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R T Jensen

Publications and source records attributed to R T Jensen.

At least 55 records · Page 3Linked to original sources
PubMed2000

Glycosylation of the gastrin-releasing peptide receptor and its effect on expression, G protein coupling, and receptor modulatory processes.

Many gastrointestinal G protein-coupled receptors are glycosylated; however, which potential glycosylation sites are actually glycosylated and their role in receptor transduction or receptor modulation (internalization, down-regulation, desensitization) is largely unknown. We used site-directed mutagenesis to address these issues with the gastrin-releasing peptide receptor (GRP-R). Each of the four potential glycosylation sites was mutated by converting the Asn (N) to Gln (Q). Transient expression in CHOP cells demonstrated that changing Asn(24) or Asn(191) inhibited GRP-R cell surface expression, whereas elimination of Asn(5) and Asn(20) had no effect. Using ligand cross-linking studies in stable mutants expressed in Balb 3T3 cells, all four potential extracellular sites were glycosylated with carbohydrate residues of approximately 13 kDa on Asn(5), 10 kDa on Asn(20), 5 kDa on Asn(24), and 9 kDa on Asn(191). Removal of three glycosylation sites (N5,20,24,Q mutant) did not alter receptor affinity or G protein coupling; therefore, it could be speculated that deglycosylation at Asn(191) might be responsible for the altered G protein coupling seen with complete enzymatic deglycosylation of the native receptor previously reported. Removal of any single glycosylation site did not interfere with GRP-R induced chronic desensitization or down-regulation. However, elimination of all three NH(2)-terminal sites (N5,20,24) markedly attenuated both processes, with no effect on acute homologous desensitization and with only a minimal alteration of GRP-R internalization, supporting the findings of other studies that suggest that chronic desensitization and down-regulation are functionally coupled, distinct from acute desensitization and distinct from internalization. These data show that separate and specific glycosylation sites are important for GRP-R trafficking to the cell surface, ligand binding, G protein coupling, chronic desensitization, and down-regulation.

3T3 Cells↗
PubMed2000

Rat and guinea pig pancreatic acini possess both VIP(1) and VIP(2) receptors, which mediate enzyme secretion.

Pancreatic acini from most species possess vasoactive intestinal peptide (VIP) receptors. Recently, two subtypes of VIP receptors, VIP(1)-R and VIP(2)-R, were cloned. Which subtype exists on pancreatic acini or mediates secretion is unclear. To address this, we examined pancreatic acini from both rat and guinea pig. VIP(1)-R and VIP(2)-R mRNA were identified in dispersed acini from both species by Northern blot analysis and in rat by Southern blot analysis. With the use of the VIP(2)-R-selective ligand Ro-25-1553 in both species, inhibition of binding of (125)I-labeled VIP to acini showed a biphasic pattern with a high-affinity component (10%) and a second representing 90%. The VIP(1)-R-selective ligand, [Lys(15),Arg(16),Leu(27)]VIP-(1-7)-GRF-(8-27), gave a monophasic pattern. Binding of Ro-25-1553 was better fit by a two-site model. In both rat and guinea pig acini, the dose-response curve of Ro-25-1553 for stimulation of enzyme secretion was biphasic, with a high-affinity component of 10-15% of the maximal secretion and a low-affinity component accounting for 85-90%. At low concentrations (10 nM) of Ro-25-1553 and [Lys(15),Arg(16), Leu(27)]VIP-(1-7)-GRF(8-27), which only occupy VIP receptors, a 4-fold and a 56-fold increase in cAMP occurred, respectively. These results show that both VIP(1)-R and VIP(2)-R subtypes exist on pancreatic acini of rat and guinea pig, their activation stimulates enzyme secretion by a cAMP-mediated mechanism, and the effects of VIP are mediated 90% by activation of VIP(1)-R and 10% by VIP(2)-R. Because VIP has a high affinity for both VIP-R subtypes, its effect on pancreatic acini is mediated by two receptor subtypes, which will need to be considered in future studies of the action of VIP in the pancreas.

