Cholecystokinin stimulates the recruitment of the Src–RhoA–phosphoinositide 3-kinase pathway by Vav-2 downstream of Gα13 in pancreatic acini

Substance Addiction Rehabilitation Drugs

The relapse rate of substance abusers is high, and addiction rehabilitation adjunct drugs need to be developed urgently. There have been numerous reports on blocking the formation of substance addiction, but studies on drugs that can alleviate withdrawal symptoms are very limited. Both the dopamine transporter (DAT) hypothesis and D3 dopamine receptor (D3R) hypothesis are proposed. DAT activators reduce the extracellular dopamine level, and D3R antagonists reduce the neuron's sensitivity to dopamine, both of which may exacerbate the withdrawal symptoms subsequently. The D3R partial agonist SK608 has biased signaling properties via the G-protein-dependent pathway but did not induce D3R desensitization and, thus, may be a promising drug for the withdrawal symptoms. Drugs for serotoninergic neurons or GABAergic neurons and anti-inflammatory drugs may have auxiliary effects to addiction treatments. Drugs that promote structural synaptic plasticity are also discussed.

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.

The relationship between the use of statins and mortality, severity, and pancreatic cancer in Danish patients with chronic pancreatitis

OBJECTIVES

Chronic pancreatitis (CP) is associated with a shortened life expectancy. Statins have anti-inflammatory properties and we aimed to evaluate the association between the use of statins and the risk of death, progression of CP, and pancreatic cancer in patients with CP.

PATIENTS AND METHODS

We carried out a nested case-cohort study and included patients with CP. We used claims of proton pump inhibitors as an active comparator. Patients with cirrhosis or cancer were excluded. We evaluated the exposure on the basis of pharmacy claims of statins. We used propensity score matching with a statins : nonstatins ratio of 1 : 1.

RESULTS

A total of 4807 patients were eligible for propensity score matching; 33% were women and the mean (SD) age at cohort entry was 56 (10) years. During follow-up, a total of 2073 (43%) patients had died and the risk of death was significantly lower among patients using statins versus no statins among 678 matched patients [hazard ratio (HR) 0.64; 95% confidence interval (CI): 0.49-0.83]. Use of statins versus no statins was associated with decreased progression of CP, with an HR of 0.21 (95% CI: 0.17-0.26). Pancreatic cancer occurred in 117 (2.4%) patients and we found a lower risk of pancreatic cancer in statin-treated patients compared with no statins, with a HR of 0.21 (95% CI: 0.06-0.70).

CONCLUSION

In this nationwide study, we found lower risks of mortality, disease progression, and pancreatic cancer in patients with CP using statins. The study is limited by its retrospective design, but supports the hypothesis that statins may affect the course of CP.

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.

Gastrointestinal hormones/neurotransmitters and growth factors can activate P21 activated kinase 2 in pancreatic acinar cells by novel mechanisms

P-21-activated kinases (PAKs) are serine/threonine kinases comprising six isoforms divided in two groups, group-I (PAK1-3)/group-II (PAK4-6) which play important roles in cell cytoskeletal dynamics, survival, secretion and proliferation and are activated by diverse stimuli. However, little is known about PAKs ability to be activated by gastrointestinal (GI) hormones/neurotransmitters/growth-factors. We used rat pancreatic acini to explore the ability of GI-hormones/neurotransmitters/growth-factors to activate Group-I-PAKs and the signaling cascades involved. Only PAK2 was present in acini. PAK2 was activated by some pancreatic growth-factors [EGF, PDGF, bFGF], by secretagogues activating phospholipase-C (PLC) [CCK, carbachol, bombesin] and by post-receptor stimulants activating PKC [TPA], but not agents only mobilizing cellular calcium or increasing cyclic AMP. CCK-activation of PAK2 required both high- and low-affinity-CCK1-receptor-state activation. It was partially reduced by PKC- or Src-inhibition, but not with PI3K-inhibitors (wortmannin, LY294002) or thapsigargin. IPA-3, which prevents PAK2 binding to small-GTPases partially inhibited PAK2-activation, as well as reduced CCK-induced ERK1/2 activation and amylase release induced by CCK or bombesin. This study demonstrates pancreatic acini, possess only one Group-I-PAK, PAK2. CCK and other GI-hormones/neurotransmitters/growth-factors activate PAK2 via small GTPases (CDC42/Rac1), PKC and SFK but not cytosolic calcium or PI3K. CCK-activation of PAK2 showed several novel features being dependent on both receptor-activation states, having PLC- and PKC-dependent/independent components and small-GTPase-dependent/independent components. These results show that PAK2 is important in signaling cascades activated by numerous pancreatic stimuli which mediate their various physiological/pathophysiological responses and thus could be a promising target for the development of therapies in some pancreatic disorders such as pancreatitis.

