• Progastrin is an 80-amino acid intracellular protein and the precursor of gastrin, a gastrointestinal hormone produced by G cells in the gastric antrum.
  • ^{Fiona M., Gribble; Frank, Reimann; Geoffrey, P. Roberts (2018). Gastrointestinal Hormones. Physiology of the Gastrointestinal Tract, Elsevier. pp. 31–70.} 
• The main function of gastrin is to regulate acid secretion.
  • ^{Rehfeld, Jens F.; Goetze, Jens Peter (2005). “2 The Post-Translational Phase of Gene Expression in Tumor Diagnosis”. Handbook of Immunohistochemistry and in Situ Hybridization of Human Carcinomas. Vol. 4. Elsevier. pp. 23–32. doi:10.1016/s1874-5784(05)80057-1. ISBN 978-0-12-369402-7.} 
• During digestion, only gastrin is released into the bloodstream and stimulates the secretion of hydrochloric acid in the stomach as well as pancreatic digestive enzymes. In humans, progastrin is encoded by the GAST gene.
  • ^{“GAST – Gastrin precursor – Homo sapiens (Human) – GAST gene & protein”. www.uniprot.org. Retrieved 2020-06-26.}
• Progastrin is expressed primarily in stomach tissue.

Discovery

• In 1905, John Sydney Edkins demonstrated the existence of a hormone responsible for the secretion of gastric acid.
  • ^{Modlin, Irvin M.; Kidd, Mark; Marks, I. N.; Tang, Laura H. (February 1997). “The pivotal role of John S. Edkins in the discovery of gastrin”. World Journal of Surgery. 21 (2): 226–34. doi:10.1007/s002689900221. ISSN 0364-2313. PMID 8995084. S2CID 28243696.} 
• This hormone was named gastric secretin or gastrin. But it was not until 1979 and later in 1987 and 1988 that progastrin was identified as the precursor to gastrin.
  •  ^{Noyes, B. E.; Mevarech, M.; Stein, R.; Agarwal, K. L. (1979-04-01). “Detection and partial sequence analysis of gastrin mRNA by using an oligodeoxynucleotide probe”. Proceedings of the National Academy of Sciences. 76 (4): 1770–4. Bibcode:1979PNAS…76.1770N. doi:10.1073/pnas.76.4.1770. ISSN 0027-8424. PMC 383472. PMID 88048.}
  • ^{Desmond, H.; Pauwels, S.; Varro, A.; Gregory, H. (1987-01-05). “Isolation and characterization of the intact gastrin precursor from a gastrinoma”. FEBS Letters. 210 (2): 185–8. doi:10.1016/0014-5793(87)81334-0. PMID 3792562. S2CID 20561440.}
  • ^{“Announcements”. Regulatory Peptides. 34 (1): 71–72. 1991. doi:10.1016/0167-0115(91)90226-7. ISSN 0167-0115. S2CID 208789664} 
• His protein sequence and mRNA were revealed.
• Not to be confused with progastrin, Pro-Gastrin-Releasing-Peptide is the precursor of Gastrin-releasing peptide (GRP), a neuropeptide which belongs to the bombesin/neuromedin B family and whose expression is important in the intestine and brain. GRP is involved in many physiological and pathophysiological processes.
  • ^{You, Benoit; Mercier, Frédéric; Assenat, Eric; Langlois-Jacques, Carole; Glehen, Olivier; Soulé, Julien; Payen, Léa; Kepenekian, Vahan; Dupuy, Marie; Belouin, Fanny; Morency, Eric (January 2020). “The oncogenic and druggable hPG80 (Progastrin) is overexpressed in multiple cancers and detected in the blood of patients”. EBioMedicine. 51: 102574. doi:10.1016/j.ebiom.2019.11.035. PMC 6938867. PMID 31877416.} 
• Gastrin-Releasing Peptide stimulates the release of gastrin and other gastrointestinal hormones. It helps regulate food intake. There are also two types of progastrin, the intracellular progastrin discussed in this article and the extracellular progastrin, mainly called hPG80.
  • ^{Benoit You, Frédéric Mercier, Eric Assenat; Alexandre Prieur; Léa Payen, Vahan Kepenekian, Marie Dupuy; Fanny Belouin, Eric Morency (January 2020). “The oncogenic and druggable hPG80 (Progastrin) is overexpressed in multiple cancers and detected in the blood of patients”. EBioMedicine. 51: 102574. doi:10.1016/j.ebiom.2019.11.035. PMC 6938867. PMID 31877416.}

Structure and production

• The GAST gene is located on chromosome 17 (17q21). It consists of three exons containing the sequence that encodes preprogastrin. Progastrin is made up of several alpha helices. The primary structure of human preprogastrin consists of a 21 amino acid signal sequence at the N-terminus followed by a spacer peptide, a bioactive domain and finally a C-terminal flanking peptide (CTFP).
  •  ^{“GAST (gastrin)”. atlasgeneticsoncology.org. Retrieved 2020-06-26.}

