Expression of peptide YY in all four islet cell types in the developing mouse pancreas suggests a common peptide YY-producing progenitor

Rat endocrine pancreatic development in relation to two homeobox gene products (Pdx-1 and Nkx 6.1)

We studied the distribution of the homeodomain proteins Pdx-1 and Nkx 6.1 in the developing rat pancreas. During early development, nuclear staining for both Pdx-1 and Nkx 6.1 occurred in most epithelial cells of the pancreatic anlage. Subsequently, Nkx 6.1 became more beta-cell-restricted, and Pdx-1 also occurred in other islet cell types and in the duodenal epithelium. During early pancreatic development, cells co-storing insulin and glucagon were regularly detected. The vast majority of these did not possess nuclear staining for either Pdx-1 or Nkx 6.1. Subsequently, cells storing insulin only appeared. Such cells displayed strongly Pdx-1- and Nkx 6.1-positive nuclei. Therefore, Nkx 6.1, like Pdx-1, may be an important factor in pancreatic development and in mature insulin cell function.

Two transgenic approaches to define the cell lineages in endocrine pancreas development

Ontogenic relationships between the different endocrine cell types of the islets of Langerhans were explored by generating transgenic mice, in which cells transcribing the glucagon, insulin, or pancreatic polypeptide genes were destroyed through the promoter-targeted expression of the diphtheria toxin A chain. In an alternate approach, to assess whether insulin cells are derived from precursors producing glucagon or PP, transgenic mice were generated bearing an insulin promoter-driven, and loxP-containing ('floxed') reporter transgene that can be irreversibly 'tagged' by recombination. They were crossed with mice expressing another transgene ('tagger') encoding Cre (cyclization recombination) recombinase in either glucagon or PP cells. The results obtained using both approaches indicate that neither glucagon nor insulin gene-expressing cells are the precursors to the other islet cells; also, they suggest that PP gene-expressing cells are necessary for the differentiation of islet insulin and somatostatin cells, through a cell lineage or a paracrine relationship.

Sorbin in the porcine gastrointestinal tract and pancreas: an immunocytochemical analysis

Sorbin is a 153-amino acid peptide that was initially discovered in the porcine duodenum. We have reported previously that this peptide regulates intestinal electrolyte transport and have described accumulation sites in the rat digestive tract. In the present study, we investigated the anatomical distribution and the site(s) of sorbin production in the porcine digestive tract using immunocytochemistry. The use of polyclonal antisera, which by cross-reaction studies were shown to be specific for different regions of the molecule, revealed a diversified distribution. Sorbin predominated in endocrine cells preferentially localized in the pyloric glands, duodenal crypts of Lieberkühn, and pancreatic islets; in the gastrointestinal tract, sorbin coexisted with Met-enkephalin or with substance P in a small fraction of serotonin-storing [enterochromaffin (ED)] cells, i.e. EC2 cells and EC1 cells, respectively; in the pancreas, sorbin coexisted with insulin in the beta-cells, also considered as serotonin-storing cells in the pig, and with EC cells in the exocrine pancreas. An enteric neuronal system containing sorbin was also reported. Our results demonstrate that sorbin is a component of the serotonin-storing cell type in the porcine gastrointestinal tract and pancreas, and suggest potential directions to investigate the functions of this new regulatory peptide.

Development of embryonic chick insulin cells in culture: beneficial effects of serum-free medium, raised nutrients, and biomatrix

A previous finding that insulin cells do not survive or differentiate in explants of embryonic avian pancreas cultured in collagen gel with a serum-containing medium has provided a model system for identification of conditions favorable for development of these cells. To this end, we here modify the substrate and the medium. The epithelial component of dorsal pancreatic buds of 5-d chick embryos was cultured for 7 d on Matrigel in serum-containing and in serum-free medium, the latter incorporating insulin, transferrin, and selenium. Endocrine cell types were distinguished by immunocytochemistry; insulin cell counts were expressed as a proportion of insulin plus glucagon cells. With serum-containing medium, Matrigel stimulated a significant increase in this proportion as compared with collagen gel--3.1% as against 0.2%; the serum-free medium further increased this proportion to 17.3%. Raising the level of essential amino acids approximately fivefold increased the latter figure somewhat (to 18.9%), but it was more than doubled (to 37.4%) by raising the glucose concentration from 10 mM to 20 mM. Raising the levels of amino acids and glucose simultaneously yielded a lesser increase (to 31.8%). Some cultures grown in collagen gel and serum-containing medium for 7 d were transferred to Matrigel and serum-free medium for a further 7 d. Insulin cell development recovered, indicating that progenitor cells had survived and were stimulated to develop by the improved conditions. This study indicates that components of the biomatrix and the medium (in particular, a raised glucose concentration) are important for the survival and differentiation of embryonic insulin cells.