Animals↗
PubMed2000

Genotype/phenotype correlation of multiple endocrine neoplasia type 1 gene mutations in sporadic gastrinomas.

Multiple endocrine neoplasia type 1 (MEN1) gene mutations are reported in some gastrinomas occurring in patients without MEN1 as well as in some other pancreatic endocrine tumors (PETs). In some inherited syndromes phenotype-genotype correlations exist for disease severity, location, or other manifestations. The purpose of the present study was to correlate mutations of the MEN1 gene in a large cohort of patients with sporadic gastrinomas to disease activity, tumor location, extent, and growth pattern. DNA was extracted from frozen gastrinomas from 51 patients and screened by dideoxyfinger-printing (ddF) for abnormalities in the 9 coding exons and adjacent splice junctions of the MEN1 gene. Tumor DNA exhibiting abnormal ddF patterns was sequenced for mutations. The findings were correlated with clinical manifestations of the disease, primary tumor site, disease extent, and tumor growth postoperatively. Tumor growth was determined by serial imaging studies. Sixteen different MEN1 gene mutations in the 51 sporadic gastrinomas (31%) were identified (11 truncating, 4 missense, and 1 in-frame deletion). Nine of the 16 mutations were located in exon 2 compared to 7 of 16 in the remaining 8 coding exons (P = 0.005 on a per nucleotide basis). Primary pancreatic or lymph node gastrinomas with a mutation had only exon 2 mutations, whereas duodenal tumors uncommonly harbored exon 2 mutations (P = 0.011). Similarly, small primary tumors (<1 cm) more frequently contained a nonexon 2 mutation (P = 0.02). There was no difference between patients with or without a mutation with respect to clinical characteristics, primary tumor site, disease extent, or proportion of patients disease free after surgery. Postoperative tumor growth tended to be more aggressive in patients with a mutation (P = 0.09). No correlation in the rate of disease-free status or postoperative tumor growth in patients with active disease to the location of the mutation was seen. These results demonstrate that the MEN1 gene is mutated in 31% of sporadic gastrinomas, and mutations are clustered between amino acids 66-166, which differs from patients with familial MEN1, in whom mutations occur throughout the gene. The presence of an MEN1 gene mutation does not correlate with clinical characteristics of patients with gastrinomas, gastrinoma extent, or growth pattern; however, the location of the mutation differed with gastrinoma location. These data suggest that mutations in the MEN1 gene are important in a proportion of sporadic gastrinomas, but the presence or absence of these mutations will not identify the clinically important subgroups with different growth patterns.

Base Sequence↗
PubMed2000

Overexpression of cyclin D1 occurs frequently in human pancreatic endocrine tumors.

The molecular pathogenesis of human pancreatic endocrine tumors (PETs) is poorly understood. Three independent animal models have pointed to the pivotal role of the G1/S cell cycle transition in pancreatic endocrine cell proliferation. We thus hypothesized that the cell cycle regulator cyclin D1 may contribute to the pathogenesis of human PETs. Overexpression of cyclin D1 was identified in 43% of cases, and no correlation was observed with clinical phenotype. The novel observation of frequent overexpression of cyclin D1 suggests that this established oncogene may be implicated in the pathogenesis of human PETs. The absence of detectable alterations in cyclin D1 genomic structure suggests that the mechanism for its oncogenic activation in PETs may be transcriptional or posttranscriptional.

Adolescent↗
PubMed2000

Expression of the calcium-sensing receptor in gastrinomas.

