Cholecystokinin activates a variety of intracellular signal transduction mechanisms in rodent pancreatic acinar cells

Therapeutic advances of targeting receptor tyrosine kinases in cancer

Receptor tyrosine kinases (RTKs), a category of transmembrane receptors, have gained significant clinical attention in oncology due to their central role in cancer pathogenesis. Genetic alterations, including mutations, amplifications, and overexpression of certain RTKs, are critical in creating environments conducive to tumor development. Following their discovery, extensive research has revealed how RTK dysregulation contributes to oncogenesis, with many cancer subtypes showing dependency on aberrant RTK signaling for their proliferation, survival and progression. These findings paved the way for targeted therapies that aim to inhibit crucial biological pathways in cancer. As a result, RTKs have emerged as primary targets in anticancer therapeutic development. Over the past two decades, this has led to the synthesis and clinical validation of numerous small molecule tyrosine kinase inhibitors (TKIs), now effectively utilized in treating various cancer types. In this manuscript we aim to provide a comprehensive understanding of the RTKs in the context of cancer. We explored the various alterations and overexpression of specific receptors across different malignancies, with special attention dedicated to the examination of current RTK inhibitors, highlighting their role as potential targeted therapies. By integrating the latest research findings and clinical evidence, we seek to elucidate the pivotal role of RTKs in cancer biology and the therapeutic efficacy of RTK inhibition with promising treatment outcomes.

Ca2+ signals in pancreatic acinar cells in response to physiological stimulation in vivo

The exocrine pancreas secretes fluid and digestive enzymes in response to parasympathetic release of acetylcholine (ACh) via the vagus nerve and the gut hormone cholecystokinin (CCK). Both secretion of fluid and exocytosis of secretory granules containing enzymes and zymogens are dependent on an increase in the cytosolic [Ca²⁺ ] in acinar cells. It is thought that the specific spatiotemporal characteristics of the Ca²⁺ signals are fundamental for appropriate secretion and that these properties are disrupted in disease states in the pancreas. While extensive research has been performed to characterize Ca²⁺ signalling in acinar cells, this has exclusively been achieved in ex vivo preparations of exocrine cells, where it is difficult to mimic physiological conditions. Here we have developed a method to optically observe pancreatic acinar Ca²⁺ signals in vivo using a genetically expressed Ca²⁺ indicator and imaged with multi-photon microscopy in live animals. In vivo, acinar cells exhibited baseline activity in fasted animals, which was dependent on CCK1 receptors (CCK1Rs). Both stimulation of intrinsic nervous input and administration of systemic CCK induced oscillatory activity in a proportion of the cells, but the maximum frequencies were vastly different. Upon feeding, oscillatory activity was also observed, which was dependent on CCK1Rs. No evidence of a vago-vagal reflex mediating the effects of CCK was observed. Our in vivo method revealed the spatial and temporal profile of physiologically evoked Ca²⁺ signals, which will provide new insights into future studies of the mechanisms underlying exocrine physiology and that are disrupted in pathological conditions. KEY POINTS: In the exocrine pancreas, the spatiotemporal properties of Ca²⁺ signals are fundamentally important for the appropriate stimulation of secretion by the neurotransmitter acetylcholine and gut hormone cholecystokinin. These characteristics were previously defined in ex vivo studies. Here we report the spatiotemporal characteristics of Ca²⁺ signals in vivo in response to physiological stimulation in a mouse engineered to express a Ca²⁺ indicator in acinar cells. Specific Ca²⁺ 'signatures' probably important for stimulating secretion are evoked in vivo in fasted animals, by feeding, neural stimulation and cholecystokinin administration. The Ca²⁺ signals are probably the result of the direct action of ACh and CCK on acinar cells and not indirectly through a vago-vagal reflex.

Systemic Bile Acids Affect the Severity of Acute Pancreatitis in Mice Depending on Their Hydrophobicity and the Disease Pathogenesis

Acute pancreatitis (AP) is a major, globally increasing gastrointestinal disease and a biliary origin is the most common cause. However, the effects of bile acids (BAs), given systemically, on the pancreas and on disease severity remains elusive. In this study, we have investigated the roles of different circulating BAs in animal models for AP to elucidate their impact on disease severity and the underlying pathomechanisms. BAs were incubated on isolated acini and AP was induced through repetitive injections of caerulein or L-arginine; pancreatic duct ligation (PDL); or combined biliopancreatic duct ligation (BPDL). Disease severity was assessed using biochemical and histological parameters. Serum cholecystokinin (CCK) concentrations were determined via enzyme immunoassay. The binding of the CCK1 receptor was measured using fluorescence-labeled CCK. In isolated acini, hydrophobic BAs mitigated the damaging effects of CCK. The same BAs further enhanced pancreatitis in L-arginine- and PDL-based pancreatitis, whereas they ameliorated pancreatic damage in the caerulein and BPDL models. Mechanistically, the binding affinity of the CCK1 receptor was significantly reduced by hydrophobic BAs. The hydrophobicity of BAs and the involvement of CCK seem to be relevant in the course of AP. Systemic BAs may affect the severity of AP by interfering with the CCK1 receptor.

Neuropeptide System Regulation of Prefrontal Cortex Circuitry: Implications for Neuropsychiatric Disorders

Neuropeptides, a diverse class of signaling molecules in the nervous system, modulate various biological effects including membrane excitability, synaptic transmission and synaptogenesis, gene expression, and glial cell architecture and function. To date, most of what is known about neuropeptide action is limited to subcortical brain structures and tissue outside of the central nervous system. Thus, there is a knowledge gap in our understanding of neuropeptide function within cortical circuits. In this review, we provide a comprehensive overview of various families of neuropeptides and their cognate receptors that are expressed in the prefrontal cortex (PFC). Specifically, we highlight dynorphin, enkephalin, corticotropin-releasing factor, cholecystokinin, somatostatin, neuropeptide Y, and vasoactive intestinal peptide. Further, we review the implication of neuropeptide signaling in prefrontal cortical circuit function and use as potential therapeutic targets. Together, this review summarizes established knowledge and highlights unknowns of neuropeptide modulation of neural function underlying various biological effects while offering insights for future research. An increased emphasis in this area of study is necessary to elucidate basic principles of the diverse signaling molecules used in cortical circuits beyond fast excitatory and inhibitory transmitters as well as consider components of neuropeptide action in the PFC as a potential therapeutic target for neurological disorders. Therefore, this review not only sheds light on the importance of cortical neuropeptide studies, but also provides a comprehensive overview of neuropeptide action in the PFC to serve as a roadmap for future studies in this field.

Structures of the human cholecystokinin 1 (CCK1) receptor bound to Gs and Gq mimetic proteins provide insight into mechanisms of G protein selectivity

G protein-coupled receptors (GPCRs) are critical regulators of cellular function acting via heterotrimeric G proteins as their primary transducers with individual GPCRs capable of pleiotropic coupling to multiple G proteins. Structural features governing G protein selectivity and promiscuity are currently unclear. Here, we used cryo-electron microscopy (cryo-EM) to determine structures of the cholecystokinin (CCK) type 1 receptor (CCK1R) bound to the CCK peptide agonist, CCK-8 and 2 distinct transducer proteins, its primary transducer Gq, and the more weakly coupled Gs. As seen with other Gq/11-GPCR complexes, the Gq-α5 helix (αH5) bound to a relatively narrow pocket in the CCK1R core. Surprisingly, the backbone of the CCK1R and volume of the G protein binding pocket were essentially equivalent when Gs was bound, with the Gs αH5 displaying a conformation that arises from "unwinding" of the far carboxyl-terminal residues, compared to canonically Gs coupled receptors. Thus, integrated changes in the conformations of both the receptor and G protein are likely to play critical roles in the promiscuous coupling of individual GPCRs.

Pancreatic triglyceride lipase mediates lipotoxic systemic inflammation

Visceral adipose tissue plays a critical role in numerous diseases. Although imaging studies often show adipose involvement in abdominal diseases, their outcomes may vary from being a mild self-limited illness to one with systemic inflammation and organ failure. We therefore compared the pattern of visceral adipose injury during acute pancreatitis and acute diverticulitis to determine its role in organ failure. Acute pancreatitis-associated adipose tissue had ongoing lipolysis in the absence of adipocyte triglyceride lipase (ATGL). Pancreatic lipase injected into mouse visceral adipose tissue hydrolyzed adipose triglyceride and generated excess nonesterified fatty acids (NEFAs), which caused organ failure in the absence of acute pancreatitis. Pancreatic triglyceride lipase (PNLIP) increased in adipose tissue during pancreatitis and entered adipocytes by multiple mechanisms, hydrolyzing adipose triglyceride and generating excess NEFAs. During pancreatitis, obese PNLIP-knockout mice, unlike obese adipocyte-specific ATGL knockouts, had lower visceral adipose tissue lipolysis, milder inflammation, less severe organ failure, and improved survival. PNLIP-knockout mice, unlike ATGL knockouts, were protected from adipocyte-induced pancreatic acinar injury without affecting NEFA signaling or acute pancreatitis induction. Therefore, during pancreatitis, unlike diverticulitis, PNLIP leaking into visceral adipose tissue can cause excessive visceral adipose tissue lipolysis independently of adipocyte-autonomous ATGL, and thereby worsen organ failure.

