Acinar Cell Proliferation Research Articles

Expression and localization of prominin-1 in isoproterenol-treated rat parotid gland

Prominin-1 (CD133) is a pentaspan cholesterol-binding membrane glycoprotein. Chronic treatment with isoproterenol, a beta-receptor agonist, induces several dramatic effects on salivary glands, such as enhanced DNA synthesis and proliferation of salivary acinar cells. In addition, the biosynthetic pathways of membrane lipids may be altered by the isoproterenol stimulation. The purpose of this study was to investigate the effect of isoproterenol administration on prominin-1 expression profiles in rat parotid gland by means of PCR and immunohistochemistry. Rats were chronically treated with the beta-adrenergic agonist for 1, 3, and 7 days. Our results showed that isoproterenol-treatment caused a down-regulation of prominin-1 on day 3 and 7 of treatment, as well as a differential immunostaining distribution pattern. This study suggests that isoproterenol-treatment may represent a useful tool to explore the molecular mechanisms involved in the synthesis and release of prominin-1. Such efforts could contribute to the development of diagnostic tools based on the detection of prominin-1 in biological fluids, such as saliva.

Insulin-Like Growth Factor–1 Preserves Salivary Gland Function After Fractionated Radiation

Radiotherapy for head-and-neck cancer consists of fractionated radiation treatments that cause significant damage to salivary glands leading to chronic salivary gland dysfunction with only limited prevention and treatment options currently available. This study examines the feasibility of IGF-1 in preserving salivary gland function following a fractionated radiation treatment regimen in a pre-clinical model. Mice were exposed to fractionated radiation, and salivary gland function and histological analyses of structure, apoptosis, and proliferation were evaluated. In this study, we report that treatment with fractionated doses of radiation results in a significant level of apoptotic cells in FVB mice after each fraction, which is significantly decreased in transgenic mice expressing a constitutively active mutant of Akt1 (myr-Akt1). Salivary gland function is significantly reduced in FVB mice exposed to fractionated radiation; however, myr-Akt1 transgenic mice maintain salivary function under the same treatment conditions. Injection into FVB mice of recombinant insulin-like growth factor-1 (IGF-1), which activates endogenous Akt, suppressed acute apoptosis and preserved salivary gland function after fractionated doses of radiation 30 to 90 days after treatment. FVB mice exposed to fractionated radiation had significantly lower levels of proliferating cell nuclear antigen-positive salivary acinar cells 90 days after treatment, which correlated with a chronic loss of function. In contrast, FVB mice injected with IGF-1 before each radiation treatment exhibited acinar cell proliferation rates similar to those of untreated controls. These studies suggest that activation of IGF-1-mediated pathways before head-and-neck radiation could modulate radiation-induced salivary gland dysfunction and maintain glandular homeostasis.

TRβ is the critical thyroid hormone receptor isoform in T3-induced proliferation of hepatocytes and pancreatic acinar cells

Thyroid hormones elicit many cellular and metabolic effects in various organs. Most of these actions, including mitogenesis, are mediated by the thyroid hormone 3,5,3'-triiodo-l-thyronine (T3) nuclear receptors (TRs). They are transcription factors, expressed as different isoforms encoded by the TRalpha and TRbeta genes. Here, experiments were performed to determine whether (i) T3-induces hepatocyte proliferation in mouse liver and pancreas, and, (ii) which TR isoform, is responsible for its mitogenic effect. Cell proliferation was measured by bromodeoxyuridine (BrdU) incorporation after T3 or the TRbeta agonist GC-1 in liver and pancreas of CD-1, C57BL, or TRalpha(0/0) mice. Cell cycle-associated proteins were measured by Western blot. T3 added to the diet at a concentration of 4 mg/kg caused a striking increase in BrdU incorporation in mouse hepatocytes. Increased BrdU incorporation was associated with enhanced protein levels of cyclin D1 and PCNA and decreased levels of p27. Treatment with GC-1, a selective agonist of the TRbeta isoform, also induced a strong mitogenic response of mouse hepatocytes and pancreatic acinar cells which was similar to that elicited by T3. Finally, treatment with T3 of mice TRalpha(0/0) induced a proliferative response in the liver and pancreas, similar to that of their wild type counterpart. These results demonstrate that T3 is a powerful inducer of cell proliferation in mouse liver and suggest that the beta-isoform is responsible for the hepatomitogenic activity of T3. The same isoform seems to also mediate the proliferation of mouse pancreatic acinar cells.

