cholecystokinin and Insulinoma

The cholecystokinin-2 receptor (CCK2R), is expressed in cancers where it contributes to tumor progression. The CCK2R is over-expressed in a sub-set of tumors, allowing its use in tumor targeting with a radiolabel ligand. Since discrepancies between mRNA levels and CCK2R binding sites were noticed, we searched for abnormally spliced variants in tumors from various origins having been previously reported to frequently express cholecystokinin receptors, such as medullary thyroid carcinomas, gastrointestinal stromal tumors, leiomyomas and leiomyosarcomas, and gastroenteropancreatic tumors. A variant of the CCK2R coding for a putative five-transmembrane domains receptor has been cloned. This variant represented as much as 6% of CCK2R levels. Ectopic expression in COS-7 cells revealed that this variant lacks biological activity due to its sequestration in endoplasmic reticulum. When co-expressed with the CCK2R, this variant diminished membrane density of the CCK2R and CCK2R-mediated activity (phospholipase-C and ERK activation). In conclusion, a novel splice variant acting as a dominant negative on membrane density of the CCK2R may be of importance for the pathophysiology of certain tumors and for their in vivo CCK2R-targeting.

Topics: Alternative Splicing; Amino Acid Sequence; Animals; Binding Sites; Carcinoma, Medullary; Chlorocebus aethiops; Cholecystokinin; COS Cells; Extracellular Signal-Regulated MAP Kinases; Gastrins; Gastrointestinal Neoplasms; Gastrointestinal Stromal Tumors; Humans; Insulinoma; Leiomyoma; Leiomyosarcoma; Molecular Sequence Data; Pancreatic Neoplasms; Protein Structure, Tertiary; Receptor, Cholecystokinin B; RNA, Messenger; Signal Transduction; Thyroid Neoplasms; Type C Phospholipases

The endothelial differentiation gene (EDG) receptors are a class of G protein-coupled receptors. EDG-1, -3, -5, -6, and -8 bind the bioactive lipid sphingosine-1-phosphate (SPP) as the primary signaling ligand. EDG-2, -4, and -7 bind the ligand lysophosphatidic acid. EDG-1, -2, -3, -5, -6, and -7, but not -8, mRNAs were expressed in isolated rat pancreatic islets, whereas INS-1 insulinoma cells expressed only EDG-1, -2, -3, and -5 mRNAs. EDG-4 mRNA was expressed in mouse islets. EDG-1 mRNA but not EDG-3 mRNA was rapidly induced relative to 18S rRNA after stimulation of isolated islets with phorbol 12-myristate 13-acetate (PMA) or cholecystokinin-8S for 2 h. The protein kinase C inhibitor GF 109203X blocked the EDG-1 induction by PMA. Similarly, in islets stimulated for 2 h with 17 mmol/l glucose, the relative EDG-1 mRNA levels increased almost twofold compared with levels in control islets at 5.5 mmol/l glucose. In contrast, after 11 mmol/l glucose stimulation for 7 days, the relative levels of rat islet EDG-1 mRNA were significantly reduced to 54% below that of islets cultured at 5.5 mmol/l glucose. There was no change in relative EDG-3 mRNA levels. Stimulation of EDG receptors in islets and INS-1 cells with SPP inhibited glucagon-like peptide 1 (GLP-1)-stimulated cAMP production and insulin secretion in a concentration-dependent manner. Pertussis toxin antagonized the SPP effects on insulin release. Thus, EDG receptors are expressed in pancreatic islet beta-cells and G(i) seems to mediate the inhibition by SPP of adenylyl cyclase and cAMP formation and inhibition of the stimulation of insulin secretion by GLP-1.

Topics: Animals; Carcinogens; Cell Differentiation; Cholecystokinin; Cyclic AMP; Endothelium; Gene Expression; Glucose; GTP-Binding Protein alpha Subunits, Gs; In Vitro Techniques; Insulinoma; Islets of Langerhans; Lysophospholipids; Male; Mice; Mice, Inbred C57BL; Rats; Rats, Sprague-Dawley; Receptors, Cell Surface; Receptors, G-Protein-Coupled; Receptors, Lysophospholipid; RNA, Messenger; Sphingosine; Tetradecanoylphorbol Acetate; Tumor Cells, Cultured