Extracellular calcium levels are able to influence the secretion of gastrin by gastrinomas and possibly affect the growth pattern. The molecular mechanisms of these functions are not known. The purpose of the present study was to investigate the presence of the calcium-sensing receptor (CaR) in 10 gastrinomas and determine the extent of expression in the tumors. The amounts of CaR messenger ribonucleic acid in eight tumors were determined by quantitative RT-PCR. Protein expression was analyzed by Western blot and immunohistochemistry using a monoclonal antibody (ADD). CaR messenger ribonucleic acid was detected in all gastrinomas with levels ranging from 0.04-3.16 times the amount of beta-actin transcripts. The Western blot showed a major immunoreactive band at 250 kDa and a minor at 140 kDa, corresponding to the receptor dimer and monomer, respectively. Immunohistochemistry demonstrated variable membranous staining in all gastrinomas and normal pancreatic islets. No staining was observed in the normal liver, lymph node, or exocrine pancreas. We conclude that the CaR is present in all gastrinomas, with expression varying by 80-fold. It probably contributes to the calcium-stimulated gastrin release by gastrinomas. Whether the density of the CaR is a determining factor of the magnitude of this gastrin release or plays a role in regulating the growth pattern of the gastrinoma, as it does in other cells, remains unclear at present.

Adult↗
PubMed2000

Alterations in the p16INK4a/CDKN2A tumor suppressor gene in gastrinomas.

The p16INK4a/CDKN2A gene (p16INK4a) is frequently altered by homozygous deletion, mutation, or methylation in many nonendocrine tumors, and these alterations may be predictive of recurrence, tumor growth, or aggressiveness. Whether this is true of neuroendocrine tumors such as gastrinomas is unclear. To address this question we analyzed the gastrinomas from 44 patients for p16INK4a gene mutations and correlated the results to the tumor's biological behavior, growth pattern, and aggressiveness. No gastrinomas had mutations of exon 1 or exon 2 of the p16INK4a gene, although polymorphisms were found in 54%. No homozygous deletions were found. In 52% of the gastrinomas, hypermethylation of a 5'-CpG island of the p16INK4a gene promoter was found. To assess the growth behavior of the gastrinomas, all patients were assessed yearly with at least three conventional imaging studies (computed tomography scan, magnetic resonance imaging, and ultrasound), and since 1994 have been assessed with radionuclide scanning using [111In-diethylenetriamine pentaacetic acid,DPhe1]octreotide. The mean follow-up was 5.1+/-0.4 yr (range, 1.2-11.7). The presence or absence of methylation of the p16INK4a gene did not correlate with clinical characteristics of the gastrinoma, biological behavior (gastrin release and basal or maximal acid output), the presence or absence of known prognostic factors (tumor size, gastrinoma location, lymph node metastases, liver metastases, and curability), or growth pattern of the gastrinoma postresection. These results indicate that methylation of the p16INK4a gene is the most common gene alteration described to date in gastrinomas. Furthermore, because it is independent of disease stage it is probably an early event in the pathogenesis and because it is independent of the primary gastrinoma location, which is now thought to have different origins, methylation of the p16INK4a gene is probably a central process in the molecular pathogenesis of these tumors.

Adolescent↗
PubMed2000

Two amino acids in the sixth transmembrane segment of the mouse gastrin-releasing peptide receptor are important for receptor activation.

The gastrin-releasing peptide receptor (GRP-R) is a G protein-coupled receptor that mediates a variety of cellular responses, including cell growth and modulation of neuronal activity by activation of heterotrimeric GTP-binding proteins in the Gq family. To understand the regulation of GRP-R signaling we have substituted alanine for each of 10 amino acid residues within the transmembrane (TM) helices of the GRP-R predicted to project into the binding pocket of the receptor and analyzed the importance of each of these residues for receptor function. Two mutations showed selective loss of either agonist (Y285A) or antagonist (F313A) affinity for the GRP-R. In addition, we identified two amino acid residues, Phe(270) and Asn(281), in the sixth TM segment, which are important for receptor-G protein interaction. In a competition-binding assay with an antagonist radioligand, bombesin showed a 20- to 100-fold decreased affinity for the N281A and F270A mutant GRP-R compared with wild-type GRP-R. The saturation-binding isotherms are best fit by a two-state model, indicating that the receptors are in either a low-affinity (K(D2)) or a high-affinity (K(D1)) state. The ratio of the two affinities (K(D2)/K(D1)) was significantly increased for both mutants compared with wild-type GRP-R, whereas the fraction of mutant receptors in the high-affinity state (R(1)) was decreased. GDP/guanosine-5'-O-(3-thio)triphosphate exchange catalyzed by the N281A mutant was lower than that observed for the wild-type GRP-R. However, for both mutants, bombesin was still able to stimulate 1,4,5-inositol triphosphate in transfected cells albeit with reduced activity. We conclude that these two TM residues are important for receptor-G protein coupling, and postulate that each mutation may affect GRP-R conformational change to the high-affinity, G protein-coupled state.