Cloning and characterization of a novel neuropeptide Y receptor subtype in the zebrafish

Neuropeptide Y (NPY), peptide YY (PYY), and pancreatic polypeptide (PP) form a family of structurally related peptides. As we have previously isolated clones for NPY and PYY from the zebrafish (Danio rerio), we wished to clone the receptors for these peptides to allow correlation of ligand and receptor distribution. We describe here the cloning and functional expression of a receptor with equally high identity to the NPY-Y1 receptor as to the recently cloned Y4/PP1 and Y6 receptors with an overall amino acid sequence identity of approximately 50%. Furthermore, the zebrafish receptor gene lacks the intron present in the coding region in vertebrate Y1 genes. These features strongly suggest that the zebrafish receptor represents a separate subtype. Hence, we have named it zYb for zebrafish Y-receptor b. (We have also discovered a unique receptor called zYa.) The zYb receptor has a binding profile that is reminiscent of Y1 with affinities for NPY and PYY in the low picomolar range, whereas affinities for Y2-selective ligands are considerably lower. It couples to adenylyl cyclase by inhibiting cAMP synthesis. Receptor mRNA was detected by reverse transcription polymerase chain reaction (RT-PCR) in brain, eye, and intestine. The binding profile and amino acid identity show that the zebrafish zYb receptor is related to Y1 but represents a distinct subtype that is likely to be present also in mammals.

Diabetes, defective pancreatic morphogenesis, and abnormal enteroendocrine differentiation in BETA2/neuroD-deficient mice

Candidate transcription factors involved in pancreatic endocrine development have been isolated using insulin gene regulation as a paradigm. The cell-type restricted basic helix-loop-helix (bHLH) gene, BETA2/NeuroD, expressed in pancreatic endocrine cells, the intestine, and the brain, activates insulin gene transcription and can induce neurons to differentiate. To understand the importance of BETA2 in pancreatic endocrine cell differentiation, mice lacking a functional BETA2 gene were generated by gene targeting experiments. Mice carrying a targeted disruption of the BETA2 gene developed severe diabetes and died perinatally. Homozygous BETA2 null mice had a striking reduction in the number of insulin-producing beta cells and failed to develop mature islets. Islet morphogenesis appeared to be arrested between E14.5 and E17.5, a period characterized by major expansion of the beta cell population. The presence of severe diabetes in these mice suggests that proper islet structure plays an important role in blood glucose homeostasis. In addition, secretin- and cholecystokinin-producing enteroendocrine cells failed to develop in the absence of BETA2. The absence of these two pancreatic secretagogs may explain the abnormal cellular polarity and inability to secrete zymogen granules in pancreatic acinar exocrine cells. The nervous system appeared to develop normally, despite abundant expression of BETA2 in differentiating neurons. Thus, BETA2 is critical for the normal development of several specialized cell types arising from the gut endoderm.

Growth-promoting interaction of IGF-II with the insulin receptor during mouse embryonic development

Genetic analyses of dwarfing phenotypes resulting from targeted mutagenesis of the genes encoding the insulin-like growth factors (IGF-I and IGF-II) and their cognate type 1 IGF receptor (IGF1R) have demonstrated that this signaling system is a major determinant of mouse embryonic growth. Of the two IGF ligands, IGF-I interacts exclusively with IGF1R, whereas IGF-II recognizes an additional receptor (XR), because the growth retardation of embryos lacking both IGR1R and IGF-II (30% of normal birthweight) is more severe than that manifested in either class of single Igf1r or Igf2 null mutants (45 and 60% of normal, respectively). To determine whether XR is the insulin receptor (IR), we examined embryos nullizygous for both Igf1r and Insr. While the growth of embryos lacking solely IR is affected very mildly and only at the end of gestation, concomitant absence of IGF1R results in a severe growth-deficiency phenotype (30% of normal size at birth) that is first detected at Embryonic Day 13.5 and is also characterized by transient edema, curly tail, generalized organ hypoplasia, including the muscles, developmental delays in ossification, and thin epidermis. The Igf1r/Insr double nullizygotes are phenotypically indistinguishable from double mutants lacking IGF1R and IGF-II and from other double and triple mutants in which all of the IGF ligand/receptor interactions have been eliminated. Therefore, these results provide genetic evidence that the growth-promoting function of IGF-II during mouse embryogenesis is mediated in part by signaling through the insulin receptor.

