Bombesin binding and biological effects on pancreatic acinar AR42J cells

Tyrosine phosphatase PTP1B modulates store-operated calcium influx

We have studied modulation of "store-operated calcium influx" by tyrosine phosphatases in the pancreatic acinar cell line AR42J and in HEK 293 cells. We show that inhibition of tyrosine phosphatases by bis-(N,N-dimethyl-hydroxamido) hydrooxovanadate (DMHV) leads to an increase in Ca(2+) release-activated Ca(2+) (CRAC) entry. This effect can be blocked in the presence of 2-aminoethyldiphenyl borate (2-APB). Furthermore, transfection of HEK 293 cells with the human wild-type tyrosine phosphatase PTP1B leads to inhibition of CRAC influx, whereas transfection with the substrate-trapping mutant of PTP1B (D181A) slightly increases Ca(2+) influx. It also decreases enzymatic activity of PTP1B as compared to non-transfected cells. Our data suggest that CRAC influx is modulated by tyrosine phosphorylation and dephosphorylation which involves the tyrosine phosphatase PTP1B.

Release of digestive enzymes from the crustacean hepatopancreas: effect of vertebrate gastrointestinal hormones

Vertebrate gastrointestinal hormones were tested on their ability to liberate digestive enzymes from the crustacean midgut gland. CCK-8 (desulfated form), gastrin, bombesin, secretin, and substance P were detected to release enzymes. Maximal concentrations observed were 5 nM CCK for protease release, 1 nM gastrin for protease and 100 nM for amylase release, 100 nM bombesin for protease release, 10 nM secretin for amylase and protease release, and 100 nM substance P for protease release. Unlike in vertebrates, glucagon was unable to stimulate enzyme release in crustaceans, this also applies to the counterpart insulin. These results may support the assumption that Crustacea possess endogenous factors resembling the above mentioned vertebrate hormones, at least in such a way that the appropriate receptors have the capacity to accept these hormones.

AR4-2J cells: a model to study polypeptide hormone receptors

The AR4-2J cell line is derived from a transplantable tumour of the exocrine rat pancreas. Acinar in origin, this cell line contains significant amounts of amylase and can be grown in continuous culture. Many in vitro studies have been done using these cells; these studies were often complemented with in vivo experiments on animals. Particularly, many polypeptide hormones interacting with specific receptors located on the cell membrane have been analysed. The accurate knowledge of the hormone-receptor interactions has allowed to design interesting analogs of these hormones. In several cases, these compounds are powerful antagonists and are able to control cell proliferation induced by the corresponding polypeptide hormones. Other cell lines are useful to understand human pancreatic cancer. These human cell lines (Capan 1, Panc-1 for example) are of ductal origin and differ from AR4-2J cells, especially regarding the distribution of several polypeptide hormone and growth factor receptors. Both models are important for basic studies of neuropeptides, gastrointestinal peptides and their receptors, as well as for a better understanding of the underlying mechanisms of human pancreatic cancer.

Bombesin activation of phospholipase C beta 1 in rat acinar pancreatic cells involves the pertussis toxin-sensitive G alpha i3 protein

Bombesin stimulation of inositol 1,4,5-trisphosphate (Ins P3) formation in rat sonicated pancreatic acinar cells was inhibited by an antibody directed against the pertussis toxin (PTX)-sensitive GTP-binding G alpha i3 protein but not by an anti-G alpha q-11 antibody. After solubilization and gel filtration, [125I-Tyr4]bombesin binding sites were recovered in a peak of protein of 67 approximately 90 kDa with a maximal enrichment corresponding to a molecular mass of 83-kDa. Results obtained from the non-hydrolysable GTP analog guanosine-5'-[gamma-thio]triphosphate (GTP gamma S) binding, PTX-stimulated ADP-ribosylation and immunoblotting showed that the 83-kDa fraction contained the G alpha i3 protein but not the G alpha q-11 protein. Furthermore, GTP gamma S increased the bombesin binding dissociation constant (KD) from 0.32 to 0.60 nM, while the anti-G alpha i3 antibody decreased the maximal binding capacity (Bmax) from 50 to 25 fmol/mg protein without affecting the KD. Mixing solubilized bombesin binding sites with a phospholipase C (PLC) preparation from rat pancreas reconstituted a bombesin-stimulated PLC activity which was markedly inhibited by the anti-G alpha i3 antibody but unaffected by the anti-G alpha q-11 antibody. In addition, this stimulation was inhibited by an anti-PLC beta 1 antibody. This result supports the involvement of the PLC beta 1 isoform in bombesin receptor activation.

