Pancreastatin producing cell line from human pancreatic islet cell tumor

Expression and Molecular Regulation of the Cox2 Gene in Gastroenteropancreatic Neuroendocrine Tumors and Antiproliferation of Nonsteroidal Anti-Inflammatory Drugs (NSAIDs)

Background

Gastroenteropancreatic neuroendocrine tumors (GEP-NETs) has had a significant increase over the past 4 decades. The pathophysiological role of the cyclooxygenase-2 (cox-2) gene and factors responsible for the expression in GEP-NETs is of clinical value. Current study determined the expression of cox-2 gene in human GEP-NET tissues and corresponding cell lines, investigated the molecular mechanisms underlying the regulation of cox-2 gene expression and assessed the effect of nonsteroidal anti-inflammatory drugs (NSAIDs) on both anchorage-dependent and independent growth of GEP-NET cells.

Material/Methods

GEP-NET tissues and QGP-1, BON, and LCC-18 GEP-NET cell lines were used. The expression of cox-2 gene was analyzed by immunohistochemistry, western blot, RT-PCR, and enzyme immunoassay. Transient transfection and luciferase assays along with electrophoretic mobility shift assays were conducted to explore the regulation of cox-2 gene expression. The effect of COX-inhibitors on GEP-NET cell growth was determined by proliferation assays and colony growth assessment.

Results

We found 87.8% of GEP-NET tissues stained positive for COX-2. QGP-1 and LCC-18 cells expressed cox-2 gene. PGE2 (prostaglandin E2) amounts quantified in the supernatants of NET cells matched to cox-2 expression level. The CRE-E-box element (−56 to −48 bp) and binding of USF1, USF2, and CREB transcription factors to this proximal promoter element were essential for cox-2 promoter activity in GEP-NET cells. COX-2-specific inhibitor NS-398 potently and dose-dependently inhibited PGE2 release from QGP-1 cells. Interestingly, both NS-398 and acetylic salicylic acid effectively suppressed proliferation of QGP-1 and BON cells in a dose-dependent manner.

Conclusions

The majority of GEP-NETs over express cox-2 gene. The binding of CREB and USF-1/-2 transcription factors to a proximal, overlapping CRE-Ebox element is the underlying mechanism for cox-2 gene expression. NSAIDs potently suppressed the proliferations and may offer a novel approach for chemoprevention and therapy of GEP-NETs.

Expression of cyclo-oxygenase-2 in gastrointestinal carcinoid tumors

BACKGROUND

Cyclo-oxygenase (COX)-2 overexpression is observed in various neoplasms and COX-2 inhibition has been attempted as prevention and/or therapy in these neoplasms. Carcinoid tumors are thought to arise from neuroendocrine cells and originate mainly in the gastrointestinal tract. Cyclo-oxygenase-2 is reportedly expressed in neuroendocrine cells of normal colorectal mucosa. The role of COX in carcinoids has not previously been investigated. The aim of the present paper was to clarify the expression of COX-1 and -2, and their role in human gastrointestinal carcinoids.

METHODS

Expression of COX-1 and -2 was studied immunohistochemically in 38 gastrointestinal carcinoids. Five bronchopulmonary and seven metastatic carcinoids were also examined, for comparison with gastrointestinal carcinoids. The immunohistochemical score (IHS) was calculated from staining intensity and immunoreactive cell population, and ranked according to four grades (negative to strong).

RESULTS

Cyclo-oxygenase-2 was expressed in all gastrointestinal carcinoids (weak, 1; moderate, 13; strong, 24) and bronchopulmonary carcinoids (weak, 1; moderate, 4), as well as their metastases (moderate, 3; strong, 4). The IHS of COX-2 in larger tumors was significantly lower than that in smaller tumors. However, the IHS of COX-2 at the advancing tumor edge was significantly higher than that at the centers of tumors >or=10 mm in size. Faint COX-1 expression was detected in only one duodenal, one rectal and four bronchopulmonary carcinoids.

CONCLUSIONS

Enhanced COX-2 expression was observed in gastrointestinal as well as bronchopulmonary carcinoids and their metastases, especially at the advancing edges of the tumors. Cyclo-oxygenase-2 may play a role in carcinoid progression.

