cyclin-d1 and gastrin-17

As gastrin may play a role in the pathophysiology of gastrointestinal (GI) malignancies, the elucidation of the mechanisms governing gastrin-induced proliferation has recently gained considerable interest. Several studies have reported that a large percentage of colorectal tumours overexpress or stabilise the beta-catenin oncoprotein. We thus sought to determine whether gastrin might regulate beta-catenin expression in colorectal tumour cells. Amidated gastrin-17 (G-17), one of the major circulating forms of gastrin, not only enhanced beta-catenin protein expression, but also one of its target genes, cyclin D1. Furthermore, activation of beta-catenin-dependent transcription by gastrin was confirmed by an increase in LEF-1 reporter activity, as well as enhanced cyclin D1 promoter activity. Finally, G-17 prolonged the tau(1/2) of beta-catenin protein, demonstrating that gastrin appears to exert its mitogenic effects on colorectal tumour cells, at least in part, by stabilising beta-catenin.

Topics: Animals; beta Catenin; Blotting, Northern; Blotting, Western; Cell Line, Tumor; Colorectal Neoplasms; Cyclin D1; Cytoskeletal Proteins; Gastrins; Mice; Promoter Regions, Genetic; Trans-Activators; Transcription, Genetic

Gastrin and its precursors promote proliferation in different gastrointestinal cells. Since mature, amidated gastrin (G-17) can induce cyclin D1, we determined whether G-17-mediated induction of cyclin D1 transcription involved Wnt signaling and CRE-binding protein (CREB) pathways. Our studies indicate that G-17 induces protein, mRNA expression and transcription of the G(1)-specific marker cyclin D1, in the gastric adenocarcinoma cell line AGSE (expressing the gastrin/cholecystokinin B receptor). This was associated with an increase in steady-state levels of total and nonphospho beta-catenin and its nuclear translocation, indicating the activation of the Wnt-signaling pathway. In addition, G-17-mediated increase in cyclin D1 transcription was significantly attenuated by axin or dominant-negative (dn) T-cell factor 4(TCF4), suggesting crosstalk of G-17 with the Wnt-signaling pathway. Mutational analysis indicated that this effect was mediated through the cyclic AMP response element (CRE) (predominantly) and the TCF sites in the cyclin D1 promoter, which was also inhibited by dnCREB. Furthermore, G-17 stimulation resulted in increased CRE-responsive reporter activity and CREB phosphorylation, indicating an activation of CREB. Chromatin immunoprecipitation studies revealed a G-17-mediated increase in the interaction of beta-catenin with cyclin D1 CRE, which was attenuated by dnTCF4 and dnCREB. These results indicate that G-17 induces cyclin D1 transcription, via the activation of beta-catenin and CREB pathways.

Topics: beta Catenin; Cyclic AMP Response Element-Binding Protein; Cyclin D1; Cytoskeletal Proteins; G1 Phase; Gastrins; Humans; Proto-Oncogene Proteins; S Phase; Signal Transduction; Stomach Neoplasms; Trans-Activators; Transcription, Genetic; Wnt Proteins; Zebrafish Proteins

Gastrin is a gastrointestinal (GI) peptide that possesses potent trophic effects on most of the normal and neoplastic mucosa of the GI tract. Despite abundant evidence for these properties, the mechanisms governing gastrin-induced proliferation are still largely unknown. To elucidate the mechanisms by which gastrin might influence mitogenesis in gastric adenocarcinoma, we analyzed its effects on the human cell line AGS-B. Amidated gastrin (G-17), one of the major circulating forms of gastrin, induced a concentration-dependent increase in [3H]thymidine incorporation of cells in culture, with the maximum effective concentration occurring with 20 nM G-17. This effect was significantly attenuated by the gastrin-specific receptor antagonist L-365260. In addition, we found that G-17 induced a significant increase in the levels of cyclin D1 transcripts, protein, and promoter activity. The results of these studies indicate that gastrin appears to exert its mitogenic effects on gastric adenocarcinoma, at least in part, through changes in cyclin D1 expression.

Topics: Adenocarcinoma; beta Catenin; Cell Division; Cyclin D1; Cytoskeletal Proteins; Dose-Response Relationship, Drug; Gastrins; Gene Expression Regulation, Neoplastic; Hormones; Humans; Promoter Regions, Genetic; RNA, Messenger; Stomach Neoplasms; Trans-Activators; Tumor Cells, Cultured

Gastrin is a gastrointestinal peptide that possesses potent trophic properties on both normal and neoplastic cells of gastrointestinal origin. Previous studies have indicated that chronic hypergastrinaemia increases the risk of colorectal cancer and cancer growth and that interruption of the effects of gastrin could be a potential target in the treatment of colorectal cancer. Here we demonstrate that gastrin leads to a dose-dependent increase in colon cancer cell proliferation and tumour growth in vitro and in vivo, and that this increment is progressively reversed by pretreatment with the cyclo-oxygenase-2 inhibitor NS-398. Gastrin was able to induce cyclo-oxygenase-2 protein expression, as well as the synthesis of prostaglandin E2, the major product of cyclo-oxygenase. Moreover, gastrin leads to approximately a two-fold induction of cyclo-oxygenase-2 promoter activity in transiently transfected cells. The results of these studies demonstrate that cyclo-oxygenase-2 appears to represent one of the downstream targets of gastrin and that selective cyclo-oxygenase-2 inhibition is capable of reversing the trophic properties of gastrin and presumably might prevent the growth of colorectal cancer induced by hypergastrinaemia.

Topics: Adenocarcinoma; Animals; Cell Division; Colonic Neoplasms; Cyclin D1; Cyclooxygenase 2; Cyclooxygenase 2 Inhibitors; Cyclooxygenase Inhibitors; Dinoprostone; DNA Replication; Dose-Response Relationship, Drug; Gastrins; Gene Expression Regulation, Neoplastic; Genes, Reporter; Isoenzymes; Male; Mice; Mice, Inbred BALB C; Neoplasm Proteins; Neoplasm Transplantation; Nitrobenzenes; Proliferating Cell Nuclear Antigen; Promoter Regions, Genetic; Prostaglandin-Endoperoxide Synthases; Receptors, Cholecystokinin; Substrate Specificity; Sulfonamides; Transfection; Tumor Cells, Cultured