Replacement of Rbpj with Rbpjl in the PTF1 complex controls the final maturation of pancreatic acinar cells

Degradation meets development: Implications in β-cell development and diabetes

Pancreatic development is orchestrated by timely synthesis and degradation of stage-specific transcription factors (TFs). The transition from one stage to another stage is dependent on the precise expression of the developmentally relevant TFs. Persistent expression of particular TF would impede the exit from the progenitor stage to the matured cell type. Intracellular protein degradation-mediated protein turnover contributes to a major extent to the turnover of these TFs and thereby dictates the development of different tissues. Since even subtle changes in the crucial cellular pathways would dramatically impact pancreatic β-cell performance, it is generally acknowledged that the biological activity of these pathways is tightly regulated by protein synthesis and degradation process. Intracellular protein degradation is executed majorly by the ubiquitin proteasome system (UPS) and Lysosomal degradation pathway. As more than 90% of the TFs are targeted to proteasomal degradation, this review aims to examine the crucial role of UPS in normal pancreatic β-cell development and how dysfunction of these pathways manifests in metabolic syndromes such as diabetes. Such understanding would facilitate designing a faithful approach to obtain a therapeutic quality of β-cells from stem cells.

Regulation of multiple signaling pathways promotes the consistent expansion of human pancreatic progenitors in defined conditions

The unlimited expansion of human progenitor cells in vitro could unlock many prospects for regenerative medicine. However, it remains an important challenge as it requires the decoupling of the mechanisms supporting progenitor self-renewal and expansion from those mechanisms promoting their differentiation. This study focuses on the expansion of human pluripotent stem (hPS) cell-derived pancreatic progenitors (PP) to advance novel therapies for diabetes. We obtained mechanistic insights into PP expansion requirements and identified conditions for the robust and unlimited expansion of hPS cell-derived PP cells under GMP-compliant conditions through a hypothesis-driven iterative approach. We show that the combined stimulation of specific mitogenic pathways, suppression of retinoic acid signaling, and inhibition of selected branches of the TGFβ and Wnt signaling pathways are necessary for the effective decoupling of PP proliferation from differentiation. This enabled the reproducible, 2000-fold, over 10 passages and 40-45 d, expansion of PDX1+/SOX9+/NKX6-1+ PP cells. Transcriptome analyses confirmed the stabilization of PP identity and the effective suppression of differentiation. Using these conditions, PDX1+/SOX9+/NKX6-1+ PP cells, derived from different, both XY and XX, hPS cell lines, were enriched to nearly 90% homogeneity and expanded with very similar kinetics and efficiency. Furthermore, non-expanded and expanded PP cells, from different hPS cell lines, were differentiated in microwells into homogeneous islet-like clusters (SC-islets) with very similar efficiency. These clusters contained abundant β-cells of comparable functionality as assessed by glucose-stimulated insulin secretion assays. These findings established the signaling requirements to decouple PP proliferation from differentiation and allowed the consistent expansion of hPS cell-derived PP cells. They will enable the establishment of large banks of GMP-produced PP cells derived from diverse hPS cell lines. This approach will streamline SC-islet production for further development of the differentiation process, diabetes research, personalized medicine, and cell therapies.

The role of noncoding RNAs in pancreatic birth defects

Congenital defects in the pancreas can cause severe health issues such as pancreatic cancer and diabetes which require lifelong treatment. Regenerating healthy pancreatic cells to replace malfunctioning cells has been considered a promising cure for pancreatic diseases including birth defects. However, such therapies are currently unavailable in the clinic. The developmental gene regulatory network underlying pancreatic development must be reactivated for in vivo regeneration and recapitulated in vitro for cell replacement therapy. Thus, understanding the mechanisms driving pancreatic development will pave the way for regenerative therapies. Pancreatic progenitor cells are the precursors of all pancreatic cells which use epigenetic changes to control gene expression during differentiation to generate all of the distinct pancreatic cell types. Epigenetic changes involving DNA methylation and histone modifications can be controlled by noncoding RNAs (ncRNAs). Indeed, increasing evidence suggests that ncRNAs are indispensable for proper organogenesis. Here, we summarize recent insight into the role of ncRNAs in the epigenetic regulation of pancreatic development. We further discuss how disruptions in ncRNA biogenesis and expression lead to developmental defects and diseases. This review summarizes in vivo data from animal models and in vitro studies using stem cell differentiation as a model for pancreatic development.

Key transcriptional effectors of the pancreatic acinar phenotype and oncogenic transformation

Proper maintenance of mature cellular phenotypes is essential for stable physiology, suppression of disease states, and resistance to oncogenic transformation. We describe the transcriptional regulatory roles of four key DNA-binding transcription factors (Ptf1a, Nr5a2, Foxa2 and Gata4) that sit at the top of a regulatory hierarchy controlling all aspects of a highly differentiated cell-type-the mature pancreatic acinar cell (PAC). Selective inactivation of Ptf1a, Nr5a2, Foxa2 and Gata4 individually in mouse adult PACs rapidly altered the transcriptome and differentiation status of PACs. The changes most emphatically included transcription of the genes for the secretory digestive enzymes (which conscript more than 90% of acinar cell protein synthesis), a potent anabolic metabolism that provides the energy and materials for protein synthesis, suppressed and properly balanced cellular replication, and susceptibility to transformation by oncogenic KrasG12D. The simultaneous inactivation of Foxa2 and Gata4 caused a greater-than-additive disruption of gene expression and uncovered their collaboration to maintain Ptf1a expression and control PAC replication. A measure of PAC dedifferentiation ranked the effects of the conditional knockouts as Foxa2+Gata4 > Ptf1a > Nr5a2 > Foxa2 > Gata4. Whereas the loss of Ptf1a or Nr5a2 greatly accelerated Kras-mediated transformation of mature acinar cells in vivo, the absence of Foxa2, Gata4, or Foxa2+Gata4 together blocked transformation completely, despite extensive dedifferentiation. A lack of correlation between PAC dedifferentiation and sensitivity to oncogenic KrasG12D negates the simple proposition that the level of differentiation determines acinar cell resistance to transformation.