Nonsteroidal anti-inflammatory drugs inhibit growth of human neuroendocrine tumor cells via G1 cell-cycle arrest

Therapeutic options to inhibit growth of human NETs of the GEP system are limited. Since NSAIDs might provide an antiproliferative treatment alternative with acceptable toxicity, we examined the effects of different NSAIDs on growth and survival in a representative set of human GEP NET cell lines. Growth and apoptosis were determined based on cell numbers, cell-cycle analyses, kinase assays, DNA fragmentation and PARP cleavage. Expression of COX and cell cycle-regulatory molecules was examined by immunoblotting and reporter gene assays. Depending on the drug and cell line investigated, NSAID treatment resulted in profound growth inhibition of GEP NET cells. Growth-inhibitory effects were achieved with either COX-2 selective (NS398) or unselective (indomethacin, sulindac) compounds. Cell-cycle analyses documented a G1 arrest in NSAID-treated GEP NET populations. In addition, 100 microM sulindac or indomethacin induced apoptosis. All 3 COX inhibitors prevented CDK-2 activation. In parallel to the NSAID-mediated reduction of CDK-2 activity, p21(cip-1) promoter activity and cellular p21(cip-1) levels increased and p21(cip-1) was sequestered into CDK-2 complexes. Thus, the G1 arrest likely resulted from p21(cip-1)-dependent inhibition of CDK-2 activity. At therapeutically relevant concentrations, sulindac significantly reduced GEP NET cell numbers, whereas IFN-alpha and octreotide remained ineffective. The extent of growth inhibition in GEP NETs was comparable to the antiproliferative effects of sulindac in established NSAID-sensitive cell models. NSAIDs acted as potent antiproliferative agents in GEP NET cells via G1 cell-cycle arrest and might therefore offer a therapeutic alternative to current treatment modalities.

Expression of chromogranin A and somatostatin receptors in pancreatic AR42J cells

The exocrine pancreatic cell line AR42J is also known to display some neuroendocrine (NE) features. We have extended this fact by showing that AR42J cells express mRNA of chromogranin A (CgA), display immunoreactivity (IR) to CgA, and secrete its cleavage product pancreastatin. A sparse occurrence of typical NE secretion granules, together with only a faint IR to conventional NE markers, indicates that the NE cells are of a poorly differentiated type. CgA promoter reporter plasmid experiments showed that gastrin, epidermal growth factor, and phorbol 12-myristate 13-acetate, induce upregulation of CgA after 24 h. By RT-PCR, it was found that AR42J expresses all of the five subtypes of the somatostatin (SST) receptor (SSTR) family, except SSTR4. The existence of functional SSTRs was confirmed by showing that the SST analog octreotide could inhibit gastrin-induced proliferation. Thus, the AR42J cell line may function as a valuable experimental model to study the regulation of CgA and SSTRs in poorly differentiated NE tumor cells.

Structural and biological characterization of chromofungin, the antifungal chromogranin A-(47-66)-derived peptide

Vasostatin-I, the natural fragment of chromogranin A-(1-76), is a neuropeptide able to kill a large variety of fungi and yeast cells in the micromolar range. We have examined the antifungal properties of synthetic vasostatin-I-related peptides. The most active shortest peptide, named chromofungin, corresponds to the sequence Arg(47)-Leu(66). Extensive (1)H NMR analysis revealed that it adopts a helical structure. The biophysical mechanism implicated in the interaction of chromofungin with fungi and yeast cells was studied, showing the penetration of this peptide with different lipid monolayers. In order to examine thoroughly the antifungal activity of chromofungin, confocal laser microscopy was used to demonstrate the ability of the rhodamine-labeled peptide to interact with the fungal cell wall, to cross the plasma membrane, and to accumulate in Aspergillus fumigatus, Alternaria brassicola, and Candida albicans. Our present data reveal that chromofungin inhibits calcineurin activity, extending a previous observation that the N-terminal region of chromogranin A interacts with calmodulin in the presence of calcium. Therefore, the destabilization of fungal wall and plasma membrane, together with the possible intracellular inhibition of calmodulin-dependent enzymes, is likely to represent the mechanism by which vasostatin-I and chromofungin exert antifungal activity.

