Expression of cholecystokinin-2/gastrin receptor in the murine pancreas modulates cell adhesion and cell differentiation in vivo

Gene expression meta-analysis in diffuse low-grade glioma and the corresponding histological subtypes

Diffuse low-grade glioma (DLGG) is a well-differentiated, slow-growing tumour with an inherent tendency to progress to high-grade glioma. The potential roles of genetic alterations in DLGG development have not yet been fully delineated. Therefore, the current study performed an integrated gene expression meta-analysis of eight independent, publicly available microarray datasets including 291 DLGGs and 83 non-glioma (NG) samples to identify gene expression signatures associated with DLGG. Using INMEX, 708 differentially expressed genes (DEGs) (385 upregulated and 323 downregulated genes) were identified in DLGG compared to NG. Furthermore, 497 DEGs (222 upregulated and 275 downregulated genes) corresponding to two histological types were identified. Of these, high expression of HIP1R significantly correlated with increased overall survival, whereas high expression of TBXAS1 significantly correlated with decreased overall survival. Additionally, network-based meta-analysis identified FN1 and APP as the key hub genes in DLGG compared with NG. PTPN6 and CUL3 were the key hub genes identified in the astrocytoma relative to the oligodendroglioma. Further immunohistochemical validation revealed that MTHFD2 and SPARC were positively expressed in DLGG, whereas RBP4 was positively expressed in NG. These findings reveal potential molecular biomarkers for diagnosis and therapy in patients with DLGG and provide a rich and novel candidate reservoir for future studies.

Mechanistic insights into the activity of Ptf1-p48 (pancreas transcription factor 1a): probing the interactions levels of Ptf1-p48 with E2A-E47 (transcription factor E2-alpha) and ID3 (inhibitor of DNA binding 3)

Ptf1-p48 (Pancreas specific transcription factor 1a) is transcription regulatory protein known for the activation of exocrine specific genes. Downregulation of its expression formulates early stages of pancreatic adenocarcinoma as deduced by its association with oncogenic bHLH (Basic Helix-Loop-Helix) protein ID3 (Inhibitor of DNA binding 3) protein whose overexpression induces cytoplasmic mislocalization of Ptf1-p48. The precise mechanism and/or functional role of Ptf1-p48in promoting pancreatic cancer is vague. The structural features of the Ptf1-p48 and its dimerization with E47 (Transcription factor E2-alpha) and ID3 mediated by their HLH (Helix-Loop-Helix) domain were perceived through MD (Molecular Dynamics) simulations of 50 ns. The interactions formed by the HLH domain in both Ptf1-E47 and Ptf1-ID3 complexes are favored by the synergistic movement of their domain helices. Accordingly, in the Ptf1-E47 complex α7 of Ptf1-p48 and α1 helix of E47 along with the loop residues of their HLH domain exhibit transitions marked by inward movement toward each other and forms polar and charged interactions. In the Ptf1-ID3 complex, α8 of Ptf1-p48 moves toward the α3 helix of ID3 and forms hydrogen bonds. The interface analysis also reveals better interface in the Ptf1-p48 complex than the Ptf1-ID3 evident by energetics and number of hydrogen bonds. The interactions in each of these complexes, supported by angular displacement and mode vector analyzes, comprehensibly describe the considerable structural changes induced upon dimer formation. It thereby gives an insight into the interfaces that could help in designing of potential inhibitors for ID3 to curb the cancer cell growth.

MiR-148a regulates the growth and apoptosis in pancreatic cancer by targeting CCKBR and Bcl-2

Our previous studies have revealed that miR-148a is downregulated in pancreatic cancer. Bioinformatics analysis has shown cholecystokinin-B receptor (CCKBR) and B cell lymphoma (Bcl-2) to be potential targets of miR-148a. But the pathophysiologic role of miR-148a and its relevance to the growth and development of pancreatic cancer are yet to be investigated. The purpose of this study is to elucidate the molecular mechanisms where miR-148a acts as a tumor suppressor in pancreatic cancer. Our results showed significant downregulation of miR-148a in 28 pancreatic cancer tissue samples and five pancreatic cancer cell lines, compared with their non-tumor counterparts by qRT-PCR. MiR-148a was found to not only inhibit the proliferation of pancreatic cancer cells (PANC-1 and AsPC-1) in vitro by MTT assay and colony formation assay, but also to promote cells apoptosis in vitro by Annexin V-FITC apoptosis detection and caspase activity assay. Using western blot and luciferase activity assay, CCKBR and Bcl-2 were identified as targets of miR-148a. Moreover, we also found that the expression of Bcl-2 lacking in 3'UTR could abrogate the pro-apoptosis function of miR-148a. These findings suggest the importance of miR-148a's targeting of CCKBR and Bcl-2 in the regulation of pancreatic cancer growth and apoptosis.