3T3 Cells↗
PubMed2000

Ability of somatostatin receptor scintigraphy to identify patients with gastric carcinoids: a prospective study.

UNLABELLED: Gastric carcinoids are of increasing clinical concern because they may develop in hypergastrinemic states, especially with the increased chronic use of potent acid suppressants that can cause hypergastrinemia. However, gastric carcinoids are difficult to diagnose. Somatostatin receptor scintigraphy (SRS) has a high sensitivity and specificity for localizing carcinoids in other locations. The purpose of this study was to determine whether SRS could localize gastric carcinoids. METHODS: Two groups of patients with Zollinger-Ellison syndrome (ZES) with hypergastrinemia, each having a different increased risk of developing gastric carcinoids, were studied. One hundred sixty-two consecutive patients with ZES were studied prospectively, with 39 having multiple endocrine neoplasia, type 1 (MEN-1) (high increased risk), and 123 not having MEN-1 (low increased risk). Patients were admitted to the hospital initially and then yearly, undergoing SRS with SPECT, upper gastrointestinal endoscopy, and Jumbo Cup biopsies of any gastric abnormalities, as well as random biopsies of the gastric body. Tumor localization studies were also performed. Both the results of the routine SRS interpretation and the results of a masked review, with particular attention to the stomach of high risk MEN-1 patients, were correlated with the gastric biopsy results. RESULTS: Gastric SRS localization was positive in 19 (12%) of 162 patients. Sixteen patients had a gastric carcinoid, and 12 of these patients had SRS localization. The sensitivity of SRS in localizing a gastric carcinoid was 75%, with a specificity of 95%. Positive and negative predictive values were 63% and 97%, respectively. CONCLUSION: SRS is a noninvasive method that can identify patients with gastric carcinoids with a reasonable sensitivity and a high specificity. SRS should prove useful in the treatment of patients with hypergastrinemic states that have an increased incidence of gastric carcinoids. In patients with MEN-1, one must realize that localization in the upper abdomen on SRS may be caused by a gastric carcinoid and not a pancreatic endocrine tumor.

Carcinoid Tumor↗
PubMed1999

Cholecystokinin activates PYK2/CAKbeta by a phospholipase C-dependent mechanism and its association with the mitogen-activated protein kinase signaling pathway in pancreatic acinar cells.

