MTI/G-Gly mice and hGAS mice, overexpressing glycineextended gastrin (G-Gly) and progastrin, respectively, display colonic mucosa hyperplasia, hyperproliferation, and an increased susceptibility to intestinal neoplasia. Here, we have used these transgenic mice to analyze in vivo the modulation of intracellular signaling pathways that may be responsible for the proliferative effects of gastrin precursors. The expression, activation, and localization of signaling and cell-to-cell adhesion molecules were studied using immunofluorescence and Western blot techniques on colonic tissues derived from MTI/G-Gly, hGAS, or wild-type FVB/N mice. These analyses revealed an up-regulation of Src tyrosine kinase and related signaling pathways [phosphatidyl inositol 3V -kinase (PI3K)/ Akt, Janus-activated kinase (JAK) 2, signal transducer and activator of transcription (STAT) 3, and extracellular-signal regulated kinases (ERK)] in both MTI/G-Gly and hGAS mice compared with the wild-type control animals as well as an overexpression of transforming growth factor-A (TGF-A). In contrast, overexpression of the gastrin precursors did not affect the activation status of STAT1 nor the expression and the distribution of adhesion proteins ( focal adhesion kinase, cadherins, and catenins). We report for the first time that the transition from a normal colonic epithelium to a hyperproliferative epithelium in MTI/G-Gly and hGAS mice may be a consequence of the up-regulation of Src, PI3K/Akt, JAK2, STAT3, ERKs, and TGF-A. Deregulation of cell adhesion, a late event in tumor progression, does not occur in these transgenic models. (Cancer Res 2005; 65(7): 2770-7)

To date very few G protein-coupled receptors (GPCRs) have been shown to be connected to the Janus kinase (JAK)/STAT pathway. Thus our understanding of the mechanisms involved in the activation of this signaling pathway by GPCRs remains limited. In addition, little is known about the role of the JAK pathway in the physiological or pathophysiological functions of GPCRs. Here, we described a new mechanism of JAK activation that involves G␣ q proteins. Indeed, transfection of a constitutively activated mutant of G␣ q (Q209L) in COS-7 cells demonstrated that G␣ q is able to associate and activate JAK2. In addition, we showed that this mechanism is used to activate JAK2 by a GPCR principally coupled to G q , the CCK2 receptor (CCK2R), and involves a highly conserved sequence in GPCRs, the NPXXY motif. In a pancreatic tumor cell line expressing the endogenous CCK2R, we demonstrated the activation of the JAK2/STAT3 pathway by this receptor and the involvement of this signaling pathway in the proliferative effects of the CCK2R. In addition, we showed in vivo that the targeted CCK2R expression in pancreas of Elas-CCK2 mice leads to the activation of JAK2 and STAT3. This process may contribute to the increase of pancreas growth as well as the formation of preneoplastic lesions leading to pancreatic tumor development observed in these transgenic animals.

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 b1-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 b1-integrin induced by gastrin. Our results also showed that gastrin modulates cell-substrate adhesion via b1-integrin. Indeed, using blocking anti-b1-integrin monoclonal antibodies, we completely reversed the increase in cellsubstrate adhesion induced by gastrin. In addition, we observed that in response to gastrin, b1-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 b1-integrin. This process may contribute to pancreatic tumour development observed in these transgenic animals.

In humans, initial events of pancreatic carcinogenesis remain unknown, and the question of whether this cancer, which has a ductal phenotype, exclusively arises from duct cells has been raised. Previous studies have demonstrated that transgenic expression of the CCK2 receptor in acinar cells of ElasCCK2 mice plays a role in the development of pancreatic neoplasia. The aim of our study was to examine initial steps of carcinogenesis in ElasCCK2 mice, adding a supplementary defect by using a chemical carcinogen, azaserine. Results of posttreatment sequential immunohistochemical examinations and quantifications demonstrate that mice responded to azaserine. Transition of acinar cells into duct-like cells expressing Pdx1 and gastrin, as well as proliferation of acinar cells, were transiently observed in both transgenic and control mice. The carcinogen also induced formation of preneoplastic lesions, adenomas, exhibiting properties of autonomous growth. Importantly, expression of the CCK2 receptor increased the susceptibility of pancreas to azaserine. Indeed, treated ElasCCK2 mice exhibited larger areas of pancreatic acinar-ductal transition, increased cellular proliferation as well as larger adenomas areas vs. control mice. These amplified responses may be related to auto/paracrine stimulation of CCK2 receptor by gastrin expressed in newly formed duct-like cells. Our results demonstrate that activation of CCK2 receptor and azaserine result in cumulative effects to favor the emergence of a risk situation that is a potential site for initiation of carcinogenesis. ' 2005 Wiley-Liss, Inc.Key words: G protein coupled receptors; CCK2 receptor; precancerous conditions; gastrin; transdifferentiation; experimental animal model; developmental gene Peptides of the cholecystokinin (CCK)/gastrin family are present in the gastrointestinal tract where they are known to physiologically regulate gallbladder and bowel motility, pancreatic and gastric secretion as well as growth and trophicity of gastrointestinal epithelial mucosa. 1 Two receptors that mediate the actions of cholecystokinin and gastrin have been pharmacologically classified as CCK1 and CCK2 receptors on the basis of their binding affinity for their natural ligands. While the CCK1 receptor is highly selective towards cholecystokinin vs. gastrin, the CCK2 receptor binds the 2 agonists with similar high affinities. 2 Both are G-protein coupled receptors with extrinsic tyrosine kinase activity. They activate many intracellular mediators classically described in the regulation of mitogenesis by growth factors. 3 Mitogen-activated protein kinases, ERK1/2, Jun kinase and p38MAPK, as well as the phosphatidylinositol 3-kinase (PI3K) and early responsive genes (c-fos, c-myc and c-jun), are known targets of gastrin. 4-7 Several groups including ours, have documented the contribution of Src and focal adhesion kinase (Fak) families' tyrosine kinases upstream the activation of these pathways. 4,8 The role of gastrin and CCK2 receptors as positive regulators of proliferation of normal...

In ElasCCK2 transgenic mice expressing cholecystokinin (CCK2) receptor in acinar cells, pancreatic phenotypic alterations and preneoplastic lesions are observed. We determined whether activation of phospholipase C gamma1 (PLCc1), known to contribute to the tumorigenesis pathophysiology, could take place as a new signaling pathway induced by the CCK2 receptor. Overexpression and activation of the PLCc1 in response to gastrin was observed in acinar cells. The possibility that the C-terminal tyrosine 438 of the CCK2 receptor associates with the SH2 domains of PLCc1 was examined. A specific interaction was demonstrated using surface plasmon resonance, confirmed in a cellular system and by molecular modeling.