Acting on Hormone Receptors with Minimal Side Effect on Cell Proliferation: A Timely Challenge Illustrated with GLP-1R and GPER

G protein-coupled receptors (GPCRs) constitute a large family of receptors that sense molecules outside the cell and activate inside signal transduction pathways and cellular responses. GPCR are involved in a wide variety of physiological processes, including in the neuroendocrine system. GPCR are also involved in many diseases and are the target of 30% of marketed medicinal drugs. Whereas the majority of the GPCR-targeting drugs have proved their therapeutic benefit, some of them were associated with undesired effects. We develop two examples of used drugs whose therapeutic benefits are tarnished by carcinogenesis risks. The chronic administration of glucagon-like peptide-1 (GLP-1) analogs widely used to treat type-2 diabetes was associated with an increased risk of pancreatic or thyroid cancers. The long-term treatment with the estrogen antagonist tamoxifen, developed to target breast cancer overexpressing estrogen receptors ER, presents agonist activity on the G protein-coupled estrogen receptor which is associated with an increased incidence of endometrial cancer and breast cancer resistance to hormonotherapy. We point out and discuss the need of pharmacological studies to understand and overcome the undesired effects associated with the chronic administration of GPCR ligands. In fact, biological effects triggered by GPCR often result from the activation of multiple intracellular signaling pathways. Deciphering which signaling networks are engaged following GPCR activation appears to be primordial to unveil their contribution in the physiological and physiopathological processes. The development of biased agonists to elucidate the role of the different signaling mechanisms mediated by GPCR activation will allow the generation of new therapeutic agents with improved efficacy and reduced side effects. In this regard, the identification of GLP-1R biased ligands promoting insulin secretion without inducing pro-tumoral effects would offer therapeutic benefit.

Cholecystokinin and gastrin receptors targeting in gastrointestinal cancer

Cholecystokinin and Gastrin are amongst the first gastrointestinal hormone discovered. In addition to classical actions (contraction of gallbladder, growth and secretion in the stomach and pancreas), these also act as growth stimulants for gastrointestinal malignancies and cell lines. Growth of these tumours is inhibited by antagonists of the cholecystokinin and gastrin receptors. These receptors provides most promising approach in clinical oncology and several specific radiolabelled ligands have been synthesized for specific tumour targeting and therapy of tumours overexpressing these receptors. Therefore, definition of the molecular structure of the receptor involved in the autocrine/paracrine loop may contribute to novel therapies for gastrointestinal cancer. Hence, this review tries to focus on the role and distribution of these hormones and their receptors in gastrointestinal cancer with a brief talk about the clinical trial using available agonist and antagonist in gastrointestinal cancers.

αV integrin: A new gastrin target in human pancreatic cancer cells

AIM: To analyse α_V integrin expression induced by gastrin in pancreatic cancer models.

METHODS: α_V integrin mRNA expression in human pancreatic cancer cells was analysed using a “cancer genes” array and confirmed by real-time reverse transcription-polymerase chain reaction (PCR). Western blotting and semi-quantitative immunohistochemistry were used to examine protein levels in human pancreatic cancer cell lines and pancreatic tissues, respectively. The role of α_V integrin on gastrin-induced cell adhesion was examined using blocking anti-α_V integrin monoclonal antibodies. Adherent cells were quantified by staining with crystal violet.

RESULTS: Using a “cancer genes” array we identified α_V integrin as a new gastrin target gene in human pancreatic cancer cells. A quantitative real-time PCR approach was used to confirm α_V integrin gene expression. We also demonstrate that Src family kinases and the PI 3-kinase, two signalling pathways specifically activated by the CCK-2 receptor (CCK2R), are involved in gastrin-mediated α_V integrin expression. In contrast, inhibition of the ERK pathway was without any effect on α_V integrin expression induced by gastrin. Our results also show that gastrin modulates cell adhesion viaα_V integrins. Indeed, in vitro adhesion assays performed on fibronectin show that gastrin significantly increases adhesion of pancreatic cancer cells. The use of blocking anti-α_V integrin monoclonal antibodies completely reversed the increase in cell-substrate adhesion induced by gastrin. In addition, we showed in vivo that the targeted CCK2R expression in the pancreas of Elas-CCK2 mice, leads to the overexpression of α_V integrin. This process may contribute to pancreatic tumour development observed in these transgenic animals.