Hydrogen-rich saline ameliorates the severity of l-arginine-induced acute pancreatitis in rats

Molecular hydrogen, which reacts with the hydroxyl radical, has been considered as a novel antioxidant. Here, we evaluated the protective effects of hydrogen-rich saline on the l-arginine ( l-Arg)-induced acute pancreatitis (AP). AP was induced in Sprague–Dawley rats by giving two intraperitoneal injections of l-Arg, each at concentrations of 250 mg/100 g body weight, with an interval of 1 h. Hydrogen-rich saline (>0.6 mM, 6 ml/kg) or saline (6 ml/kg) was administered, respectively, via tail vein 15 min after each l-Arg administration. Severity of AP was assessed by analysis of serum amylase activity, pancreatic water content and histology. Samples of pancreas were taken for measuring malondialdehyde and myeloperoxidase. Apoptosis in pancreatic acinar cell was determined with terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling technique (TUNEL). Expression of proliferating cell nuclear antigen (PCNA) and nuclear factor kappa B (NF-κB) were detected with immunohistochemistry. Hydrogen-rich saline treatment significantly attenuated the severity of l-Arg-induced AP by ameliorating the increased serum amylase activity, inhibiting neutrophil infiltration, lipid oxidation and pancreatic tissue edema. Moreover, hydrogen-rich saline treatment could promote acinar cell proliferation, inhibit apoptosis and NF-κB activation. These results indicate that hydrogen treatment has a protective effect against AP, and the effect is possibly due to its ability to inhibit oxidative stress, apoptosis, NF-κB activation and to promote acinar cell proliferation.

Pancreatic secretory trypsin inhibitor: More than a trypsin inhibitor

Kazal-type serine protease inhibitor is one of the most important and widely distributed protease inhibitor families. Pancreatic secretory trypsin inhibitor (PSTI), also known as serine protease inhibitor Kazal type I(SPINK1), binds rapidly to trypsin, inhibits its activity and is likely to protect the pancreas from prematurely activated trypsinogen. Therefore, it is an important factor in the onset of pancreatitis. Recent studies found that PSTI/SPINK1 is also involved in self-regulation of acinar cell phagocytosis, proliferation and growth of a variety of cell lines. In addition, it takes part in the response to inflammatory factor or injury and is highly related to adult type II citrullinemia.

Inhibition of Transforming Growth Factor β Signaling by Halofuginone as a Modality for Pancreas Fibrosis Prevention

Chronic pancreatitis is characterized by inflammation and fibrosis. We evaluated the efficacy of halofuginone, an inhibitor of collagen synthesis and myofibroblast activation, in preventing cerulein-induced pancreas fibrosis. Collagen synthesis was evaluated by in situ hybridization and staining. Levels of prolyl 4-hydroxylase beta (P4Hbeta), cytoglobin/stellate cell activation-associated protein (Cygb/STAP), transgelin, tissue inhibitors of metalloproteinases, serum response factor, transforming growth factor beta (TGFbeta), Smad3, and pancreatitis-associated protein 1 (PAP-1) were determined by immunohistochemistry. Metalloproteinase activity was evaluated by zymography. Halofuginone prevented cerulein-dependent increase in collagen synthesis, collagen cross-linking enzyme P4Hbeta, Cygb/STAP, and tissue inhibitors of metalloproteinase 2. Halofuginone did not affect TGFbeta levels in cerulein-treated mice but inhibited serum response factor synthesis and Smad3 phosphorylation. In culture, halofuginone inhibited pancreatic stellate cell (PSC) proliferation and TGFbeta-dependent increase in Cygb/STAP and transgelin synthesis and metalloproteinase 2 activity. Halofuginone increased c-Jun N-terminal kinase phosphorylation in PSCs derived from cerulein-treated mice. Halofuginone prevented the increase in acinar cell proliferation and further increased the cerulein-dependent PAP-1 synthesis. Halofuginone inhibits Smad3 phosphorylation and increases c-Jun N-terminal kinase phosphorylation, leading to the inhibition of PSC activation and consequent prevention of fibrosis. Halofuginone increased the synthesis of PAP-1, which further reduces pancreas fibrosis. Thus, halofuginone might serve as a novel therapy for pancreas fibrosis.