PYK2/CAKbeta is a recently described cytoplasmic tyrosine kinase related to p125 focal adhesion kinase (p125(FAK)) that can be activated by a number of stimuli including growth factors, lipids, and some G protein-coupled receptors. Studies suggest PYK2/CAKbeta may be important for coupling various G protein-coupled receptors to the mitogen-activated protein kinase (MAPK) cascade. The hormone neurotransmitter cholecystokinin (CCK) is known to activate both phospholipase C-dependent cascades and MAPK signaling pathways; however, the relationship between these remain unclear. In rat pancreatic acini, CCK-8 (10 nM) rapidly stimulated tyrosine phosphorylation and activation of PYK2/CAKbeta by both activation of high affinity and low affinity CCK(A) receptor states. Blockage of CCK-stimulated increases in protein kinase C activity or CCK-stimulated increases in [Ca(2+)](i), inhibited by 40-50% PYK2/CAKbeta but not p125(FAK) tyrosine phosphorylation. Simultaneous blockage of both phospholipase C cascades inhibited PYK2/CAKbeta tyrosine phosphorylation completely and p125(FAK) tyrosine phosphorylation by 50%. CCK-8 stimulated a rapid increase in PYK2/CAKbeta kinase activity assessed by both an in vitro kinase assay and autophosphorylation. Total PYK2/CAKbeta under basal conditions was largely localized (77 +/- 7%) in the membrane fraction, whereas total p125(FAK) was largely localized (86 +/- 3%) in the cytosolic fraction. With CCK stimulation, both p125(FAK) and PYK2/CAKbeta translocated to the plasma membrane. Moreover CCK stimulation causes a rapid formation of both PYK2/CAKbeta-Grb2 and PYK2/CAKbeta-Crk complexes. These results demonstrate that PYK2/CAKbeta and p125(FAK) are regulated differently by CCK(A) receptor stimulation and that PYK2/CAKbeta is probably an important mediator of downstream signals by CCK-8, especially in its ability to activate the MAPK signaling pathway, which possibly mediates CCK growth effects in normal and neoplastic tissues.

Adaptor Proteins, Signal Transducing↗
PubMed1999

Surgery to cure the Zollinger-Ellison syndrome.

BACKGROUND AND METHODS: The role of surgery in patients with the Zollinger-Ellison syndrome is controversial. To determine the efficacy of surgery in patients with this syndrome, we followed 151 consecutive patients who underwent laparotomy between 1981 and 1998. Of these patients, 123 had sporadic gastrinomas and 28 had multiple endocrine neoplasia type 1 with an imaged tumor of at least 3 cm in diameter. Tumor-localization studies and functional localization studies were performed routinely. All patients underwent surgery according to a similar operative protocol, and all patients who had surgery after 1986 underwent duodenotomy. RESULTS: The 151 patients underwent 180 exploratory operations. The mean (+/-SD) follow-up after the first operation was 8+/-4 years. Gastrinomas were found in 141 of the patients (93 percent), including all of the last 81 patients to undergo surgery. The tumors were located in the duodenum in 74 patients (49 percent) and in the pancreas in 36 patients (24 percent); however, primary tumors were found in lymph nodes in 17 patients (11 percent) and in another location in 13 patients (9 percent). The primary location was unknown in 24 patients (16 percent). Among the patients with sporadic gastrinomas, 34 percent were free of disease at 10 years, as compared with none of the patients with multiple endocrine neoplasia type 1. The overall 10-year survival rate was 94 percent. CONCLUSIONS: All patients with the Zollinger-Ellison syndrome who do not have multiple endocrine neoplasia type 1 or metastatic disease should be offered surgical exploration for possible cure.

Adult↗
PubMed1999

An aspartate residue at the extracellular boundary of TMII and an arginine residue in TMVII of the gastrin-releasing peptide receptor interact to facilitate heterotrimeric G protein coupling.

The mammalian bombesin receptor subfamily of G protein-coupled receptors currently consists of the gastrin-releasing peptide receptor (GRP-R), neuromedin B receptor, and bombesin receptor subtype 3. All three receptors contain a conserved aspartate residue (D98) at the extracellular boundary of transmembrane domain II and a conserved arginine residue (R309) near the extracellular boundary of transmembrane domain VII. To evaluate the functional role of these residues, site-directed GRP-R mutants were expressed in fibroblasts and assayed for their ability to both bind agonist and catalyze exchange of guanine nucleotides. Alanine substitution at GRP-R position 98 or 309 reduced agonist binding affinity by 24- and 56-fold, respectively, compared to wild-type GRP-R. Single swap GRP-R mutations either resulted in no receptor expression in the membrane (D98R) or the protein was not able to bind agonist (R309D). In contrast, the double swap mutation (D98R/R309D) had high-affinity agonist binding, reduced from wild-type GRP-R by only 6-fold. In situ reconstitution of urea-extracted membranes expressing either wild-type or mutant (D98A or R309A) GRP-R with G(q) indicated that alanine substitution greatly reduced G protein catalytic exchange compared to wild-type GRP-R. The D98R/R309D GRP-R had both a higher intrinsic basal activity and a higher overall catalytic exchange activity compared to wild-type; however, the wild-type GRP-R produced a larger agonist-stimulated response relative to the double swap mutant. Taken together, these data show that GRP-R residues D98 and R309 are critical for efficient coupling of GRP-R to G(q). Furthermore, our findings are consistent with a salt bridge interaction between these two polar and oppositely charged amino acids that maintains the proper receptor conformation necessary to interact with G proteins.

