Interferon regulatory factor-2 regulates exocytosis mechanisms mediated by SNAREs in pancreatic acinar cells

Rab7 localized on zymogen granules is involved in maturation but not in autophagy or regulated exocytosis in pancreatic acinar cells

Rab7 is known to function in the autophagy and endocytosis pathways in eukaryocytes and is related to various diseases. We recently reported that Rab7 plays a protective role against acute pancreatitis. However, its physiological function in exocytic cells remains unclear. Therefore, we investigated the role of Rab7 in pancreas-specific Rab7 knockout mice (Rab7Δpan). Immunofluorescence microscopy revealed that Rab7 colocalized with amylase in pancreatic acinar cells of wild-type mice, but not in Rab7Δpan mice. Western blotting confirmed Rab7 localization in the zymogen granule (ZG) membranes of wild-type mice. Cholecystokinin (CCK)-stimulated amylase secretion examined using isolated pancreatic acini was similar in Rab7Δpan and wild-type mice. In contrast, electron microscopy revealed that the diameters of ZGs were shorter and the number of ZGs was larger in the pancreatic acinar cells of Rab7Δpan mice than in those of wild-type mice. However, the number of ZGs decreased in both Rab7Δpan and wild-type mice after 24 h of starvation. In addition, the amount of amylase in the pancreas was decreased in both Rab7Δpan and wild-type mice. These data indicate that Rab7 localized on ZGs plays a crucial role in the maturation of ZGs but not in their autophagy or regulated exocytosis in pancreatic acinar cells.

Genetic susceptibility to post-endoscopic retrograde cholangiopancreatography pancreatitis identified in propensity score-matched analysis

BACKGROUND/AIMS

A previous history of post-endoscopic retrograde cholangiopancreatography (ERCP) pancreatitis (PEP) is a risk factor for PEP, suggesting that there may be a genetic predisposition to PEP. However, nothing is known about this yet. The aim of this study was to identify genetic variations associated with PEP.

METHODS

A cohort of high-risk PEP patients was queried from December 2016 to January 2019. For each PEP case, two propensity score-matched controls were selected. Whole exome sequencing was performed using blood samples. Genetic variants reported to be related to pancreatitis were identified. To discover genetic variants that predispose to PEP, a logistic regression analysis with clinical adjustment was performed. Gene-wise analyses were also conducted.

RESULTS

Totals of 25 PEP patients and 50 matched controls were enrolled. Among the genetic variants reported to be associated with pancreatitis, only CASR rs1042636 was identified, and it showed no significant difference between the case and control groups. A total of 54,269 non-synonymous variants from 14,313 genes was identified. Logistic regression analysis of these variants showed that the IRF2BP1 rs60158447 GC genotype was significantly associated with the occurrence of PEP (odds ratio 2.248, FDR q value = 0.005). Gene-wise analyses did not show any significant results.

CONCLUSION

This study found that the IRF2BP1 gene variant was significantly associated with PEP. This genetic variant is a highly targeted PEP risk factor candidate and can be used for screening high-risk PEP groups before ERCP through future validation. (ClinicalTrials.gov no. NCT02928718).

Loss of CAPS2/Cadps2 leads to exocrine pancreatic cell injury and intracellular accumulation of secretory granules in mice