Action

• The production of gastrin allows the production of gastric acid during food intake to be promoted. Progastrin has also been shown to be expressed in other healthy tissues (cerebellum, pituitary gland, pancreas, testicles), but to a much lesser extent than in the stomach and in different forms.
  • ^{Schalling, M; Persson, H; Pelto-Huikko, M; Odum, L (1990-08-01). “Expression and localization of gastrin messenger RNA and peptide in spermatogenic cells”. Journal of Clinical Investigation. 86 (2): 660–9. doi:10.1172/JCI114758. ISSN 0021-9738. PMC 296774. PMID 2117026.}
  • ^{Bardram, Linda (1990). “Progastrin in serum from Zollinger-Ellison patients”. Gastroenterology. 98 (6): 1420–6. doi:10.1016/0016-5085(90)91071-D. PMID 2338186.}
  • ^{Rehfeld, J.F. (1991). “Progastrin and its products in the cerebellum”. Neuropeptides. 20 (4): 239–45. doi:10.1016/0143-4179(91)90014-A. PMID 1812406. S2CID 21211891}
  •  ^{Larsson, L.; Rehfeld, J. (1981-08-14). “Pituitary gastrins occur in corticotrophs and melanotrophs”. Science. 213 (4509): 768–70. Bibcode:1981Sci…213..768L. doi:10.1126/science.6266012. ISSN 0036-8075. PMID 6266012.} 
• For example, carboxyamide gastrin is found in the testicles.
  • ^{Zavala‐Pompa, Angel; Ro, Jae Y.; El‐Naggar, Adel; OrdóNtez, Nelson G. (1993). “Primary carcinoid tumor of testis. Immunohistochemical, ultrastructural, and DNA flow cytometric study of three cases with a review of the literature”. Cancer. 72 (5): 1726–32. doi:10.1002/1097-0142(19930901)72:5<1726::aid-cncr2820720536>3.0.co;2-s. ISSN 1097-0142. PMID 7688660. Retrieved 2020-06-26.} 
• However, the role of progastrin in these organs is not clearly established.

Biosynthesis

• In humans, the GAST gene encodes a 101-amino acid precursor peptide, preprogastrin.
  • ^{“GAST (gastrin)”. atlasgeneticsoncology.org. Retrieved 2020-06-26.} 
• The latter is synthesized and matured in the endoplasmic reticulum. Upon initiation of translation, the signal sequence facilitating the translocation of the polypeptide is eliminated by a membrane-bound signal peptidase. This enzyme cleaves the born polypeptide chain between alanine residue 21 and serine 22 to generate the 80-amino acid peptide progastrin. The progastrin is then cleaved by an enzyme to give the main circulating biologically active forms of gastrin: gastrin-34 and gastrin-17, in sulfated and unsulfated forms. Both sulfation and phosphorylation play a role in the maturation process: they increase the maturation of progastrin. While phosphorylation can also affect the conversion of intermediate products with carboxy-terminal glycine (G34-Gly and G17-Gly) to mature gastrins.
  • ^{Bishop, L; Dimaline, R; Blackmore, C; Deavall, D (1998). “Modulation of the cleavage of the gastrin precursor by prohormone phosphorylation”. Gastroenterology. 115 (5): 1154–62. doi:10.1016/S0016-5085(98)70086-1. PMID 9797370} 
• Small amounts of gastrin-52 (also called component 1), gastrin-14 (mini-gastrin) and even smaller fragments were detected in the serum.
  • ^{Rehfeld, Jens F.; Goetze, Jens Peter (2005). “2 The Post-Translational Phase of Gene Expression in Tumor Diagnosis”. Handbook of Immunohistochemistry and in Situ Hybridization of Human Carcinomas. Vol. 4. Elsevier. pp. 23–32. doi:10.1016/s1874-5784(05)80057-1. ISBN 978-0-12-369402-7.} 
• At this stage, two pathways of post-translational modifications exist within the antral G cells. In the dominant pathway, progastrin is cleaved at three sites, resulting in two major bioactive gastrins, gastrin-34 and gastrin-17. In the putative alternative pathway, progastrin can be cleaved only at the dibasic site closest to the C-terminus, resulting in the synthesis of gastrin-71.
  •  ^{“GAST – Gastrin precursor – Homo sapiens (Human) – GAST gene & protein”. www.uniprot.org. Retrieved 2020-06-26.} 
• The other maturation products, in particular G34-Gly, G17-Gly and CTFP have various functions. CTFP has been described as capable of inducing or inhibiting apoptosis, depending on the tissue or cell type involved. After the progastrin conversion step, there is a passage through the secretory pathway.