Intracellular Ca2+ signals in human-derived pancreatic somatostatin-secreting cells (QGP-1N)

Single-cell microfluorimetry techniques have been used to examine the effects of acetylcholine (0.1-100 microM) on the intracellular free calcium ion concentration ([Ca2+]i) in a human-derived pancreatic somatostatin-secreting cell line, QGP-1N. When applied to the bath solution, acetylcholine was found to evoke a marked and rapid increase in [Ca2+]i at all concentrations tested. These responses were either sustained, or associated with the generation of complex patterns of [Ca2+]i transients. Overall, the pattern of response was concentration related. In general, 0.1-10 microM acetylcholine initiated a series of repetitive oscillations in cytoplasmic Ca2+, whilst at higher concentrations the responses consisted of a rapid rise in [Ca2+]i followed by a smaller more sustained increase. Without external Ca2+, 100 microM acetylcholine caused only a transient rise in [Ca2+]i, whereas lower concentrations of the agonist were able to initiate, but not maintain, [Ca2+]i oscillations. Acetylcholine-evoked Ca2+ signals were abolished by atropine (1-10 microM), verapamil (100 microM) and caffeine (20 mM). Nifedipine failed to have any significant effect upon agonist-evoked increases in [Ca2+]i, whilst 50 mM KCl, used to depolarise the cell membrane, only elicited a transient increase in [Ca2+]i. Ryanodine (50-500 nM) and caffeine (1-20 mM) did not increase basal Ca2+ levels, but the Ca(2+)-ATPase inhibitors 2,5-di(tert-butyl)-hydroquinone (TBQ) and thapsigargin both elevated [Ca2+]i levels. These data demonstrate for the first time cytosolic Ca2+ signals in single isolated somatostatin-secreting cells of the pancreas. We have demonstrated that acetylcholine will evoke both Ca2+ influx and Ca2+ mobilisation, and we have partially addressed the subcellular mechanism responsible for these events.

Production and secretion of chromogranin A and pancreastatin by the human pancreatic carcinoma cell line QGP-1N on stimulation with carbachol

Chromogranin A (CGA) is thought to be a precursor of pancreastatin (PST). Carbachol (Cch) stimulated the secretion of CGA and PST from QGP-1N cells derived from a human pancreatic islet cell tumor. Atropine inhibited the secretion of both. Sodium fluoride, phorbol ester, and calcium ionophore also stimulated the secretion of both. Cch (10(-5) M) stimulated inositol 1,4,5-trisphosphate production in QGP-1N cells. Stimulation with Cch increased the total amount of PST in the cells and the medium 1.7-fold and decreased the amount of CGA in the cells and medium. QGP-1N cells were labelled with [35S]methionine, and then CGA and PST in the cells and medium were immunoprecipitated with specific antisera, and separated by electrophoresis in polyacrylamide gel. Stimulation with Cch resulted in an increase in the intensity of PST-immunoreactive bands and a decrease in those of CGA-immunoreactive bands. Cch did not increase the cellular level of CGA messenger RNA. These results suggested that (1) the secretion of CGA and PST from QGP-1N cells is regulated mainly through muscarinic receptors coupled with activation of polyphosphoinositide breakdown by a G protein, with intracellular calcium ion and protein kinase C playing a role in the stimulus-secretion coupling and that (2) Cch may induce the secretion of PST and CGA and processing from CGA to PST.

Pancreastatin molecular forms in normal human plasma

Circulating molecular forms with pancreastatin (PST)-like immunoreactivity in plasma from normal subjects were examined. An immunoreactive form corresponding to a human PST-like sequence [human chromogranin-A-(250-301)] (hPST-52) and a larger form (mol wt 15-21 kDa) were detected by gel filtration of plasma from normal subjects. On high performance liquid chromatography, predominant immunoreactive forms coeluted with the three larger forms which were purified from the xenograft of human pancreatic islet cell carcinoma cell line QGP-1N cells and with synthetic hPST-52. The fraction containing larger forms purified from xenograft of QGP-1N cells had biological activity equivalent to that of hPST-52 on the inhibition of pancreatic exocrine secretion. These results suggest that the larger molecular forms as well as hPST-52 may be physiologically important circulating forms of PST in human.