Pancreas-specific Pten deficiency causes partial resistance to diabetes and elevated hepatic AKT signaling

PTEN, a negative regulator of the phosphatidylinositol-3-kinase/AKT pathway, is an important modulator of insulin signaling. To determine the metabolic function of pancreatic Pten, we generated pancreas-specific Pten knockout (PPKO) mice. PPKO mice had enlarged pancreas and elevated proliferation of acinar cells. They also exhibited hypoglycemia, hypoinsulinemia, and altered amino metabolism. Notably, PPKO mice showed delayed onset of streptozotocin (STZ)-induced diabetes and sex-biased resistance to high-fat-diet (HFD)-induced diabetes. To investigate the mechanism for the resistance to HFD-induced hyperglycemia in PPKO mice, we evaluated AKT phosphorylation in major insulin-responsive tissues: the liver, muscle, and fat. We found that Pten loss in the pancreas causes the elevation of AKT signaling in the liver. The phosphorylation of AKT and its downstream substrate GSK3beta was increased in the liver of PPKO mice, while PTEN level was decreased without detectable excision of Pten allele in the liver of PPKO mice. Proteomics analysis revealed dramatically decreased level of 78-kDa glucose-regulated protein (GRP78) in the liver of PPKO mice, which may also contribute to the lower blood glucose level of PPKO mice fed with HFD. Together, our findings reveal a novel response in the liver to pancreatic defect in metabolic regulation, adding a new dimension to understanding diabetes resistance.

Intercalated duct cells in the rat parotid gland may behave as tissue stem cells

This study was conducted to determine whether intercalated duct cells in the rat parotid gland have the properties of tissue stem cells. After induction of cellular proliferation by repeated administration of isoproterenol (IPR), a beta-adrenergic agonist, proliferation activity in acinar, intralobular, and intercalated ductal cells was quantified using Ki-67 immunohistochemistry. The total number of each type of component cell in a gland was also estimated in the course of IPR treatment. IPR was found to induce proliferation of acinar and intercalated duct cells, but not intralobular duct cells. The total number of acinar cells in a gland on day 5 of IPR treatment was 1.6 times of that at day 0 (baseline). In contrast, the total numbers of intercalated and intralobular duct cells did not change from baseline, indicating a high possibility that the proliferated intercalated duct cells differentiated into acinar cells. On days 2 to 3 of IPR treatment, intercalated duct cells with amylase-positive secretory granules were recognized in a region very close to the acini, and were suspected of being transitional cells from intercalated duct to acinar cells. This quantitative study indicates that intercalated duct cells may have the properties of tissue stem cells upon IPR stimulation.

Enhanced proliferation of acinar and progenitor cells by prophylactic pilocarpine treatment underlies the observed amelioration of radiation injury to parotid glands

