Glycine-extended gastrin exerts growth-promoting effects on human colon cancer cells.
BACKGROUND
Since human colon cancers often contain significant quantities of progastrin-processing intermediates, we sought to explore the possibility that the biosynthetic precursor of fully processed amidated gastrin, glycine-extended gastrin, may exert trophic effects on human colonic cancer cells.


METHODS
Binding of radiolabeled glycine-extended and amidated gastrins was assessed on five human cancer cell lines: LoVo, HT 29, HCT 116, Colo 320DM, and T 84. Trophic actions of the peptides were assessed by increases in [3H]thymidine incorporation and cell number. Gastrin expression was determined by northern blot and radioimmunoassay.


RESULTS
Amidated gastrin did not bind to or stimulate the growth of any of the five cell lines. In contrast, saturable binding of radiolabeled glycine-extended gastrin was seen on LoVo and HT 29 cells that was not inhibited by amidated gastrin (10(-6) M) nor by a gastrin/CCKB receptor antagonist (PD 134308). Glycine-extended gastrin induced a dose-dependent increase in [3H]thymidine uptake in LoVo (143 +/- 8% versus control at 10(-10) M) and HT 29 (151 +/- 11% versus control at 10(-10) M) cells that was not inhibited by PD 134308 or by a mitogen-activated protein (MAP) or ERK kinase (MEK) inhibitor (PD 98509). Glycine-extended gastrin did stimulate jun-kinase activity in LoVo and HT 29 cells. The two cell lines expressed the gastrin gene at low levels and secreted small amounts of amidated gastrin and glycine-extended gastrin into the media.


CONCLUSIONS
Glycine-extended gastrin receptors are present on human colon cancer cells that mediate glycine-extended gastrin's trophic effects via a MEK-independent mechanism. This suggests that glycine-extended gastrin and its novel receptors may play a role in colon cancer cell growth.
Stepan
V M
VM
Department of Pediatrics, University of Michigan, Medical Center, Ann Arbor 48109-0658, USA.
Sawada
M
M
Todisco
A
A
Dickinson
C J
CJ
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D001665:Binding Sites; D001667:Binding, Competitive; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000187:drug effects / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D003110:Colonic Neoplasms / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology*; D004268:DNA-Binding Proteins; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D005755:Gastrins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D048031:JNK Mitogen-Activated Protein Kinases; D008536:Meglumine / Q000031:analogs & derivatives / Q000494:pharmacology; D020928:Mitogen-Activated Protein Kinases; D010446:Peptide Fragments / Q000378:metabolism* / Q000494:pharmacology*; D011499:Protein Processing, Post-Translational; D011518:Proto-Oncogene Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011949:Receptors, Cholecystokinin / Q000187:drug effects / Q000378:metabolism*; D011994:Recombinant Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D020218:Response Elements; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014157:Transcription Factors; D014407:Tumor Cells, Cultured; D050807:ets-Domain Protein Elk-1
D000970:Antineoplastic Agents; D004268:DNA-Binding Proteins; C494114:Elk1 protein, rat; D004791:Enzyme Inhibitors; D005419:Flavonoids; D005755:Gastrins; D007211:Indoles; D010446:Peptide Fragments; D011518:Proto-Oncogene Proteins; D011949:Receptors, Cholecystokinin; D011994:Recombinant Proteins; D014157:Transcription Factors; D050807:ets-Domain Protein Elk-1; C097084:gastrin (2-17)-Gly, Leu(15)-; C065599:PD 134308; D008536:Meglumine; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D013755:Tetradecanoylphorbol Acetate; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one