CONCLUSION: α_V integrin is a new gastrin target in pancreatic cancer models and contributes to gastrin effects on cell adhesion.

Id3 modulates cellular localization of bHLH Ptf1-p48 protein

Ptf1-p48 is a pancreas-specific bHLH transcriptional protein, which, in the normal adult pancreas, shows a restricted expression in acinar cells where it is predominantly localized in the nucleus and activates the transcription of exocrine-specific genes. Ptf1-p48 partners with two proteins to form the PTF1 active complex: a bHLH E-protein and suppressor of hairless RBP-J. Cytoplasmic mislocalization of Ptf1-p48 has been reported in pancreatic pathologies, suggesting its contribution in the early steps of pancreatic carcinogenesis. The aim of the our work was to elucidate the mechanisms regulating Ptf1-p48 subcellular localization. We hypothesized a role of Id proteins acting in a dominant-negative fashion by heterodimerizing with bHLH proteins. We reproduced Ptf1-p48 cytoplasmic mislocalization in acinar AR4-2J cells and demonstrated that a proliferative signal elicited by gastrin leads to increases in Id3 protein expression and levels of Id3/E47 and Id3/Ptf1-p48 interactions, and a decrease in the level of E47/Ptf1-p48 interaction. By contrast, Id3 silencing reversed the cytoplasmic mislocalization of Ptf1-p48 induced by gastrin. As E47 is responsible for the nuclear import of the PTF1 complex, disruption of this complex via Id3 interactions with both E47 and Ptf1-p48 appears to induce cytoplasmic mislocalization of Ptf1-p48. We then found that Ptf1-p48 is either absent or mislocalized in the cytoplasm and Id3 is overexpressed in human and murine pancreatic preneoplastic lesions. Our data provide novel insight into the regulation of Ptf1-p48 function and provide evidence that Ptf1-p48 cytoplasmic mislocalization and Id3 overexpression are early events in pancreatic cancer progression.

Crosstalk between insulin/insulin-like growth factor-1 receptors and G protein-coupled receptor signaling systems: a novel target for the antidiabetic drug metformin in pancreatic cancer

Insulin/insulin-like growth factor 1(IGF-1) receptors and G protein-coupled receptors (GPCR) signaling systems are implicated in autocrine-paracrine stimulation of a variety of malignancies, including ductal adenocarcinoma of the pancreas, one of the most lethal human diseases. Novel targets for pancreatic cancer therapy are urgently needed. We identified a crosstalk between insulin/IGF-1 receptors and GPCR signaling systems in pancreatic cancer cells, leading to enhanced signaling, DNA synthesis, and proliferation. Crosstalk between these signaling systems depends on mammalian target of rapamycin (mTOR) complex 1 (mTORC1). Metformin, the most widely used drug in the treatment of type 2 diabetes, activates AMP kinase (AMPK), which negatively regulates mTORC1. Recent results show that metformin-induced activation of AMPK disrupts crosstalk between insulin/IGF-1 receptor and GPCR signaling in pancreatic cancer cells and inhibits the growth of these cells in xenograft models. Given that insulin/IGF-1 and GPCRs are implicated in other malignancies, a similar crosstalk mechanism may be operative in other cancer cell types. Recent epidemiological studies linked administration of metformin with a reduced risk of pancreatic, breast, and prostate cancer in diabetic patients. We posit that crosstalk between insulin/IGF-1 receptor and GPCR signaling is a mechanism for promoting the development of certain types of cancer and a target for the prevention and therapy of these diseases via metformin administration.