Background Administration of pilocarpine before irradiation can ameliorate radiation-induced hyposalivation. Indirect evidence suggests that this effect may be mediated through induction of a compensatory response. In this study, this hypothesis is tested directly, by assessing the proliferation of progenitor and secretory cells in irradiated and non-irradiated parotid gland tissue. Methods In a rat model, parotid glands were unilaterally irradiated with a single dose of 15 Gy, 60 min after administration of pilocarpine (4.0 mg/kg). Rats were sacrificed for proliferating cell nuclear antigen (PCNA) labelling, assessing the number of proliferating progenitor and secretory cells, before, and 10 h, 1, 3, 7, 10, 20 and 30 days after irradiation. Results A small radiation-induced increase in PCNA expressing cells was observed, both in the acinar (secretory cells) and intercalated duct cell (containing the progenitor cells) compartment. This increment was significantly enhanced in pilocarpine pre-treated glands. In fact, in this group of animals increased proliferation was observed both in the irradiated and the shielded gland. Conclusions Amelioration of early loss of rat salivary gland function after radiation by pilocarpine pre-treatment is, at least in part, due to compensatory mechanisms through increased proliferation of undamaged cells.

β-Cell Proliferation, but Not Neogenesis, Following 60% Partial Pancreatectomy Is Impaired in the Absence of FoxM1

OBJECTIVE—This study was designed to determine whether the transcription factor FoxM1 was required for regeneration of β-cell mass via proliferation and/or neogenesis in the adult after 60% partial pancreatectomy (PPx).RESEARCH DESIGN AND METHODS—Adult mice with a pancreas-wide deletion of Foxm1 (Foxm1flox/flox;Pdx1-Cre [FoxM1Δpanc]) and their control littermates (Foxm1flox/flox) were subjected to PPx or a sham operation, after which islet expression of Foxm1 and several target genes, β-cell mass, proliferation, β-cell size, islet size, islet density, and neurogenin-3 expression were analyzed.RESULTS—In control mice, PPx stimulated β-cell proliferation and neogenesis and upregulated Foxm1 and several of its known targets (Plk1, Cenp-a, Birc5/Survivin, and Ccnb1) in islets. Within 1 week post-PPx, control mice underwent significant regeneration of β-cell mass, and average islet size within the regenerating lobe was similar to that after a sham operation. However, FoxM1Δpanc mice exhibited specific impairments in β-cell mass regeneration and islet growth after PPx, with reduced proliferation of α- and β-cells but no impairments in acinar or ductal cell proliferation. Interestingly, FoxM1 was not required for proliferation of β-cells within small endocrine cell clusters located in the regenerating portion of the pancreas but was specifically required for proliferation of β-cells within larger islets. Additionally, FoxM1 was not required for β-cell neogenesis following PPx.CONCLUSIONS—Our results indicate that FoxM1 is partially required for increased β-cell proliferation, but not β-cell neogenesis, stimulated by PPx. Furthermore, FoxM1 seems to be dispensable for proliferation of β-cells following neogenesis but is required for proliferation of preexisting β-cells.

Conditional inactivation of Myc impairs development of the exocrine pancreas

Recent studies have shown that Wnt/beta-catenin signaling is essential for development of the exocrine pancreas, but the role of beta-catenin-dependent target genes such as Myc during pancreatic development is not well known. Here, we show that tissue-specific deletion of Myc causes a slightly accelerated differentiation of pancreatic epithelial cells into endocrine cells and perturbs the proliferation of pancreatic progenitors and acinar precursor cells during early development, resulting in a severe reduction of the epithelial cell mass of pancreatic buds and an extensive acinar hypoplasia. Loss of Myc does not affect the expression of the tissue-specific transcription factor PTF1a, which is required for the differentiation of acinar cells. In contrast to its role for exocrine cell growth, the development of endocrine cell lineages is not significantly disturbed. These data suggest that Myc is required for the expansion of the exocrine pancreas. Our observations are consistent with the findings in beta-catenin-deficient pancreas, suggesting that Wnt/beta-catenin signaling affects the proliferation of pancreatic epithelial cells and acinar precursors through its target gene Myc.

