Control of CCK gene transcription by PACAP in STC-1 cells

Cholecystokinin-From Local Gut Hormone to Ubiquitous Messenger

Cholecystokinin (CCK) was discovered in 1928 in jejunal extracts as a gallbladder contraction factor. It was later shown to be member of a peptide family, which are all ligands for the CCK₁ and CCK₂ receptors. CCK peptides are known to be synthetized in small intestinal endocrine I-cells and cerebral neurons. But in addition, CCK is expressed in several endocrine glands (pituitary cells, thyroid C-cells, pancreatic islets, the adrenals, and the testes); in peripheral nerves; in cortical and medullary kidney cells; in cardial myocytes; and in cells of the immune system. CCK peptides stimulate pancreatic enzyme secretion and growth, gallbladder contraction, and gut motility, satiety and inhibit acid secretion from the stomach. Moreover, they are major neurotransmitters in the brain and the periphery. CCK peptides also stimulate calcitonin, insulin, and glucagon secretion, and they may act as natriuretic peptides in the kidneys. CCK peptides are derived from proCCK with a C-terminal bioactive YMGWMDFamide sequence, in which the Y-residue is partly O-sulfated. The plasma forms are CCK-58, -33, -22, and -8, whereas the small CCK-8 and -5 are potent neurotransmitters. Over the last decades, CCK expression has also been encountered in tumors (neuroendocrine tumors, cerebral astrocytomas, gliomas, acoustic neuromas, and specific pediatric tumors). Recently, a metastastic islet cell tumor was found to cause a specific CCKoma syndrome, suggesting that circulating CCK may be a useful tumor marker.

Glucagon-like peptide-1 and cholecystokinin production and signaling in the pancreatic islet as an adaptive response to obesity

Precise control of blood glucose is dependent on adequate β‐cell mass and function. Thus, reductions in β‐cell mass and function lead to insufficient insulin production to meet demand, and result in diabetes. Recent evidence suggests that paracrine signaling in the islet might be important in obesity, and disruption of this signaling could play a role in the pathogenesis of diabetes. For example, we recently discovered a novel islet incretin axis where glucagon‐like peptide‐1 regulates β‐cell production of another classic gut hormone, cholecystokinin. This axis is stimulated by obesity, and plays a role in enhancing β‐cell survival. In the present review, we place our observations in the wider context of the literature on incretin regulation in the islet, and discuss the potential for therapeutic targeting of these pathways.

Pharmacology and physiology of gastrointestinal enteroendocrine cells

Gastrointestinal (GI) polypeptides are secreted from enteroendocrine cells (EECs). Recent technical advances and the identification of endogenous and synthetic ligands have enabled exploration of the pharmacology and physiology of EECs. Enteroendocrine signaling pathways stimulating hormone secretion involve multiple nutrient transporters and G protein-coupled receptors (GPCRs), which are activated simultaneously under prevailing nutrient conditions in the intestine following a meal. The majority of studies investigate hormone secretion from EECs in response to single ligands and although the mechanisms behind how individual signaling pathways generate a hormonal output have been well characterized, our understanding of how these signaling pathways converge to generate a single hormone secretory response is still in its infancy. However, a picture is beginning to emerge of how nutrients and full, partial, or allosteric GPCR ligands differentially regulate the enteroendocrine system and its interaction with the enteric and central nervous system. So far, activation of multiple pathways underlies drug discovery efforts to harness the therapeutic potential of the enteroendocrine system to mimic the phenotypic changes observed in patients who have undergone Roux-en-Y gastric surgery. Typically obese patients exhibit ∼30% weight loss and greater than 80% of obese diabetics show remission of diabetes. Targeting combinations of enteroendocrine signaling pathways that work synergistically may manifest with significant, differentiated EEC secretory efficacy. Furthermore, allosteric modulators with their increased selectivity, self-limiting activity, and structural novelty may translate into more promising enteroendocrine drugs. Together with the potential to bias enteroendocrine GPCR signaling and/or to activate multiple divergent signaling pathways highlights the considerable range of therapeutic possibilities available. Here, we review the pharmacology and physiology of the EEC system.