Inferring regulators of cell identity in the human adult pancreas

Cellular identity during development is under the control of transcription factors that form gene regulatory networks. However, the transcription factors and gene regulatory networks underlying cellular identity in the human adult pancreas remain largely unexplored. Here, we integrate multiple single-cell RNA-sequencing datasets of the human adult pancreas, totaling 7393 cells, and comprehensively reconstruct gene regulatory networks. We show that a network of 142 transcription factors forms distinct regulatory modules that characterize pancreatic cell types. We present evidence that our approach identifies regulators of cell identity and cell states in the human adult pancreas. We predict that HEYL, BHLHE41 and JUND are active in acinar, beta and alpha cells, respectively, and show that these proteins are present in the human adult pancreas as well as in human induced pluripotent stem cell (hiPSC)-derived islet cells. Using single-cell transcriptomics, we found that JUND represses beta cell genes in hiPSC-alpha cells. BHLHE41 depletion induced apoptosis in primary pancreatic islets. The comprehensive gene regulatory network atlas can be explored interactively online. We anticipate our analysis to be the starting point for a more sophisticated dissection of how transcription factors regulate cell identity and cell states in the human adult pancreas.

RBPJ Deficiency Sensitizes Pancreatic Acinar Cells to KRAS-Mediated Pancreatic Intraepithelial Neoplasia Initiation

BACKGROUND AND AIMS

Development of pancreatic ductal adenocarcinoma (PDAC) is a multistep process intensively studied; however, precocious diagnosis and effective therapy still remain unsatisfactory. The role for Notch signaling in PDAC has been discussed controversially, as both cancer-promoting and cancer-antagonizing functions have been described. Thus, an improved understanding of the underlying molecular mechanisms is necessary. Here, we focused on RBPJ, the receiving transcription factor in the Notch pathway, examined its expression pattern in PDAC, and characterized its function in mouse models of pancreatic cancer development and in the regeneration process after acute pancreatitis.

METHODS

Conditional transgenic mouse models were used for functional analysis of RBPJ in the adult pancreas, initiation of PDAC precursor lesions, and pancreatic regeneration. Pancreata and primary acinar cells were tested for acinar-to-ductal metaplasia together with immunohistology and comprehensive transcriptional profiling by RNA sequencing.

RESULTS

We identified reduced RBPJ expression in a subset of human PDAC specimens. Ptf1α-CreERT-driven depletion of RBPJ in transgenic mice revealed that its function is dispensable for the homeostasis and maintenance of adult acinar cells. However, primary RBPJ-deficient acinar cells underwent acinar-to-ductal differentiation in ex vivo. Importantly, oncogenic KRAS expression in the context of RBPJ deficiency facilitated the development of pancreatic intraepithelial neoplasia lesions with massive fibrotic stroma formation. Interestingly, RNA-sequencing data revealed a transcriptional profile associated with the cytokine/chemokine and extracellular matrix changes. In addition, lack of RBPJ delays the course of acute pancreatitis and critically impairs it in the context of KRASG12D expression.

CONCLUSIONS

Our findings imply that downregulation of RBPJ in PDAC patients derepresses Notch targets and promotes KRAS-mediated pancreatic acinar cells transformation and desmoplasia development.

Intrapancreatic fat, pancreatitis, and pancreatic cancer

Pancreatic cancer is typically detected at an advanced stage, and is refractory to most forms of treatment, contributing to poor survival outcomes. The incidence of pancreatic cancer is gradually increasing, linked to an aging population and increasing rates of obesity and pancreatitis, which are risk factors for this cancer. Sources of risk include adipokine signaling from fat cells throughout the body, elevated levels of intrapancreatic intrapancreatic adipocytes (IPAs), inflammatory signals arising from pancreas-infiltrating immune cells and a fibrotic environment induced by recurring cycles of pancreatic obstruction and acinar cell lysis. Once cancers become established, reorganization of pancreatic tissue typically excludes IPAs from the tumor microenvironment, which instead consists of cancer cells embedded in a specialized microenvironment derived from cancer-associated fibroblasts (CAFs). While cancer cell interactions with CAFs and immune cells have been the topic of much investigation, mechanistic studies of the source and function of IPAs in the pre-cancerous niche are much less developed. Intriguingly, an extensive review of studies addressing the accumulation and activity of IPAs in the pancreas reveals that unexpectedly diverse group of factors cause replacement of acinar tissue with IPAs, particularly in the mouse models that are essential tools for research into pancreatic cancer. Genes implicated in regulation of IPA accumulation include KRAS, MYC, TGF-β, periostin, HNF1, and regulators of ductal ciliation and ER stress, among others. These findings emphasize the importance of studying pancreas-damaging factors in the pre-cancerous environment, and have significant implications for the interpretation of data from mouse models for pancreatic cancer.