The type 2 Ca2+-dependent activator protein for secretion (CAPS2/CADPS2) regulates dense-core vesicle trafficking and exocytosis and is involved in the regulated release of catecholamines, peptidergic hormones, and neuromodulators. CAPS2 is expressed in the pancreatic exocrine acinar cells that produce and secrete digestive enzymes. However, the functional role of CAPS2 in vesicular trafficking and/or exocytosis of non-regulatory proteins in the exocrine pancreas remains to be determined. Here, we analyzed the morpho-pathological indicators of the pancreatic exocrine pathway in Cadps2-deficient mouse models using histochemistry, biochemistry, and electron microscopy. We used whole exosome sequencing to identify CADPS2 variants in patients with chronic pancreatitis (CP). Caps2/Cadps2-knockout (KO) mice exhibited morphophysiological abnormalities in the exocrine pancreas, including excessive accumulation of secretory granules (zymogen granules) and their amylase content in the cytoplasm, deterioration of the fine intracellular membrane structures (disorganized rough endoplasmic reticulum, dilated Golgi cisternae, and the appearance of empty vesicles and autophagic-like vacuoles), as well as exocrine pancreatic cell injury, including acinar cell atrophy, increased fibrosis, and inflammatory cell infiltration. Pancreas-specific Cadps2 conditional KO mice exhibited pathological abnormalities in the exocrine pancreas similar to the global Cadps2 KO mice, indicating that these phenotypes were caused either directly or indirectly by CAPS2 deficiency in the pancreas. Furthermore, we identified a rare variant in the exon3 coding region of CADPS2 in a non-alcoholic patient with CP and showed that Cadps2-dex3 mice lacking CAPS2 exon3 exhibited symptoms similar to those exhibited by the Cadps2 KO and cKO mice. These results suggest that CAPS2 is critical for the proper functioning of the pancreatic exocrine pathway, and its deficiency is associated with a risk of pancreatic acinar cell pathology.

The IRF2/CENP-N/AKT signaling axis promotes proliferation, cell cycling and apoptosis resistance in nasopharyngeal carcinoma cells by increasing aerobic glycolysis

Background

Centromere protein N (CENP-N) has been reported to be highly expressed in malignancies, but its role and mechanism in nasopharyngeal carcinoma (NPC) are unknown.

Methods

Abnormal CENP-N expression from NPC microarrays of GEO database was analyzed. CENP-N expression level was confirmed in NPC tissues and cell lines. Stable CENP-N knockdown and overexpression NPC cell lines were established, and transcriptome sequencing after CENP-N knockdown was performed. In vitro and in vivo experiments were performed to test the impact of CENP-N knockdown in NPC cells. ChIP and dual luciferase reporter assays were used to verify the combination of IRF2 and CENP-N. Western blot analysis, cellular immunofluorescence, immunoprecipitation and GST pulldown assays were used to verify the combination of CENP-N and AKT.

Results

CENP-N was confirmed to be aberrantly highly expressed in NPC tissues and cell lines and to be associated with high ¹⁸F-FDG uptake in cancer nests and poor patient prognosis. Transcriptome sequencing after CENP-N knockdown revealed that genes with altered expression were enriched in pathways related to glucose metabolism, cell cycle regulation. CENP-N knockdown inhibited glucose metabolism, cell proliferation, cell cycling and promoted apoptosis. IRF2 is a transcription factor for CENP-N and directly promotes CENP-N expression in NPC cells. CENP-N affects the glucose metabolism, proliferation, cell cycling and apoptosis of NPC cells in vitro and in vivo through the AKT pathway. CENP-N formed a complex with AKT in NPC cells. Both an AKT inhibitor (MK-2206) and a LDHA inhibitor (GSK2837808A) blocked the effect of CENP-N overexpression on NPC cells by promoting aerobic glycolysis, proliferation, cell cycling and apoptosis resistance.

Conclusions

The IRF2/CENP-N/AKT axis promotes malignant biological behaviors in NPC cells by increasing aerobic glycolysis, and the IRF2/CENP-N/AKT signaling axis is expected to be a new target for NPC therapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-021-02191-3.

Susceptibility Factors and Cellular Mechanisms Underlying Alcoholic Pancreatitis

Alcohol is a major cause of acute and chronic pancreatitis. There have been some recent advances in the understanding of the mechanisms underlying alcoholic pancreatitis, which include perturbation in mitochondrial function and autophagy and ectopic exocytosis, with some of these cellular events involving membrane fusion soluble N-ethylmaleimide-sensitive factor receptor protein receptor proteins. Although new insights have been unraveled recently, the precise mechanisms remain complex, and their finer details have yet to be established. The overall pathophysiology of pancreatitis involves not only the pancreatic acinar cells but also the stellate cells and duct cells. Why only some are more susceptible to pancreatitis and with increased severity, while others are not, would suggest that there may be undefined protective factors or mechanisms that enhance recovery and regeneration after injury. Furthermore, there are confounding influences of lifestyle factors such as smoking and diet, and genetic background. Whereas alcohol and smoking cessation and a generally healthy lifestyle are intuitively the advice given to these patients afflicted with alcoholic pancreatitis in order to reduce disease recurrence and progression, there is as yet no specific treatment. A more complete understanding of the pathogenesis of pancreatitis from which novel therapeutic targets could be identified will have a great impact, particularly with the stubbornly high fatality (>30%) of severe pancreatitis. This review focuses on the susceptibility factors and underlying cellular mechanisms of alcohol injury on the exocrine pancreas.