629 Aging Attenuates PI3K/AKT Activation and Proliferation of Pancreatic Acinar Cells

629 Aging Attenuates PI3K/AKT Activation and Proliferation of Pancreatic Acinar Cells

A COOPERATIVE MODEL FOR PANCREATIC CANCER

Alterations in the TGFβ pathways have been found to be present in pancreatitis and more than 50% of pancreatic tumors. In transgenic animals, functional inactivation of TGFβ signaling targeted to acinar cells results in increased proliferation of pancreatic acinar cells and severely perturbed acinar differentiation. Unfortunately, with the exception of few proteins, the molecular machinery responsible for the long-term changes by which TGFβ induces neoplastic transformation in both, human and experimental models is not well understood. To better define the molecular events that participate in carcinogenesis by TGFβ inactivation, here, we have sought to characterize novel molecular alterations in the pancreas of mice overexpressing dominant negative TGFβ Receptor II, which results in inactivation of the TGFβ pathway, by using a combination of gene profiling and bioinformatics-based pathway reconstruction modeling. Subsequently, we chose to further characterize the expression and function on the most significantly upregulated gene, E6AP, which is an ubiquitin protein ligase displaying oncogenic properties by directly marking p53 for degradation by 26S proteasome. Further analysis and validation of these results by RT-PCR and immunohistochemical methods demonstrated increased expression of this molecule in the acinar cell compartment of TGFβ inactive mutants. Studies performed in pancreatic cells using inactivating mutants or constitutively active variants of several members of the TGFβ pathway reveal that the mechanisms involved in TGFβ regulation of E6AP are SMAD-independent. Thus, these results, using a controlled genetic animal model, suggest that the TGFβ and p53 tumor suppressor pathways are functionally interdependent and may crosstalk at the level of E6AP. Our findings distinctively represent excellent mechanistic information supporting the tumor suppressor role of TGFβ through E6AP from the p53 pathway.

Primary Culture of Pancreatic (Human) Acinar Cells

The acinar cell culture plays a very important role in research of pancreatic pathophysiology. The aim of this study was to establish a long-term culture of human (foetal) pancreatic acinar cells in standardized nutrient media with supplements. Acinar cells were prepared from pancreatic tissues obtained from aborted foetus (> or =35 weeks) with no prior pancreatic complications by collagenase digestion and cultured using different media and supplements. The purity and phenotype of acinar cells was confirmed by various staining techniques and FACS. The acinar cell proliferation was determined at different time intervals by Bromo-deoxyuridine (BrdU) incorporation, and metabolic enzyme activity was analysed. The acini could be cultured and maintained in Ham's F-12 K/M199 media in the presence of 5% BSA, 0.1 mg/ml STI, 10 ng/ml EGF, and 10% FCS with the same morphological appearance as that of freshly prepared for 12 days with maximum viability of 80-85% and formation of monolayer without extracellular matrix. A significant BrdU incorporation of acinar cells in primary culture was observed which was maximum (105%) at day four. Higher amylase and lipase activity was seen in freshly isolated acinar cells which decreased with time of the culture. The established human pancreatic acinar cell culture may act as an excellent model to study exocrine dysfunction or pancreatitis in response to acinar cell injury.

NF-κB p65 regulates nuclear translocation of Ku70 via degradation of heat shock cognate protein 70 in pancreatic acinar AR42J cells

Ku proteins such as Ku70 and Ku80 play key roles in multiple nuclear processes. Nuclear translocation of Ku70 is independent of Ku80 translocation and mediated by nuclear localization signal (NLS) receptors including importin-α. In the present study using pancreatic acinar AR42J cells, heat shock cognate protein 70 (Hsc70) was identified as the protein associated with NLS of Ku70. Interaction of Ku70 with importin-α and nuclear translocation of Ku70 was suppressed by overexpression of Hsc70, but enhanced by downregulation of Hsc70. The results suggest that the formation of Ku70 complex with Hsc70 prevents NLS of Ku70 from access of importin-α and inhibits nuclear translocation of Ku70. Since NF-κB p65 activation induced the decrease of Hsc70 level, the interaction of Ku70 with importin-α and nuclear translocation of Ku70 increased upon the activation of NF-κB p65. NF-κB p65 induced cell proliferation through decrease of Hsc70 levels and increase of nuclear translocation of Ku70. In the cells treated with cerulein as a physiological stimulus to activate NF-κB p65, nuclear translocation of Ku70 increased through NF-κB p65-mediated decrease of Hsc70 level. The results suggest that the involvement of NF-κB p65 in nuclear translocation of Ku70 may be mediated by Hsc70 degradation, which may play a key role in cell proliferation of pancreatic acinar AR42J cells.