Contributing mechanisms underlying desensitization of cholecystokinin-induced activation of primary nodose ganglia neurons

Cholecystokinin (CCK) is a gut-derived peptide that potently promotes satiety and facilitates gastric function in part by activating G protein-coupled CCK1 receptors on primary vagal afferent neurons. CCK signaling is dynamic and rapidly desensitizes, due to decreases in either receptor function and the resulting signal cascade, ion channel effectors, or both. Here we report a decay-time analytical approach using fluorescent calcium imaging that relates peak and steady-state calcium responses in dissociated vagal afferent neurons, enabling discrimination between receptor and ion channel effector functions. We found desensitization of CCK-induced activation was predictable, consistent across cells, and strongly concentration dependent. The decay-time constant (tau) was inversely proportional to CCK concentration, apparently reflecting the extent of receptor activation. To test this possibility, we directly manipulated the ion channel effector(s) with either decreased bath calcium or the broad-spectrum pore blocker ruthenium red. Conductance inhibition diminished the magnitude of the CCK responses without altering decay kinetics, confirming changes in tau reflect changes in receptor function selectively. Next, we investigated the contributions of the PKC and PKA signaling cascades on the magnitude and decay-time constants of CCK calcium responses. While inhibition of either PKC or PKA increased CCK calcium response magnitude, only general PKC inhibition significantly decreased the decay-time constant. These findings suggest that PKC alters CCK receptor signaling dynamics, while PKA alters the ion channel effector of the CCK response. This analytical approach should prove useful in understanding receptor/effector changes underlying acute desensitization of G-protein coupled signaling and provide insight into CCK receptor dynamics.

Group II p21-activated kinase, PAK4, is needed for activation of focal adhesion kinases, MAPK, GSK3, and β-catenin in rat pancreatic acinar cells

PAK4 is the only member of the Group II p21-activated kinases (PAKs) present in rat pancreatic acinar cells and is activated by gastrointestinal hormones/neurotransmitters stimulating PLC/cAMP and by various pancreatic growth factors. However, little is known of the role of PAK4 activation in cellular signaling cascades in pancreatic acinar cells. In the present study, we examined the role of PAK4's participation in five different cholecystokinin-8 (CCK-8)-stimulated signaling pathways (PI3K/Akt, MAPK, focal adhesion kinase, GSK3, and β-catenin), which mediate many of its physiological acinar-cell effects, as well as effects in pathophysiological conditions. To define PAK4's role, the effect of two different PAK4 inhibitors, PF-3758309 and LCH-7749944, was examined under experimental conditions that only inhibited PAK4 activation and not activation of the other pancreatic PAK, Group I PAK2. The inhibitors' effects on activation of these five signaling cascades by both physiological and pathophysiological concentrations of CCK, as well as by 12-O-tetradecanoylphobol-13-acetate (TPA), a PKC-activator, were examined. CCK/TPA activation of focal adhesion kinases(PYK2/p125^FAK) and the accompanying adapter proteins (paxillin/p130^CAS), Mek1/2, and p44/42, but not c-Raf or other MAPKs (JNK/p38), were mediated by PAK4. Activation of PI3K/Akt/p70s6K was independent of PAK4, whereas GSK3 and β-catenin stimulation was PAK4-dependent. These results, coupled with recent studies showing PAK4 is important in pancreatic fluid/electrolyte/enzyme secretion and acinar cell growth, show that PAK4 plays an important role in different cellular signaling cascades, which have been shown to mediate numerous physiological and pathophysiological processes in pancreatic acinar cells.NEW & NOTEWORTHY In pancreatic acinar cells, cholecystokinin (CCK) or 12-O-tetradecanoylphobol-13-acetate (TPA) activation of focal adhesion kinases (p125^FAK,PYK2) and its accompanying adapter proteins, p130CAS/paxillin; Mek1/2, p44/42, GSK3, and β-catenin are mediated by PAK4. PI3K/Akt/p70s6K, c-Raf, JNK, or p38 pathways are independent of PAK4 activation.

Akt1 signalling supports acinar proliferation and limits acinar-to-ductal metaplasia formation upon induction of acute pancreatitis

Molecular signalling mediated by the phosphatidylinositol-3-kinase (PI3K)-Akt axis is a key regulator of cellular functions. Importantly, alteration of the PI3K-Akt signalling underlies the development of different human diseases, thus prompting the investigation of the pathway as a molecular target for pharmacologic intervention. In this regard, recent studies showed that small molecule inhibitors of PI3K, the upstream regulator of the pathway, reduced the development of inflammation during acute pancreatitis, a highly debilitating and potentially lethal disease. Here we investigated whether a specific reduction of Akt activity, by using either pharmacologic Akt inhibition, or genetic inactivation of the Akt1 isoform selectively in pancreatic acinar cells, is effective in ameliorating the onset and progression of the disease. We discovered that systemic reduction of Akt activity did not protect the pancreas from initial damage and only transiently delayed leukocyte recruitment. However, reduction of Akt activity decreased acinar proliferation and exacerbated acinar-to-ductal metaplasia (ADM) formation, two critical events in the progression of pancreatitis. These phenotypes were recapitulated upon conditional inactivation of Akt1 in acinar cells, which resulted in reduced expression of 4E-BP1, a multifunctional protein of key importance in cell proliferation and metaplasia formation. Collectively, our results highlight the critical role played by Akt1 during the development of acute pancreatitis in the control of acinar cell proliferation and ADM formation. In addition, these results harbour important translational implications as they raise the concern that inhibitors of PI3K-Akt signalling pathways may negatively affect the regeneration of the pancreas. Finally, this work provides the basis for further investigating the potential of Akt1 activators to boost pancreatic regeneration following inflammatory insults. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Cholecystokinin (CCK) Regulation of Pancreatic Acinar Cells: Physiological Actions and Signal Transduction Mechanisms

Pancreatic acinar cells synthesize and secrete about 20 digestive enzymes and ancillary proteins with the processes that match the supply of these enzymes to their need in digestion being regulated by a number of hormones (CCK, secretin and insulin), neurotransmitters (acetylcholine and VIP) and growth factors (EGF and IGF). Of these regulators, one of the most important and best studied is the gastrointestinal hormone, cholecystokinin (CCK). Furthermore, the acinar cell has become a model for seven transmembrane, heterotrimeric G protein coupled receptors to regulate multiple processes by distinct signal transduction cascades. In this review, we briefly describe the chemistry and physiology of CCK and then consider the major physiological effects of CCK on pancreatic acinar cells. The majority of the review is devoted to the physiologic signaling pathways activated by CCK receptors and heterotrimeric G proteins and the functions they affect. The pathways covered include the traditional second messenger pathways PLC-IP3-Ca²⁺ , DAG-PKC, and AC-cAMP-PKA/EPAC that primarily relate to secretion. Then there are the protein-protein interaction pathways Akt-mTOR-S6K, the three major MAPK pathways (ERK, JNK, and p38 MAPK), and Ca²⁺ -calcineurin-NFAT pathways that primarily regulate non-secretory processes including biosynthesis and growth, and several miscellaneous pathways that include the Rho family small G proteins, PKD, FAK, and Src that may regulate both secretory and nonsecretory processes but are not as well understood. © 2019 American Physiological Society. Compr Physiol 9:535-564, 2019.

Evidence That Calcium Entry Into Calcium-Transporting Dental Enamel Cells Is Regulated by Cholecystokinin, Acetylcholine and ATP

Dental enamel is formed by specialized epithelial cells which handle large quantities of Ca²⁺ while producing the most highly mineralized tissue. However, the mechanisms used by enamel cells to handle bulk Ca²⁺ safely remain unclear. Our previous work contradicted the dogma that Ca²⁺ is ferried through the cytosol of Ca²⁺-transporting cells and instead suggested an organelle-based route across enamel cells. This new paradigm involves endoplasmic reticulum (ER)-associated Ca²⁺ stores and their concomitant refilling by store-operated Ca²⁺ entry (SOCE) mediated by Ca²⁺ release activated Ca²⁺ (CRAC) channels. Given that Ca²⁺ handling is maximal during the enamel-mineralization stage (maturation), we anticipated that SOCE would also be elevated then. Confirmation was obtained here using single-cell recordings of cytosolic Ca²⁺ concentration ([Ca²⁺]_cyt) in rat ameloblasts. A candidate SOCE agonist, cholecystokinin (CCK), was found to be upregulated during maturation, with Cck transcript abundance reaching 30% of that in brain. CCK-receptor transcripts were also detected and Ca²⁺ imaging showed that CCK stimulation increased [Ca²⁺]_cyt in a dose-responsive manner that was sensitive to CRAC-channel inhibitors. Similar effects were observed with two other SOCE activators, acetylcholine and ATP, whose receptors were also found in enamel cells. These results provide the first evidence of a potential regulatory system for SOCE in enamel cells and so strengthen the Ca²⁺ transcytosis paradigm for ER-based transport of bulk Ca²⁺. Our findings also implicate enamel cells as a new physiological target of CCK and raise the possibility of an auto/paracrine system for regulating Ca²⁺ transport.