3T3 Cells↗
PubMed1999

Pharmacology and cell biology of the bombesin receptor subtype 4 (BB4-R).

Recently, a fourth member of the bombesin (Bn) receptor family (fBB4-R) was isolated from a cDNA library from the brain of the frog, Bombina orientalis. Its pharmacology and cell biology are largely unknown, and no known natural cell lines or tissues possess sufficient numbers of fBB4-R's to allow either of these to be determined. To address these issues, we have used three different strategies. fBB4-R expression in cells widely used for other Bn receptor subtypes was unsuccessful as was expression in two frog cell lines. However, stable fBB4-R cell lines were obtained in CHO-K1 cells which were shown to faithfully demonstrate the correct pharmacology of the related Bn receptor, the GRP receptor, when expressed in these cells. [DPhe6,betaAla11,Phe13,Nle14]Bn(6-14) was found to have high affinity (Ki = 0.4 nM) for the fBB4 receptor and 125I-[DTyr6,betaala11,Phe13,Nle14]Bn(6-14) to be an excellent ligand for this receptor. The fBB4-R had a unique pharmacology for naturally occurring Bn-related agonists, with the presence of a penultimate phenylalanine being critical for high-affinity interaction. It also had a unique profile for six classes of Bn antagonists. The fBB4-R was coupled to phospholipase C with activation increasing [3H]inositol phosphates and mobilizing Ca2+ almost entirely from cellular sources. There was a close correlation between agonist the receptor occupation and the receptor activation. Three of the five classes of Bn receptor antagonists that interacted with higher affinity with the fBB4-R functioned as fBB4-R antagonists and two as partial agonists. fBB4-R activation stimulated increases in phospholipase D (PLD) over the same range of concentrations at which it activated phospholipase C. These results demonstrate that the fBB4 receptor has a unique pharmacology for agonists and antagonists and is coupled to phospholipase C and D. The availability of these cell lines, this novel ligand, and the identification of three classes of antagonists that can be used as lead compounds should facilitate the further investigation of the pharmacology and cell biology of the BB4 receptor.

3T3 Cells↗
PubMed1999

The bombesin receptor subtypes have distinct G protein specificities.

We used an in situ reconstitution assay to examine the receptor coupling to purified G protein alpha subunits by the bombesin receptor family, including gastrin-releasing peptide receptor (GRP-R), neuromedin B receptor (NMB-R), and bombesin receptor subtype 3 (BRS-3). Cells expressing GRP-R or NMB-R catalyzed the activation of squid retinal Galphaq and mouse Galphaq but not bovine retinal Galphat or bovine brain Galphai/o. The GRP-R- and NMB-R-catalyzed activations of Galphaq were dependent upon and enhanced by different betagamma dimers in the same rank order as follows: bovine brain betagamma > beta1gamma2 >> beta1gamma1. Despite these qualitative similarities, GRP-R and NMB-R had distinct kinetic properties in receptor-G protein coupling. GRP-R had higher affinities for bovine brain betagamma, beta1gamma1, and beta1gamma2 and squid retinal Galphaq. In addition, GRP-R showed higher catalytic activity on squid Galphaq. Like GRP-R and NMB-R, BRS-3 did not catalyze GTPgammaS binding to Galphai/o or Galphat. However, BRS-3 showed little, if any, coupling with squid Galphaq but clearly activated mouse Galphaq. GRP-R and NMB-R catalyzed GTPgammaS binding to both squid and mouse Galphaq, with GRP-R activating squid Galphaq more effectively, and NMB-R also showed slight preference for squid Galphaq. These studies reveal that the structurally similar bombesin receptor subtypes, in particular BRS-3, possess distinct coupling preferences among members of the Galphaq family.