Gastrin, cholecystokinin and gastrointestinal tract functions in mammals

The aim of the present review is to synthesise and summarise our recent knowledge on the involvement of cholecystokinin (CCK) and gastrin peptides and their receptors in the control of digestive functions and more generally their role in the field of nutrition in mammals. First, we examined the release of these peptides from the gut, focusing on their molecular forms, the factors regulating their release and the signalling pathways mediating their effects. Second, general physiological effects of CCK and gastrin peptides are described with regard to their specific receptors and the role of CCK on vagal mucosal afferent nerve activities. Local effects of CCK and gastrin in the gut are also reported, including gut development, gastrointestinal motility and control of pancreatic functions through vagal afferent pathways, including NO. Third, some examples of the intervention of the CCK and gastrin peptides are exposed in diseases, taking into account intervention of the classical receptor subtypes (CCK1 and CCK2 receptors) and their heterodimerisation as well as CCK-C receptor subtype. Finally, applications and future challenges are suggested in the nutritional field (performances) and in therapy with regards to the molecular forms or in relation with the type of receptor as well as new techniques to be utilised in detection or in therapy of disease. In conclusion, the present review underlines recent developments in this field: CCK and gastrin peptides and their receptors are the key factor of nutritional aspects; a better understanding of the mechanisms involved may increase the efficiency of the nutritional functions and the treatment of abnormalities under pathological conditions.

p/CAF modulates the activity of the transcription factor p48/Ptf1a involved in pancreatic acinar differentiation

p48, also called Ptf1a (pancreas-specific transcription factor 1a), is a tissue-restricted bHLH (basic helix loop helix) transcription factor which is critical for pancreatic commitment during development and for the activation and maintenance of the acinar differentiation programme in the exocrine pancreas. High-level expression of exocrine digestive enzymes, a hallmark of mature acinar cells, depends largely on the trimeric complex PTF1, formed by p48, RBP-L (recombination signal-binding protein 1-like) and a class A bHLH protein. In addition, p48 induces cell-cycle exit by controlling G1/S-phase progression. However, the mechanisms that mediate PTF1-dependent gene activation are poorly understood. In the present study, we report that p48 increases transcription through two activation domains located in its N-terminal region by recruiting transcriptional co-activators. The histone acetyltransferase cofactor p/CAF {p300/CBP [CREB (cAMP-response-element-binding protein)-binding protein]-associated factor} interacts with p48 in acinar cells in vivo and is associated with the promoter region of acinar genes targeted by the PTF1 complex. p/CAF potentiates PTF1 transcriptional activity by enhancing selectively the p48 transactivation activity. p/CAF promotes the nuclear accumulation of p48 and its in vivo acetylation in Lys200. The K200R mutation abolishes the transcriptional activity of p48, as well as its capacity to functionally co-operate with RBP-L to ensure effective PTF1-driven transcription, indicating that p/CAF-mediated acetylation of p48 is required for the full transcriptional activity of PTF1. In contrast, p/CAF did not co-operate with p48 in its growth regulatory effects. These results support a critical and selective role of p/CAF in PTF1-dependent gene activation during acinar differentiation.

Reg genes are CCK2 receptor targets in ElasCCK2 mice pancreas

We previously demonstrated that expression of the gastrin receptor, CCK2R, in pancreatic acini of transgenic ElasCCK2 mice induced alteration of acinar morphology and differentiation, increased sensitivity to a carcinogen and development of preneoplastic lesions and tumours. Reg proteins are suggested to be involved in pancreatic cancer and in regeneration of endocrine pancreas. Reg I gene is a known target of gastrin. We examined whether an expression of CCK2R in the pancreatic acini of ElasCCK2 mice is linked to induction of Reg proteins expression. We analyzed Reg expression by Western-blot and immunohistochemistry in pancreas from ElasCCK2 and control mice. Islet neogenesis, glucose homeostasis, insulin secretion and content were also evaluated. Reg I is exclusively produced in acini in ElasCCK2 and control mice. In tumoral pancreas, Reg I and Reg III proteins are expressed in duct-like cells in preneoplastic lesions or in the periphery of tumours and in adjacent acini. The expression of Reg III proteins is increased in ElasCCK2 pancreas before the development of preneoplastic lesions in a subpopulation of islet cells and in small islet-like cell clusters dispersed within the acinar tissue. Several criteria of an enhanced neogenesis are fulfilled in ElasCCK2 pancreas. Moreover, ElasCCK2 mice have an improved response to glucose load, an increased insulin secretion and a doubling of insulin content compared to control mice. We show that Reg proteins are targets of CCK2R activation and are induced during early steps of carcinogenesis in ElasCCK2 mice pancreas. Alterations of exocrine tissue homeostasis in ElasCCK2 pancreas concomitantly activate regenerative responses of the endocrine pancreas possibly linked to paracrine actions of Reg III proteins.