Transcriptional Maintenance of Pancreatic Acinar Identity, Differentiation, and Homeostasis by PTF1A

Maintenance of cell type identity is crucial for health, yet little is known of the regulation that sustains the long-term stability of differentiated phenotypes. To investigate the roles that key transcriptional regulators play in adult differentiated cells, we examined the effects of depletion of the developmental master regulator PTF1A on the specialized phenotype of the adult pancreatic acinar cell in vivo Transcriptome sequencing and chromatin immunoprecipitation sequencing results showed that PTF1A maintains the expression of genes for all cellular processes dedicated to the production of the secretory digestive enzymes, a highly attuned surveillance of unfolded proteins, and a heightened unfolded protein response (UPR). Control by PTF1A is direct on target genes and indirect through a ten-member transcription factor network. Depletion of PTF1A causes an imbalance that overwhelms the UPR, induces cellular injury, and provokes acinar metaplasia. Compromised cellular identity occurs by derepression of characteristic stomach genes, some of which are also associated with pancreatic ductal cells. The loss of acinar cell homeostasis, differentiation, and identity is directly relevant to the pathologies of pancreatitis and pancreatic adenocarcinoma.

Animal models of gastrointestinal and liver diseases. Animal models of acute and chronic pancreatitis

Animal models of pancreatitis are useful for elucidating the pathogenesis of pancreatitis and developing and testing novel interventions. In this review, we aim to summarize the most commonly used animal models, overview their pathophysiology, and discuss their strengths and limitations. We will also briefly describe common animal study procedures and refer readers to more detailed protocols in the literature. Although animal models include pigs, dogs, opossums, and other animals, we will mainly focus on rodent models because of their popularity. Autoimmune pancreatitis and genetically engineered animal models will be reviewed elsewhere.

Metabolic Actions of the Type 1 Cholecystokinin Receptor: Its Potential as a Therapeutic Target

Cholecystokinin (CCK) regulates appetite and reduces food intake by activating the type 1 CCK receptor (CCK1R). Attempts to develop CCK1R agonists for obesity have yielded active agents that have not reached clinical practice. Here we discuss why, along with new strategies to target CCK1R more effectively. We examine signaling events and the possibility of developing agents that exhibit ligand-directed bias, to dissociate satiety activity from undesirable side effects. Potential allosteric sites of modulation are also discussed, along with desired properties of a positive allosteric modulator (PAM) without intrinsic agonist action as another strategy to treat obesity. These new types of CCK1R-active drugs could be useful as standalone agents or as part of a rational drug combination for management of obesity.

Evaluation of Pancreatic Amylase mRNA upon Cholinergic Stimulation of Secretion

The primary function of the exocrine pancreas consists of the synthesis and secretion of several digestive enzymes. It is well established that amylase secretion by rat pancreatic tissue or by isolated acinar cells in culture can be stimulated by the cholinergic agonist carbachol. However, the effect of this secretagogue on enzyme synthesis remains unclear. Some studies demonstrated increases in rates of synthesis, whereas others reported increases in secretion with or without decreases in synthesis. We have evaluated changes in pancreatic amylase mRNA and total RNA after a single injection of carbachol and under fasting conditions. Two approaches in molecular morphology were applied on rat pancreatic tissue: in situ hybridization and RNase A-gold. Both revealed decreases in RNA labeling at the level of the rough endoplasmic reticulum (RER) 5 min after stimulation of secretion and after fasting. Gradual recovery was registered 15 and 30 min after stimulation of secretion. Northern blotting confirmed drastic decreases in amylase mRNA 5 min after stimulation and after fasting. The combination of such different approaches has demonstrated drastic decreases in RNA at the RER level, reflecting declines in rates of synthesis at the translational level under all conditions tested.

Src kinases play a novel dual role in acute pancreatitis affecting severity but no role in stimulated enzyme secretion

In pancreatic acinar cells, the Src family of kinases (SFK) is involved in the activation of several signaling cascades that are implicated in mediating cellular processes (growth, cytoskeletal changes, apoptosis). However, the role of SFKs in various physiological responses such as enzyme secretion or in pathophysiological processes such as acute pancreatitis is either controversial, unknown, or incompletely understood. To address this, in this study, we investigated the role/mechanisms of SFKs in acute pancreatitis and enzyme release. Enzyme secretion was studied in rat dispersed pancreatic acini, in vitro acute-pancreatitis-like changes induced by supramaximal COOH-terminal octapeptide of cholecystokinin (CCK). SFK involvement assessed using the chemical SFK inhibitor (PP2) with its inactive control, 4-amino-7-phenylpyrazol[3,4-d]pyrimidine (PP3), under experimental conditions, markedly inhibiting SFK activation. In CCK-stimulated pancreatic acinar cells, activation occurred of trypsinogen, various MAP kinases (p42/44, JNK), transcription factors (signal transducer and activator of transcription-3, nuclear factor-κB, activator protein-1), caspases (3, 8, and 9) inducing apoptosis, LDH release reflective of necrosis, and various chemokines secreted (monocyte chemotactic protein-1, macrophage inflammatory protein-1α, regulated on activation, normal T cell expressed and secreted). All were inhibited by PP2, not by PP3, except caspase activation leading to apoptosis, which was increased, and trypsin activation, which was unaffected, as was CCK-induced amylase release. These results demonstrate SFK activation is playing a dual role in acute pancreatitis, inhibiting apoptosis and promoting necrosis as well as chemokine/cytokine release inducing inflammation, leading to more severe disease, as well as not affecting secretion. Thus, our studies indicate that SFK is a key mediator of inflammation and pancreatic acinar cell death in acute pancreatitis, suggesting it could be a potential therapeutic target in acute pancreatitis.

Endoplasmic reticulum stress is activated in acute pancreatitis

Endoplasmic reticulum (ER) is one of the most important cell organelles in the body, regulating protein synthesis, folding and aggregation. Endoplasmic reticulum stress (ERS) is a particular subcellular pathological process involving an imbalance of homeostasis and ER disorder. In the early stage of ERS, cells show a protective unfolded protein response that changes the cellular transcriptional and translational programs to alleviate the process. Therefore, a certain degree of ERS can activate the protective adaptation of cells, whereas sustained severe ERS triggers an apoptotic signal and leads to apoptosis. Acute pancreatitis is a disease caused by trypsin digestion of the pancreas, although the pathogenesis is not completely understood. However, a close association has been suggested between pancreatitis and ERS. This article reviewed relevant research advances and discussed the effect of ERS on the development and progression of acute pancreatitis.

Atp2c2 Is Transcribed From a Unique Transcriptional Start Site in Mouse Pancreatic Acinar Cells

Proper regulation of cytosolic Ca(2+) is critical for pancreatic acinar cell function. Disruptions in normal Ca(2+) concentrations affect numerous cellular functions and are associated with pancreatitis. Membrane pumps and channels regulate cytosolic Ca(2+) homeostasis by promoting rapid Ca(2+) movement. Determining how expression of Ca(2+) modulators is regulated and the cellular alterations that occur upon changes in expression can provide insight into initiating events of pancreatitis. The goal of this study was to delineate the gene structure and regulation of a novel pancreas-specific isoform for Secretory Pathway Ca(2+) ATPase 2 (termed SPCA2C), which is encoded from the Atp2c2 gene. Using Next Generation Sequencing of RNA (RNA-seq), chromatin immunoprecipitation for epigenetic modifications and promoter-reporter assays, a novel transcriptional start site was identified that promotes expression of a transcript containing the last four exons of the Atp2c2 gene (Atp2c2c). This region was enriched for epigenetic marks and pancreatic transcription factors that promote gene activation. Promoter activity for regions upstream of the ATG codon in Atp2c2's 24th exon was observed in vitro but not in in vivo. Translation from this ATG encodes a protein aligned with the carboxy terminal of SPCA2. Functional analysis in HEK 293A cells indicates a unique role for SPCA2C in increasing cytosolic Ca(2+) . RNA analysis indicates that the decreased Atp2c2c expression observed early in experimental pancreatitis reflects a global molecular response of acinar cells to reduce cytosolic Ca(2+) levels. Combined, these results suggest SPCA2C affects Ca(2+) homeostasis in pancreatic acinar cells in a unique fashion relative to other Ca(2+) ATPases. J. Cell. Physiol. 231: 2768-2778, 2016. © 2016 Wiley Periodicals, Inc.