Ca2+ signaling through secretagogue and growth factor receptors on pancreatic AR42J cells

Intracellular signaling by an increase in [Ca2+]i was observed in pancreatic AR42J cells in response to agonists whose receptors are G-protein coupled including cholecystokinin (CCK), bombesin, carbachol, substance P, pituitary adenylate cyclase activating peptide (PACAP), bradykinin, ATP, calcitonin gene related peptide (CGRP), and in response to growth factors EGF and FGF whose receptors are tyrosine kinases. The response to growth factors was smaller both in magnitude and in the percentage of cells responding but was independent of extracellular Ca2+. CCK and carbachol induced sizeable increases in inositol phosphates while growth factors did not. The responses to both carbachol and EGF, however, were blocked by the phospholipase C inhibitor U73122. The tyrosine kinase inhibitor, genestein, blocked the response to EGF but not that to CCK. These data are consistent with two types of signaling mechanisms in AR42J cells. Secretagogues act on receptors which couple through G proteins to induce a large amount of inositol phosphate production and subsequent intracellular Ca2+ mobilization. Growth factors act on receptors which signal through tyrosine kinase activity and in this cell type produced limited amounts of inositol phosphate and a smaller increase in intracellular Ca2+.

Rat pancreatic AR42J cells. Amphicrine cells as an in vitro model to study peptide hormone receptor regulation

The rat pancreatic acinar tumor cell line, AR42J, is widely used to study pancreatic acinar cell biology and biochemistry. In addition to the well-documented exocrine cell features, we have identified by immunofluorescence and by electron microscopy the co-expression of small neuroendocrine (NE) vesicles using the NE vesicle-specific markers synaptophysin and "protein S.V.2." AR24J cells store [3H]GABA, which is secreted upon potassium depolarization in a calcium-dependent manner. In addition, we found the expression of the receptor for the neurotransmitter substance P by using a receptor-specific cDNA probe. Glucocorticoid treatment, which profoundly inhibits cellular growth and induces differentiation, results in a rapid decrease of substance P receptor (SPR) gene expression as assessed by Northern blot analysis. Intracellular Ca2+ mobilization was then determined in response to substance P in control cells and glucocorticoid-pretreated cells by dual wavelength spectrophotometry using fura-2 in single cells. Glucocorticoid-mediated down-regulation of substance P receptors resulted in a dose- and time-dependent decrease of the intracellular Ca2+ mobilization stimulated by substance P. In summary, these data indicate that AR42J cells display an amphicrine phenotype with two differentially regulated secretory pathways; during glucocorticoid-induced differentiation, the cells become less sensitive to substance P stimulation as a consequence of reduced gene expression of the substance P receptor.

Bombesin receptor gene expression in rat pancreatic acinar AR42J cells: transcriptional regulation by glucocorticoids

BACKGROUND/AIMS

This study investigated the correlation between glucocorticoid-regulated gene expression of the bombesin receptor (BR) and cellular sensitivity to bombesin stimulation in the rat pancreatic acinar cell line AR42J.

METHODS

BR gene expression was assessed using a cloned complementary DNA probe and radioligand binding assays. Intracellular Ca2+ mobilization was assessed by dual wavelength spectrophotometry using fura-2 in single cells.

RESULTS

Dexamethasone resulted in a rapid dose- and time-dependent decrease of BR messenger RNA levels with maximal inhibition to 25% +/- 2% of controls (n = 4) after 6 hours of hormone treatment. BR messenger RNA half-life was approximately 120 minutes and was not affected by dexamethasone pretreatment; nuclear run-on analysis showed a decreased transcription rate of the BR to approximately 25% of control after hormonal treatment. Radioligand binding studies showed a time-dependent decrease of specific bombesin binding to 25% +/- 8% of control after 48 hours of hormone treatment. Down-regulation of BR gene expression by dexamethasone resulted in a time- and dose-dependent decrease of intracellular Ca2+ mobilization after bombesin stimulation compared with untreated controls.