Early Intra-Acinar Events in Pathogenesis of Pancreatitis

Premature activation of digestive enzymes in the pancreas has been linked to development of pancreatitis for more than a century. Recent development of novel models to study the role of pathologic enzyme activation has led to advances in our understanding of the mechanisms of pancreatic injury. Colocalization of zymogen and lysosomal fraction occurs early after pancreatitis-causing stimulus. Cathepsin B activates trypsinogen in these colocalized organelles. Active trypsin increases permeability of these organelles resulting in leakage of cathepsin B into the cytosol leading to acinar cell death. Although trypsin-mediated cell death leads to pancreatic injury in early stages of pancreatitis, multiple parallel mechanisms, including activation of inflammatory cascades, endoplasmic reticulum stress, autophagy, and mitochondrial dysfunction in the acinar cells are now recognized to be important in driving the profound systemic inflammatory response and extensive pancreatic injury seen in acute pancreatitis. Chymotrypsin, another acinar protease, has recently been shown be play critical role in clearance of pathologically activated trypsin protecting against pancreatic injury. Mutations in trypsin and other genes thought to be associated with pathologic enzyme activation (such as serine protease inhibitor 1) have been found in familial forms of pancreatitis. Sustained intra-acinar activation of nuclear factor κB pathway seems to be key pathogenic mechanism in chronic pancreatitis. Better understanding of these mechanisms will hopefully allow us to improve treatment strategies in acute and chronic pancreatitis.

Disruption of Small GTPase Rab7 Exacerbates the Severity of Acute Pancreatitis in Experimental Mouse Models

Although aberrations of intracellular vesicle transport systems towards lysosomes including autophagy and endocytosis are involved in the onset and progression of acute pancreatitis, the molecular mechanisms underlying such aberrations remain unclear. The pathways of autophagy and endocytosis are closely related, and Rab7 plays crucial roles in both. In this study, we analyzed the function of Rab7 in acute pancreatitis using pancreas-specific Rab7 knockout (Rab7Δpan) mice. In Rab7Δpan pancreatic acinar cells, the maturation steps of both endosomes and autophagosomes were deteriorated, and the lysosomal functions were affected. In experimental models of acute pancreatitis, the histopathological severity, serum amylase concentration and intra-pancreatic trypsin activity were significantly higher in Rab7Δpan mice than in wild-type mice. Furthermore, the autophagy process was blocked in Rab7Δpan pancreas compared with wild-type mice. In addition, larger autophagic vacuoles that colocalize with early endosome antigen 1 (EEA1) but not with lysosomal-associated membrane protein (LAMP)-1 were much more frequently formed in Rab7Δpan pancreatic acinar cells. Accordingly, Rab7 deficiency exacerbates the severity of acute pancreatitis by impairing the autophagic and endocytic pathways toward lysosomes.

Requirement of Gαq/Gα11 Signaling in the Preservation of Mouse Intestinal Epithelial Homeostasis

BACKGROUND & AIMS

Proliferation, differentiation, and morphogenesis of the intestinal epithelium are tightly regulated by a number of molecular pathways. Coordinated action of intestine is achieved by gastrointestinal hormones, most of which exert these actions through G-protein-coupled receptors. We herein investigated the role of Gα_q/11-mediated signaling in intestinal homeostasis.