The neuropeptide Y (Y4) receptor is highly expressed in neurones of the rat dorsal vagal complex

Recently, the cDNA encoding the Y4 neuropeptide Y (NPY) receptor cDNA was cloned from a rat genomic library. The Y4 receptor is characterized by having a high affinity for pancreatic polypeptide (PP) and peptide YY (PYY). By using in situ hybridization histochemistry with 35S-labelled riboprobes, we have visualized the cellular expression of mRNA encoding the Y4 receptor protein in the rat dorsal vagal complex at the light microscopical level. High densities of silver grains were observed over neurones of the dorsal vagal motor nucleus, and over neurones of a subregion of the nucleus of the solitary tract known as the subnucleus gelatinosus. Furthermore, cells within the ventral margin of the area postrema expressed high levels of Y4 mRNA. These observations indicate that circulating PP and/or NPY/PYY via the blood-brain barrier-free area postrema and subpostremal area could influence neurones of the dorsal vagal complex with profound influence on numerous homeostatic mechanisms governed by this nuclear complex.

The basic helix-loop-helix transcription factor BETA2/NeuroD is expressed in mammalian enteroendocrine cells and activates secretin gene expression

The gene encoding the hormone secretin is expressed only in enteroendocrine S cells and insulin-producing pancreatic beta cells during development. A 120-bp enhancer directs cell-specific expression of the rat secretin gene in secretin-expressing cells. The enhancer includes an E-box sequence, CAGCTG, which is important for transcriptional activity. To further characterize the role of the E box, a consensus binding site for basic helix-loop-helix (bHLH) proteins, we have examined factors that interact with this element in the secretin gene. The results suggest that transcription is activated by a recently isolated tissue-specific bHLH protein, BETA2, heterodimerized to the ubiquitously expressed bHLH proteins, Pan 1 and Pan 2, the rodent homologues of E47 and E12. The importance of BETA2 for transcriptional activation of secretin is further illustrated by antisense experiments inhibiting BETA2 expression in secretin-producing cell lines, which resulted in the inhibition of most E box-dependent transcription. Expression of BETA2 in a nonendocrine cell line conferred the ability to express secretin-reporter genes that are transcribed at minimal levels in the absence of BETA2. Secretin-producing enteroendocrine cells in the murine small intestine showed specific immunostaining with BETA2 antibodies, corroborating observations in cell lines. Thus BETA2 is to our knowledge the first transcription factor identified that specifically activates cell type-specific expression of an intestinal hormone gene.

Apoptosis participates in the remodeling of the endocrine pancreas in the neonatal rat

In rodents, shortly after birth a lack of increase in pancreatic weight and in islet mass have been reported during a time of overall body weight increase. To understand this regulation of the neonatal growth of the beta cell mass, we studied Sprague Dawley rats at 2, 9, 13, 17, 20, 24, and 31 days of age for beta cell replication, beta cell mass, and cell size and for the presence of cell apoptosis. beta cell mass was stable from 2-20 days (range: 0.91 +/- 0.2 to 1.33 +/- 0.23 mg) and increased thereafter. beta cell replication progressively decreased. Condensed apoptotic nuclei were identified and counted on paraffin sections using the fluorescent dye propidium iodide. Apoptotic beta cell nuclei were found at a basal rate (1.54 +/- 0.22%) at 2, 9, and again after 20 days of age. However, at 13 and 17 days, the incidence of apoptosis was significantly increased (3.64 +/- 0.45%). The decreased replication and the increased incidence of apoptosis in the beta cells strongly suggest a wave of neogenesis of beta cells to maintain the constant beta cell mass. These data show that the endocrine pancreas undergoes significant modification during neonatal life and that apoptosis is an important mechanism in this remodeling of the beta cell mass. Whether a selective deletion of some population of beta cells occurs is unclear, but a dysregulation of this remodeling process could have important effects on the pancreatic beta cell mass.