Glucagon-Like Peptide-1 Regulates Cholecystokinin Production in β-Cells to Protect From Apoptosis

Cholecystokinin (CCK) is a classic gut hormone that is also expressed in the pancreatic islet, where it is highly up-regulated with obesity. Loss of CCK results in increased β-cell apoptosis in obese mice. Similarly, islet α-cells produce increased amounts of another gut peptide, glucagon-like peptide 1 (GLP-1), in response to cytokine and nutrient stimulation. GLP-1 also protects β-cells from apoptosis via cAMP-mediated mechanisms. Therefore, we hypothesized that the activation of islet-derived CCK and GLP-1 may be linked. We show here that both human and mouse islets secrete active GLP-1 as a function of body mass index/obesity. Furthermore, GLP-1 can rapidly stimulate β-cell CCK production and secretion through direct targeting by the cAMP-modulated transcription factor, cAMP response element binding protein (CREB). We find that cAMP-mediated signaling is required for Cck expression, but CCK regulation by cAMP does not require stimulatory levels of glucose or insulin secretion. We also show that CREB directly targets the Cck promoter in islets from obese (Leptin(ob/ob)) mice. Finally, we demonstrate that the ability of GLP-1 to protect β-cells from cytokine-induced apoptosis is partially dependent on CCK receptor signaling. Taken together, our work suggests that in obesity, active GLP-1 produced in the islet stimulates CCK production and secretion in a paracrine manner via cAMP and CREB. This intraislet incretin loop may be one mechanism whereby GLP-1 protects β-cells from apoptosis.

DeltaFosB indirectly regulates Cck promoter activity

Some of the important biochemical, structural, and behavioral changes induced by chronic exposure to drugs of abuse appear to be mediated by the highly stable transcription factor DeltaFosB. Previous work has shown that DeltaFosB overexpression in mice for 2weeks leads to an increase in the expression of numerous genes in striatum, most of which are later downregulated following 8weeks of FosB expression. Interestingly, a large number of these genes were also upregulated in mice overexpressing the transcription factor CREB. It was unclear from this study, however, whether short-term DeltaFosB regulates these genes via CREB. Here, we find that 2weeks of DeltaFosB overexpression increases CREB expression in striatum, an effect that dissipates by 8weeks. The early induction is associated with increased CREB binding to certain target gene promoters in this brain region. Surprisingly, one gene that was a suspected CREB target based on previous reports, cholecystokinin (Cck), was not controlled by CREB in striatum. To further investigate the regulation of Cck following DeltaFosB overexpression, we confirmed that short-term DeltaFosB overexpression increases both Cck promoter activity and gene expression. It also increases binding activity at a putative CREB binding site (CRE) in the Cck promoter. However, while the CRE site is necessary for normal basal expression of Cck, it is not required for DeltaFosB induction of Cck. Taken together, these results suggest that while short-term DeltaFosB induction increases CREB expression and activity at certain gene promoters, this is not the only mechanism by which genes are upregulated under these conditions.

Peptide-YY is released by the intestinal cell line STC-1

Dietary modulation of the response of gut satiety hormones, which partly regulate food intake, provides a promising treatment for overweight and obesity. Gut-derived cell lines such as STC-1 are widely used to investigate these hormonal responses to nutrients. To date, no peptide-YY (PYY) secreting cell line has been identified. The aim of this study was to investigate whether STC-1 cells are able to secrete PYY and if so, whether dietary compounds can modulate PYY secretion. The effects of fatty acid types C4:0, C12:0, C14:0, C16:0, and C18:0 on PYY release were investigated by measuring PYY in the supernatant after 30, 60, 90, and 120 min of incubation, respectively, using RIA assays. The STC-1 cells were able to secrete PYY in a time-dependent manner. It was shown that after 30 min, C4:0, C12:0, C16:0, and C18:0 caused increased PYY levels compared to the control. At time points 60 and 90 min, C4:0 and C18:0 induced elevated PYY levels compared to the control. After 120 min, C4:0, C14:0, and C18:0 caused elevated levels compared to the control. We are the first to show that the STC-1 cells are also able to secrete PYY next to cholecystokinin (CCK) and glucagon-like peptide 1 (GLP-1). Addition of fatty acids resulted in increased levels of PYY, which is consistent with the literature describing human studies. We conclude that the STC-1 cell line provides an appropriate cell line for screening the effects of ingredients on the release of the satiety-related gut hormones CCK, GLP-1, and PYY.