NFIC regulates ribosomal biology and ER stress in pancreatic acinar cells and restrains PDAC initiation

Pancreatic acinar cells rely on PTF1 and other transcription factors to deploy their transcriptional program. We identify NFIC as a NR5A2 interactor and regulator of acinar differentiation. NFIC binding sites are enriched in NR5A2 ChIP-Sequencing peaks. Nfic knockout mice have a smaller, histologically normal, pancreas with reduced acinar gene expression. NFIC binds and regulates the promoters of acinar genes and those involved in RNA/protein metabolism, and Nfic knockout pancreata show defective ribosomal RNA maturation. NFIC dampens the endoplasmic reticulum stress program through binding to gene promoters and is required for resolution of Tunicamycin-mediated stress. NFIC is down-regulated during caerulein pancreatitis and is required for recovery after damage. Normal human pancreata with low levels of NFIC transcripts display reduced expression of genes down-regulated in Nfic knockout mice. NFIC expression is down-regulated in mouse and human pancreatic ductal adenocarcinoma. Consistently, Nfic knockout mice develop a higher number of mutant Kras-driven pre-neoplastic lesions.

Comprehensive DNA Methylation Analysis Indicates That Pancreatic Intraepithelial Neoplasia Lesions Are Acinar-Derived and Epigenetically Primed for Carcinogenesis

Pancreatic ductal adenocarcinoma (PDAC) is believed to arise from the accumulation of a series of somatic mutations and is also frequently associated with pancreatic intraepithelial neoplasia (PanIN) lesions. However, there is still debate as to whether the cell type-of-origin of PanINs and PDACs in humans is acinar or ductal. As cell type identity is maintained epigenetically, DNA methylation changes during pancreatic neoplasia can provide a compelling perspective to examine this question. Here, we performed laser-capture microdissection on surgically resected specimens from 18 patients to isolate, with high purity, DNA for whole-genome bisulfite sequencing from four relevant cell types: acini, nonneoplastic ducts, PanIN lesions, and PDAC lesions. Differentially methylated regions (DMR) were identified using two complementary analytical approaches: bsseq, which identifies any DMRs but is particularly useful for large block-like DMRs, and informME, which profiles the potential energy landscape across the genome and is particularly useful for identifying differential methylation entropy. Both global methylation profiles and block DMRs clearly implicated an acinar origin for PanINs. At the gene level, PanIN lesions exhibited an intermediate acinar-ductal phenotype resembling acinar-to-ductal metaplasia. In 97.6% of PanIN-specific DMRs, PanIN lesions had an intermediate methylation level between normal and PDAC, which suggests from an information theory perspective that PanIN lesions are epigenetically primed to progress to PDAC. Thus, epigenomic analysis complements histopathology to define molecular progression toward PDAC. The shared epigenetic lineage between PanIN and PDAC lesions could provide an opportunity for prevention by targeting aberrantly methylated progression-related genes.

SIGNIFICANCE

Analysis of DNA methylation landscapes provides insights into the cell-of-origin of PanIN lesions, clarifies the role of PanIN lesions as metaplastic precursors to human PDAC, and suggests potential targets for chemoprevention.

Transcriptional Profile of Human Pancreatic Acinar Ductal Metaplasia

BACKGROUND AND AIMS

Aberrant acinar to ductal metaplasia (ADM), one of the earliest events involved in exocrine pancreatic cancer development, is typically studied using pancreata from genetically engineered mouse models.

METHODS

We used primary, human pancreatic acinar cells from organ donors to evaluate the transcriptional and pathway profiles during the course of ADM.

RESULTS

Following 6 days of three-dimensional culture on Matrigel, acinar cells underwent morphological and molecular changes indicative of ADM. mRNA from 14 donors' paired cells (day 0, acinar phenotype and day 6, ductal phenotype) was subjected to whole transcriptome sequencing. Acinar cell specific genes were significantly downregulated in the samples from the day 6 cultures while ductal cell-specific genes were upregulated. Several regulons of ADM were identified including transcription factors with reduced activity (PTF1A, RBPJL, and BHLHA15) and those ductal and progenitor transcription factors with increased activity (HNF1B, SOX11, and SOX4). Cells with the ductal phenotype contained higher expression of genes increased in pancreatic cancer while cells with an acinar phenotype had lower expression of cancer-associated genes.

CONCLUSION

Our findings support the relevancy of human in vitro models to study pancreas cancer pathogenesis and exocrine cell plasticity.

Blockade of the Arid5a/IL-6/STAT3 axis underlies the anti-inflammatory effect of Rbpjl in acute pancreatitis

Background

The microarray data analysis predicted that Rbpjl is poorly expressed in acute pancreatitis (AP). Activated IL-6/STAT3 signaling is further known to contribute to the progression of AP through immune regulation, and both IL-6 and STAT3 were bioinformatically predicted to interact with Arid5a. Accordingly, we aimed to investigate the potential involvement of the Arid5a/IL-6/STAT3 axis in the regulatory role of Rbpjl in the inflammation of AP.