Several immortalized cell lines serve as models for procholecystokinin (pro-CCK) processing. Rin5F cells, derived from a rat insulinoma, and STC-1 cells, derived from a murine intestinal tumor, process pro-CCK mainly to amidated CCK 8. Both also make significant quantities of amidated CCK 22, a slightly larger form found in the gut. Many modifications are necessary during pro-CCK processing including cleavages performed by endoproteases, the identities of which are unknown. A candidate endoprotease is prohormone convertase 1 (PC1) also known as PC3, a Ca2+-dependent serine endoprotease of the subtilisin family. Constitutive expression of antisense PC1 message in stably transfected Rin5F cells resulted in a significant reduction of the cellular content of CCK 8 as measured by radioimmunoassay. Several affected cell lines displayed about 80% reduction in CCK content in early passages after transfection. Expression of antisense PC1 message in these cell lines resulted in a selective depletion of CCK 8 and a comparative sparing of CCK 22. The induction of antisense PC1 message within a single subclone of Rin5F cells using the Lac Switch system also resulted in a significant inhibition of CCK content. Expression of antisense PC1 message in a stably transfected STC-1 cell line also resulted in a decrease in CCK content and in PC1 protein expression, and the specific depletion of CCK 8 with comparative sparing of CCK 22. These observations support the hypothesis that PC1 is necessary for pro-CCK processing in Rin5F and STC-1 cells and suggests a role for PC1 endoprotease in the biosynthesis of CCK 8 in vivo.

Topics: Animals; Aspartic Acid Endopeptidases; Cholecystokinin; Chromatography, Gel; Insulinoma; Intestinal Neoplasms; Models, Chemical; Oligonucleotides, Antisense; Pancreatic Neoplasms; Peptide Fragments; Proprotein Convertases; Rats; Sincalide; Tumor Cells, Cultured

To review our experiences in order to high-light some important lessons learned in the treatment of patients with neuroendocrine gut neoplasms.. Retrospective analysis of case series of 70 patients with neuroendocrine gut neoplasms treated between 1983 and 1993. The clinical features of individual patients illustrate lessons in surgical treatment.. University hospitals with tertiary care referral practice.. The main intervention was abdominal exploration in 43 patients, with resection of the primary tumor in 39 and of hepatic metastases in four.. To describe the tumors seen and to identify major lessons learned.. Of 70 patients with neuroendocrine tumors treated, 31 had carcinoid tumors, 10 each had insulinomas and gastrinomas, five had vipomas, nine had non-functioning islet cell tumors, three had glucagonomas, and one each had somatostatinoma and a possible cholecystokinin-secreting tumor (or CCKoma). Important lessons learned include: (1) the importance of preoperative tumor localization; (2) in multiple endocrine neoplasia, type I syndrome, the tumor found may not be the one responsible for the patient's symptoms; (3) solitary sporadic tumors secreting multiple peptides may mimic multiple tumors in multiple endocrine neoplasia, type I syndrome; (4) one needs to be prepared for the unexpected, such as the carcinoid crisis; (5) resection may sometimes be necessary even with advanced local disease; and (6) selected patients may benefit from pancreaticoduodenectomy.. These rare tumors are interesting in their clinical presentation and can be challenging in their treatment.

Topics: Adenoma, Islet Cell; Adult; Aged; Carcinoid Tumor; Cholecystokinin; Diagnosis, Differential; Digestive System Neoplasms; Female; Gastrinoma; Glucagonoma; Humans; Insulinoma; Male; Middle Aged; Multiple Endocrine Neoplasia; Neuroendocrine Tumors; Pancreatectomy; Retrospective Studies; Somatostatinoma; Vipoma

The rat insulinoma RIN 5F and the mouse pituitary AtT-20 cell line, which are known to express several biologically active peptides, were found to express CCK mRNA, to correctly process, and to release immunoreactive cholecystokinin (CCK) peptides. They expressed low levels of these peptides (about 0.4 and 0.2 ng/mg protein, respectively) and both cell lines processed pro-CCK to a form which co-eluted with CCK 8 sulfate on Sephadex gel filtration chromatography and HPLC. The major CCK 8 immunoreactive peptide which they secreted co-eluted with CCK 8 on Sephadex G-50 chromatography. The secretion of CCK from both cell lines was significantly enhanced by treatment for 24 h with forskolin + IBMX (3-isobutyl-1-methyl-xanthine, a phosphodiesterase inhibitor). This treatment also doubled the CCK content of the AtT-20 cells. It appears that the ability of different endocrine tumor cells to express and process CCK is not as uncommon as previously thought. These cells should be useful for future studies of CCK expression, processing, and regulation of secretion.

Topics: 1-Methyl-3-isobutylxanthine; Animals; Blotting, Northern; Cholecystokinin; Chromatography, High Pressure Liquid; Colforsin; Cyclic AMP; Gene Expression; Insulinoma; Mice; Pancreatic Neoplasms; Pituitary Neoplasms; Protein Precursors; Rats; RNA, Messenger; Sincalide; Tumor Cells, Cultured

Topics: Adenoma, Islet Cell; Cholecystokinin; Glucagonoma; Humans; Insulinoma; Pancreatic Neoplasms; RNA, Messenger

Topics: Acute Disease; Adenocarcinoma; Carcinoma; Cholangiopancreatography, Endoscopic Retrograde; Cholecystokinin; Chronic Disease; Humans; Insulinoma; Pancreatic Diseases; Pancreatic Neoplasms; Pancreatitis; Secretin; Time Factors; Zollinger-Ellison Syndrome