Amino Acid Sequence↗
PubMed1999

Prospective study of the value of serum chromogranin A or serum gastrin levels in the assessment of the presence, extent, or growth of gastrinomas.

BACKGROUND: Serum chromogranin A levels (CgA) are reported by some authors to be of clinical utility for assessing the presence or absence of a pancreatic endocrine tumor and tumor extent or growth. The aim of the current study was to assess this finding and compare the results with those from serum gastrin determinations (FSG) in a large cohort of patients with gastrinomas. METHODS: In 112 consecutive patients with the Zollinger-Ellison syndrome serum CgA and FSG levels were measured and correlated with disease activity, extent of disease, and the presence of multiple endocrine neoplasia type-1 (MEN-1) or gastric carcinoid tumors. RESULTS: Serum CgA levels drawn on 2 consecutive days correlated closely (P < 0.00001) as did serum gastrin levels. Serum CgA levels correlated significantly with FSG levels (P < 0.00001). Serum CgA and FSG levels were significantly higher in patients with active disease than in disease free patients (P < 0.00001). The sensitivity for the presence of disease was higher for CgA compared with FSG (92% vs. 80%; P = 0.021). However, the specificity of CgA was 67%. Serum CgA levels were not significantly different in the four disease categories (stable extrahepatic disease, increasing extrahepatic disease, stable liver metastases, and increasing liver metastases). FSG levels were significantly lower in patients with stable extrahepatic disease compared with those with increasing extrahepatic disease. However, both tumor markers decreased significantly with a gastrinoma resection in five patients. The presence of MEN-1 or a gastric carcinoid tumor did not influence the results. CONCLUSIONS: The results of the current study showed that serum CgA and FSG levels both are sensitive tumor markers for the detection of a gastrinoma; however, CgA levels have a relatively low specificity. Neither the magnitude of the serum CgA nor gastrin level correlated with tumor growth or tumor extent and therefore cannot be used to determine these variables. However, in contrast to some other studies, the results of the current study show that changes in serum CgA or gastrin in a given patient with time are related to the tumor extent and not to gastric mucosal changes due to hypergastrinemia.

Adult↗
PubMed1999

CCKA receptor activation stimulates p130(Cas) tyrosine phosphorylation, translocation, and association with Crk in rat pancreatic acinar cells.