Notch Signaling Is Required for Exocrine Regeneration After Acute Pancreatitis

The mechanisms for tissue regeneration and renewal after acute pancreatitis are not well understood but may involve activation of Notch signaling. To study the effect of Notch signaling ablation during acute experimental pancreatitis, we used a chemical and genetic approach to ablate Notch signaling in cerulein-induced pancreatitis in mice. Acute pancreatitis was induced by cerulein treatment in mice treated with the gamma-secretase inhibitor dibenzazepine or in conditional Notch1 knockout mice. Mice were characterized using immunohistologic, biochemical, and molecular methods. To investigate Notch and beta-catenin interaction, acinar 266-6 cells were analyzed using transfection and biochemical assays. Loss of Notch signaling results in impaired regeneration after acute pancreatitis with fewer mature acinar cells in dibenzazepine-treated and Notch1-deficient mice in the regenerative phase 3 days after induction. beta-catenin expression was increased and prolonged during exocrine regeneration. Crosstalk between Notch and beta-catenin-mediated signaling was identified, with Notch1-IC inhibiting beta-catenin-mediated transcriptional activity. This inhibition was dependent on a functional RAM domain. Inhibition of Notch signaling in vivo leads to impaired regeneration of the exocrine pancreas after acute pancreatitis. Our results suggest an interaction of Notch and Wnt signaling in pancreatic acinar cells, providing evidence for a role of these pathways in the regulation of the maturation process of acinar cells.

ABROGATION OF TGFβ SIGNALING IN THE PANCREAS OF MICE OVEREXPRESSING DOMINANT NEGATIVE TGFβ RECEPTOR II SHOWS ALTERATION OF ONCOGENIC COMPONENTS OF THE P53 PATHWAY

Genetic alterations in the TGF-β pathways have been found to be present in more than 50% of pancreatic tumors. In transgenic animals, functional inactivation of TGF-β signaling targeted to acinar cells results in increased proliferation of pancreatic acinar cells and severely perturbed acinar differentiation. Unfortunately, with the exception of few proteins, the molecular machinery responsible for the long-term changes by which TFG-β induces neoplastic transformation in both, human and experimental models is not well understood. To better define the molecular events that participate in carcinogenesis by TGFβ inactivation, here, we have sought to characterize novel molecular alterations in the pancreas of mice overexpressing dominant negative TGFβ Receptor II, which results in inactivation of the TGFβ pathway,by using a combination of gene profiling and bioinformatics-based pathway reconstruction modeling. Subsequently, we chose to further characterize the expression and function on the most significantly upregulated gene, E6AP, which is an ubiquitin protein ligase displaying oncogenic properties by directly marking p53 for degradation by 26S proteasome. Further analysis and validation of these results by RT-PCR and immunohistochemical methods demonstrated increased expression of this molecule in the acinar cell compartment of TGFβ inactive mutants. Studies performed in pancreatic cells using inactivating mutants or constitutively active variants of several members of the TGFβ pathway reveal that the mechanisms involved in TGFβ regulation of E6AP are SMAD-independent. Thus, these results, using a controlled genetic animal model, suggest that the TGFβ and p53 tumor suppressor pathways are functionally interdependent and may crosstalk at the level of E6AP. Our findings distinctively represent excellent mechanistic information supporting the tumor suppressor role of TGFβ through E6AP from the p53 pathway. RU is supported by Mayo Cancer Center and NIH Grants DK52913 and DK5662.