Paxillin kinase linker (PKL) regulates Vav2 signaling during cell spreading and migration

The Rho family of GTPases plays an important role in coordinating dynamic changes in the cell migration machinery after integrin engagement with the extracellular matrix. Rho GTPases are activated by guanine nucleotide exchange factors (GEFs) and negatively regulated by GTPase-activating proteins (GAPs). However, the mechanisms by which GEFs and GAPs are spatially and temporally regulated are poorly understood. Here the activity of the proto-oncogene Vav2, a GEF for Rac1, RhoA, and Cdc42, is shown to be regulated by a phosphorylation-dependent interaction with the ArfGAP PKL (GIT2). PKL is required for Vav2 activation downstream of integrin engagement and epidermal growth factor (EGF) stimulation. In turn, Vav2 regulates the subsequent redistribution of PKL and the Rac1 GEF β-PIX to focal adhesions after EGF stimulation, suggesting a feedforward signaling loop that coordinates PKL-dependent Vav2 activation and PKL localization. Of interest, Vav2 is required for the efficient localization of PKL and β-PIX to the leading edge of migrating cells, and knockdown of Vav2 results in a decrease in directional persistence and polarization in migrating cells, suggesting a coordination between PKL/Vav2 signaling and PKL/β-PIX signaling during cell migration.

Ethanol impairs the assembly and disassembly of actin cytoskeleton and cell adhesion via the RhoA signaling pathway, catenin p120 and E-cadherin in CCK-stimulated pancreatic acini

The purpose of the present study was to evaluate the effects of EtOH on RhoA, actin cytoskeleton, catenin p120 and E-cadherin and their interactions in CCK-stimulated rat pancreatic acini. In isolated rat pancreatic acinar cells, CCK stimulation enhanced protein expression and association of RhoA, G(α13), Vav-2, catenin p120 and E-cadherin. CCK induced translocation and activation of RhoA and actin-filamentous assembly and disassembly. RhoA was diffusely localized throughout the acinar cell in the resting state and redistributed to the apical site in response to submaximal CCK stimulation and to a lesser extent in response to supramaximal CCK stimulation. Ethanol and subsequent submaximal CCK stimulation mimicked the effect of supramaximal CCK stimulation in terms of amylase secretion and morphologic effects. However, inhibition of RhoA translocation and activation were observed only with ethanol pretreatment. Ethanol followed by supramaximal CCK stimulation disrupted the well-defined localization of catenin p120 and E-cadherin around the lateral plasma membrane. These data suggest that ethanol impaired the assembly and disassembly of actin cytoskeleton and impaired cell-cell adhesion via the RhoA signaling pathways, catenin p120 and E-cadherin in CCK-stimulated pancreatic acini.

CCK activates RhoA and Rac1 differentially through Galpha13 and Galphaq in mouse pancreatic acini

Cholecystokinin (CCK) has been shown to activate RhoA and Rac1, as well as reorganize the actin cytoskeleton and, thereby, modify acinar morphology and amylase secretion in mouse pancreatic acini. The aim of the present study was to determine which heterotrimeric G proteins activate RhoA and Rac1 upon CCK stimulation. Galpha(13), but not Galpha(12), was identified in mouse pancreatic acini by RT-PCR and Western blotting. Using specific assays for RhoA and Rac1 activation, we showed that only active Galpha(13) activated RhoA. By contrast, active Galpha(13) and Galpha(q), but not Galpha(s), slightly increased GTP-bound Rac1 levels. A greater increase in Rac1 activation was observed when active Galpha(13) and active Galpha(q) were coexpressed. Galpha(i) was not required for CCK-induced RhoA or Rac1 activation. The regulator of G protein signaling (RGS) domain of p115-Rho guanine nucleotide exchange factor (p115-RGS), a specific inhibitor of Galpha(12/13)-mediated signaling, abolished CCK-stimulated RhoA activation. By contrast, both RGS-2, an inhibitor of Galpha(q), and p115-RGS abolished CCK-induced Rac1 activation, which was PLC pathway-independent. Active Galpha(q) and Galpha(13), but not Galpha(s), induced morphological changes and actin redistribution similar to 1 nM CCK. CCK-induced actin cytoskeletal reorganization was inhibited by RGS-2, but not by p115-RGS, whereas CCK-induced amylase secretion was blocked by both inhibitors. Together, these findings indicate that, in mouse pancreatic acini, Galpha(13) links CCK stimulation to the activation of RhoA, whereas both Galpha(13) and Galpha(q) link CCK stimulation to the activation of Rac1. CCK-induced actin cytoskeletal reorganization is mainly mediated by Galpha(q). By contrast, Galpha(13) and Galpha(q) signaling are required for CCK-induced amylase secretion.