Methods

Pancreatic acinar cells were exposed to lipopolysaccharide (LPS) to induce the pancreatic cell damage, and mice were subjected to supramaximal cerulein stimulation to induce AP. Expression patterns of Rbpjl and the Arid5a/IL-6/STAT3 axis were measured in mouse and cell models. Their expression was further manipulated to explore their effects on pancreatic cell injury and inflammation, as reflected by cell viability and apoptosis as well as reactive oxygen species (ROS) accumulation and proinflammatory cytokine secretion. Moreover, ChIP, EMSA, and dual-luciferase reporter assays were carried out to identify the interactions between Rbpjl and Arid5a.

Results

Rbpjl was found to be down-regulated in pancreatic tissues of AP mice and LPS-induced pancreatic acinar cells, while re-expression of Rbpjl led to enhanced cell viability, suppressed LPS-induced inflammation and ROS accumulation, and alleviation of AP-induced damage. Mechanistically, Rbpjl could bind to the promoter region of Arid5a and down-regulated its expression, thus repressing the activation of the IL-6/STAT3 signal axis. Furthermore, Rbpjl impaired Arid5a-dependent IL-6/STAT3 activation, hence alleviating pancreatic acinar cell inflammation. Furthermore, these effects were validated with in vivo experiments.

Conclusion

Collectively, our findings highlight that Rbpjl attenuates AP by down-regulating Arid5a and inactivating the IL-6/STAT3 pathway.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00819-1.

Loss of LAT1 sex-dependently delays recovery after caerulein-induced acute pancreatitis

BACKGROUND

The expression of amino acid transporters is known to vary during acute pancreatitis (AP) except for LAT1 (slc7a5), the expression of which remains stable. LAT1 supports cell growth by importing leucine and thereby stimulates mammalian target of rapamycin (mTOR) activity, a phenomenon often observed in cancer cells. The mechanisms by which LAT1 influences physiological and pathophysiological processes and affects disease progression in the pancreas are not yet known.

AIM

To evaluate the role of LAT1 in the development of and recovery from AP.

METHODS

AP was induced with caerulein (cae) injections in female and male mice expressing LAT1 or after its knockout (LAT1 Cre/LoxP). The development of the initial AP injury and its recovery were followed for seven days after cae injections by daily measuring body weight, assessing microscopical tissue architecture, mRNA and protein expression, protein synthesis, and enzyme activity levels, as well as by testing the recruitment of immune cells by FACS and ELISA.

RESULTS

The initial injury, evaluated by measurements of plasma amylase, lipase, and trypsin activity, as well as the gene expression of dedifferentiation markers, did not differ between the groups. However, early metabolic adaptations that support regeneration at later stages were blunted in LAT1 knockout mice. Especially in females, we observed less mTOR reactivation and dysfunctional autophagy. The later regeneration phase was clearly delayed in female LAT1 knockout mice, which did not regain normal expression of the pancreas-specific differentiation markers recombining binding protein suppressor of hairless-like protein (rbpjl) and basic helix-loop-helix family member A15 (mist1). Amylase mRNA and protein levels remained lower, and, strikingly, female LAT1 knockout mice presented signs of fibrosis lasting until day seven. In contrast, pancreas morphology had returned to normal in wild-type littermates.

CONCLUSION

LAT1 supports the regeneration of acinar cells after AP. Female mice lacking LAT1 exhibited more pronounced alterations than male mice, indicating a sexual dimorphism of amino acid metabolism.

Acinar to ductal cell trans-differentiation: A prelude to dysplasia and pancreatic ductal adenocarcinoma

Pancreatic cancer (PC) is the deadliest neoplastic epithelial malignancies and is projected to be the second leading cause of cancer-related mortality by 2024. Five years overall survival being ~10%, mortality and incidence rates are disturbing. Acinar to ductal cell metaplasia (ADM) encompasses cellular reprogramming and phenotypic switch-over, making it a cardinal event in tumor initiation. Differential cues and varied regulatory factors drive synchronous functions of metaplastic cell populations leading to multiple cell fates and physiological outcomes. ADM is a precursor for developing early pre-neoplastic lesions further progressing into PC due to oncogenic signaling. Hence delineating molecular events guiding tumor initiation may provide cues for regenerative medicine and precision onco-medicine. Therefore, understanding PC pathogenesis and early diagnosis are crucial. We hereby provide a timely overview of the current progress in this direction and future perspectives we foresee unfolding in the best interest of patient well-being and better clinical management of PC.

The unfolded protein response: An emerging therapeutic target for pancreatitis and pancreatic ductal adenocarcinoma

Pancreatitis is a debilitating disease involving inflammation and fibrosis of the exocrine pancreas. Recurrent or chronic forms of pancreatitis are a significant risk factor for pancreatic ductal adenocarcinoma. While genetic factors have been identified for both pathologies, environmental stresses play a large role in their etiology. All cells have adapted mechanisms to handle acute environmental stress that alters energy demands. A common pathway involved in the stress response involves endoplasmic reticulum stress and the unfolded protein response (UPR). While rapidly activated by many external stressors, in the pancreas the UPR plays a fundamental biological role, likely due to the high protein demands in acinar cells. Despite this, increased UPR activity is observed in response to acute injury or following exposure to risk factors associated with pancreatitis and pancreatic cancer. Studies in animal and cell cultures models show the importance of affecting the UPR in the context of both diseases, and inhibitors have been developed for several specific mediators of the UPR. Given the importance of the UPR to normal acinar cell function, efforts to affect the UPR in the context of disease must be able to specifically target pathology vs. physiology. In this review, we highlight the importance of the UPR to normal and pathological conditions of the exocrine pancreas. We discuss recent studies suggesting the UPR may be involved in the initiation and progression of pancreatitis and PDAC, as well as contributing to chemoresistance that occurs in pancreatic cancer. Finally, we discuss the potential of targeting the UPR for treatment.