Developmental expression of NPY, PYY and PP in the rat pancreas and their coexistence with islet hormones

It has been suggested that members of the neuropeptide Y (NPY) family of regulatory peptides [NPY, peptide YY (PYY) and pancreatic polypeptide (PP)] play an important role in the development of the endocrine pancreas. The development of rat endocrine pancreas from embryonic (E) day 12 until 30 days postpartum (P) was studied with emphasis on NPY, PYY and PP and their co-existence with insulin, glucagon and somatostatin using single and double immunostaining and in situ hybridization. Already at E12, PYY was detectable in small endocrine cell clusters and found to be co-localised with both insulin and glucagon, which at this stage occurred in the same cells. At E16 most of the insulin-immunoreactive (IR) cells were distinct from the glucagon/PYY-IR cells. Interestingly, at E16 NPY mRNA, and at E17 NPY immunoreactivity appeared in a few, scattered endocrine cells. Virtually all NPY-IR endocrine cells were insulin-producing beta cells. At E18 the endocrine cells started to form typical islets with centrally located insulin/NPY-IR cells surrounded by glucagon/PYY-IR cells. AT E20-E21, the vast majority of insulin-producing cells also expressed NPY. However, at birth (day 0) islet cell NPY mRNA was lacking. Postnatally the number and immunostaining intensity of NPY-IR islet cells rapidly declined, being non-detectable at P5. Cells containing PP immunoreactivity and PP mRNA were first detected at E21. The adult pattern of islet peptide distribution, with NPY confined to neuronal elements. PYY and PP exclusively in endocrine cells, was established at P5. The beta cell expression of NPY during the latter part of embryogenesis coincides with the prepartal glucocorticoid surge and with rapid islet cell replication and differentiation. This is compatible with steroid induction of NPY expression and with a role for NPY in the maturation of beta cells and their hormone release, which occurs in the immediate neonatal period.

Independent requirement for ISL1 in formation of pancreatic mesenchyme and islet cells

The mammalian pancreas is a specialized derivative of the primitive gut endoderm and controls many homeostatic functions through the activity of its component exocrine acinar and endocrine islet cells. The LIM homeodomain protein ISL1 is expressed in all classes of islet cells in the adult and its expression in the embryo is initiated soon after the islet cells have left the cell cycle. ISL1 is also expressed in mesenchymal cells that surround the dorsal but not ventral evagination of the gut endoderm, which together comprise the pancreatic anlagen. To define the role of ISL1 in the development of the pancreas, we have now analysed acinar and islet cell differentiation in mice deficient in ISL1 function. Dorsal pancreatic mesenchyme does not form in ISL1-mutant embryos and there is an associated failure of exocrine cell differentiation in the dorsal but not the ventral pancreas. There is also a complete loss of differentiated islet cells. Exocrine, but not endocrine, cell differentiation in the dorsal pancreas can be rescued in vitro by provision of mesenchyme derived from wild-type embryos. These results indicate that ISL1, by virtue of its requirement for the formation of dorsal mesenchyme, is necessary for the development of the dorsal exocrine pancreas, and also that ISL1 function in pancreatic endodermal cells is required for the generation of all endocrine islet cells.

Pancreatic development and maturation of the islet B cell. Studies of pluripotent islet cultures

Pancreas organogenesis is a highly regulated process, in which two anlage evaginate from the primitive gut. They later fuse, and, under the influence of the surrounding mesenchyme, the mature organ develops, being mainly composed of ductal, exocrine and endocrine compartments. Early buds are characterized by a branching morphogenesis of the ductal epithelium from which endocrine and exocrine precursor cells bud to eventually form the two other compartments. The three compartments are thought to be of common endodermal origin; in contrast to earlier hypotheses, which suggested that the endocrine compartment was of neuroectodermal origin. It is thus generally believed that the pancreatic endocrine-lineage possesses the ability to mature along a differentiation pathway that shares many characteristics with those of neuronal differentiation. During recent years, studies of insulin-gene regulation and, in particular, the tissue-specific transcriptional control of insulin-gene activity have provided information on pancreas development in general. The present review summarizes these findings, with a special focus on our own studies on pluripotent endocrine cultures of rat pancreas.

