Activation of the mTOR signalling pathway is required for pancreatic growth in protease-inhibitor-fed mice.

Department of Molecular and Integrative Physiology, The University of Michigan Medical School, Ann Arbor, MI 48109, USA.
The Journal of Physiology (Impact Factor: 4.54). 07/2006; 573(Pt 3):775-86. DOI: 10.1113/jphysiol.2006.106914
Source: PubMed

ABSTRACT Cholecystokinin (CCK)-induced pancreatic growth in mice involves parallel increases in DNA and protein. The mammalian target of rapamycin (mTOR) signalling pathway regulates mRNA translation and its activation is implicated in growth of various tissues. The aim of this study was to elucidate whether mTOR activation is required for pancreatic growth in a mouse model of increased endogenous CCK release. In mice fed chow containing the synthetic protease inhibitor camostat, protein synthetic rates and phosphorylation of two downstream targets of mTOR, eukaryotic initiation factor 4E binding protein 1 (4E-BP1) and the ribosomal protein S6 (S6), increased in comparison with fasted controls. The camostat-induced increases in protein synthesis and 4E-BP1 and S6 phosphorylation were almost totally abolished by administration of the mTOR inhibitor rapamycin 1 h prior to camostat feeding. In contrast, the phosphorylation of ERK1/2 and JNK and the expression of the early response genes c-jun, c-fos, ATF3 and egr-1 induced by camostat feeding were not affected by rapamycin. In mice fed camostat for 7 days, the ratio of pancreatic to body weight increased by 143%, but when rapamycin was administered daily this was reduced to a 22% increase. Changes in pancreatic mass were paralleled by protein and DNA content following camostat feeding and rapamycin administration. Moreover, while BrdU incorporation, an indicator of DNA synthesis, was increased to 448% of control values after 2 days of camostat feeding, rapamycin administration completely inhibited this increase. We conclude that the mTOR signalling pathway is required for CCK-induced cell division and pancreatic growth.


Available from: Louis G D'Alecy, Sep 30, 2014
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Feeding mice with protease inhibitor (PI) leads to increased endogenous cholecystokinin (CCK) release and results in pancreatic growth. This adaptive response requires calcineurin (CN)-NFAT and AKT-mTOR pathways, but the genes involved, the dynamics of their expression, and other regulatory pathways remain unknown. Here, we examined the early (1-8 h) transcriptional program that underlies pancreatic growth. We found 314 upregulated and 219 downregulated genes with diverse temporal and functional profiles. Several new identifications include the following: stress response genes Gdf15 and Txnip, metabolic mediators Pitpnc1 and Hmges2, as well as components of growth factor response Fgf21, Atf3, and Egr1. The genes fell into seven self-organizing clusters, each with a distinct pattern of expression; a representative gene within each of the upregulated clusters (Egr1, Gadd45b, Rgs2, and Serpinb1a) was validated by qRT-PCR. Genes up at any point throughout the time course and CN-dependent genes were subjected to further bioinformatics-based networking and promoter analysis, yielding STATs as potential transcriptional regulators. As shown by PCR, qPCR, and Western blots, the active phospho-form of STAT3 and the Jak-STAT feedback inhibitor Socs2 were both increased throughout early pancreatic growth. Moreover, immunohistochemistry showed a CCK-dependent and acinar cell-specific increase in nuclear localization of p-STAT3, with >75% nuclear occupancy in PI-fed mice vs. <0.1% in controls. Thus, the study identified novel genes likely to be important for CCK-driven pancreatic growth, characterized and biologically validated the dynamic pattern of their expression and investigated STAT-Socs signaling as a new player in this trophic response.
    Physiological Genomics 01/2012; 44(1):14-24. DOI:10.1152/physiolgenomics.00255.2010 · 2.81 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: 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. 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 PD0325901 and trametinib (GSK1120212). It was determined that PD0325901 given twice 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. PD0325901 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. PD0325901 blocked adaptive growth when given prior to cell-cycle initiation but not after mitogenesis had been established. Furthermore, GSK1120212 a chemically distinct inhibitor of the ERK pathway that is now approved for clinical use inhibited growth similar to PD0325901. These data demonstrate that the ERK pathway is required for CCK-stimulated pancreatic adaptive growth.
    AJP Gastrointestinal and Liver Physiology 08/2014; 307(7). DOI:10.1152/ajpgi.00163.2014 · 3.74 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    AJP Gastrointestinal and Liver Physiology 03/2012; 302(12):G1381-96. DOI:10.1152/ajpgi.00129.2010 · 3.74 Impact Factor