Transcription Factor RBPJL Is Able to Repress Notch Target Gene Expression but Is Non-Responsive to Notch Activation

Simple Summary

The transcription factor RBPJ is an integral part of the Notch signaling cascade. RBPJ can function as a coactivator when Notch signaling is activated but acts as a repressor in the absence of a Notch stimulus. Here, we characterized the function of RBPJL, a pancreas-specific paralog of RBPJ. Upon depletion of RBPJ using CRISPR/Cas9, we observed specific upregulation of Notch target gene expression. Reconstitution with RBPJL can compensate for the lack of RBPJ function in the repression of Notch target genes but is not able to mediate the Notch-dependent activation of gene expression. On the molecular level, we identified a limited capacity of RBPJL to interact with activated Notch1–4.

Abstract

The Notch signaling pathway is an evolutionary conserved signal transduction cascade present in almost all tissues and is required for embryonic and postnatal development, as well as for stem cell maintenance, but it is also implicated in tumorigenesis including pancreatic cancer and leukemia. The transcription factor RBPJ forms a coactivator complex in the presence of a Notch signal, whereas it represses Notch target genes in the absence of a Notch stimulus. In the pancreas, a specific paralog of RBPJ, called RBPJL, is expressed and found as part of the heterotrimeric PTF1-complex. However, the function of RBPJL in Notch signaling remains elusive. Using molecular modeling, biochemical and functional assays, as well as single-molecule time-lapse imaging, we show that RBPJL and RBPJ, despite limited sequence homology, possess a high degree of structural similarity. RBPJL is specifically expressed in the exocrine pancreas, whereas it is mostly undetectable in pancreatic tumour cell lines. Importantly, RBPJL is not able to interact with Notch−1 to −4 and it does not support Notch-mediated transactivation. However, RBPJL can bind to canonical RBPJ DNA elements and shows migration dynamics comparable to that of RBPJ in the nuclei of living cells. Importantly, RBPJL is able to interact with SHARP/SPEN, the central corepressor of the Notch pathway. In line with this, RBPJL is able to fully reconstitute transcriptional repression at Notch target genes in cells lacking RBPJ. Together, RBPJL can act as an antagonist of RBPJ, which renders cells unresponsive to the activation of Notch.

Commitment and oncogene-induced plasticity of human stem cell-derived pancreatic acinar and ductal organoids

The exocrine pancreas, consisting of ducts and acini, is the site of origin of pancreatitis and pancreatic ductal adenocarcinoma (PDAC). Our understanding of the genesis and progression of human pancreatic diseases, including PDAC, is limited because of challenges in maintaining human acinar and ductal cells in culture. Here we report induction of human pluripotent stem cells toward pancreatic ductal and acinar organoids that recapitulate properties of the neonatal exocrine pancreas. Expression of the PDAC-associated oncogene GNAS^R201C induces cystic growth more effectively in ductal than acinar organoids, whereas KRAS^G12D is more effective in modeling cancer in vivo when expressed in acinar compared with ductal organoids. KRAS^G12D, but not GNAS^R201C, induces acinar-to-ductal metaplasia-like changes in culture and in vivo. We develop a renewable source of ductal and acinar organoids for modeling exocrine development and diseases and demonstrate lineage tropism and plasticity for oncogene action in the human pancreas.

Transcriptome Profile of Next-Generation Sequencing Data Relate to Proliferation Aberration of Nasopharyngeal Carcinoma Patients in Indonesia

OBJECTIVE

Nasopharyngeal carcinoma (NPC) is the most common cancer arising from epithelial cells of the nasopharynx in  Indonesia. This study aims to determine the differential level of gene expression in NPC patients when compared with normal individuals. Transcriptome profiling analysis was performed using RNA-Seq technology to determine the differential gene expression relate to proliferation aberration that occurs in NPC patients compared with normal individuals. So we get the transcriptomic profile of Indonesia NPC patients.

METHODS

In this study, we used 9 samples, 7 NPC samples and 2 normal samples as control.  Fresh tissue of tumor samples was collected from biopsy, and normal samples were collected brushing technique. The total RNA was isolated from fresh tissue samples and brushing samples using the Rneasy® RNA Extraction Mini Kit. The cDNA library was generated using TruSeq® RNA Library Preparation Kit V2, and its concentration was determined using qPCR. The library was sequenced using the Next-Generation Sequencing (NGS) Illumina Next Seq 550 platform. The raw sequence data quality was analyzed using FastQC and interpreted using HISAT2, HTSeq, edgeR, and PANTHER.

RESULTS

From the analysis, 25493 gene transcripts were expressed, with 1956 genes were significantly upregulated, 90 genes were significantly downregulated in NPC samples, and 23897 genes didn't change the expression level significantly (p <0.05), 10 of which genes were associated with cell proliferation. These genes are involved in the regulation of cancer cell proliferation through several signaling pathways, which are the apoptosis signaling pathway, IGF signaling pathway, Notch signaling pathway, and P13K signaling pathway.