METHODS

Intestinal tissues from control (Gnaq^flox/floxGna11^+/+ ), Int-G_q knock-out (KO) (VilCre^+/-Gnaq^flox/floxGna11^+/+ ), G₁₁ KO (Gnaq^flox/floxGna11^-/- ), and Int-G_q/G₁₁ double knock-out (DKO) (VilCre^+/-Gnaq^flox/floxGna11^-/- ) mice were examined by microscopy, transmission electron microscopy, and immunohistochemistry. The effect of Gα_q/11-mediated signaling was studied in the cell lineage, proliferation, and apoptosis. Dextran sodium sulfate (DSS) colitis was induced to study the role of Gα_q/11 in colon.

RESULTS

Paneth cells were enlarged, increased in number, and mislocalized in Int-Gq/G11 DKO small intestine. Paneth cells also reacted with PAS and Muc2 antibody, indicating an intermediate character of Paneth and goblet cells. The nuclear β-catenin, T-cell factor 1, and Sox9 expression were reduced severely in the crypt base of Int-Gq/G11 DKO intestine. Proliferation was activated in the crypt base and apoptosis was enhanced along the crypt. Int-Gq/G11 DKO mice were susceptible to DSS colitis. Proliferation was inhibited in the crypt of unaffected and regenerative areas. Cystic crypts, periodic acid-Schiff-positive cells, and Muc2-positive cells were unusually observed in the ulcerative region.

CONCLUSIONS

The Gα_q/11-mediated pathway plays a pivotal role in the preservation of intestinal homeostasis, especially in Paneth cell maturation and positioning. Wnt/β-catenin signaling was reduced significantly in the crypt base in Gα_q/G₁₁-deficient mice, resulting in the defective maturation of Paneth cells, induction of differentiation toward goblet cells, and susceptibility to DSS colitis.

Bioinformatic screening of autoimmune disease genes and protein structure prediction with FAMS for drug discovery

Autoimmune diseases are often intractable because their causes are unknown. Identifying which genes contribute to these diseases may allow us to understand the pathogenesis, but it is difficult to determine which genes contribute to disease. Recently, epigenetic information has been considered to activate/deactivate disease-related genes. Thus, it may also be useful to study epigenetic information that differs between healthy controls and patients with autoimmune disease. Among several types of epigenetic information, promoter methylation is believed to be one of the most important factors. Here, we propose that principal component analysis is useful to identify specific gene promoters that are differently methylated between the normal healthy controls and patients with autoimmune disease. Full Automatic Modeling System (FAMS) was used to predict the three-dimensional structures of selected proteins and successfully inferred relatively confident structures. Several possibilities of the application to the drug discovery based on obtained structures are discussed.

The roles of interferon regulatory factors 1 and 2 in the progression of human pancreatic cancer

OBJECTIVE

Pancreatic cancer is one of the most malignant diseases worldwide. Interferon regulatory factor (IRF) 1 and IRF2 function as a tumor suppressor and oncoprotein, respectively, in several types of cancers. We investigated whether IRF1 and IRF2 are involved in the progression of pancreatic cancer.

METHODS

We examined the expressions of IRF1 and IRF2 in pancreatic cancer specimens and analyzed the association with clinicopathologic features. We evaluated the biological effects of IRF1 and IRF2 using a pancreatic cancer cell line.

RESULTS

The expression levels of IRF1 and IRF2 were decreased and increased, respectively, in the pancreatic cancer cells compared with those observed in the paired normal areas. A higher expression of IRF1 was associated with better features of tumor differentiation, infiltration depth, tumor size, and survival, whereas that of IRF2 was associated with a worse feature of tumor infiltration depth. Interferon regulatory factor 2-overexpressing PANC-1 cells exhibited an increase in cell growth, less apoptotic features, and chemoresistance to gemcitabine treatment. In contrast, IRF1-overexpressing cells exhibited the opposite characteristics.

CONCLUSIONS

Interferon regulatory factors 1 and 2 may regulate the progression of pancreatic cancer by functioning as an antioncoprotein and oncoprotein, respectively. These molecules may serve as potential targets of therapy.

New insights into the pathogenesis of pancreatitis

PURPOSE OF REVIEW

In this article, we review important advances in our understanding of the mechanisms of pancreatitis.