Involvement of myristoylated alanine-rich C kinase substrate phosphorylation and translocation in cholecystokinin-induced amylase release in rat pancreatic acini

Cholecystokinin (CCK) is a gastrointestinal hormone that induces exocytotic amylase release in pancreatic acinar cells. The activation of protein kinase C (PKC) is involved in the CCK-induced pancreatic amylase release. Myristoylated alanine-rich C kinase substrate (MARCKS) is a ubiquitously expressed substrate of PKC. MARCKS has been implicated in membrane trafficking in several cell types. The phosphorylation of MARCKS by PKC results in the translocation of MARCKS from the membrane to the cytosol. Here, we studied the involvement of MARCKS in the CCK-induced amylase release in rat pancreatic acini. Employing Western blotting, we detected MARCKS protein in the rat pancreatic acini. CCK induced MARCKS phosphorylation. A PKC-δ inhibitor, rottlerin, inhibited the CCK-induced MARCKS phosphorylation and amylase release. In the translocation assay, we also observed CCK-induced PKC-δ activation. An immunohistochemistry study showed that CCK induced MARCKS translocation from the membrane to the cytosol. When acini were lysed by a detergent, Triton X-100, CCK partially induced displacement of the MARCKS from the GM1a-rich detergent-resistant membrane fractions (DRMs) in which Syntaxin2 is distributed. A MARCKS-related peptide inhibited the CCK-induced amylase release. These findings suggest that MARCKS phosphorylation by PKC-δ and then MARCKS translocation from the GM1a-rich DRMs to the cytosol are involved in the CCK-induced amylase release in pancreatic acinar cells.

The p21-activated kinase, PAK2, is important in the activation of numerous pancreatic acinar cell signaling cascades and in the onset of early pancreatitis events

In a recent study we explored Group-1-p21-activated kinases (GP.1-PAKs) in rat pancreatic acini. Only PAK2 was present; it was activated by gastrointestinal-hormones/neurotransmitters and growth factors in a PKC-, Src- and small-GTPase-mediated manner. PAK2 was required for enzyme-secretion and ERK/1-2-activation. In the present study we examined PAK2's role in CCK and TPA-activation of important distal signaling cascades mediating their physiological/pathophysiological effects and analyzed its role in pathophysiological processes important in early pancreatitis. In rat pancreatic acini, PAK2-inhibition by the specific, GP.1.PAK-inhibitor, IPA-3-suppressed cholecystokinin (CCK)/TPA-stimulated activation of focal-adhesion kinases and mitogen-activated protein-kinases. PAK2-inhibition reversed the dual stimulatory/inhibitory effect of CCK/TPA on the PI3K/Akt/GSK-3β pathway. However, its inhibition did not affect PKC activation. PAK2-inhibition protected acini from CCK-induced ROS-generation; caspase/trypsin-activation, important in early pancreatitis; as well as from cell-necrosis. Furthermore, PAK2-inhibition reduced proteolytic-activation of PAK-2p34, which is involved in programmed-cell-death. To ensure that the study did not only rely in the specificity of IPA-3 as a PAK inhibitor, we used two other approaches for PAK inhibition, FRAX597 a ATP-competitive-GP.1-PAKs-inhibitor and infection with a PAK2-dominant negative(DN)-Advirus. Those two approaches confirmed the results obtained with IPA-3. This study demonstrates that PAK2 is important in mediating CCK's effect on the activation of signaling-pathways known to mediate its physiological/pathophysiological responses including several cellular processes linked to the onset of pancreatitis. Our results suggest that PAK2 could be a new, important therapeutic target to consider for the treatment of diseases involving deregulation of pancreatic acinar cells.

Phosphatidylinositol 3-Kinase: A Link Between Inflammation and Pancreatic Cancer

Even though a strong association between inflammation and cancer has been widely accepted, the underlying precise molecular mechanisms are still largely unknown. A complex signaling network between tumor and stromal cells is responsible for the infiltration of inflammatory cells into the cancer microenvironment. Tumor stromal cells such as pancreatic stellate cells (PSCs) and immune cells create a microenvironment that protects cancer cells through a complex interaction, ultimately facilitating their local proliferation and their migration to different sites. Furthermore, PSCs have multiple functions related to local immunity, angiogenesis, inflammation, and fibrosis. Recently, many studies have shown that members of the phosphoinositol-3-phosphate kinase (PI3K) family are activated in tumor cells, PSCs, and tumor-infiltrating inflammatory cells to promote cancer growth. Proinflammatory cytokines and chemokines secreted by immune cells and fibroblasts within the tumor environment can activate the PI3K pathway both in cancer and inflammatory cells. In this review, we focus on the central role of the PI3K pathway in regulating the cross talk between immune/stromal cells and cancer cells. Understanding the role of the PI3K pathway in the development of chronic pancreatitis and cancer is crucial for the discovery of novel and efficacious treatment options.

Diminished mTOR signaling: a common mode of action for endocrine longevity factors

Since the initial observation that a calorie-restricted (CR) diet can extend rodent lifespan, many genetic and pharmaceutical interventions that also extend lifespan in mammals have been discovered. The mechanism by which CR and these other interventions extend lifespan is the subject of significant debate and research. One proposed mechanism is that CR promotes longevity by increasing insulin sensitivity, but recent findings that dissociate longevity and insulin sensitivity cast doubt on this hypothesis. These findings can be reconciled if longevity is promoted not via increased insulin sensitivity, but instead via decreased PI3K/Akt/mTOR pathway signaling. This review presents a unifying hypothesis that explains the lifespan-extending effects of a variety of genetic mutations and pharmaceutical interventions and points towards new molecular pathways which may also be leveraged to promote healthy aging.

ERK activation is required for CCK-mediated pancreatic adaptive growth in mice

High levels of cholecystokinin (CCK) can stimulate pancreatic adaptive growth in which mature acinar cells divide, leading to enhanced pancreatic mass with parallel increases in protein, DNA, RNA, and digestive enzyme content. Prolonged release of CCK can be induced by feeding trypsin inhibitor (TI) to disrupt normal feedback control. This leads to exocrine growth in a CCK-dependent manner. The extracellular signal-related kinase (ERK) pathway regulates many proliferative processes in various tissues and disease models. The aim of this study was to evaluate the role of ERK signaling in pancreatic adaptive growth using the MEK inhibitors PD-0325901 and trametinib (GSK-1120212). It was determined that PD-0325901 given two times daily by gavage or mixed into powdered chow was an effective and specific inhibitor of ERK signaling in vivo. TI-containing chow led to a robust increase in pancreatic mass, protein, DNA, and RNA content. This pancreatic adaptive growth was blocked in mice fed chow containing the MEK inhibitors. PD-0325901 blocked TI-induced ERK-regulated early response genes, cell-cycle proteins, and mitogenesis by acinar cells. It was determined that ERK signaling is necessary for the initiation of pancreatic adaptive growth but not necessary to maintain it. PD-0325901 blocked adaptive growth when given before cell-cycle initiation but not after mitogenesis had been established. Furthermore, GSK-1120212, a chemically distinct inhibitor of the ERK pathway that is now approved for clinical use, inhibited growth similar to PD-0325901. These data demonstrate that the ERK pathway is required for CCK-stimulated pancreatic adaptive growth.

Hormonal signaling in the gut

The gut is anatomically positioned to play a critical role in the regulation of metabolic homeostasis, providing negative feedback via nutrient sensing and local hormonal signaling. Gut hormones, such as cholecystokinin (CCK) and glucagon-like peptide-1 (GLP-1), are released following a meal and act on local receptors to regulate glycemia via a neuronal gut-brain axis. Additionally, jejunal nutrient sensing and leptin action are demonstrated to suppress glucose production, and both are required for the rapid antidiabetic effect of duodenal jejunal bypass surgery. Strategies aimed at targeting local gut hormonal signaling pathways may prove to be efficacious therapeutic options to improve glucose control in diabetes.

The subfornical organ: a novel site of action of cholecystokinin

The subfornical organ (SFO) is an important sensory circumventricular organ implicated in the regulation of fluid homeostasis and energy balance. We investigated whether the SFO is activated by the hormone cholecystokinin (CCK). CCK₁ and CCK₂ receptors were identified in the SFO by RT-PCR. Dissociated SFO neurons that responded to CCK (40/77), were mostly depolarized (9.2 ± 0.9 mV, 30/77), but some were hyperpolarized (-7.3 ± 1.1 mV, 10/77). We next examined the responses of SFO neurons in vivo to CCK (16 μg/kg ip), in the presence and absence of CCK₁ or CCK₂ receptor antagonists (devazepide; 600 μg/kg and L-365,260; 100 μg/kg, respectively), using the functional activation markers c-Fos and phosphorylated extracellular signal-related kinase (p-ERK). The nucleus of the solitary tract (NTS) served as a control for CCK-induced activity. There was a significant increase in c-Fos expression in the NTS (259.2 ± 20.8 neurons) compared with vehicle (47.5 ± 2.5). Similarly, in the SFO, c-Fos was expressed in 40.5 ± 10.6 neurons in CCK-treated compared with 6.6 ± 2.7 in vehicle-treated rats (P < 0.01). Devazepide significantly reduced the effects of CCK in the NTS but not in SFO. L-365,260 blocked the effects of CCK in both brain regions. CCK increased the number of p-ERK neurons in NTS (27.0 ± 4.0) as well as SFO (18.0 ± 4.0), compared with vehicle (8.0 ± 2.6 and 4.3 ± 0.6, respectively; P < 0.05). Both devazepide and L-365,260 reduced CCK-induced p-ERK in NTS, but only L-365,260 reduced it in the SFO. In conclusion, the SFO represents a novel brain region at which circulating CCK may act via CCK₂ receptors to influence central autonomic control.