CONCLUSION

There were significant differences in gene expression levels between NPC patients and normal individuals. Each gene that has changed the expression level plays a role in regulating various pathways that lead to cell proliferation aberration in NPC cases.

ID1 Mediates Escape from TGFβ Tumor Suppression in Pancreatic Cancer

TGFβ is an important tumor suppressor in pancreatic ductal adenocarcinoma (PDA), yet inactivation of TGFβ pathway components occurs in only half of PDA cases. TGFβ cooperates with oncogenic RAS signaling to trigger epithelial-to-mesenchymal transition (EMT) in premalignant pancreatic epithelial progenitors, which is coupled to apoptosis owing to an imbalance of SOX4 and KLF5 transcription factors. We report that PDAs that develop with the TGFβ pathway intact avert this apoptotic effect via ID1. ID1 family members are expressed in PDA progenitor cells and encode components of a set of core transcriptional regulators shared by PDAs. PDA progression selects against TGFβ-mediated repression of ID1. The sustained expression of ID1 uncouples EMT from apoptosis in PDA progenitors. AKT signaling and mechanisms linked to low-frequency genetic events converge on ID1 to preserve its expression in PDA. Our results identify ID1 as a crucial node and potential therapeutic target in PDA. SIGNIFICANCE: Half of PDAs escape TGFβ-induced tumor suppression without inactivating the TGFβ pathway. We report that ID1 expression is selected for in PDAs and that ID1 uncouples TGFβ-induced EMT from apoptosis. ID1 thus emerges as a crucial regulatory node and a target of interest in PDA.This article is highlighted in the In This Issue feature, p. 1.

GATA factors in pancreas development and disease

There is an urgent need for the development of novel therapeutics options for diabetic patients given the high prevalence of diabetes worldwide and that, currently, there is no cure for this disease. The transplantation of pancreatic islets that contain insulin-producing cells is a promising therapeutic alternative, particularly for type 1 diabetes. However, the shortage of organ donors constitutes a major limitation for this approach; thus, developing alternative sources of insulin-producing cells is of critical importance. In the last decade, our knowledge of the molecular mechanisms controlling embryonic pancreas development has significantly advanced. More importantly, this knowledge has provided the basis for the in vitro generation of insulin-producing cells from stem cells. Recent studies have revealed that GATA transcription factors are involved in various stages of pancreas formation and in the adult ß cell function. Here, we review the fundamental role of GATA transcription factors in pancreas morphogenesis and their association with congenital diseases associated with pancreas.

Defining multistep cell fate decision pathways during pancreatic development at single-cell resolution

The generation of terminally differentiated cell lineages during organogenesis requires multiple, coordinated cell fate choice steps. However, this process has not been clearly delineated, especially in complex solid organs such as the pancreas. Here, we performed single-cell RNA-sequencing in pancreatic cells sorted from multiple genetically modified reporter mouse strains at embryonic stages E9.5-E17.5. We deciphered the developmental trajectories and regulatory strategies of the exocrine and endocrine pancreatic lineages as well as intermediate progenitor populations along the developmental pathways. Notably, we discovered previously undefined programs representing the earliest events in islet α- and β-cell lineage allocation as well as the developmental pathway of the "first wave" of α-cell generation. Furthermore, we demonstrated that repressing ERK pathway activity is essential for inducing both α- and β-lineage differentiation. This study provides key insights into the regulatory mechanisms underlying cell fate choice and stepwise cell fate commitment and can be used as a resource to guide the induction of functional islet lineage cells from stem cells in vitro.

Transcription factor Ptf1a in development, diseases and reprogramming

The transcription factor Ptf1a is a crucial helix-loop-helix (bHLH) protein selectively expressed in the pancreas, retina, spinal cord, brain, and enteric nervous system. Ptf1a is preferably assembled into a transcription trimeric complex PTF1 with an E protein and Rbpj (or Rbpjl). In pancreatic development, Ptf1a is indispensable in controlling the expansion of multipotent progenitor cells as well as the specification and maintenance of the acinar cells. In neural tissues, Ptf1a is transiently expressed in the post-mitotic cells and specifies the inhibitory neuronal cell fates, mostly mediated by downstream genes such as Tfap2a/b and Prdm13. Mutations in the coding and non-coding regulatory sequences resulting in Ptf1a gain- or loss-of-function are associated with genetic diseases such as pancreatic and cerebellar agenesis in the rodent and human. Surprisingly, Ptf1a alone is sufficient to reprogram mouse or human fibroblasts into tripotential neural stem cells. Its pleiotropic functions in many biological processes remain to be deciphered in the future.

Pancreatic acinar differentiation is guided by differential laminin deposition

Endothelial cells play multiple roles during pancreas organogenesis. First, they are required to instruct endoderm-derived pancreatic progenitor cells to initiate branching morphogenesis. Later, blood vessels promote β-cell differentiation but also limit acinar development. In this work, we show how endothelial cells might signal to pancreatic progenitors and spatially regulate acinar differentiation. Using an ex vivo culture system of undifferentiated E12.5 pancreata, we demonstrate that embryonic endothelial progenitor cells and their conditioned medium prevent the expression of two members of the pro-acinar transcriptional PTF1L-complex. This effect is not mediated by SPARC, a protein abundantly released in the medium conditioned by endothelial progenitors. On the contrary, heterotrimeric laminin-α1β1γ1, also produced by endothelial progenitor cells, can repress acinar differentiation when used on its own on pancreatic explants. Lastly, we found that laminin-α1 is predominantly found in vivo around the pancreatic trunk cells, as compared to the tip cells, at E14.5. In conclusion, we propose that expression or deposition of laminin-α1β1γ1 around the trunk cells, where blood vessels are predominantly localized, prevent acinar differentiation of these cells. On the contrary, transient decreased expression or deposition of laminin-α1β1γ1 around the tip cells would allow PTF1L-complex formation and acinar differentiation.