Aldosterone stimulates elastogenesis in cardiac fibroblasts via mineralocorticoid receptor-independent action involving the consecutive activation of Galpha13, c-Src, the insulin-like growth factor-I receptor, and phosphatidylinositol 3-kinase/Akt

We previously demonstrated that aldosterone, which stimulates collagen production through the mineralocorticoid receptor (MR)-dependent pathway, also induces elastogenesis via a parallel MR-independent mechanism involving insulin-like growth factor-I receptor (IGF-IR) signaling. The present study provides a more detailed explanation of this signaling pathway. Our data demonstrate that small interfering RNA-driven elimination of MR in cardiac fibroblasts does not inhibit aldosterone-induced IGF-IR phosphorylation and subsequent increase in elastin production. These results exclude the involvement of the MR in aldosterone-induced increases in elastin production. Results of further experiments aimed at identifying the upstream signaling component(s) that might be activated by aldosterone also eliminate the putative involvement of pertussis toxin-sensitive Galphai proteins, which have previously been shown to be responsible for some MR-independent effects of aldosterone. Instead, we found that small interfering RNA-dependent elimination of another heterotrimeric G protein, Galpha13, eliminates aldosterone-induced elastogenesis. We further demonstrate that aldosterone first engages Galpha13 and then promotes its transient interaction with c-Src, which constitutes a prerequisite step for aldosterone-dependent activation of the IGF-IR and propagation of consecutive downstream elastogenic signaling involving phosphatidylinositol 3-kinase/Akt. In summary, the data we present reveal new details of an MR-independent cellular signaling pathway through which aldosterone stimulates elastogenesis in human cardiac fibroblasts.

Gastrointestinal growth factors and hormones have divergent effects on Akt activation

Akt is a central regulator of apoptosis, cell growth and survival. Growth factors and some G-protein-coupled receptors (GPCR) regulate Akt. Whereas growth-factor activation of Akt has been extensively studied, the regulation of Akt by GPCR's, especially gastrointestinal hormones/neurotransmitters, remains unclear. To address this area, in this study the effects of GI growth factors and hormones/neurotransmitters were investigated in rat pancreatic acinar cells which are high responsive to these agents. Pancreatic acini expressed Akt and 5 of 7 known pancreatic growth-factors stimulate Akt phosphorylation (T308, S473) and translocation. These effects are mediated by p85 phosphorylation and activation of PI3K. GI hormones increasing intracellular cAMP had similar effects. However, GI-hormones/neurotransmitters [CCK, bombesin, carbachol] activating phospholipase C (PLC) inhibited basal and growth-factor-stimulated Akt activation. Detailed studies with CCK, which has both physiological and pathophysiological effects on pancreatic acinar cells at different concentrations, demonstrated CCK has a biphasic effect: at low concentrations (pM) stimulating Akt by a Src-dependent mechanism and at higher concentrations (nM) inhibited basal and stimulated Akt translocation, phosphorylation and activation, by de-phosphorylating p85 resulting in decreasing PI3K activity. This effect required activation of both limbs of the PLC-pathway and a protein tyrosine phosphatase, but was not mediated by p44/42 MAPK, Src or activation of a serine phosphatase. Akt inhibition by CCK was also found in vivo and in Panc-1 cancer cells where it inhibited serum-mediated rescue from apoptosis. These results demonstrate that GI growth factors as well as gastrointestinal hormones/neurotransmitters with different cellular basis of action can all regulate Akt phosphorylation in pancreatic acinar cells. This regulation is complex with phospholipase C agents such as CCK, because both stimulatory and inhibitory effects can be seen, which are mediated by different mechanisms.

Small G proteins as key regulators of pancreatic digestive enzyme secretion

Small GTP-binding (G) proteins act as molecular switches to regulate a number of cellular processes, including vesicular transport. Emerging evidence indicates that small G proteins regulate a number of steps in the secretion of pancreatic acinar cells. Diverse small G proteins have been localized at discrete compartments along the secretory pathway and particularly on the secretory granule. Rab3D, Rab27B, and Rap1 are present on the granule membrane and play a role in the steps leading up to exocytosis. Whether the function of these G proteins is simply to ensure appropriate targeting or if they are involved as regulatory molecules is discussed. Most evidence suggests that Rab3D and Rab27B play a role in tethering the secretory granule to its target membrane. Other Rabs have been identified on the secretory granule that are associated with different steps in the secretory pathway. The Rho family small G proteins RhoA and Rac1 also regulate secretion through remodeling of the actin cytoskeleton. Possible mechanisms for regulation of these G proteins and their effector molecules are considered.

