TRANSDUCTION of a mitogenic signal from the cell membrane to the nucleus involves the adapter proteins SHC and Grb2, which mediate activation of the Ras/mitogen-activated protein (MAP) kinase pathway^1–5. In contrast to receptor tyrosine kinases (RTKs), the signalling steps leading to Ras/MAP kinase activation by G-protein-coupled receptors (GPCRs) are still poorly characterized but appear to include βγ subunits of heterotrimeric G-proteins and as-yet unidentified tyrosine kinases^6–8. We report here that the epidermal growth factor receptor (EGFR) and the neu oncoprotein become rapidly tyrosine-phosphorylated upon stimulation of Rat-1 cells with the GPCR agonists endothelin-1, lysophosphatic acid and thrombin, suggesting that there is an intracellular mechanism for transactivation. Specific inhibition of EGFR function by either the selective tyrphostin AG1478 or a dominant-negative EGFR mutant suppressed MAP kinase activation and strongly inhibited induction of fos gene expression and DNA synthesis. Our results demonstrate a role for RTKs as downstream mediators in GPCR mitogenic signalling and suggest a ligand-independent mechanism of RTK activation through intracellular signal crosstalk.

David Whitcomb, Bernie Devlin and colleagues report the results of a genome-wide association study of pancreatitis. They identify common variants at two loci associated with risk of this disease, including one on the X chromosome that shows strong evidence of interaction with alcohol consumption. Pancreatitis is a complex, progressively destructive inflammatory disorder. Alcohol was long thought to be the primary causative agent, but genetic contributions have been of interest since the discovery that rare PRSS1, CFTR and SPINK1 variants were associated with pancreatitis risk. We now report two associations at genome-wide significance identified and replicated at PRSS1-PRSS2 (P < 1 × 10−12) and X-linked CLDN2 (P < 1 × 10−21) through a two-stage genome-wide study (stage 1: 676 cases and 4,507 controls; stage 2: 910 cases and 4,170 controls). The PRSS1 variant likely affects disease susceptibility by altering expression of the primary trypsinogen gene. The CLDN2 risk allele is associated with atypical localization of claudin-2 in pancreatic acinar cells. The homozygous (or hemizygous in males) CLDN2 genotype confers the greatest risk, and its alleles interact with alcohol consumption to amplify risk. These results could partially explain the high frequency of alcohol-related pancreatitis in men (male hemizygote frequency is 0.26, whereas female homozygote frequency is 0.07).

Pancreatitis starts with primarily sterile local inflammation that induces systemic inflammatory response syndrome, followed by compensatory anti-inflammatory response syndrome (CARS). We investigated the mechanisms of these processes in mice and human serum. We induced severe acute pancreatitis by partial duct ligation with caerulein stimulation or intraperitoneal injection of l-arginine in mice with deletion of interleukin (IL)12B, NLRP3, or IL18 and in mice given MCC950, a small molecule inhibitor of the NLRP3-inflammasome. Pancreata were collected from mice and analyzed by histology, and cytokine levels were measured in serum samples. We measured activation of adaptive immune responses in mice with pancreatitis by flow cytometry analysis of T cells (CD25 and CD69) isolated from the spleen. Differentiation of T-helper (Th1) cells, Th2 cells, and T-regulatory cells was determined by nuclear staining for TBET, GATA3, and FOXP3. We performed transcriptome analysis of mouse lymph nodes and bone marrow-derived macrophages after incubation with acini. We measured levels of cytokines in serum samples from patients with mild and severe acute pancreatitis. Activation of the adaptive immune response in mice was initiated by macrophage-derived, caspase 1-processed cytokines and required activation of NLRP3 (confirmed in serum samples from patients with pancreatitis). Spleen cells from mice with pancreatitis had increases in Th2 cells but not in Th1 cells. Bone marrow-derived macrophages secreted IL1B and IL18, but not IL12, after co-incubation with pancreatic acini. T-cell activation and severity of acute pancreatitis did not differ significantly between IL12B-deficient and control mice. In contrast, NLRP3- or IL18-deficient mice had reduced activation of T cells and no increase in Th2 cell-mediated responses compared with control mice. The systemic type 2 immune response was mediated by macrophage-derived cytokines of the IL1 family. Specifically, IL18 induced a Th2 cell-mediated response in the absence of IL12. MCC950 significantly reduced neutrophil infiltration, T-cell activation, and disease severity in mice. In mice with severe pancreatitis, we found systemic inflammatory response syndrome and compensatory anti-inflammatory response syndrome developed in parallel. Infiltrating macrophages promote inflammation and simultaneously induce a Th2 cell-mediated response via IL18. Inhibition of NLRP3 reduces systemic inflammatory response syndrome and compensatory anti-inflammatory response syndrome and might be used to treat patients with severe pancreatitis.