4-Phenylbutyric acid reduces endoplasmic reticulum stress, trypsin activation, and acinar cell apoptosis while increasing secretion in rat pancreatic acini

OBJECTIVES

Endoplasmic reticulum (ER) stress leads to misfolded proteins inside the ER and initiates unfolded protein response (UPR). Unfolded protein response components are involved in pancreatic function and activated during pancreatitis. However, the exact role of ER stress in the exocrine pancreas is unclear. The present study examined the effects of 4-phenylbutyric acid (4-PBA), an ER chaperone, on acini and UPR components.

METHODS

Rat acini were stimulated with cholecystokinin (10 pmol/L to 10 nmol/L) with or without preincubation of 4-PBA. The UPR components were analyzed, including chaperone-binding protein, protein kinaselike ER kinase, X-box-binding protein 1, c-Jun NH(2)-terminal kinase, CCAAT/enhancer-binding protein homologous protein, caspase 3, and apoptosis. Effects of 4-PBA were measured on secretion, calcium, and trypsin activation.

RESULTS

4-Phenylbutyric acid led to an increase of secretion, whereas trypsin activation with supraphysiological cholecystokinin was significantly reduced. 4-Phenylbutyric acid prevented chaperone-binding protein up-regulation, diminished protein kinaselike ER kinase, and c-Jun NH2-terminal kinase phosphorylation, prohibited X-box-binding protein 1 splicing and CCAAT/enhancer-binding protein homologous protein expression, caspase 3 activation, and apoptosis caused by supraphysiological cholecystokinin.

CONCLUSION

By incubation with 4-PBA, beneficial in urea cycle deficiency, it was possible to enhance enzyme secretion to suppress trypsin activation, UPR activation, and proapoptotic pathways. The data hint new perspectives for the use of chemical chaperones in pancreatic diseases.

c-Jun/AP-1 is required for CCK-induced pancreatic acinar cell dedifferentiation and DNA synthesis in vitro

Endogenous CCK plays an important role in pancreatic regeneration after pancreatitis. We used primary culture of mouse pancreatic acinar cells to evaluate the effect of CCK on acinar cell morphology and gene expression and to determine signaling pathways required for proliferation of acinar cells in vitro. Over 4 days in culture, cells grew out from acini and formed patches of monolayer, which displayed a reduced expression of acinar cell markers including digestive enzymes and Mist1 and an increased expression of ductal and embryonic markers, including cytokeratin 7, β-catenin, E-cadherin, pdx-1, and nestin. There was no appearance of stellate cell markers. CCK enhanced cellular spreading, DNA synthesis, and cyclin D1 expression. When signaling pathways were evaluated, CCK stimulation increased c-Jun expression, JNK and ERK activity, and AP-1 activation. Chemical inhibitors of JNK and ERK pathways, dominant-negative JNK and c-Jun, and c-Jun shRNA significantly inhibited CCK-induced DNA synthesis, CCK-induced AP-1 activation, and cyclin D1 expression. Furthermore, dominant-negative c-Jun reduced the increased expression of β-catenin and the decreased expression of amylase during culture. These results show that MAPK/c-Jun/AP-1 pathway plays an important role in pancreatic acinar cell dedifferentiation and proliferation in culture. Monolayer culture can serve as a model to study acinar cell proliferation similar to regeneration after pancreatitis in vivo.

Activation of protein kinase Cδ leads to increased pancreatic acinar cell dedifferentiation in the absence of MIST1

Pancreatic ductal adenocarcinoma (PDAC) has a 5 year survival rate post-diagnosis of < 5%. Individuals with chronic pancreatitis (CP) are 20-fold more likely to develop PDAC, making it a significant risk factor for PDAC. While the relationship for the increased susceptibility to PDAC is unknown, loss of the acinar cell phenotype is common to both pathologies. Pancreatic acinar cells can dedifferentiate or trans-differentiate into a number of cell types including duct cells, β cells, hepatocytes and adipocytes. Knowledge of the molecular pathways that regulate this plasticity should provide insight into PDAC and CP. MIST1 (encoded by Bhlha15 in mice) is a transcription factor required for complete acinar cell maturation. The goal of this study was to examine the plasticity of acinar cells that do not express MIST1 (Mist1(-/-) ). The fate of acinar cells from C57Bl6 or congenic Mist1(-/-) mice expressing an acinar specific, tamoxifen-inducible Cre recombinase mated to Rosa26 reporter LacZ mice (Mist1(CreERT/-) R26r) was determined following culture in a three-dimensional collagen matrix. Mist1(CreERT/-) R26r acini showed increased acinar dedifferentiation, formation of ductal cysts and transient increases in PDX1 expression compared to wild-type acinar cells. Other progenitor cell markers, including Foxa1, Sox9, Sca1 and Hes1, were elevated only in Mist1(-/-) cultures. Analysis of protein kinase C (PKC) isoforms by western blot and immunofluorescence identified increased PKCε accumulation and nuclear localization of PKCδ that correlated with increased duct formation. Treatment with rottlerin, a PKCδ-specific inhibitor, but not the PKCε-specific antagonist εV1-2, reduced acinar dedifferentiation, progenitor gene expression and ductal cyst formation. Immunocytochemistry on CP or PDAC tissue samples showed reduced MIST1 expression combined with increased nuclear PKCδ accumulation. These results suggest that the loss of MIST1 is a common event during PDAC and CP and events that affect MIST1 function and expression may increase susceptibility to these pathologies.

Comparative pharmacology of cholecystokinin induced activation of cultured vagal afferent neurons from rats and mice

Cholecystokinin (CCK) facilitates the process of satiation via activation of vagal afferent neurons innervating the upper gastrointestinal tract. Recent findings indicate CCK acts on these neurons via a ruthenium red (RuR) sensitive pathway that involves members of the vanilloid (V) subfamily of transient receptor potential (TRP) channels. To further test this mechanism, the mouse provides an ideal model in which genetic tools could be applied. However, whether CCK acts by similar mechanism(s) in mice has not been determined. In the present study we explored the actions of CCK on nodose neurons isolated from Sprague Dawley (SD) rat and two strains of mice; C57BL/6 and BalbC using fluorescence-based calcium imaging. With minor exceptions nodose neurons isolated from all species/strains behaved similarly. They all respond to brief depolarization with a large calcium transient. A significant subset of neurons responded to capsaicin (CAP), a TRPV1 agonist, although neurons from C57BL/6 were 10-fold more sensitive to CAP than SD rats or BalbC mice, and a significantly smaller fraction of neurons from BalbC mice responded to CAP. CCK-8 dose-dependently activated a subpopulation of neurons with similar dose dependency, percent responders, and overlap between CCK and CAP responsiveness. In all species/strains CCK-8 induced activation was significantly attenuated (but not completely blocked) by pretreatment with the TRPV channel blocker RuR. Surprisingly, the CCK analogue JMV-180, which is reported to have pure antagonistic properties in rat but mixed agonist/antagonist properties in mice, behaved as a pure antagonist to CCK in both rat and mouse neurons. The pure antagonistic action of JMV-180 in this in vitro preparation suggests that prior reported differential effects of JMV-180 on satiation in rats versus mouse must be mediated by a site other than vagal afferent activation.

Age-dependent reduction of the PI3K regulatory subunit p85α suppresses pancreatic acinar cell proliferation

The phosphatidylinositol 3-kinase (PI3K)/Akt pathway is important for tissue proliferation. Previously, we found that tissue regeneration after partial pancreatic resection was markedly attenuated in aged mice as compared to young mice and that this attenuation was because of an age-dependent reduction of PI3K/Akt signaling in the pancreatic acini; however, the mechanisms for the age-associated decline of pancreatic PI3K/Akt signaling remained unknown. To better delineate the mechanisms for the decreased PI3K/Akt activation with aging, age-associated changes in cell proliferation and PI3K/Akt signaling were investigated in the present study using in vitro primary pancreatic acinar cell cultures derived from young and aged mice. In response to treatment with insulin-like growth factor 1 (IGF-1), acinar cells from young but not aged mice showed increased activation of PI3K/Akt signaling and cell proliferation, indicating that intrinsic cellular mechanisms cause the age-associated changes in pancreatic acinar cells. We also found that the expression of PI3K p85α subunit, but not IGF-1 receptor or other PI3K subunits, was significantly reduced in pancreatic acinar cells from aged mice; this age-associated reduction of p85α was confirmed in both mouse and human pancreatic tissues. Finally, small interfering RNA (siRNA)-mediated knockdown of p85α expression in acinar cells from young mice resulted in markedly attenuated activation of PI3K/Akt downstream signaling in response to IGF-1. From these results, we conclude that exocrine pancreatic expression of PI3K p85α subunit is attenuated by aging, which is likely responsible for the age-associated decrease in activation of pancreatic PI3K signaling and acinar cell proliferation in response to growth-promoting stimuli.

