Gastrin and glycine-extended progastrin processing intermediates induce different programs of early gene activation.
We recently reported that gastrin and glycine-extended progastrin processing intermediates (G-Gly) exert growth-promoting effects on AR4-2J cells (derived from rat pancreas) via interaction with distinct receptors. In this study we sought to investigate the mechanisms by which gastrin and G-Gly stimulate cell proliferation. While gastrin increased [Ca2+]i in AR4-2J cells, G-Gly had no effect. Similarly, G-Gly had no effect either on basal and 10(-7) M vasoactive intestinal polypeptide-stimulated cAMP generation, although gastrin is known to inhibit cAMP generation. Gastrin dose dependently stimulated AR4-2J cell mRNA content of both c-fos and c-jun, two genes known to function in regulating cell proliferation, but G-Gly had no effect. Gastrin also induced the expression of luciferase in AR4-2J cells transfected with a construct consisting of a luciferase reporter gene coupled to the serum response element of the c-fos gene promoter. In similar fashion, gastrin stimulated the activity of mitogen-activated protein kinase, an enzyme known to mediate the induction of the c-fos serum response element in response to growth factor stimulation. Although G-Gly had none of these effects of gastrin in AR4-2J cells, it stimulated activity of c-Jun amino-terminal kinase, an enzyme known to phosphorylate and transcriptionally activate c-Jun. These data support the notion that gastrin stimulates cell proliferation by inducing c-fos and c-jun gene expression, while G-Gly acts by post-translationally regulating early gene transcriptional activation. Our studies represent a novel model in which both the precursor and the product of a key processing reaction, peptide alpha-amidation, act cooperatively to stimulate cell proliferation via distinct receptors linked to different signal transduction pathways.
D000818:Animals; D002118:Calcium / Q000378:metabolism; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism; D005755:Gastrins / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects* / Q000502:physiology; D016762:Genes, fos; D016259:Genes, myc; D008156:Luciferases / Q000096:biosynthesis; D010179:Pancreas; D010446:Peptide Fragments / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D011499:Protein Processing, Post-Translational; D012333:RNA, Messenger / Q000032:analysis / Q000096:biosynthesis; D051381:Rats; D015398:Signal Transduction; D015533:Transcriptional Activation; D014162:Transfection
D005755:Gastrins; D010446:Peptide Fragments; D012333:RNA, Messenger; C097084:gastrin (2-17)-Gly, Leu(15)-; D000242:Cyclic AMP; D008156:Luciferases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002118:Calcium