CONCLUSIONS

Glucocorticoids decrease BR gene transcription. The subsequent decrease in cellular BR number renders AR42J cells less sensitive for bombesin-stimulated intracellular Ca2+ mobilization.

Effect of vasoactive intestinal peptide, carbachol and other agonists on the membrane voltage of pancreatic duct cells

The regulation of pancreatic exocrine secretion involves hormonal, neural and neurohormonal components. Many agonists are known to be effective in pancreatic acinar cells, but less is known about the ducts. Therefore, we wanted to investigate the influence of various agonists on isolated perfused pancreatic ducts and, as a physiological response, we measured the basolateral membrane voltage of the duct cells (Vbl) with microelectrodes. Pancreatic ducts were dissected from pancreas of normal rats and bathed in a HCO(3-)(-containing solution. Under control conditions, the average Vbl was between -50 and -70 mV. Vasoactive intestinal peptide (VIP) and carbachol (CCH) reversibly depolarized Vbl when applied to the bath. VIP (9 x 10(-9) mol/l) depolarized Vbl from -72 +/- 3 mV to -53 +/- 3 mV (n = 20) and CCH (10(-5) mol/l) from -62 +/- 3 to -35 +/- 4 mV (n = 10). Furthermore, a decrease of the Cl- concentration in the lumen led to an increase of VIP-induced depolarization of Vbl, suggesting that a luminal Cl- conductance was increased. Cholecystokinin (CCK, 10(-10)-10(-7) mol/l) and bombesin (10(-8), 10(-5) mol/l), which stimulate pancreatic exocrine secretion in acini or whole glands, showed no significant effect on Vbl of the duct cells tested in our preparation (n = 7, 6). Neurotensin (10(-8) mol/l) had a marked depolarizing effect in two out of ten cases; Vbl depolarized from about -65 mV to -29 mV and the effect was reversible. Substance P (2 x 10(-7) mol/l), alone or in combination with secretin, had no effect on Vbl of the tested duct cells (n = 11).(ABSTRACT TRUNCATED AT 250 WORDS)

Somatostatin inhibition of phosphoinositides turnover in isolated rat acinar pancreatic cells: interaction with bombesin

The effects of somatostatin-14 and bombesin on [3H]inositol phosphate accumulation were studied in 24 h myo-[3H]inositol-prelabeled cultured rat acinar cells. Bombesin, 10 nM, stimulated basal formation of phosphatidyl monophosphate (InsP1), phosphatidyl 4,5-biphosphate (InsP2) and inositol 1,4,5-triphosphate (InsP3) by 128 +/- 5.2%, 147 +/- 10% and 155 +/- 5%, respectively. At 5 s, the ED50 value for InsP3 stimulation was 0.70 +/- 0.2 nM. This stimulation was partly blocked (64 +/- 0.04% inhibition) by 10 ng/ml Bordetella pertussis toxin. In contrast to bombesin, somatostatin, 10 nM, inhibited basal InsP1, InsP2 and InsP3 formation. At 5 s, the inhibition degree for InsP3 was 18 +/- 2.5% and the IC50s values 1 +/- 0.09 nM, 1 +/- 0.12 nM and 0.07 +/- 0.005 nM for InsP1, InsP2 and InsP3, respectively. Bombesin-stimulated InsP3 formation was also inhibited by somatostatin. At 5 s, the inhibition degree was 85 +/- 3.5% at 10 nM and the IC50 value, 0.10 +/- 0.05 nM. Furthermore, somatostatin inhibition of bombesin stimulation was partly blocked (66 +/- 4% inhibition) by Bordetella pertussis toxin. These data therefore suggest that the acinar pancreatic cells contain a somatostatin receptor exerting a negative control on basal and bombesin receptor-stimulated phosphatidyl inositol turnover.