Protein Methyltransferase Inhibition Decreases Endocrine Specification Through the Upregulation of Aldh1b1 Expression

Understanding the mechanisms that promote the specification of pancreas progenitors and regulate their self-renewal and differentiation will help to maintain and expand pancreas progenitor cells derived from human pluripotent stem (hPS) cells. This will improve the efficiency of current differentiation protocols of hPS cells into β-cells and bring such cells closer to clinical applications for the therapy of diabetes. Aldehyde dehydrogenase 1b1 (Aldh1b1) is a mitochondrial enzyme expressed specifically in progenitor cells during mouse pancreas development, and we have shown that its functional inactivation leads to accelerated differentiation and deficient β-cells. In this report, we aimed to identify small molecule inducers of Aldh1b1 expression taking advantage of a mouse embryonic stem (mES) cell Aldh1b1 lacZ reporter line and a pancreas differentiation protocol directing mES cells into pancreatic progenitors. We identified AMI-5, a protein methyltransferase inhibitor, as an Aldh1b1 inducer and showed that it can maintain Aldh1b1 expression in embryonic pancreas explants. This led to a selective reduction in endocrine specification. This effect was due to a downregulation of Ngn3, and it was mediated through Aldh1b1 since the effect was abolished in Aldh1b1 null pancreata. The findings implicated methyltransferase activity in the regulation of endocrine differentiation and showed that methyltransferases can act through specific regulators during pancreas differentiation. Stem Cells 2019;37:640-651.

Exocrine tissue-driven TFF2 prevents apoptotic cell death of endocrine lineage during pancreas organogenesis

During embryogenesis, exocrine and endocrine pancreatic tissues are formed in distinct regions within the branched ductal structure in mice. We previously reported that exocrine-specific inactivation of Pdx1 by Elastase-Cre caused not only hypoplastic exocrine formation but also substantial endocrine defects resulting in diabetic phenotype, indicating the existence of an exocrine-driven factor(s) that regulates proper endocrine development. In this study, we identified Trefoil Factor 2 (TFF2) as an exocrine gene expressed from embryonic day 16.5 to adulthood in normal mice but significantly less in our Pdx1 mutants. Using in vitro explant culture of embryonic pancreatic tissue, we demonstrated that TFF2 prevented the apoptosis of insulin-producing cells but that antagonizing CXCR4, a known TFF2 receptor, suppressed this anti-apoptotic effect in the mutants. Furthermore, the antagonist in normal pancreatic tissue accelerated the apoptosis of insulin-producing cells, indicating that the TFF2/CXCR4 axis maintains embryonic insulin-producing cells in normal development. TFF2 also suppressed the apoptosis of Nkx6.1+ endocrine precursors in mutant pancreata, but this effect was unperturbed by the CXCR4 antagonist, suggesting the existence of an unknown receptor for TFF2. These findings suggest TFF2 is a novel exocrine factor that supports the survival of endocrine cells in the multiple stages of organogenesis through distinct receptors.

c-Myc downregulation is required for preacinar to acinar maturation and pancreatic homeostasis

BACKGROUND AND AIMS

c-Myc is highly expressed in pancreatic multipotent progenitor cells (MPC) and in pancreatic cancer. The transition from MPC to unipotent acinar progenitors is associated with c-Myc downregulation; a role for c-Myc in this process, and its possible relationship to a role in cancer, has not been established.

DESIGN

Using coimmunoprecipitation assays, we demonstrate that c-Myc and Ptf1a interact. Using reverse transcriptase qPCR, western blot and immunofluorescence, we show the erosion of the acinar programme. To analyse the genomic distribution of c-Myc and Ptf1a and the global transcriptomic profile, we used ChIP-seq and RNA-seq, respectively; validation was performed with ChIP-qPCR and RT-qPCR. Lineage-tracing experiments were used to follow the effect of c-Myc overexpression in preacinar cells on acinar differentiation.

RESULTS

c-Myc binds and represses the transcriptional activity of Ptf1a. c-Myc overexpression in preacinar cells leads to a massive erosion of differentiation. In adult Ela1-Myc mice: (1) c-Myc binds to Ptf1a, and Tcf3 is downregulated; (2) Ptf1a and c-Myc display partially overlapping chromatin occupancy but do not bind the same E-boxes; (3) at the proximal promoter of genes coding for digestive enzymes, we find reduced PTF1 binding and increased levels of repressive chromatin marks and PRC2 complex components. Lineage tracing of committed acinar precursors reveals that c-Myc overexpression does not restore multipotency but allows the persistence of a preacinar-like cell population. In addition, mutant KRas can lead to c-Myc overexpression and acinar dysregulation.

CONCLUSIONS

c-Myc repression during development is crucial for the maturation of preacinar cells, and c-Myc overexpression can contribute to pancreatic carcinogenesis through the induction of a dedifferentiated state.