Effects of active immunization against cholecystokinin 8 on performance, contents of serum hormones, and expressions of CCK gene and CCK receptor gene in pigs

This study was conducted to investigate the effects of active immunization against cholecystokinin 8 (CCK(8)) on the content of serum CCK, expression of CCK, and CCK receptor gene in pigs. The subjects for this experiment were 15 pigs divided into three groups (5 pigs per group). The treated groups were immunized with CCK(8) conjugated to human serum albumin (HSA). The control group was immunized with same dosage of HSA. The average daily gain of pig fed with 250 microg CCK was significantly increased (P < 0.05), compared with the control group (0 microg CCK). The content of CCK(8), insulin, and leptin in serum was significantly (P < 0.05) decreased and the titer of CCK(8) antibody was significantly (P < 0.05) increased in treated groups compared to the control group. The levels of CCK gene and CCK receptor gene expression in jejunum, pituitary, and pancreas of the treated groups were significantly (P < 0.05) lower than that of the control group. It is concluded that optimal active immunization against CCK(8) could increase the content of CCK antibody and suppress CCK gene and CCK receptor gene expressions and in result improve feed intake and growth performance of pigs.

Enteroendocrine cell expression of a cholecystokinin gene construct in transgenic mice and cultured cells

CCK is predominantly expressed in subsets of endocrine cells in the intestine and neurons in the brain. We evaluated the expression of a CCK gene construct in transgenic mice and cultured cells to identify a genomic region that directs correct tissue- and cell-specific expression in enteroendocrine cells. The CCKL1 transgene contained 6.4 kb of mouse Cck fused to lacZ. Expression was evaluated in three transgenic lines (J11, J12, J14) by measurement of beta-galactosidase in tissue homogenates and frozen sections. Correct tissue-specific expression was observed, with beta-galactosidase activity detected in intestine and brain. However, there were differences seen in cell-specific expression in the intestine. Line J14 exhibited expression in CCK-endocrine cells, with expressing cells arising at the normal time during fetal development. However, transgene expression in line J12 intestine was limited to neurons of the enteric nervous system, which reflect an early fetal expression pattern for CCK. Analysis of an additional 15 transgenic founder mice demonstrated intestinal expression in 40% of transgenics, with expressing mice following either an endocrine cell pattern or a neuronal pattern in approximately equal numbers. CCKL1 transfection analysis in cultured cells also demonstrated enteroendocrine cell expression, with 100-fold enhanced activity in the enteroendocrine cell line STC-1 compared with nonendocrine cell lines. The results suggest that the minimal cis-regulatory DNA elements necessary for appropriate CCK expression in enteroendocrine cells reside within the 6.4-kb mouse genomic fragment.

Stimulation of MMP-7 (matrilysin) by Helicobacter pylori in human gastric epithelial cells: role in epithelial cell migration

Epithelial cell responses to bacterial infection include induction of matrix metalloproteinase 7 (MMP-7). Here, we identify increased MMP-7 expression in the gastric epithelium in response to the oncogenic bacterium Helicobacter pylori, and report on the mechanisms and consequences for gastric epithelial cell migration. In patients infected with H. pylori, there was increased MMP-7 in gastric biopsies detected by western blot. MMP-7 was localized to the advancing edge of migrating gastric epithelial cell colonies, including lamellipodia. Rates of spreading of gastric gland cells were higher in H. pylori-infected cultures compared with control, and this was inhibited by antisense oligonucleotides to MMP-7. Complementary data were obtained in a gastric cancer cell line (AGS cells). In the latter, H. pylori induced expression of an MMP-7-luciferase promoter/reporter vector through mechanisms that involved activation of Rho and Rac. RhoA acted through activation of both NF-kappaB and AP-1, whereas Rac activated NF-kappaB but not AP-1. MMP-7 is commonly upregulated in gastric cancer; since H. pylori is a recognized gastric carcinogen, the data suggest a new mechanism by which the bacterium might predispose towards gastric neoplasia.

Cholecystokinin gene transcription: promoter elements, transcription factors and signaling pathways

Cholecystokinin (CCK) is a neuropeptide expressed in the small intestine and in the central and peripheral nervous system. CCK gene expression is both spatially and temporally regulated. In neurons CCK production is increased by growth factors, cyclic adenosine 3', 5'-monophosphate (cAMP), dopamine, estrogen, and injury situations, while intestinal CCK expression is mainly regulated by food intake. The function of the proximal CCK promoter has been examined by transfection of human CCK-CAT reporter constructs in cultured cells, DNase I footprinting and gel shift assays. These studies have led to the identification of regulatory elements and transcription factors important for basal and stimulated gene expression and depicted the signaling pathways involved in growth factor and cAMP induced CCK transcription. The review outlines the current knowledge of the regulation of CCK transcription and describes the role of putative transcription factors in tissue-specific CCK gene expression.