The amphicrine pancreatic cell line AR42J: a model system for combined studies on exocrine and endocrine secretion

Secretory vesicles of both the exocrine and the endocrine pancreas have been isolated and characterized in molecular terms from pancreatic tissue and primary cell cultures. Studies on pancreatic secretory processes could be further facilitated by the use of permanent cell lines that respond to secretory stimuli with a regulated secretory response. We now present biochemical, morphological and secretory studies on the rat pancreatic acinar cell line AR42J. This cell line is characterized by the presence of digestive enzyme-containing dense core vesicles, which are released in response to cholecystokinin. In addition, we present evidence that these cells also contain small neuroendocrine-specific vesicles, as evidenced by the expression of the neuroendocrine-specific vesicle proteins synaptophysin and S.V.2. Corresponding to these mixed exocrine-neuroendocrine features, we also found considerable amounts of the neurotransmitters glycine, glutamine and gamma-aminobutyric acid (GABA), as well as the rate-limiting enzyme in GABA synthesis, glutamic acid decarboxylase (GAD) (EC 4.1.1.15) expressed in these cells. We demonstrated a specific uptake mechanism for radioactively-labelled GABA by these cells. In addition, GABA was released from intracellular storage pools by nicotinic receptor stimulation or membrane depolarization. In summary, AR42J cells represent the first amphicrine pancreatic cell line with the combined expression of exocrine and neuroendocrine secretory organelles, both of which follow a regulated secretory pathway in response to various secretory stimuli.

Mechanisms of activated Ca2+ entry in the rat pancreatoma cell line, AR4-2J

The characteristics of Ca2+ entry activated by surface receptor agonists and membrane depolarization were studied in the rat pancreatoma cell line, AR4-2J. Ca2+ mobilization activated by substance P, bombesin, or muscarinic receptor stimulation was found to involve both Ca2+ release and entry. In addition, depolarization of the surface membrane of AR4-2J cells with elevated concentrations of K+ activated Ca2+ entry. Ca2+ entry induced by membrane depolarization was inhibited by the L-channel antagonist, nimodipine, while that due to surface receptor agonists was not inhibited by this agent. The microsomal Ca(2+)-ATPase inhibitor, thapsigargin, caused both depletion of the agonist-sensitive intracellular Ca2+ pool and sustained Ca2+ influx indistinguishable from that produced by bombesin or methacholine. These results confirm that, unlike the pancreatic acinar cells from which they are presumably derived, AR4-2J cells express voltage-sensitive, dihydropyridine-inhibitable Ca2+ channels. However, in contrast to previous reports with this cell line, in the AR4-2J cells in use in our laboratory, and under our experimental conditions, surface receptor agonists (including substance P) do not cause Ca2+ influx through voltage-sensitive Ca2+ channels. Instead, we conclude that agonist-activated Ca2+ mobilization is initiated by (1,4,5)IP3-mediated intracellular Ca2+ release and that Ca2+ influx is regulated primarily, if not exclusively, by the state of depletion of the (1,4,5)IP3-sensitive intracellular Ca2+ pool.

Regulation of amylase and chymotrypsinogen expression by dexamethasone and caerulein in serum-free-cultured pancreatic acinar AR4-2J cells. Influence of glucose

The direct effects of dexamethasone and caerulein on two pancreatic enzymes, amylase and chymotrypsin, were determined in AR4-2J cells cultured under serum-free conditions at two glucose concentrations (1.0 and 4.5 g/l). In the absence of any hormone, the higher glucose concentration resulted in a 1.6-1.8-fold increase in the basal levels of amylase and chymotrypsinogen. Dexamethasone (50 nM) increased the biosynthesis and mRNA levels of both enzymes at both glucose concentrations. However, dexamethasone had a more pronounced effect on amylase biosynthesis (5-fold induction) than on chymotrypsinogen biosynthesis (1.8-fold induction). The parallel increases in mRNA and protein indicated the existence of pre-translational regulation. This is in contrast with what was observed in serum-containing media, where a translational regulation of amylase biosynthesis took place, probably under the control of both glucose and some serum factors. By contrast, caerulein (10 nM) exerted a more specific action on chymotrypsinogen. The increases in chymotrypsinogen mRNA were 2.2- and 2.1-fold, and increases in chymotrypsin activity were 1.6- and 2.9-fold at 1.0 and 4.5 g of glucose/litre respectively. Thus the regulation by caerulein occurred mainly through the enhancement of chymotrypsinogen transcription and/or mRNA stabilization.