Pancreas transcription factor 1alpha expression is regulated in pancreatitis

BACKGROUND

Expression of acinar cell-specific genes requires the pancreas transcription factor 1alpha (Ptf1alpha). p48 is the only component of Ptf1alpha that is involved in both acinar gene regulation and pancreatic ontogenesis.

MATERIALS AND METHODS

To determine whether Ptf1alpha/p48 expression is regulated during pancreatitis, acute pancreatitis was induced in rats by repeated caerulein injections; early chronic pancreatitis by the combined administration of caerulein and cyclosporin A; and focal pancreas fibrosis by trinitrobenzene sulfonic acid infusion into the pancreatic duct. AR42J cells were used to examine caerulein effects on acinar cells. Ptf1alpha/p48 expression was examined using immunohistochemistry, Western blotting, and qRT-PCR methods.

RESULTS

In acute pancreatitis, Ptf1alpha/p48 decreased markedly within 6 h as determined by Western blotting and immunohistochemistry. After 24 h, Ptf1alpha/p48 increased continuously and normalized at day six. In contrast, pancreas amylase reached a nadir at 48 h, when Ptf1alpha/p48 had largely recovered. In the early chronic pancreatitis model Ptf1alpha/p48 levels did not completely recover even at day 14, and this was associated with a failure to restore normal histology and amylase content. qRT-PCR showed that p48 mRNA were reduced after pancreatitis induction and were followed by a decrease in elastase mRNA. In the focal pancreas fibrosis model, Ptf1alpha/p48 expression was undetectable in areas with substantial acinar cell loss and tubular complexes. Caerulein did not affect Ptf1alpha/p48 expression in AR42J cells.

CONCLUSIONS

Ptf1alpha/p48 protein and mRNA levels are regulated in acute and chronic experimental pancreatitis. Inability to re-express Ptf1alpha/p48 after injury may preclude acinar cell differentiation and appropriate pancreatic regeneration.

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.

Cholecystokinin-2 receptor modulates cell adhesion through beta 1-integrin in human pancreatic cancer cells

Several lines of evidence suggest that gastrin and the CCK-2 receptor (CCK2R) could contribute to pancreatic carcinogenesis by modulating processes such as proliferation, cell adhesion or migration. In the current study, we used a 'cancer gene array' and identified beta1-integrin subunit as a new gastrin-regulated gene in human pancreatic cancer cells. We also demonstrated that Src family kinases and the phosphatidylinositol-3-kinase (PI-3-kinase) pathway play a crucial role in the expression of beta1-integrin induced by gastrin. Our results also showed that gastrin modulates cell-substrate adhesion via beta1-integrin. Indeed, using blocking anti-beta1-integrin monoclonal antibodies, we completely reversed the increase in cell-substrate adhesion induced by gastrin. In addition, we observed that in response to gastrin, beta1-integrin is tyrosine phosphorylated by Src family kinases and associates with paxillin, a scaffold protein involved in focal adhesion and integrin signalling. This mechanism might be involved in gastrin-induced cell adhesion. Moreover, we showed in vivo that targeted CCK2R expression in the pancreas of Elas-CCK2 mice leads to the overexpression of beta1-integrin. This process may contribute to pancreatic tumour development observed in these transgenic animals.

Gastrin and cancer: a review

In 1905, a Cambridge physiologist, John Sydney Edkins, initially identified a hormone responsible of gastric acid secretion, which he called gastric secretin, or gastrin. While gastrin's role in acid secretion is now well defined, more recent studies have implicated the various isoforms of gastrin in cancer. Important advances in the last decade have included the recognition of biological activity for processing intermediates such as progastrin and the glycine-extended gastrin. Here, we give an overview of the roles of these peptides in cancer, highlighted by molecular, cellular and integrated studies on animal models for progastrin-derived peptides and their receptors.

Signaling the junctions in gut epithelium

This Perspective summarizes recent developments in our understanding of the signaling pathways involved in the regulation of epithelial cell adhesion in the gut. The role of phosphatidylinositol 3-kinase signaling in the modulation of adherens junctions, and the connections between tight junctions and nuclear transcription factors, are discussed. The effect of gastrins on adherens and tight junctions is presented as an example of the regulation of adhesion by growth factors. The consequences of dysregulation of adherens junctions and tight junctions for human pathology are also considered.