Molecular characterization of a second mouse pancreatic polypeptide receptor and its inactivated human homologue

The family of mammalian neuropeptide Y (NPY)/peptide YY (PYY)/pancreatic polypeptide (PP) receptors comprises several G protein-coupled receptors, i.e. Y1, Y2, and Y4/PP1. We now report cloning of a novel member of this family named PP2. The coding region of the mouse PP2 gene reveals no introns and predicts a seven transmembrane domain (TM) receptor of 371 amino acids. Percent identities of the mouse PP2 to mouse Y1, mouse Y4/PP1 and human Y2 receptors are 53, 42, and 31, respectively. The mouse PP2 receptor expressed in COS cells binds rat 125I-PP with high affinity, i.e. IC50 = 65 pM. Pharmacological characterization of 125I-PP binding shows a rank order of potency of PP >> PYY >/= NPY, which is similar to that of the mouse Y4/PP1 receptor. Mouse PP2 transcripts were not detectable by Northern analysis in adult tissues and in 11-, 15-, and 17-day-old embryos. However, a 9.8-kb PP2 transcript was detectable in 7-day-old mouse embryo, i.e. prior to the organogenesis of pancreas and the onset of PP production. We have also cloned the human homologue of PP2, which is a single copy gene and maps to human chromosome 5q31. Surprisingly, the human PP2 cDNAs and gene sequences display a single base deletion in the coding region. This frameshifting mutation predicts a truncated receptor of 290 amino acids without TM7. Transfection of COS-7 cells with several different human PP2 expression constructs failed to confirm any specific binding of 125I-PP, 125I-PYY, or 125I-NPY to cell membranes. These data suggest that in mouse there are at least two PP receptors, Y4/PP1 and PP2, whereas in humans, PP2 is either functionally inactive or it has acquired a PP-independent function.

mRNA profiling of rat islet tumors reveals nkx 6.1 as a beta-cell-specific homeodomain transcription factor

Development of a high capacity multiplex reverse transcriptase-polymerase chain reaction protocol has allowed us to screen lineage related rat islet tumors classified as alpha-, beta-, and delta-like as judged by their hormone profile for differential expression of more than 50 selected genes. We find that in addition to insulin the insulinoma express the normal beta-cell markers Pdx-1, IAPP, and Glut-2, and that these markers are absent from the glucagonoma: a reflection of the normal alpha-cell. Furthermore, this study suggests that the GLP-1, glucagon, GIP, IGF-1, and insulin receptors as well as E-cadherin, R-cadherin, Id-1, and Id-2 are differentially expressed within the islet of Langerhans. Importantly, insulinoma-specific expression of the recently cloned homeodomain protein Nkx 6.1 predicted beta-cell-specific expression in the normal islet. Immunohistochemistry using antibodies raised against recombinant Nkx 6.1 did indeed localize Nkx 6.1 expression exclusively to the nuclei of normal islet beta-cells. Apart from pancreatic islets only the antral part of the stomach contained Nkx 6.1 mRNA. We conclude that multiplex reverse transcriptase-polymerase chain reaction-based mRNA profiling is a powerful tool to identify differentially expressed genes within phenotypically related cells and propose that Nkx 6.1 is involved in specifying the unique characteristics of the beta-cell.

Immunogold labelling of neuroendocrine peptides with special reference to antibody specificity and multiple staining techniques

Immunogold methods have been very important for research on the neuroendocrine system. The compatibility of immunogold probes with optimal contrasting for electron microscopy has made localizations of neuroendocrine peptides to different subtypes of secretory organelles possible and, currently, methods using covalent attachment of nanogold particles to antibodies and neuropeptide ligands hold promise for immunocytochemistry, receptor localizations and in situ hybridizations. Multihormonal phenotypes are a hallmark of both the developing and mature neuroendocrine system. The possibility to localize multiple coexisting messengers by multilabelling immunogold methods is emphasized, and different methods for achieving this are discussed. The most difficult part of immunocytochemistry involves definitions and interpretations of specificity, and a number of limitations and control procedures are discussed.