Under pathological conditions

• As early as 1996, it was demonstrated that the expression of the GAST gene is required for the cellular tumorigenicity of human colorectal cancer. The GAST gene has been shown to be a downstream target of the β-catenin/TCF-4 signalling pathway. Transfection of a construct expressing a constitutively active form of β-catenin triples the activity of the GAST gene promoter.
  • ^{Koh, Theodore J.; Bulitta, Clemens J.; Fleming, John V.; Dockray, Graham J. (2000-08-15). “Gastrin is a target of the β-catenin/TCF-4 growth-signaling pathway in a model of intestinal polyposis”. Journal of Clinical Investigation. 106 (4): 533–9. doi:10.1172/JCI9476. ISSN 0021-9738. PMC 380254. PMID 10953028.} 
• This study establishes a link between progastrin and cancer across many cellular functions involving the Wnt pathway in a cancer cell, starting with its importance for cancer stem cell survival.
  • ^{Prieur, Alexandre; Dominique Joubert, Monica; Habif, Guillaume; Flaceliere, Maud (2017). “Targeting the Wnt Pathway and Cancer Stem Cells with Anti-progastrin Humanized Antibodies as a Potential Treatment for K-RAS-Mutated Colorectal Cancer”. Clinical Cancer Research. 23 (17): 5267–5280. doi:10.1158/1078-0432.CCR-17-0533. ISSN 1078-0432. PMID 28600477. S2CID 22085894. Retrieved 2020-06-23.} 
• In pathological situations, progastrin is secreted by tumor cells into the bloodstream and is referred to as hPG80.
  •  ^{You, Benoit; Mercier, Frédéric; Assenat, Eric; Langlois-Jacques, Carole (2020). “The oncogenic and druggable hPG80 (Progastrin) is overexpressed in multiple cancers and detected in the blood of patients”. EBioMedicine. 51: 102574. doi:10.1016/j.ebiom.2019.11.035. PMC 6938867. PMID 31877416.}
• The expression of progastrin in many cancers has been demonstrated.
  • ^{Kochman, Michael Lee; DelValle, John; Dickinson, Chris John; Boland, C.Richard (1992). “Post-translational processing of gastrin in neoplastic human colonic tissues”. Biochemical and Biophysical Research Communications. 189 (2): 1165–9. doi:10.1016/0006-291X(92)92326-S. hdl:2027.42/29682. PMID 1472026.} 
• It has been noted that in colorectal cancers, progastrin is more than 700 times more abundant than amidated gastrin.
  • ^{Nemeth, J; Taylor, B; Pauwels, S; Varro, A (1993-01-01). “Identification of progastrin derived peptides in colorectal carcinoma extracts”. Gut. 34 (1): 90–5. doi:10.1136/gut.34.1.90. ISSN 0017-5749. PMC 1374107. PMID 8432459.} 
• Another study showed that colorectal carcinomas have progastrin-derived peptides that are not converted to gastrin.
  • ^{Van Solinge, Wouter W.; Nielsen, Finn C.; Friis-Hansen, Lennart; Falkmer, Ursula G. (1993). “Expression but incomplete maturation of progastrin in colorectal carcinomas”. Gastroenterology. 104 (4): 1099–107. doi:10.1016/0016-5085(93)90279-l. ISSN 0016-5085. PMID 8462798} 
• Finally, it has been shown that half of the tumor cells express progastrin. Ovarian, liver and pancreatic cancers present the same scenario: unmatured progastrin is more abundant than amidated gastrin.
  • ^{Caplin, Martyn; Khan, Kosser; Savage, Kay; Rode, Jurgen (1999). “Expression and processing of gastrin in hepatocellular carcinoma, fibrolamellar carcinoma and cholangiocarcinoma”. Journal of Hepatology. 30 (3): 519–26. doi:10.1016/S0168-8278(99)80114-7. PMID 10190738.}
  • ^{Caplin, M.; Savage, K.; Khan, K.; Brett, B. (2000-08-01). “Expression and processing of gastrin in pancreatic adenocarcinoma: Gastrin and pancreatic cancer”. British Journal of Surgery. 87 (8): 1035–40. doi:10.1046/j.1365-2168.2000.01488.x. PMID 10931047. S2CID 24292877.}
  • ^{Singh, P.; Xu, Z.; Dai, B.; Rajaraman, S. (1994-03-01). “Incomplete processing of progastrin expressed by human colon cancer cells: role of noncarboxyamidated gastrins”. American Journal of Physiology. Gastrointestinal and Liver Physiology. 266 (3): G459-68. doi:10.1152/ajpgi.1994.266.3.G459. ISSN 0193-1857. PMID 8166285.} 
• This is because progastrin is not fully matured and is secreted into the bloodstream for many cancers.

Categories: 

• Human hormones

From Wikipedia where this page was last updated July 16, 2021

A novel method to detect hPG80 (human circulating progastrin) in the blood – Analytical Methods (RSC Publishing)