Tauroursodeoxycholic acid reduces endoplasmic reticulum stress, acinar cell damage, and systemic inflammation in acute pancreatitis

In acute pancreatitis, endoplasmic reticulum (ER) stress prompts an accumulation of malfolded proteins inside the ER, initiating the unfolded protein response (UPR). Because the ER chaperone tauroursodeoxycholic acid (TUDCA) is known to inhibit the UPR in vitro, this study examined the in vivo effects of TUDCA in an acute experimental pancreatitis model. Acute pancreatitis was induced in Wistar rats using caerulein, with or without prior TUDCA treatment. UPR components were analyzed, including chaperone binding protein (BiP), phosphorylated protein kinase-like ER kinase (pPERK), X-box binding protein (XBP)-1, phosphorylated c-Jun NH(2)-terminal kinase (pJNK), CCAAT/enhancer binding protein homologues protein, and caspase 12 and 3 activation. In addition, pancreatitis biomarkers were measured, such as serum amylase, trypsin activation, edema formation, histology, and the inflammatory reaction in pancreatic and lung tissue. TUDCA treatment reduced intracellular trypsin activation, edema formation, and cell damage, while leaving amylase levels unaltered. The activation of myeloperoxidase was clearly reduced in pancreas and lung. Furthermore, TUDCA prevented caerulein-induced BiP upregulation, reduced XBP-1 splicing, and caspase 12 and 3 activation. It accelerated the downregulation of pJNK. In controls without pancreatitis, TUDCA showed cytoprotective effects including pPERK signaling and activation of downstream targets. We concluded that ER stress responses activated in acute pancreatitis are grossly attenuated by TUDCA. The chaperone reduced the UPR and inhibited ER stress-associated proapoptotic pathways. TUDCA has a cytoprotective potential in the exocrine pancreas. These data hint at new perspectives for an employment of chemical chaperones, such as TUDCA, in prevention of acute pancreatitis.

PKCθ activation in pancreatic acinar cells by gastrointestinal hormones/neurotransmitters and growth factors is needed for stimulation of numerous important cellular signaling cascades

The novel PKCθ isoform is highly expressed in T-cells, brain and skeletal muscle and originally thought to have a restricted distribution. It has been extensively studied in T-cells and shown to be important for apoptosis, T-cell activation and proliferation. Recent studies showed its presence in other tissues and importance in insulin signaling, lung surfactant secretion, intestinal barrier permeability, platelet and mast-cell functions. However, little information is available for PKCθ activation by gastrointestinal (GI) hormones/neurotransmitters and growth factors. In the present study we used rat pancreatic acinar cells to explore their ability to activate PKCθ and the possible interactions with important cellular mediators of their actions. Particular attention was paid to cholecystokinin (CCK), a physiological regulator of pancreatic function and important in pathological processes affecting acinar function, like pancreatitis. PKCθ-protein/mRNA was present in the pancreatic acini, and T538-PKCθ phosphorylation/activation was stimulated only by hormones/neurotransmitters activating phospholipase C. PKCθ was activated in time- and dose-related manner by CCK, mediated 30% by high-affinity CCK(A)-receptor activation. CCK stimulated PKCθ translocation from cytosol to membrane. PKCθ inhibition (by pseudostrate-inhibitor or dominant negative) inhibited CCK- and TPA-stimulation of PKD, Src, RafC, PYK2, p125(FAK) and IKKα/β, but not basal/stimulated enzyme secretion. Also CCK- and TPA-induced PKCθ activation produced an increment in PKCθ's direct association with AKT, RafA, RafC and Lyn. These results show for the first time the PKCθ presence in pancreatic acinar cells, its activation by some GI hormones/neurotransmitters and involvement in important cell signaling pathways mediating physiological responses (enzyme secretion, proliferation, apoptosis, cytokine expression, and pathological responses like pancreatitis and cancer growth).

Pharmacological investigations of the cellular transduction pathways used by cholecystokinin to activate nodose neurons

Cholecystokinin (CCK) directly activates vagal afferent neurons resulting in coordinated gastrointestinal functions and satiation. In vitro, the effects of CCK on dissociated vagal afferent neurons are mediated via activation of the vanilloid family of transient receptor potential (TRPV) cation channels leading to membrane depolarization and an increase in cytosolic calcium. However, the cellular transduction pathway(s) involved in this process between CCK receptors and channel opening have not been identified. To address this question, we monitored CCK-induced cytosolic calcium responses in dissociated nodose neurons from rat in the presence or absence of reagents that interact with various intracellular signaling pathways. We found that the phospholipase C (PLC) inhibitor U-73122 significantly attenuated CCK-induced responses, whereas the inactive analog U-73433 had no effect. Responses to CCK were also cross-desensitized by a brief pretreatment with m-3M3FBS, a PLC stimulator. Together these observations strongly support the participation of PLC in the effects of CCK on vagal afferent neurons. In contrast, pharmacological antagonism of phospholipase A(2), protein kinase A, and phosphatidylinositol 3-kinase revealed that they are not critical in the CCK-induced calcium response in nodose neurons. Further investigations of the cellular pathways downstream of PLC showed that neither protein kinase C (PKC) nor generation of diacylglycerol (DAG) or release of calcium from intracellular stores participates in the response to CCK. These results suggest that alteration of membrane phosphatidylinositol 4,5-bisphosphate (PIP(2)) content by PLC activity mediates CCK-induced calcium response and that this pathway may underlie the vagally-mediated actions of CCK to induce satiation and alter gastrointestinal functions.

Tauroursodeoxycholic acid reduces endoplasmic reticulum stress, trypsin activation, and acinar cell apoptosis while increasing secretion in rat pancreatic acini

Endoplasmic reticulum (ER) stress leads to accumulation of un- or misfolded proteins inside the ER and initiates the unfolded protein response (UPR). Several UPR components are physiologically involved in pancreatic development and are pathophysiologically activated during acute pancreatitis. However, the exact role of ER stress in exocrine pancreatic acini is mainly unclear. The present study examined the effects of tauroursodeoxycholic acid (TUDCA), a known ER chaperone, on acinar function and UPR components. Isolated rat pancreatic acini were stimulated by increasing concentrations of cholecystokinin (CCK-8) with or without preincubation of TUDCA. UPR components were analyzed, including chaperone binding protein (BiP), protein kinase-like ER kinase (PERK), X-box binding protein (XBP)-1, c-Jun NH(2)-terminal kinase (JNK), CCAAT/enhancer binding protein homologues protein (CHOP), caspase 3 activation, and apoptosis. In addition, TUDCA effects were measured on amylase secretion, calcium signaling, trypsin, and cathepsin B activation. TUDCA preincubation led to a significant increase in amylase secretion after CCK-8 stimulation, a 50% reduction of intracellular trypsin activation, and reduced cathepsin B activity, although the effects for cathepsin B were not statistical significant. Furthermore, TUDCA prevented the CCK-8-induced BiP upregulation, diminished PERK and JNK phosphorylation, and prohibited the expression of CHOP, caspase 3 activation and apoptosis. XBP-1 splicing was not altered. ER stress response mechanisms are activated in pancreatic inflammation. Chemical chaperones enhance enzyme secretion of pancreatic acini, reduce ER stress responses, and attenuate ER stress-associated apoptosis. These data hint new perspectives for an employment of chemical chaperones in the therapy of acute pancreatitis.

CCK1 and CCK2 receptors are expressed on pancreatic stellate cells and induce collagen production

The gastrointestinal hormone cholecystokinin (CCK) can induce acute pancreatitis in rodents through its action on acinar cells. Treatment with CCK, in combination with other agents, represents the most commonly used model to induce experimental chronic pancreatitis. Pancreatic stellate cells (PSC) are responsible for pancreatic fibrosis and therefore play a predominant role in the genesis of chronic pancreatitis. However, it is not known whether PSC express CCK receptors. Using real time PCR techniques, we demonstrate that CCK1 and CCK2 receptors are expressed on rat PSC. Interestingly both CCK and gastrin significantly induced type I collagen synthesis. Moreover, both inhibit proliferation. These effects are comparable with TGF-β-stimulated PSC. Furthermore, the natural agonists CCK and gastrin induce activation of pro-fibrogenic pathways Akt, ERK, and Src. Using specific CCK1 and CCK2 receptor (CCK2R) inhibitors, we found that Akt activation is mainly mediated by CCK2R. Akt activation by CCK and gastrin could be inhibited by the PI3K inhibitor wortmannin. Activation of ERK and the downstream target Elk-1 could be inhibited by the MEK inhibitor U0126. These data suggest that CCK and gastrin have direct activating effects on PSC, are able to induce collagen synthesis in these cells, and therefore appear to be important regulators of pancreatic fibrogenesis. Furthermore, similar to TGF-β, both CCK and gastrin inhibit proliferation in PSC.