Secretion of neurotensin from a human pancreatic islet cell carcinoma cell line (QGP-1N)

Effects of various secretagogues on secretion of neurotensin from a pancreatic islet cell carcinoma cell line (QGP-1N) were examined. Carbachol stimulated secretion of neurotensin concentration-dependently in the range of 10(-6) - 10(-4) M. The neurotensin secretion stimulated with 10(-5) M carbachol was completely inhibited by atropine at 10(-5) M. Phorbol ester and calcium ionophore (A23187) stimulated secretion of neurotensin. The removal of extracellular Ca2+ suppressed the secretion through the stimulation with 10(-5) M carbachol. Fluoride, an activator of guanine nucleotide-binding (G) protein, stimulated secretion of neurotensin. Neurotensin released into culture medium through stimulation with carbachol coeluted with neurotensin 1-13 on a gel-chromatography. Our results suggest that secretion of neurotensin from QGP-1N cells is mainly regulated by acetylcholine through muscarinic receptors coupled to G protein and that an increase in intracellular Ca2+ and protein kinase C play an important role in stimulus-secretion coupling.

Camptothecin analog (CPT-11)-sensitive human pancreatic tumor cell line QGP-1N shows resistance to SN-38, an active metabolite of CPT-11

In the course of our study to determine the cross-sensitivity between CPT-11 and its active metabolite, SN-38, we found a SN-38-resistant human pancreatic tumor cell line, QGP-1N, which shows sensitivity to CPT-11. The IC50 of SN-38 was 152 times greater for QGP-1N than for SUIT-2, also a human pancreatic tumor cell line, whose IC50 of CPT-11 was similar to that for QGP-1N. The uptakes of CPT-11 and SN-38 and the intracellular conversion of CPT-11 to SN-38 could not explain the difference in sensitivity. DNA synthesis of QGP-1N cells was inhibited by CPT-11 which did not affect that of SUIT-2, while SN-38 inhibited the DNA synthesis of SUIT-2 at lower concentrations than that of QGP-1N. The inhibition test of topoisomerase I catalytic activity by CPT-11 or SN-38 revealed no difference in the biochemical properties of the topoisomerase I enzymes to the compounds between these two cell lines. These results indicate that CPT-11 should have its own inhibitory effect on DNA synthesis through a yet unknown mechanism in QGP-1N cells, although SN-38 plays an essential role in the antitumor activity of CPT-11 in SUIT-2 cells. In some cases, the antitumor effect of CPT-11 might be consequent not only on SN-38 but also on CPT-11 itself.

Interaction between phosphoinositide turnover system and cyclic AMP pathway for the secretion of pancreastatin and somatostatin from QGP-1N cells

It is found that secretion of pancreastatin and somatostatin from QGP-1N cells is regulated through muscarinic receptor-mediated activation of phosphatidylinositide hydrolysis system. In this report, whether the cAMP pathway interacts with the phosphoinositide turnover system for the secretion of pancreastatin and somatostatin from QGP-1N cells through muscarinic receptors was studied. Stimulation of QGP-1N cells with carbachol increased intracellular cAMP levels. The carbachol-induced increase in cAMP levels was inhibited by atropine. Calcium ionophore (A23187) and phorbol 12-myristate 13-acetate increased cAMP synthesis. Dibutyryl cAMP, forskolin and theophylline stimulated secretion of pancreastatin and somatostatin. When either dibutyryl cAMP, forskolin or theophylline was added in culture medium with A23187, phorbol ester or carbachol, a synergistic effect was found on pancreastatin and somatostatin secretion. These results suggest that interaction between the phosphoinositide turnover system and the cAMP pathway occurs in QGP-1N cells through muscarinic receptor stimulation for the secretion of pancreastatin and somatostatin.

Differential expression of DNA topoisomerase I gene between CPT-11 acquired- and native-resistant human pancreatic tumor cell lines: detected by RNA/PCR-based quantitation assay

RNA/PCR quantitation method was developed to determine DNA Topoisomerase I(Topo I)-specific mRNA in order to study its gene expression in CPT-11 sensitive, acquired- or native-resistant human pancreatic tumor cell lines. The results were supported by Northern blotting and Western blotting analyses. Acquired-resistant cells have shown decreased levels of Topo I mRNA, compared with their parental cells. On the contrary, in the wild type cells no correlation was shown between sensitivity and gene expression. On the other, specific Topo I activity of the native resistant cell lines was fairly lower than that of sensitive cell lines, suggesting that immunoreactive Topo I protein contains low levels of active form enzyme which could be targets of CPT-11 in these native-resistant ones. Finally, the different mechanisms might be operative between acquired- and native-resistant tumor cells.