RECENT FINDINGS

The relative contributions of intrapancreatic trypsinogen activation and nuclear factor kappa B (NFκB) activation, the two major early independent cellular events in pancreatitis, have been investigated using novel genetic models. Trypsinogen activation has traditionally held the spotlight for many decades as the central pathogenic event of pancreatitis. However, recent experimental evidence points to the role of trypsin activation in early acinar cell damage but not in the inflammatory response of acute pancreatitis, which was shown to be induced by NFκB activation. Further, chronic pancreatitis developed independently of trypsinogen activation in the caerulein model. Sustained NFκB activation, but not persistent intra-acinar expression of active trypsin, was shown to result in chronic pancreatitis. Calcineurin-NFAT (nuclear factor of activated T-cells) signaling was shown to mediate downstream effects of pathologic rise in intracellular calcium. Interleukin-6 was identified as a key cytokine mediating pancreatitis-associated lung injury.

SUMMARY

Recent advances challenge the long-believed trypsin-centered understanding of pancreatitis. It is becoming increasingly clear that activation of intense inflammatory signaling mechanisms in acinar cells is crucial to the pathogenesis of pancreatitis, which may explain the strong systemic inflammatory response in pancreatitis.

Corticotropin-releasing factor receptor 2 mediates sex-specific cellular stress responses

Although females suffer twice as much as males from stress-related disorders, sex-specific participating and pathogenic cellular stress mechanisms remain uncharacterized. Using corticotropin-releasing factor receptor 2-deficient (Crhr2-/-) and wild-type (WT) mice, we show that CRF receptor type 2 (CRF2) and its high-affinity ligand, urocortin 1 (Ucn1), are key mediators of the endoplasmic reticulum (ER) stress response in a murine model of acute pancreatic inflammation. Ucn1 was expressed de novo in acinar cells of male, but not female WT mice during acute inflammation. Upon insult, acinar Ucn1 induction was markedly attenuated in male but not female Crhr2-/- mice. Crhr2-/- mice of both sexes show exacerbated acinar cell inflammation and necrosis. Electron microscopy showed mild ER damage in WT male mice and markedly distorted ER structure in Crhr2-/- male mice during pancreatitis. WT and Crhr2-/- female mice showed similarly distorted ER ultrastructure that was less severe than distortion seen in Crhr2-/- male mice. Damage in ER structure was accompanied by increased ubiquitination, peIF2, and mistargeted localization of vimentin in WT mice that was further exacerbated in Crhr2-/- mice of both sexes during pancreatitis. Exogenous Ucn1 rescued many aspects of histological damage and cellular stress response, including restoration of ER structure in male WT and Crhr2-/- mice, but not in females. Instead, females often showed increased damage. Thus, specific cellular pathways involved in coping and resolution seem to be distinct to each sex. Our results demonstrate the importance of identifying sex-specific pathogenic mechanisms and their value in designing effective therapeutics.

Differences in the degree of cerulein-induced chronic pancreatitis in C57BL/6 mouse substrains lead to new insights in identification of potential risk factors in the development of chronic pancreatitis

A frequently used experimental model of chronic pancreatitis (CP) recapitulating human disease is repeated injection of cerulein into mice. C57BL/6 is the most commonly used inbred mouse strain for biomedical research, but widespread demand has led to generation of several substrains with subtly different phenotypes. In this study, two common substrains, C57BL/6J and C57BL/6NHsd, exhibited different degrees of CP, with C57BL/6J being more susceptible to repetitive cerulein-induced CP as assessed by pancreatic atrophy, pancreatic morphological changes, and fibrosis. We hypothesized that the deficiency of nicotinamide nucleotide transhydrogenase (NNT) protein in C57BL/6J is responsible for the more severe C57BL/6J phenotype but the parameters of CP in NNT-expressing transgenic mice generated on a C57BL6/J background do not differ with those of wild-type C57BL/6J. The highly similar genetic backgrounds but different CP phenotypes of these two substrains presents a unique opportunity to discover genes important in pathogenesis of CP. We therefore performed whole mouse genome Affymetrix microarray analysis of pancreatic gene expression of C57BL/6J and C57BL/6NHsd before and after induction of CP. Genes with differentially regulated expression between the two substrains that might be candidates in CP progression included Mmp7, Pcolce2, Itih4, Wdfy1, and Vtn. We also identified several genes associated with development of CP in both substrains, including RIKEN cDNA 1810009J06 gene (trypsinogen 5), Ccl8, and Ccl6.