Objective Pancreatic cancer is characterised by invasive tumour spread and early metastasis formation. During epithelial–mesenchymal transition, loss of the cell adhesion molecule E-cadherin is frequent and can be caused by genetic or epigenetic modifications, recruitment of transcriptional activators/repressors or post-translational modifications. A study was undertaken to investigate how E-cadherin expression in human pancreatic adenocarcinoma and pancreatic cancer cell lines is regulated. Methods In 25 human pancreatic cancer resection specimens, the coding region of the E-cadherin gene (CDH1) was sequenced for somatic mutations. The tumour samples and 11 established human pancreatic cancer cell lines were analysed by immunohistochemistry, western blot analysis, chromatin immunoprecipitation and methylation-specific PCR. The role of specific histone deacetylase inhibitors (HDACi) on pancreatic tumour cell migration and proliferation was studied in vitro. Results Neither somatic mutations nor CDH1 promoter hypermethylation were found to be responsible for downregulation of E-cadherin in pancreatic cancer. In the transcriptionally active CDH1 promoter, acetylation of histones H3 and H4 was detected whereas HDAC1 and HDAC2 were found attached only to a silent promoter. Expression of ZEB1, a transcription factor known to recruit HDACs, was seen in E-cadherin-deficient cell lines in which ZEB1/HDAC complexes were found attached to the CDH1 promoter. Moreover, knockdown of ZEB1 prevented HDAC from binding to the CDH1 promoter, resulting in histone acetylation and expression of E-cadherin. HDACi treatment attenuated tumour cell migration and proliferation. Conclusions These findings imply an important role for histone deacetylation in the downregulation of E-cadherin in human pancreatic cancer. Recruitment of HDACs to the CDH1 promoter is regulated by the transcription factor ZEB1, and inhibition of HDACs may be a promising antitumour therapy for pancreatic cancer.

Background & Aims Acute pancreatitis is characterized by premature intracellular activation of digestive proteases within pancreatic acini and a consecutive systemic inflammatory response. We investigated how these processes interact during severe pancreatitis in mice. Methods Pancreatitis was induced in C57Bl/6 wild-type (control), cathepsin B (CTSB)-knockout, and cathepsin L-knockout mice by partial pancreatic duct ligation with supramaximal caerulein injection, or by repetitive supramaximal caerulein injections alone. Immune cells that infiltrated the pancreas were characterized by immunofluorescence detection of Ly6g, CD206, and CD68. Macrophages were isolated from bone marrow and incubated with bovine trypsinogen or isolated acinar cells; the macrophages were then transferred into pancreatitis control or cathepsin-knockout mice. Activities of proteases and nuclear factor (NF)-κB were determined using fluorogenic substrates and trypsin activity was blocked by nafamostat. Cytokine levels were measured using a cytometric bead array. We performed immunohistochemical analyses to detect trypsinogen, CD206, and CD68 in human chronic pancreatitis (n = 13) and acute necrotizing pancreatitis (n = 15) specimens. Results Macrophages were the predominant immune cell population that migrated into the pancreas during induction of pancreatitis in control mice. CD68-positive macrophages were found to phagocytose acinar cell components, including zymogen-containing vesicles, in pancreata from mice with pancreatitis, as well as human necrotic pancreatic tissues. Trypsinogen became activated in macrophages cultured with purified trypsinogen or co-cultured with pancreatic acini and in pancreata of mice with pancreatitis; trypsinogen activation required macrophage endocytosis and expression and activity of CTSB, and was sensitive to pH. Activation of trypsinogen in macrophages resulted in translocation of NF-kB and production of inflammatory cytokines; mice without trypsinogen activation (CTSB-knockout mice) in macrophages developed less severe pancreatitis compared with control mice. Transfer of macrophage from control mice to CTSB-knockout mice increased the severity of pancreatitis. Inhibition of trypsin activity in macrophages prevented translocation of NF-κB and production of inflammatory cytokines. Conclusions Studying pancreatitis in mice, we found activation of digestive proteases to occur not only in acinar cells but also in macrophages that infiltrate pancreatic tissue. Activation of the proteases in macrophage occurs during endocytosis of zymogen-containing vesicles, and depends on pH and CTSB. This process involves macrophage activation via NF-κB-translocation, and contributes to systemic inflammation and severity of pancreatitis.

Chronic pancreatitis is a common inflammatory disease of the pancreas. Mutations in the genes encoding cationic trypsinogen (PRSS1)¹ and the pancreatic secretory trypsin inhibitor (SPINK1)² are associated with chronic pancreatitis. Because increased proteolytic activity owing to mutated PRSS1 enhances the risk for chronic pancreatitis, mutations in the gene encoding anionic trypsinogen (PRSS2) may also predispose to disease. Here we analyzed PRSS2 in individuals with chronic pancreatitis and controls and found, to our surprise, that a variant of codon 191 (G191R) is overrepresented in control subjects: G191R was present in 220/6,459 (3.4%) controls but in only 32/2,466 (1.3%) affected individuals (odds ratio 0.37; P = 1.1 × 10⁻⁸). Upon activation by enterokinase or trypsin, purified recombinant G191R protein showed a complete loss of trypsin activity owing to the introduction of a new tryptic cleavage site that renders the enzyme hypersensitive to autocatalytic proteolysis. In conclusion, the G191R variant of PRSS2 mitigates intrapancreatic trypsin activity and thereby protects against chronic pancreatitis.