Proglucagon processing in islet and intestinal cell lines

To investigate the factors involved in the post-translational processing of proglucagon, we have examined the proglucagon-derived peptides (PGDPs) expressed in normal mouse pancreas and intestine, as well as in both islet (InR1-G9, RIN 1056A) and intestinal (STC-1) cell lines. N-terminal proglucagon processing was similar to that of normal mouse pancreas in InR1-G9 cells, but differed in RIN 1056A and STC-1 cells, which contained significant amounts of glucagon as well as the intestinal PGDPs, glicentin and oxyntomodulin. The C-terminal end of proglucagon was processed to small amounts of glucagon-like peptide-1 in InR1-G9 and RIN 1056A cells, as in normal pancreas, while processing was more extensive in both STC-1 cells and normal intestine. Northern blot analysis of mRNA transcripts for the prohormone convertases, PC1 and PC2, in the 3 cell lines demonstrated correlations between PC2 and the presence of glucagon, as well as between PC1 and production of the intestinal PGDPs. These findings provide support for the suggestion that PC1 and PC2 play roles in the tissue-specific post-translational processing of proglucagon.

Evolution of neuropeptide Y, peptide YY and pancreatic polypeptide

The neuropeptide Y family of peptides consists of neuropeptide Y (NPY), which is expressed in the central and peripheral nervous systems, and peptide YY (PYY) and pancreatic polypeptide (PP) which are gut endocrine peptides. All three peptides are 36 amino acids long and act on G-protein-coupled receptors. NPY and PYY are present in all vertebrates, whereas PP probably arose as a copy of PYY in an early tetrapod ancestor. NPY is one of the most conserved peptides during evolution and no gnathostome (jawed) species differs from the ancestral gnathostome sequence at more than five positions. PYY is more variable, particularly in mammals which have nine differences to the gnathostome ancestor. PP may be the most rapidly evolving neuroendocrine peptide among tetrapods with only 50% identity between mammals, birds, and amphibians. Ancestral gnathostome NPY and PYY seem to have differed at only four positions, suggesting that the gene duplication occurred shortly before the appearance of the gnathostomes. The two peptides differ from one another at 9-12 positions in tetrapod species and share at least two receptor subtypes in mammals. In bony and cartilaginous fishes, NPY and PYY have only 5-6 differences which, together with more extensive neuronal localization of PYY, indicate an even greater functional overlap between the two peptides in these animal groups. The emergence of sequence information for several receptor subtypes from various species will shed additional light on the evolution of the functions of the NPY-family peptides.

Peptide YY expression is an early event in colonic endocrine cell differentiation: evidence from normal and transgenic mice

The hormone peptide YY is produced by endocrine cells in the pancreas, ileum and colon. We have previously shown that peptide YY is coexpressed in all four islet cell types in the murine pancreas when they first appear, suggesting a common peptide YY-producing progenitor. In the colon, peptide YY has been frequently identified in glucagon-expressing L-type endocrine cells. Characterization of colonic endocrine tumors in transgenic mice expressing simian virus 40 large T antigen under the control of the peptide YY gene 5′ flanking region revealed tumor cells producing not only peptide YY and glucagon, but also neurotensin, cholecystokinin, substance P, serotonin, secretin, and gastrin. This suggested that multiple enteroendocrine lineages were related to peptide YY-producing cells. Subsequent examination of the ontogeny of colonic endocrine differentiation in nontransgenic mice revealed that peptide YY was the first hormone to appear during development, at embryonic day 15.5. Between embryonic days 16.5 and 18.5, cells expressing glucagon, cholecystokinin, substance P, serotonin, secretin, neurotensin, gastrin and somatostatin first appeared and peptide YY was coexpressed in each cell type at this time. Peptide YY coexpression continued in a significant fraction of most enteroendocrine cell types throughout fetal and postnatal development and into adulthood, with the exception of serotonin-producing cells. This latter population of cells expanded dramatically after birth with rare coexpression of peptide YY. These studies indicate that expression of peptide YY is an early event in colonic endocrine differentiation and support the existence of a common progenitor for all endocrine cells in the colon.

Adjuvant hormonal treatment with peptide YY or its analog decreases human pancreatic carcinoma growth

BACKGROUND

Recent studies have revealed decreased pancreatic cancer cell growth upon administration of peptide YY (PYY). We examined whether adjuvant treatment with PYY or its synthetic analog, BIM-43004, would decrease human pancreatic adenocarcinoma growth.

MATERIALS AND METHODS

Human pancreatic ductal adenocarcinomas, MiaPaCa-2 and BxPC-3, were cultured and assessed for growth by MTT assay. Pancreatic cancer cells received 500 pmol of PYY or BIM-43004 for 24 hours prior to 5-fluorouracil (5-FU; 10 micrograms/mL) and leucovorin (40 micrograms/mL) administration. Cell membrane epidermal growth factor (EGF) receptors were analyzed by Western blotting after exposure to peptides and chemotherapy.