Devazepide, a nonpeptide antagonist of CCK receptors, induces apoptosis and inhibits Ewing tumor growth

The Ewing family of tumors is a group of highly malignant tumors that mainly arise in bone and most often affect children and young adults in the first two decades of life. Despite the use of multimodal therapy, the long-term disease-free survival rate of patients with Ewing tumors is still disappointingly low, making the discovery of innovative therapeutic strategies all the more necessary. We have recently shown that cholecystokinin (CCK), a neuroendocrine peptide, involved in many biological functions, including cell growth and proliferation, is a relevant target of the EWS/FLI1 oncoprotein characteristic of Ewing tumors. CCK silencing inhibits cell proliferation and tumor growth in vivo, suggesting that CCK acts as an autocrine growth factor for Ewing cells. Here, we analyzed the impact of two CCK receptor antagonists, devazepide (a CCK1-R antagonist) and L365 260 (a CCK2-R antagonist), on the growth of Ewing tumor cells. Devazepide (10 micromol/l) inhibited cell growth of four different Ewing tumor cells in vitro (range 85-88%), whereas the effect of the CCK2-R antagonist on cell growth was negligible. In a mouse tumor xenograft model, devazepide reduced tumor growth by 40%. Flow cytometry experiments showed that devazepide, but not L365 260, induced apoptosis of Ewing tumor cells. In summary, devazepide induces cell death of Ewing tumor cells, suggesting that it could represent a new therapeutic approach in the management of Ewing's tumor patients.

Phenotype of neurons in the nucleus of the solitary tract that express CCK-induced activation of the ERK signaling pathway

The satiating potency of CCK has been well characterized, including its mediation by capsaicin-sensitive vagal primary afferents. We have previously shown that peripherally administered CCK activates the MAPK-signaling cascade in a population of nucleus of the solitary tract (NTS) neurons and that preventing ERK1/2 phosphorylation partly attenuates CCK's satiating potency. The aim of this study was to identify the neurochemical phenotypes of the NTS neurons that exhibit CCK-induced activation of ERK1/2. Using confocal microscopy, we demonstrate that intraperitoneal CCK administration increases the number of neurons that express phosphorylated ERK1/2 (pERK1/2) in the medial and commissural subnuclei of the NTS and that CCK-induced expression of ERK1/2 is increased in tyrosine hydroxylase-immunoreactive neurons. Using Western blot analysis, we show that the robust increase in tyrosine hydroxylase phosphorylation obtained with intraperitoneal CCK is significantly attenuated in rats pretreated with the ERK-pathway blocker U0126 injected into the 4th ventricle. In addition, CCK injections increased pERK1/2 expression in POMC neurons in the NTS. In contrast, only the rare GAD67, neuronal nitric oxide synthase, and leptin-responsive neuron exhibited CCK-induced pERK immunoreactivity. We conclude that activation of POMC-immunoreactive neurons and tyrosine hydroxylase activity via the ERK-signaling pathway in the NTS likely contributes to CCK's satiating effects.

Complete loss of functional G protein-coupled receptors in mouse pancreatic acinar cell MPC-83

AIM: To study G-protein-coupled receptor (GPCR) in mouse exocrine pancreatic acinar cell line MPC-83.

METHODS: Cytoplasmic calcium concentration in mouse exocrine pancreatic acinar cell line MPC-83 was measured both before and after stimulation with GPCR agonists.

RESULTS: Acetylcholine (ACh, 25 nmol/L) and cholecystokinin (CCK, 5 pmol/L) induced regular calcium oscillations in freshly isolated normal mouse pancreatic acinar cells. When GPCR agonists CCK (1 μmol/L), vasopressin (VP, 1 μmol/L), substance P (5 μmol/L), histamine (10 μmol/L), phenylephrine (PE, 10 μmol/L) and ACh 100 μmol/L were added to MPC-83 cells, no change of intracellular calcium concentration was detected. After 100 nmol/L dexamethasone pre-treatment of MPC-83 cells for 72 h, MPC-83 cell proliferation was reduced, but still no calcium increases were detected after stimulation with GPCR agonists 1 μmol/L CCK, 1 μmol/L VP and 5 μmol/L substance P.

CONCLUSION: The pancreatic acinar tumor cell line MPC-83 from Kunming mice have completely lost their functional GPCR which are normally present in pancreatic acinar cells, and these cells are in extreme de-differentiation state.

CCK-8 inhibits LPS-induced IL-1beta production in pulmonary interstitial macrophages by modulating PKA, p38, and NF-kappaB pathway

The neuropeptide cholecystokinin octapeptide (CCK-8) inhibits inflammation by downregulating the expression of proinflammatory cytokines, such as tumor necrosis factor alpha and interleukin (IL) 1beta during endotoxin shock. However, the signaling mechanism of CCK-8 action has not yet been clearly elucidated. In this study, we have examined the possible signaling pathways by which CCK-8 inhibits lipopolysaccharide (LPS)-induced IL-1beta production in rat pulmonary interstitial macrophages. In macrophages, LPS is known to activate p38 kinase, which, in turn, activates nuclear factor (NF)-kappaB to induce IL-1beta production. We found that the pretreatment of cells with CCK-8 blocked the LPS-induced p38 kinase, NF-kappaB activation, and IL-1beta production. Furthermore, CCK-8 treatment activated the cyclic adenosine monophosphate-protein kinase A signaling pathway and H-89 (a protein kinase A inhibitor), abrogated the inhibitory effects of CCK-8 on p38 kinase activation and NF-kappaB activation. In addition, we also demonstrate that the specific antagonist to CCK-1 receptor (CCK-1R) and CCK-2 receptor (CCK-2R) abrogate the CCK action, and that the effects of the antagonist specific to CCK-1R is more significant. These results suggest that these responses were mediated through CCK-1R and CCK-2R, and CCK-1R might be the major receptor responsible for the anti-inflammatory effect of CCK-8. Taken together, our results indicate that the stimulation of cyclic adenosine monophosphate-protein kinase A signaling pathway by CCK-8 through CCK-1R and CCK-2R inhibits the LPS-induced activation of p38 kinase and NF-kappaB to block the IL-1beta production in rat pulmonary interstitial macrophages.

Pancreas-specific RelA/p65 truncation increases susceptibility of acini to inflammation-associated cell death following cerulein pancreatitis

Activation of the transcription factor NF-kappaB/Rel has been shown to be involved in inflammatory disease. Here we studied the role of RelA/p65, the main transactivating subunit, during acute pancreatitis using a Cre-loxP strategy. Selective truncation of the rela gene in pancreatic exocrine cells led to both severe injury of the acinar cells and systemic complications including lung and liver damage. Our data demonstrated that expression and induction of the protective pancreas-specific acute phase protein pancreatitis-associated protein 1 (PAP1) depended on RelA/p65. Lentiviral gene transfer of PAP1 cDNA reduced the extent of necrosis and infiltration in the pancreata of mice with selective truncation of RelA/p65. These results provide in vivo evidence for RelA/p65 protection of acinar cell death via upregulation of PAP1. Moreover, our data underscore the pancreas-specific role of NF-kappaB/Rel and suggest multidimensional roles of NF-kappaB/Rel in different cells and contexts during inflammation.

Postsynaptic mechanisms underlying responsiveness of amygdaloid neurons to cholecystokinin are mediated by a transient receptor potential-like current

Projection neurons of mouse basolateral amygdala responded to CCK with an inward current at a holding potential of -70 mV. This response was mediated by CCK2 receptors as indicated by agonist and antagonist effectiveness, and conveyed via G-proteins of the G(q/11) family as it was abolished in gene knockout mice. Maximal current amplitude was insensitive to extracellular potassium, cesium, and calcium ions, respectively, whereas amplitude and reversal potential critically depended upon extracellular sodium concentration. The current reversed near -20 mV consistent with activation of a mixed cationic channel reminiscent of transient receptor potential (TRP) channels. Extracellular application of the non-selective TRP channel blockers 2-APB, flufenamic acid, Gd3+, and ruthenium red, respectively, inhibited CCK induced inward currents. Single cell PCR confirmed the expression of TRPC1,4,5 and coexpression of TRPC1 with TRPC4 or TRPC5 in some cells. CCK responses were associated with depolarization leading to an increase in cell excitability.

Induction of early response genes in trypsin inhibitor-induced pancreatic growth

Endogenous CCK release induced by a synthetic trypsin inhibitor, camostat, stimulates pancreatic growth; however, the mechanisms mediating this growth are not well established. Early response genes often couple short-term signals with long-term responses. To study their participation in the pancreatic growth response, mice were fasted for 18 h and refed chow containing 0.1% camostat for 1-24 h. Expression of 18 early response genes were evaluated by quantitative PCR; mRNA for 17 of the 18 increased at 1, 2, 4, or 8 h. Protein expression for c-jun, c-fos, ATF-3, Egr-1, and JunB peaked at 2 h. Nuclear localization was confirmed by immunohistochemistry of c-fos, c-jun, and Egr-1. Refeeding regular chow induced only a small increase of c-jun and none in c-fos expression. JNKs and ERKs were activated 1 h after camostat feeding as was the phosphorylation of c-jun and ATF-2. AP-1 DNA binding evaluated by EMSA showed a significant increase 1-2 h after camostat feeding with participation of c-jun, c-fos, ATF-2, ATF-3, and JunB shown by supershift. The CCK antagonist IQM-95,333 blocked camostat feeding-induced c-jun and c-fos expression by 67 and 84%, respectively, and AP-1 DNA binding was also inhibited. In CCK-deficient mice, the maximal response of c-jun induction and AP-1 DNA binding were reduced by 64 and 70%, respectively. These results indicate that camostat feeding induces a spectrum of early response gene expression and AP-1 DNA binding and that these effects are mainly CCK dependent.