p130(Cas) (Crk-associated substrate), because of its structure as an adapter protein, can interact when tyrosine-phosphorylated with a large number of cellular proteins and therefore be an important modulator of downstream signals. A number of growth factors, lipids, and a few G protein-coupled receptors can stimulate p130(Cas) tyrosine phosphorylation. Recent studies show that tyrosine phosohorylation of intracellular proteins by the hormone/neurotransmitter cholecystokinin (CCK) in rat pancreatic acinar cells may be an important signaling cascade. In this study, we show in rat dispersed pancreatic acini CCK-8 rapidly stimulates tyrosine phosphorylation of p130(Cas), reaching a maximum (6.6 +/- 1. 4)-fold increase with a half-maximal effect at 0.3 nM. Activation of protein kinase C by TPA or increases in [Ca2+]i by the calcium ionophore A23187 stimulated p130(Cas) phosphorylation. Blockade of CCK increases in [Ca2+]i or PKC activity did not alter CCK-8-stimulated p130(Cas) phosphorylation; however, simultaneous blockage of both cascades caused a 50% inhibition. Partial inactivation by C. botulinum toxin of the small GTP-binding protein Rho caused a 41 +/- 12% decrease in the CCK-stimulated p130(Cas) phosphorylation. Disruption of the actin cytoskeleton with cytochalasin D, but not the microtubule network with colchicine, completely inhibited CCK-8-stimulated p130(Cas) phosphorylation. Total p130(Cas) under basal conditions was largely localized (70 +/- 2%) in the membrane fraction, and stimulation with CCK-8 induced total p130(Cas) translocation from the cytosolic fraction. CCK stimulation also caused a (5 +/- 1)-fold increase in p130(Cas) tyrosine phosphorylated in the plasma membrane. Treatment with tyrphostin B44 inhibited CCK-8-stimulated p130(Cas) phosphorylation, but it had no effect on p130(Cas) translocation. CCK-8 caused rapid formation of a p130(Cas)-Crk complex. In conclusion, our results demonstrate CCKA receptor activation causes rapid tyrosine phosphorylation of p130(Cas) through PLC-dependent and -independent mechanisms that require the participation of the small GTP-binding protein Rho and the integrity of the actin cytoskeleton, but not the microtubule network. Moreover, CCKA receptor activation causes translocation of p130(Cas) to the membrane and an increase in membrane tyrosine-phosphorylated p130(Cas). The translocation to the membrane does not require antecedent tyrosine phosphorylation. CCKA activation promotes the rapid formation of a p130(Cas)-Crk complex. These results suggest that p130(Cas) is likely an important modulator of downstream signals activated by CCK-8, possibly involved in regulating numerous cellular effects, such as effects on cell growth or cell shape.

Actin Cytoskeleton↗
PubMed1999

EGF stimulates tyrosine phosphorylation of focal adhesion kinase (p125FAK) and paxillin in rat pancreatic acini by a phospholipase C-independent process that depends on phosphatidylinositol 3-kinase, the small GTP-binding protein, p21rho, and the integrity of the actin cytoskeleton.

Epidermal growth factor (EGF) is a potent mitogen in many cell types including pancreatic cells. Recent studies show that the effects of some growth factors on growth and cell migration are mediated by tyrosine phosphorylation of the cytosolic tyrosine kinase p125 focal adhesion kinase (p125FAK) and the cytoskeletal protein, paxillin. The aim of the present study was to determine whether EGF activates this pathway in rat pancreatic acini and causes tyrosine phosphorylation of each of these proteins, and to examine the intracellular pathways involved. Treatment of pancreatic acini with EGF induced a rapid, concentration-dependent increase in p125FAK and paxillin tyrosine phosphorylation. Depletion of the intracellular calcium pool or inhibition of PKC activation had no effect on the response to EGF. However, inhibition of the phosphatidylinositol 3-kinase (PI3-kinase) or inactivation of p21rho inhibited EGF-stimulated phosphorylation of p125FAK and paxillin by more than 70%. Finally, cytochalasin D, a selective disrupter of the actin filament network, completely inhibited EGF-stimulated tyrosine phosphorylation of both proteins. All these treatments did not modify EGF receptor autophosphorylation in response to EGF. These results identify p125FAK and paxillin as components of the intracellular pathways stimulated after EGF receptor occupation in rat pancreatic acini. Activation of this cascade requires activation of PI3-kinase and participation of p21rho, but not PKC activation and calcium mobilization.

Actins↗
PubMed1999

Surgical resection of intracardiac gastrinoma.

There has been only one previous report of an intracardiac gastrinoma causing Zollinger-Ellison syndrome. In this communication we describe the successful surgical resection of a gastrinoma located in the interventricular septum using cardiopulmonary bypass, blood cardioplegia, and mild hypothermia. Preoperative evaluation and histologic examination of the resected tumor strongly suggest that this was a primary intracardiac gastrinoma.

Cardiopulmonary Bypass↗