RESULTS

Cancer cell growth was reduced in all groups receiving hormonal pretreatment (23% PYY/5-FU/leucovorin versus control; 27% BIM-43004/5-FU/leucovorin versus control) as compared with groups receiving 5-FU and leucovorin only (16% versus control). The EGF receptor expression was reduced by 30% in cells treated with PYY/5-FU/leucovorin and by 45% in cells treated with BIM/5-FU/leucovorin as compared with control cells without treatment.

CONCLUSION

Human pancreatic cancer cell growth is further decreased when pretreated with PYY or its synthetic analog prior to chemotherapy.

Cloning of a human receptor of the NPY receptor family with high affinity for pancreatic polypeptide and peptide YY

Neuropeptide Y (NPY), peptide YY (PYY), and pancreatic polypeptide (PP) are structurally related peptides found in all higher vertebrates. NPY is expressed exclusively in neurons, whereas PYY and PP are produced primarily in gut endocrine cells. Several receptor subtypes have been identified pharmacologically, but only the NPY/PYY receptor of subtype Y1 has been cloned. This is a heptahelix receptor that couples to G proteins. We utilized Y1 sequence information from several species to clone a novel human receptor with 43% amino acid sequence identity to human Y1 and 53% identity in the transmembrane regions. The novel receptor displays a pharmacological profile that distinguishes it from all previously described NPY family receptors. It binds PP with an affinity (Ki) of 13.8 pM, PYY with 1.44 nM, and NPY with 9.9 nM. Because these data may identify the receptor as primarily a PP receptor, we have named it PP1. In stably transfected Chinese hamster ovary cells the PP1 receptor inhibits forskolin-stimulated cAMP synthesis. Northern hybridization detected mRNA in colon, small intestine, pancreas, and prostate. As all three peptides are present in the gut through either endocrine release or innervation, all three peptides may be physiological ligands to the novel NPY family receptor PP1.

Developmental biology of the pancreas

The pancreas is an organ containing two distinct populations of cells, the exocrine cells that secrete enzymes into the digestive tract, and the endocrine cells that secrete hormones into the bloodstream. It arises from the endoderm as a dorsal and a ventral bud which fuse together to form the single organ. Mammals, birds, reptiles and amphibians have a pancreas with similar histology and mode of development, while in some fish, the islet cells are segregated as Brockmann bodies. Invertebrates do not have a pancreas, but comparable endocrine cells may be found in the gut or the brain. The early pancreatic bud shows uniform expression of the homeobox gene IPF-1 (also known as IDX-1, STF-1 or PDX), which when mutated to inactivity leads to total absence of the organ. The occurrence of heterotopic pancreas in the embryo, and also the metaplasias that can be displayed by a regenerating pancreas in the adult, both suggest that only a few gene products distinguish the pancreatic cell state from that of the surrounding tissues of duodenum, gall bladder and liver. In the developing pancreatic buds, the endocrine cells start to differentiate before the exocrine cells, and co-expression of different hormones by the same cell is often observed at early stages. Although pancreatic endocrine cells produce many gene products also characteristic of neurons, evidence from in vitro cultures and from quailchick grafts shows that they are of endogenous and not of neural crest origin. Observational studies suggest strongly that both endocrine and exocrine cells arise from the same endodermal rudiment. Development of the pancreas in embryonic life requires a trophic stimulus from the associated mesenchyme. In postnatal life, all cell types in the pancreas continue to grow. Destruction of acinar tissue by duct ligation or ethionine treatment is followed by rapid regeneration. Surgical removal of parts of the pancreas is followed by moderate but incomplete regeneration of both acini and islets. Poisoning with alloxan or streptozotocin can lead to permanent depletion of beta cells. Although the cell kinetics of the pancreas are not understood, it seems likely that there is a continuous slow turnover of cells, fed from a stem cells population in the ducts, and that the controls on the production rate of each cell type are local rather than systemic.