How does cholecystokinin stimulate exocrine pancreatic secretion? From birds, rodents, to humans

The field of cholecystokinin (CCK) stimulation of exocrine pancreatic secretion has experienced major changes in the recent past. This review attempts to summarize the present status of the field. CCK production in the intestinal I cells, the molecular forms of CCK produced and subsequently circulated in the blood, the presence or absence of CCK receptors on the isolated pancreatic acinar cells and the associated signaling for acinar cell secretion, and the actual circuits and sites of action for CCK regulation of exocrine pancreatic secretion in vivo are reviewed in different animal species with an emphasis on birds, rodents, and humans. Clear differences in the relative importance of neural and direct modes of CCK action on pancreatic acinar cells were identified. Rodents seem to be endowed with both modes of action, whereas in humans the neural mode may predominate. In birds, such as duck, the direct mode needs further assistance from pituitary adenylate cyclase-activating peptide/VIP receptors. However, much further work needs to be directed to the neural mode to map out all sites of CCK action and details of the full circuits, and we foresee a major revival for this field of research in the near future.

Cholecystokinin-8S-Induced Intracellular Calcium Signaling in Acutely Isolated Periaqueductal Gray Neurons of the Rat

Many behavior studies indicate that cholecystokinin (CCK) is related to nociception and anxiety/panic actions in the midbrain periaqueductal gray (PAG). We previously reported that a sulfated form of CCK octapeptide (CCK-8S) produced excitatory effects at both pre- and postsynaptic loci in PAG neurons using slice preparations and whole-cell patch-clamp recordings. Here, we further examined the detailed mechanism of CCK-8S in acutely isolated PAG neurons of the rat using fura-2-based imaging of intracellular Ca2+ concentration ([Ca2+]i) and whole-cell patch-clamp recordings. Application of 1 microM CCK-8S produced an increase of [Ca2+]i, and its effect did not desensitize. This CCK-8S-induced [Ca2+]i increase was inhibited by the CCK2 receptor antagonist L-365260 but not by the CCK1 receptor antagonist L-364718. In addition, the effect of CCK-8S was eliminated by removing extracellular Ca2+, but not by an addition of the intracellular Ca2+ reuptake inhibitor thapsigargin. When simultaneous recordings of [Ca2+]i imaging and whole-cell patch-clamp were performed, CCK-8S-induced [Ca2+]i increase was significantly reduced at a membrane holding potential of -60 mV while CCK-8S-induced inward current was still observed. Current-voltage plots revealed that CCK-8S-induced inward current reversed near the equilibrium potential for K+ ions with a decreased membrane conductance. However, CCK-8S produced a significant inhibition on high-voltage-activated Ca2+ channel currents. These results suggest that CCK-8S can excite PAG neurons by inhibiting K+ channels, and CCK-8S-induced [Ca2+]i increase occurs secondary to depolarization. The evidence presented here expands our understanding of cellular mechanisms for CCK-mediated anti-analgesic and anxiogenic actions in the PAG.

Signaling Proteins Associated with Diabetic-Induced Exocrine Pancreatic Insufficiency in Rats

Diabetes mellitus (DM) is associated with pancreatic atrophy and compromised digestion of carbohydrates as a result of exocrine pancreatic insufficiency and lower alpha-amylase synthesis and secretion. The reduced production of digestive enzymes is likely to be caused by deregulated protein metabolism. The relative concentrations and phosphorylation of signaling proteins associated with protein translation, such as PKB, p70S6K1, 4E-BP1, ERK1/2, and also some of those implicated in protein breakdown, such as ubiquitin and NF-kappaB, in the pancreas of streptozotocin (STZ)-induced type I diabetic pancreas were measured using Western blotting. There were significant decreases in the levels of total PKB, p70S6K, 4E-BP1, ERK1/2, and NF-kappaB in the diabetic pancreas compared to control. In contrast, the phosphorylation of p70S6K1, 4E-BP1, ERK1/2, and protein ubiquitination increased significantly compared to controls. Together, these results indicate that STZ-induced DM leads to reduced levels of enzymes mediating protein synthesis while their phosphorylation is actually increased, perhaps in an attempt to maintain protein homeostasis, which is further compromised by heightened ubiquitin-dependent protein breakdown. It is likely that these factors are responsible for pancreatic atrophy, enzyme synthesis, and net protein loss in DM.

Calcium signaling complexes in microdomains of polarized secretory cells

The highly polarized nature of epithelial cells in exocrine glands necessitates targeting, assembly into complexes and confinement of the molecules comprising the Ca(2+) signaling apparatus, to cellular microdomains. Such high degree of polarized localization has been shown for all Ca(2+) signaling molecules tested, including G protein coupled receptors and their associated proteins, Ca(2+) pumps, Ca(2+) influx channels at the plasma membrane and Ca(2+) release channels in the endoplasmic reticulum. Although the physiological significance of polarized Ca(2+) signaling is clear, little is known about the mechanism of targeting, assembly and retention of Ca(2+) signaling complexes in cellular microdomains. The present review attempts to summarize the evidence in favor of polarized expression of Ca(2+) signaling proteins at the apical pole of secretory cells with emphasis on the role of scaffolding proteins in the assembly and function of the Ca(2+) signaling complexes. The consequence of polarized enrichment of Ca(2+) signaling complexes at the apical pole is generation of an apical to basal pole gradient of cell responsiveness that, at low physiological agonist concentrations, limits Ca(2+) spikes to the apical pole, and when a Ca(2+) wave occurs, it always propagates from the apical to the basal pole. Our understanding of Ca(2+) signaling in microdomains is likely to increase rapidly with the application of techniques to controllably and selectively disrupt components of the complexes and apply high resolution recording techniques, such as TIRF microscopy to this problem.

Cellular action of cholecystokinin-8S-mediated excitatory effects in the rat periaqueductal gray

The peptide cholecystokinin (CCK) is one of the major neurotransmitters modulating satiety, nociception, and anxiety behavior. Although many behavioral studies showing anti-analgesic and anxiogenic actions of CCK have been reported, less is known about its cellular action in the central nervous system (CNS). Therefore, we examined the action of CCK in rat dorsolateral periaqueductal gray (PAG) neurons using slice preparations and whole-cell patch-clamp recordings. Application of CCK-8S produced an inward current accompanied by increased spontaneous synaptic activities. The CCK-8S-induced inward current (I(CCK)) was recovered after washout and reproduced by multiple exposures. Current-voltage plots revealed that I(CCK) reversed near the equilibrium potential for K(+) ions with a decreased membrane conductance. When several K(+) channel blockers were used, application of CdCl(2), TEA, or apamin significantly reduced I(CCK). I(CCK) was also significantly reduced by the CCK(2) receptor antagonist, L-365,260, while it was not affected by the CCK(1) receptor antagonist, L-364,718. Furthermore, we examined the effects of CCK-8S on miniature excitatory postsynaptic currents (mEPSCs) in order to determine the mechanism of CCK-mediated increase on synaptic activities. We found that CCK-8S increased the frequency of mEPSCs, but had no effect on mEPSC amplitude. This presynaptic effect persisted in the presence of CdCl(2) or Ca(2+)-free bath solution, but was completely abolished by pre-treatment with BAPTA-AM, thapsigargin or L-365,260. Taken together, our results indicate that CCK can excite PAG neurons at both pre- and postsynaptic loci via the activation of CCK(2) receptors. These effects may be important for the effects of CCK on behavior and autonomic function that are mediated via PAG neurons.

Calcineurin-dependent and calcineurin-independent signal transduction pathways activated as part of pancreatic growth

OBJECTIVE

We have recently reported that pancreatic growth driven by cholecystokinin released endogenously by feeding the synthetic trypsin inhibitor camostat requires the Ca-activated phosphatase calcineurin. In the present study, we evaluated a number of signal transduction pathways for their activation as part of the growth response and whether their activation was dependent on calcineurin.

METHODS

Male ICR mice were fed with either chow or chow plus 1 mg/g of camostat. FK506 was administered at 3 mg/kg. After various times from 12 hours to 10 days, pancreatic samples were prepared and assayed for activity of various signal transduction pathway components.

RESULTS

Camostat feeding increased the activation of extracellular signal-regulated kinases, c-Jun NH2-terminal kinases, and phosphorylation of the translation factor eukaryotic initiation factor 4E and activated the mammalian target of rapamycin pathway that leads to phosphorylation of the ribosomal protein S6 and of the eukaryotic initiation factor 4E binding protein but with different time courses. Treatment of mice with the calcineurin inhibitor FK506 totally blocked c-Jun NH2-terminal kinase activation, partially blocked the mammalian target of rapamycin pathway, and had no effect on extracellular signal-regulated kinase activation or the phosphorylation of eukaryotic initiation factor 4E.

CONCLUSIONS

The pancreatic growth response is accompanied by activation of a number of signaling pathways regulating transcription and translation, some of which are dependent on and some independent of calcineurin.