Internalization-sequestration and degradation of cholecystokinin (CCK) in tumoral rat pancreatic AR 4-2 J cells

Cholecystokinin (CCK) receptors were investigated in the tumoral acinar cell line AR 4-2 J derived from rat pancreas, after preincubation with 20 nM dexamethasone. At steady state binding at 37 degrees C (i.e., after a 5 min incubation), less than 10% of the radioactivity of [125I]BH-CCK-9 (3-(4-hydroxy-[125I]iodophenyl)propionyl (Thr34, Nle37) CCK(31-39)) could be washed away from intact cells with an ice-cold acidic medium, suggesting high and rapid internalization-sequestration of tracer. By contrast, more than 85% of the tracer dissociated rapidly after a similar acid wash from cell membranes prelabelled at steady state. In intact AR 4-2 J cells, internalization required neither energy nor the cytoskeleton framework. Tracer internalization was reversed partly but rapidly at 37 degrees C but slowly at 4 degrees C. In addition, two degradation pathways of the tracer were demonstrated, one intracellular and one extracellular. Intracellular degradation occurred at 37 degrees C but not at 20 degrees C and resulted in progressive intracellular accumulation of [125I]BH-Arg that corresponded, after 1 h at 37 degrees C, to 35% of the radioactivity specifically bound. This phenomenon was not inhibited by serine proteinase inhibitors and modestly only by monensin and chloroquine. Besides, tracer degradation at the external cell surface was still observable at 20 degrees C and yielded a peptide (probably [125I]BH-Arg-Asp-Tyr(SO3H)-Thr-Gly). This degradation pathway was partly inhibited by bacitracin and phosphoramidon while thiorphan, an inhibitor of endopeptidase EC 3.4.24.11, was without effect.

Effect of vasoactive intestinal peptide, bombesin and substance P on fluid secretion by isolated rat pancreatic ducts

1. We have used micropuncture techniques to study the regulation of fluid secretion by interlobular ducts isolated from the pancreas of copper-deficient rats. 2. Ducts isolated from different strains of Wistar rats exhibited quantitative differences in basal fluid secretion; however, secretion rates measured in the presence of secretin were similar. 3. Vasoactive intestinal peptide had no effect on fluid transport. 4. Bombesin stimulated fluid secretion, and this effect was abolished by removal of extracellular bicarbonate. 5. Substance P inhibited basal secretion, and that stimulated by bombesin and secretin. These inhibitory effects were partially reversed by spantide. 6. Substance P also inhibited fluid secretion stimulated by dibutyryl cyclic AMP and forskolin. This places the site of inhibition mediated by substance P at a point in the secretory mechanism distal to the generation of cyclic AMP. 7. We conclude that rat pancreatic duct cells possess receptors for bombesin and substance P, in addition to 'secretin-preferring' receptors. Since VIP had no effect on fluid transport, it is unlikely that 'VIP-preferring' receptors are present on rat duct cells.

Presence of highly selective receptors for PACAP (pituitary adenylate cyclase activating peptide) in membranes from the rat pancreatic acinar cell line AR 4-2J

We characterized highly selective receptors for PACAP, the pituitary adenylate cyclase activating peptide, in the tumoral acinar cell line AR 4-2J derived from the rat pancreas. PACAP, a novel hypothalamic peptide related to vasoactive intestinal peptide (VIP), was tested as the full natural 38-residue peptide (PACAP-38) and as an N-terminal amidated 27-residue derivative (PACAP-27). The binding sites showed considerable affinity for [125I]PACAP-27 (Kd = 0.4 nM) and PACAP-38, while their affinity for VIP and the parent peptide helodermin was 1000-fold lower. These receptors were coupled to adenylate cyclase, the potency of PACAP-38 and PACAP-27 (Kact = 0.2 nM) being much higher than that of VIP (Kact = 100 nM) and helodermin (Kact = 30 nM). Chemical cross-linking of [125I]PACAP-27 followed by SDS-PAGE and autoradiography revealed a specifically cross-linked peptide with an Mr of 68,000 (including 3000 for one PACAP-27 molecule).