Pancreatic Endocrine and Exocrine Cell Ontogeny From Renal Capsule–transplanted Embryonic Stem Cells in Streptozocin-injured Mice

In this study, we describe pancreatic cell ontogeny in renal capsule-transplanted embryonic stem cells (ES) after injury by streptozocin (STZ), showing pancreatogenesis in situ. Seven-week-old female BALB/c nude mice were treated with either a single 175- or 200-mg/kg STZ dose, a regimen that induces substantial beta-cell damage without overt hyperglycemia, and transplanted 24 hr later with 1 x 10(5) ES. Immunohistochemistry was performed on ES tissue at 15, 21, and 28 days after transplantation using antibodies against stage- and lineage-specific pancreatic markers. After 21 days, PDX-1+ pancreatic foci first appeared in the renal capsule and expressed both amylase and endocrine hormones (insulin, glucagon, and somatostatin). These foci increased in size by day 28 because of acinar and duct cell proliferation, whereas endocrine cells remained non-dividing, and made up 2-4% of ES tumor volume. PDX-1, Nkx6.1, Ngn3, and ISL-1 protein localization patterns in pancreatic foci were comparable with embryonic pancreatogenesis. A prevalence of multihormonal endocrine cells, a characteristic of adult beta-cell regeneration, indicated a possible divergence from embryonic islet cell development. The results indicate that beta-cell damage, without overt hyperglycemia, induces a process of fetal-like pancreatogenesis in renal capsule-transplanted ES, leading to beta-cell neogenesis.

Rbp‐j regulates expansion of pancreatic epithelial cells and their differentiation into exocrine cells during mouse development

Notch signaling regulates cell fate determination in various tissues. We have reported the generation of mice with a pancreas-specific knockout of Rbp-j using Pdx.cre mice. Those mice exhibited premature endocrine and ductal differentiation. We now generated mice in which the Rbp-j gene was inactivated in Ptf1a-expressing cells using Ptf1a.cre mice. The timing of the Cre-mediated deletion in Rbp-j(f/f) Ptf1a.cre mice is 1 day later than that in Rbp-j(f/f) Pdx.cre mice. In Rbp-j(f/f) Ptf1a.cre mouse pancreases, at E13.5, the reduced Hes1 expression was accompanied by reduced epithelial growth, but premature endocrine cell differentiation was minimal. At E15.5, Pdx1 expression was repressed and acinar cell differentiation was reduced, but an increase in acinar cell proliferation was observed during the perinatal period. Our study indicates that, in addition to its role in preventing premature differentiation of early endocrine cells, Rbp-j regulates epithelial growth, Pdx1 expression, and acinar cell differentiation during mid-pancreatic development.

Overexpression of ErbB2 in the exocrine pancreas induces an inflammatory response but not increased proliferation

Tyrosine kinase receptors such as members of the epidermal growth factor receptor family and their respective ligands are frequently overexpressed in pancreatic cancer as well as in chronic pancreatitis. In this study, the role of ErbB2 in the exocrine pancreas was examined by ectopic overexpression under the control of the proximal rat elastase promoter. Three independent transgenic mouse lines overexpressing ErbB2 were established by pronuclear injection. Pancreatic mRNA and protein levels were analyzed by real time PCR, immunohistochemistry and immunoblot analysis, RAS activity by using a specific immunoprecipitation assay and various kinase activities by phosphospecific antibodies. Overexpression of ErbB2 in the exocrine pancreas resulted in increased RAS activity and downstream activation of ERK1/2, but not in transgenic increased proliferation of acinar and ductal cells. At later timepoints, some mice showed focal areas of acinar cell damage with upregulated mRNA levels for Cyclin D1 and p16(INK4a). Despite the increased mRNA level, cyclin D1 protein levels were downregulated. We observed areas of focal infiltrations with inflammatory cells interspersed in the exocrine pancreas. NF-kappaB activity was induced in transgenic acinar cells compared with controls contributing to high levels of chemokine and cytokine gene expression such as CCR-1 and CCL3. These data suggest that overexpression of ErbB2 in acinar cells leads to increased RAS activity without cell cycle progression and mediates inflammation via NF-kappaB. We conclude that the biological response of ErbB2/RAS signaling depends highly on cellular context.