Isolation and sequencing of a cDNA clone encoding the 85 kDa human lysosomal sialoglycoprotein (hLGP85) in human metastatic pancreas islet tumor cells

A full length cDNA for a human lysosomal membrane sialoglycoprotein (hLGP85) was isolated as a probe of the cDNA of rat LGP85 (rLGP85) from the cDNA library prepared from total mRNA of QGP-1NL cells, a human pancreatic islet tumor cell with a high metastatic activity. The deduced amino acid sequence shows that hLGP85 consists of 478 amino acid residues (MW. 54,289). The protein has 10 putative N-glycosylation sites and 2 hydrophobic regions at the NH2- and near the COOH-termini, respectively. Thus, both domains probably constitute putative transmembrane domains. It exhibits 86% and 79% sequence similarities in amino acids and nucleic acids to rat lysosomal membrane sialoglycoprotein (rLGP85), respectively. The protein contained the short cytoplasmic tail at the COOH-terminus which does not form the glycine-tyrosine sequence (GY motif), the so-called lysosomal targetting signal.

Pertussis toxin non-sensitive G protein mediates cholinergic stimulation for secretion of pancreastatin and somatostatin from QGP-1N cells

To clarify the possible role of a guanine nucleotide-binding protein (G-protein) in the signal transducing system activated by carbachol, actions of carbachol on human pancreastatin producing cell line (QGP-1N) were compared with those of fluoride, a well-known activator of stimulatory (Gs) or inhibitory (Gi) G protein. 10(-5) M of carbachol as well as 20 mM of NaF stimulated secretion of pancreastatin and somatostatin and intracellular Ca2+ mobilization. These secretion and Ca2+ mobilization were not modified by pertussis toxin, an inhibitor of Gi protein. These results suggest that pancreastatin and somatostatin secretions from QGP-1N are regulated by acetylcholine through a muscarinic receptor coupled to the activation of polyphosphoinositide breakdown by a G protein, which appears to be fluoride sensitive but is other than a Gi-like protein.

Degradation of human pancreastatin-52 by human kidney extract

We examined the in vitro degradation of human pancreastatin-52 (hPST-52) and a larger molecular form (approximate 15 kDa) of human PST by an enzyme extract from human kidney. The PST-degrading activity was determined from the amount of immunoreactive PST remaining after incubation of hPST-52 or the larger molecular form with the enzyme extract. Human PST-52 was degraded to smaller molecular forms within 30 min, but the larger molecule was not degraded within 90 min. Phosphoramidon, an inhibitor of endopeptidase, metal ion chelators (EDTA and 1, 10-phenanthroline) and Cu2+ prevented the degradation of hPST-52. These results indicated that the enzyme in the kidney extract degraded hPST-52 and smaller forms of the peptide, but had no effect on the 15 kDa form.

Pancreastatin--a novel regulatory peptide?

Pancreastatin is a 49 amino acid peptide originally isolated from porcine pancreas on the basis of its C-terminal glycinamide as isolation criterion. It is derived by proteolytic processing from chromogranin A, an acidic protein component of secretory granules in endocrine and neuronal cells. The primary structures of human, porcine, bovine and rat pancreastatin have been determined on the protein or cDNA level and show 70% sequence homology. By immunocytochemistry, pancreastatin has been detected in the pituitary, adrenal gland, pancreas, CNS and throughout the gastrointestinal tract. In pancreatic islets, pancreastatin is co-localized with insulin, glucagon and somatostatin. The principle biological activities of this peptide are: inhibition of insulin release and of exocrine pancreatic secretion. These effects which can be assigned to the amidated C-terminal part of the molecule have been demonstrated in several species. Whether or not pancreastatin can be classified as a novel peptide hormone that under physiological conditions plays a role in the regulation of the endocrine and exocrine pancreas, is still a matter of controversy.