Studies in transgenic mice reveal potential relationships between secretin-producing cells and other endocrine cell types

We have produced transgenic mice expressing fusion genes consisting of 1.6 kilobase pairs of the secretin gene 5' flanking region to direct the expression of human growth hormone (hGH) or simian virus 40 large T antigen to secretin-producing cells. Analysis of different mouse tissues for hGH transcripts revealed expression in each of the major secretin-producing tissues, namely the intestine and endocrine pancrease. Multiple label immunohistochemistry demonstrated that the transgene was correctly directed to secretin cells in the intestinal tract, including a previously unrecognized population of secretin cells in the colon of adult and developing mice. In the small intestine, subpopulations of hGH-containing cells frequently coexpressed substance P, serotonin, and cholecystokinin, whereas in the colon, cells expressing hGH frequently coexpressed glucagon, peptide YY, or neurotensin. Transgenic mice expressing large T antigen in secretin cells developed poorly differentiated neuroendocrine tumors of the small intestine, well differentiated colonic tumors containing glucagon-expressing cells, and insulin-producing tumors in pancreas. These studies indicate that the major cis-regulatory sequences necessary for secretin expression in enteroendocrine cells and fetal islets are localized with 1.6 kilobase pairs of the transcriptional start site. Coexpression of reporter transgenes with several gastrointestinal hormones suggests a potential relationships between secretin cells and other enteroendocrine cell types, as well as pancreatic beta cells.

Immunolocalization of neuropeptide Y in human pancreatic endocrine tumors

Neuropeptide Y (NPY) is a 36 amino acid peptide known to inhibit glucose-stimulated insulin secretion. NPY has recently been shown to be synthetized within rat islets of Langerhans and to be secreted in a differentiated rat insulin-secreting cell line, and as to this date the localization of NPY in human endocrine pancreas has not been reported. As NPY shares high amino acid sequence homology with peptide YY (PYY) and pancreatic polypeptide (PP), the polyclonal antibodies raised against these peptides often cross-react with each other. To demonstrate the presence of NPY in the human endocrine pancreas, we used a highly specific monoclonal antibody raised against NPY and another against its C-flanking peptide (CPON). We studied three cases of hyperplasia of Langerhans islets and 11 cases of endocrine tumors of the pancreas. NPY and CPON were detected in all three cases of hyperplasia. For the 11 pancreatic tumors, five and nine of the tumors were positive for the antibodies NPY and CPON, respectively. The two negative tumors for CPON immunoreactivity were differentiated insulinomas, which showed no evidence of other hormonal secretion. In normal Langerhans islet, NPY and CPON immunoreactivities were colocalized in glucagon-producing cells (alpha-cells) and in a few insulin-secreting cell (beta-cells).(ABSTRACT TRUNCATED AT 250 WORDS)

TGF-beta 1 influences the relative development of the exocrine and endocrine pancreas in vitro

Pancreatic rudiments from E12.5 mouse embryos undergo extensive development and differentiation when cultured in three-dimensional gels of extracellular matrix proteins for up to 12 days. Whereas collagen gels promote the formation of numerous exocrine acini and relatively small clusters of endocrine cells, in basement membrane (EHS) matrices the development of endocrine cells is dramatically favoured over that of acinar tissue. Buds embedded in a collagen gel contiguous to an EHS gel also fail to develop acini, suggesting the involvement of diffusible factor(s). Addition of cytokines to cultures of pancreatic buds in collagen gels modifies the relative proportions of the epithelial components of the gland. In the presence of EGF the proportion of the tissue occupied by ducts overrides that of acinar structures, whereas the endocrine portion of the tissue is not significantly modified. TGF-beta 1 partially mimicks the effect of EHS matrix in inhibiting the development of acinar tissue without decreasing the amount of ducts and mesenchyme; TGF-beta 1 also promotes the development of endocrine cells, in particular of insulin-containing beta cells and of cells expressing genes of the PP-fold family. These results show that cytokines can modulate the development of the pancreas and suggest a role for TGF-beta 1 in regulating the balance between the acinar and endocrine portions of the gland in vivo. More generally, they are compatible with the notion that, during organogenesis, cytokines act as paracrine factors responsible for the development and maintenance of appropriate proportions of different tissue constituents.

Islet cell growth and the growth factors involved

Throughout development, growth and aging, the mass of the pancreatic islets, in particular the insulin producing beta cell, increases to meet the functional demand and maintain euglycemia. Islet growth occurs by two pathways: (a) the expansion by replication of preexisting beta cells and (b) the formation of new islets (neogenesis) by proliferation and subsequent differentiation of pancreatic ductal epithelium. Some of the factors involved in these pathways of islet growth have been defined.