AMF/PGI transactivates the MMP-3 gene through the activation of Src-RhoA-phosphatidylinositol 3-kinase signaling to induce hepatoma cell migration

We have previously shown that AMF/PGI induces hepatoma cell migration through the induction of MMP-3. This work investigates how AMF/PGI activates the MMP-3 gene. We demonstrated that AMF/PGI transactivates the MMP-3 gene promoter through AP-1. The transactivation and induction of cell migration effect of AMF/PGI directly correlates with its enzymatic activity. Various analyses showed that AMF/PGI stimulated the Src-RhoA-PI3-kinase signaling pathway, and these three signaling molecules could form a complex. Our results demonstrate a new mechanism of AMF/PGI-induced cell migration and a link between Src-RhoA-PI3-kinase, AP-1, MMP-3 and hepatoma cell migration.

Galpha12/13-mediated up-regulation of TRPC6 negatively regulates endothelin-1-induced cardiac myofibroblast formation and collagen synthesis through nuclear factor of activated T cells activation

Sustained elevation of [Ca(2+)](i) has been implicated in many cellular events. We previously reported that alpha subunits of G(12) family G proteins (Galpha(12/13)) participate in sustained Ca(2+) influx required for the activation of nuclear factor of activated T cells (NFAT), a Ca(2+)-responsive transcriptional factor, in rat neonatal cardiac fibroblasts. Here, we demonstrate that Galpha(12/13)-mediated up-regulation of canonical transient receptor potential 6 (TRPC6) channels participates in sustained Ca(2+) influx and NFAT activation by endothelin (ET)-1 treatment. Expression of constitutively active Galpha(12) or Galpha(13) increased the expression of TRPC6 proteins and basal Ca(2+) influx activity. The treatment with ET-1 increased TRPC6 protein levels through Galpha(12/13), reactive oxygen species, and c-Jun N-terminal kinase (JNK)-dependent pathways. NFAT is activated by sustained increase in [Ca(2+)](i) through up-regulated TRPC6. A Galpha(12/13)-inhibitory polypeptide derived from the regulator of the G-protein signaling domain of p115-Rho guanine nucleotide exchange factor and a JNK inhibitor, SP600125, suppressed the ET-1-induced increase in expression of marker proteins of myofibroblast formation through a Galpha(12/13)-reactive oxygen species-JNK pathway. The ET-1-induced myofibroblast formation was suppressed by overexpression of TRPC6 and CA NFAT, whereas it was enhanced by TRPC6 small interfering RNAs and cyclosporine A. These results suggest two opposite roles of Galpha(12/13) in cardiac fibroblasts. First, Galpha(12/13) mediate ET-1-induced myofibroblast formation. Second, Galpha(12/13) mediate TRPC6 up-regulation and NFAT activation that negatively regulates ET-1-induced myofibroblast formation. Furthermore, TRPC6 mediates hypertrophic responses in cardiac myocytes but suppresses fibrotic responses in cardiac fibroblasts. Thus, TRPC6 mediates opposite responses in cardiac myocytes and fibroblasts.

IL-6 induces AGS gastric cancer cell invasion via activation of the c-Src/RhoA/ROCK signaling pathway

Interleukin-6 (IL-6) is a multifunctional cytokine that is associated with the disease status and outcomes of gastric cancer. Nonetheless, the underlying mechanism of how IL-6 promotes the spread of gastric cancer is still unclear. In this study, we used a modified Boyden chamber assay to test the invasion ability of different gastric cancer cell lines. Liposome-mediated transfection was used to introduce an IL-6 expression vector into AGS cells, and the transfectants were further examined for the expression of active RhoA and phosphorylated Src using a pull-down assay and coimmunoprecipitation/Western blot analysis. Furthermore, RhoA expression in gastric adenocarcinoma specimens was investigated immunohistochemically. We documented that IL-6 could promote AGS cell motility and invasiveness, and inhibition of RhoA expression by dominant negative RhoA, C3 transferase, or dominant negative Src expressing plasmids could effectively decrease the invasiveness of IL-6 transfectants. We also documented an interaction between active RhoA and phosphorylated-Src following IL-6 treatment. Gastric cancers displaying high expression of RhoA are highly correlated with aggressive lymph node metastasis, more advanced tumor stage, histologically diffuse type and poorer survival. In conclusion, IL-6 induces AGS gastric cancer cell invasion via activation of the c-Src/RhoA/ROCK signaling pathway and RhoA expression could be used as a prognostic factor in patients with gastric adenocarcinoma.

Cholecystokinin and gastrin receptors

Cholecystokinin and gastrin receptors (CCK1R and CCK2R) are G protein-coupled receptors that have been the subject of intensive research in the last 10 years with corresponding advances in the understanding of their functioning and physiology. In this review, we first describe general properties of the receptors, such as the different signaling pathways used to exert short- and long-term effects and the structural data that explain their binding properties, activation, and regulation. We then focus on peripheral cholecystokinin receptors by describing their tissue distribution and physiological actions. Finally, pathophysiological peripheral actions of cholecystokinin receptors and their relevance in clinical disorders are reviewed.