt E, Walsh JH (2001). "Gastrin, CCK, signaling, and cancer". Annu. Rev. Physiol. 63: 49–76. doi:10.1146/annurev.physiol.63.1.49. PMID 11181948.
• Dockray GJ (2004). "Clinical endocrinology and metabolism. Gastrin". Best Pract. Res. Clin. Endocrinol. Metab. 18 (4): 555–68. doi:10.1016/j.beem.2004.07.003. PMID 15533775.
• Anlauf M, Garbrecht N, Henopp T, Schmitt A, Schlenger R, Raffel A, Krausch M, Gimm O, Eisenberger CF, Knoefel WT, Dralle H, Komminoth P, Heitz PU, Perren A, Klöppel G (2006). "Sporadic versus hereditary gastrinomas of the duodenum and pancreas: distinct clinico-pathological and epidemiological features". World J. Gastroenterol. 12 (34): 5440–6. PMID 17006979.
• Polosatov MV, Klimov PK, Masevich CG, Samartsev MA, Wünsch E (1979). "Interaction of synthetic human big gastrin with blood proteins of man and animals". Acta Hepatogastroenterol (Stuttg) 26 (2): 154–9. PMID 463490.
• Fritsch WP, Hausamen TU, Scholten T (1977). "[Gastrointestinal hormones. I. Hormones of the gastrin group]". Z Gastroenterol 15 (4): 264–76. PMID 871064.
• Higashimoto Y, Himeno S, Shinomura Y, Nagao K, Tamura T, Tarui S (1989). "Purification and structural determination of urinary NH2-terminal big gastrin fragments". Biochem. Biophys. Res. Commun. 160 (3): 1364–70. doi:10.1016/S0006-291X(89)80154-8. PMID 2730647.
• Pauwels S, Najdovski T, Dimaline R, Lee CM, Deschodt-Lanckman M (1989). "Degradation of human gastrin and CCK by endopeptidase 24.11: differential behaviour of the sulphated and unsulphated peptides". Biochim. Biophys. Acta 996 (1-2): 82–8. doi:10.1016/0167-4838(89)90098-8. PMID 2736261.
• Lund T, Geurts van Kessel AH, Haun S, Dixon JE (1986). "The genes for human gastrin and cholecystokinin are located on different chromosomes". Hum. Genet. 73 (1): 77–80. doi:10.1007/BF00292669. PMID 3011648.
• Kariya Y, Kato K, Hayashizaki Y, Himeno S, Tarui S, Matsubara K (1986). "Expression of human gastrin gene in normal and gastrinoma tissues". Gene 50 (1-3): 345–52. doi:10.1016/0378-1119(86)90338-0. PMID 3034736.
• Gregory RA, Tracy HJ, Agarwal KL, Grossman MI (1969). "Aminoacid constitution of two gastrins isolated from Zollinger-Ellison tumour tissue". Gut 10 (8): 603–8. doi:10.1136/gut.10.8.603. PMC 1552899. PMID 5822140.
• Bentley PH, Kenner GW, Sheppard RC (1966). "Structures of human gastrins I and II". Nature 209 (5023): 583–5. doi:10.1038/209583b0. PMID 5921183.
• Ito R, Sato K, Helmer T, Jay G, Agarwal K (1984). "Structural analysis of the gene encoding human gastrin: the large intron contains an Alu sequence". Proc. Natl. Acad. Sci. U.S.A. 81 (15): 4662–6. doi:10.1073/pnas.81.15.4662. PMC 391550. PMID 6087340.
• Wiborg O, Berglund L, Boel E, Norris F, Norris K, Rehfeld JF, Marcker KA, Vuust J (1984). "Structure of a human gastrin gene". Proc. Natl. Acad. Sci. U.S.A. 81 (4): 1067–9. doi:10.1073/pnas.81.4.1067. PMC 344765. PMID 6322186.
• Kato K, Hayashizaki Y, Takahashi Y, Himeno S, Matsubara K (1983). "Molecular cloning of the human gastrin gene". Nucleic Acids Res. 11 (23): 8197–203. doi:10.1093/nar/11.23.8197. PMC 326575. PMID 6324077.
• Boel E, Vuust J, Norris F, Norris K, Wind A, Rehfeld JF, Marcker KA (1983). "Molecular cloning of human gastrin cDNA: evidence for evolution of gastrin by gene duplication". Proc. Natl. Acad. Sci. U.S.A. 80 (10): 2866–9. doi:10.1073/pnas.80.10.2866. PMC 393933. PMID 6574456.
• Kato K, Himeno S, Takahashi Y, Wakabayashi T, Tarui S, Matsubara K (1983). "Molecular cloning of human gastrin precursor cDNA". Gene 26 (1): 53–7. doi:10.1016/0378-1119(83)90035-5. PMID 6689486.
• Koh TJ, Wang TC (1995). "Molecular cloning and sequencing of the murine gastrin gene". Biochem. Biophys. Res. Commun. 216 (1): 34–41. doi:10.1006/bbrc.1995.2588. PMID 7488110.
• Rehfeld JF, Hansen CP, Johnsen AH (1995). "Post-poly(Glu) cleavage and degradation modified by O-sulfated tyrosine: a novel post-translational processing mechanism". EMBO J. 14 (2): 389–96. PMC 398093. PMID 7530658.
• Rehfeld JF, Johnsen AH (1994). "Identification of gastrin component I as gastrin-71. The largest possible bioactive progastrin product". Eur. J. Biochem. 223 (3): 765–73. doi:10.1111/j.1432-1033.1994.tb19051.x. PMID 8055952.
• Varro A, Dockray GJ (1993). "Post-translational processing of progastrin: inhibition of cleavage, phosphorylation and sulphation by brefeldin A". Biochem. J. 295 (Pt 3): 813–9. PMC 1134634. PMID 8240296.

External links

• Overview at colostate.edu
• Physiology: 6/6ch4/s6ch4_14 - Essentials of Human Physiology