Autophagy and pancreatitis

Acute pancreatitis is an inflammatory disease of the exocrine pancreas that carries considerable morbidity and mortality; its pathophysiology remains poorly understood. Recent findings from experimental models and genetically altered mice summarized in this review reveal that autophagy, the principal cellular degradative pathway, is impaired in pancreatitis and that one cause of autophagy impairment is defective function of lysosomes. We propose that the lysosomal/autophagic dysfunction is a key initiating event in pancreatitis and a converging point of multiple deranged pathways. There is strong evidence supporting this hypothesis. Investigation of autophagy in pancreatitis has just started, and many questions about the "upstream" mechanisms mediating the lysosomal/autophagic dysfunction and the "downstream" links to pancreatitis pathologies need to be explored. Answers to these questions should provide insight into novel molecular targets and therapeutic strategies for treatment of pancreatitis.

Pathogenic mechanisms of acute pancreatitis

PURPOSE OF REVIEW

In this article, recent advances in the pathogenesis of acute pancreatitis have been reviewed.

RECENT FINDINGS

Pathologic intra-acinar trypsinogen activation had been hypothesized to be the central mechanism of pancreatitis for over a century. This hypothesis could be explored for the first time with the development of a novel mouse model lacking pathologic intra-acinar trypsinogen activation. It became clear that intra-acinar trypsinogen activation contributes to early acinar injury, but local and systemic inflammation progress independently during pancreatitis. Early intra-acinar nuclear factor kappa B (NFκB) activation, which occurs parallel to but independent of trypsinogen activation, may be crucial in pancreatitis. Although the mechanism of NFκB and trypsinogen activation is not entirely clear, further insights have been made into key pathogenic cellular events such as calcium signaling, mitochondrial dysfunction, endoplasmic reticulum (ER) stress, autophagy and impaired trafficking, and lysosomal and secretory responses. Cellular intrinsic damage-sensing mechanisms that lead to activation of the inflammatory response aimed at repair, but lead to disease when overwhelmed, are beginning to be understood.

SUMMARY

New findings necessitate a paradigm shift in our understanding of acute pancreatitis. Intra-acinar trypsinogen activation leads to early pancreatic injury, but the inflammatory response of acute pancreatitis develops independently, driven by early activation of inflammatory pathways.

Characterization of dsRNA-induced pancreatitis model reveals the regulatory role of IFN regulatory factor 2 (Irf2) in trypsinogen5 gene transcription

Mice deficient for interferon regulatory factor (Irf)2 (Irf2(-/-) mice) exhibit immunological abnormalities and cannot survive lymphocytic choriomeningitis virus infection. The pancreas of these animals is highly inflamed, a phenotype replicated by treatment with poly(I:C), a synthetic double-stranded RNA. Trypsinogen5 mRNA was constitutively up-regulated about 1,000-fold in Irf2(-/-) mice compared with controls as assessed by quantitative RT-PCR. Further knockout of IFNα/β receptor 1(Ifnar1) abolished poly(I:C)-induced pancreatitis but had no effect on the constitutive up-regulation of trypsinogen5 gene, indicating crucial type I IFN signaling to elicit the inflammation. Analysis of Ifnar1(-/-) mice confirmed type I IFN-dependent transcriptional activation of dsRNA-sensing pattern recognition receptor genes MDA5, RIG-I, and TLR3, which induced poly(I:C)-dependent cell death in acinar cells in the absence of IRF2. We speculate that Trypsin5, the trypsinogen5 gene product, leaking from dead acinar cells triggers a chain reaction leading to lethal pancreatitis in Irf2(-/-) mice because it is resistant to a major endogenous trypsin inhibitor, Spink3.