Manganese attenuates secretagogue-mediated phospholipid hydrolysis in AR42J cells

The effects of cholecystokinin octapeptide (CCK8), bombesin and manganese (Mn2+) on phosphatidylinositol-4,5-bisphosphate (PIP2) hydrolysis were studied in AR42J cells. One-half maximal stimulation of inositol monophosphate (InsP1) accumulation occurred at either 5 nM CCK8 or 5 nM bombesin, and maximal stimulation occurred at 30 nM for each agonist. Mn2+ did not alter basal PIP2 hydrolysis. However, addition of Mn2+ 5 min prior to stimulation with either CCK8 or bombesin for 60 min significantly attenuated [3H]InsP1 accumulation. Following brief periods of incubation with CCK8 (15 sec) Mn2+ significantly reduced inositol tris- and tetrakisphosphate accumulation. These data suggest that Mn2+ may participate in the regulation of CCK8- and bombesin-mediated generation of phosphoinositides.

Molecular characteristics and evidence for internalization of vasoactive-intestinal-peptide (VIP) receptors in the tumoral rat-pancreatic acinar cell line AR 4-2 J

1. Vasoactive intestinal peptide (VIP) receptors were investigated in the tumoral acinar cell line AR 4-2 J derived from rat pancreas [125I]Iodo-VIP binding to cell membranes showed the following IC50 values for unlabeled peptides: VIP, 0.3 nM; peptide His-IleNH2, 2 nM; helodermin, 30 nM; secretin, 100 nM. After incubation with 20 nM dexamethasone, the binding capacity increased twofold but affinities were unchanged. External [125I]iodo-VIP binding to intact cells reached steady state after 5 min at 37 degrees C, while the sequestration-internalization of the [125I]iodo-VIP-receptor complex (tested by cold acid washing) increased progressively, reaching 75% of total binding after 1 h. This phenomenon was blocked at 4 degrees C. Further data with dexamethasone, tunicamycin, cycloheximide, low temperature, and/or phenylarsine oxide, suggested a half-life of 2 days for VIP receptors and the necessity of N-glycosylation for proper translocation. 2. For chemical [125I]iodo-VIP cross-linking bis[2-(succinimidooxycarbonyloxy)ethyl]sulfone gave the best yield when compared with five other bifunctional reagents. In membranes, the main specifically cross-linked peptide had Mr 66,000 under nonreducing conditions, and migrated with lower velocity (-5%) under reducing conditions. Cross-linking was suppressed by VIP, peptide His-IleNH2 and helodermin (competitively) and also by GTP. In intact cells, the Mr of [125I]iodo-VIP-cross-linked peptides depended on the mode of cell solubilization. After direct solubilization, the major cross-linked radioactivity migrated as a smear of Mr 130,000-180,000 but an Mr-66,000 peptide was also detectable. In contrast, the solubilization of cross-linked cells detached by mild trypsinisation gave mainly the Mr-66,000 labeled peptide. This suggests that most VIP receptors in intact, attached cells were in a high-Mr complex and that mild cell treatment was sufficient to disrupt this complex.

Biological activity of oxidized and reduced iodinated bombesins

A method is reported for preparing oxidized and reduced iodinated Tyr4-bombesin. Iodogen was used to iodinate Tyr4-bombesin and the reaction products were separated by reverse-phase HPLC. The peak of oxidized label was then reduced by incubation with 725 mM dithiothreitol at 80 degrees C (pH 8.0) for one hour and the reaction products separated by HPLC as before. The reduced but not oxidized peaks of 125I-Tyr4-bombesin stimulated amylase release from rat pancreatic acini in vitro. We conclude that oxidation of bombesin producing C-terminal methionine sulfoxide destroys the biological activity of the peptide and that this form of oxidation can be reversed.