Differentiation and Inflammation: 'Best Enemies' in Gastrointestinal Carcinogenesis

While recent studies demonstrate that cancer can arise from mutant stem cells, this hypothesis does not explain why tissues without defined stem cell populations are susceptible to inflammation-driven tumorigenesis. We propose that chronic inflammatory diseases, such as colitis and pancreatitis, predispose to gastrointestinal (GI) adenocarcinoma by reprogramming differentiated cells. Focusing on colon and pancreas, we discuss recently discovered connections between inflammation and loss of cell differentiation, and propose that dysregulation of cell fate may be a novel rate-limiting step of tumorigenesis. We review studies identifying differentiation mechanisms that limit tumor initiation and that, upon reactivation, can prevent or revert the cancer cell transformed phenotype. Together, these findings suggest that differentiation-targeted treatments hold promise as a therapeutic strategy in GI cancer.

Functional and association analysis of an Amerindian-derived population-specific p.(Thr280Met) variant in RBPJL, a component of the PTF1 complex

PTF1 complex is critical for pancreatic development and maintenance of adult exocrine pancreas. As a part of our ongoing studies to identify genetic variation that contributes to type 2 diabetes (T2D) in American Indians, we analyzed variation in genes that form this complex, namely PTF1A, RBPJ, and its paralogue RBPJL. A c.839C>T (p.(Thr280Met)) variant (rs200998587:C>T, risk allele frequency = 0.03) in RBPJL, identified only in Amerindian-derived populations, associated with T2D (OR = 1.60[1.21-2.13] per Met allele, P = 0.001) and age of diabetes onset (HR = 1.40[1.14-1.72], P = 0.001). Knockdown of Rbpjl in mouse pancreatic acinar cells resulted in a significant decrease in the mRNA expression of genes encoding exocrine enzymes including Ctrb. CTRB1/2 is an established T2D locus where the protective allele associates with increased GLP-1-stimulated insulin secretion and higher expression of CTRB1/2. In vitro studies show that cells expressing the Met280 allele had lower RBPJL protein levels than cells expressing the Thr280 allele, despite having comparable levels of RNA, suggesting that the Met280 RBPJL is less stable. Additionally, luciferase assays in HEK293 cells which examined two different RBPJL responsive promoters, including the promoter for CTRB1, also identified reduced transactivation by the Met280 RBPJL. Similarly, overexpression of both Met280 and Thr280 RBPJL in mouse pancreatic acinar cells identified a significant impairment in the expression of Cel when transactivated by the Met280 RBPJL. In summary, we identified a functional, Amerindian-derived population-specific c.839C>T (p.(Thr280Met)) variant in the pancreas specific RBPJL that may modify T2D risk by regulating exocrine enzyme expression.

Dynamic landscape of pancreatic carcinogenesis reveals early molecular networks of malignancy

OBJECTIVE

The initial steps of pancreatic regeneration versus carcinogenesis are insufficiently understood. Although a combination of oncogenic Kras and inflammation has been shown to induce malignancy, molecular networks of early carcinogenesis remain poorly defined.

DESIGN

We compared early events during inflammation, regeneration and carcinogenesis on histological and transcriptional levels with a high temporal resolution using a well-established mouse model of pancreatitis and of inflammation-accelerated Kras^G12D-driven pancreatic ductal adenocarcinoma. Quantitative expression data were analysed and extensively modelled in silico.

RESULTS

We defined three distinctive phases-termed inflammation, regeneration and refinement-following induction of moderate acute pancreatitis in wild-type mice. These corresponded to different waves of proliferation of mesenchymal, progenitor-like and acinar cells. Pancreas regeneration required a coordinated transition of proliferation between progenitor-like and acinar cells. In mice harbouring an oncogenic Kras mutation and challenged with pancreatitis, there was an extended inflammatory phase and a parallel, continuous proliferation of mesenchymal, progenitor-like and acinar cells. Analysis of high-resolution transcriptional data from wild-type animals revealed that organ regeneration relied on a complex interaction of a gene network that normally governs acinar cell homeostasis, exocrine specification and intercellular signalling. In mice with oncogenic Kras, a specific carcinogenic signature was found, which was preserved in full-blown mouse pancreas cancer.

CONCLUSIONS

These data define a transcriptional signature of early pancreatic carcinogenesis and a molecular network driving formation of preneoplastic lesions, which allows for more targeted biomarker development in order to detect cancer earlier in patients with pancreatitis.

Cellular and molecular mechanisms coordinating pancreas development

The pancreas is an endoderm-derived glandular organ that participates in the regulation of systemic glucose metabolism and food digestion through the function of its endocrine and exocrine compartments, respectively. While intensive research has explored the signaling pathways and transcriptional programs that govern pancreas development, much remains to be discovered regarding the cellular processes that orchestrate pancreas morphogenesis. Here, we discuss the developmental mechanisms and principles that are known to underlie pancreas development, from induction and lineage formation to morphogenesis and organogenesis. Elucidating such principles will help to identify novel candidate disease genes and unravel the pathogenesis of pancreas-related diseases, such as diabetes, pancreatitis and cancer.

Activating transcription factor 3 promotes loss of the acinar cell phenotype in response to cerulein-induced pancreatitis in mice

Pancreatitis is a debilitating disease of the exocrine pancreas that, under chronic conditions, is a major susceptibility factor for pancreatic ductal adenocarcinoma (PDAC). Although down-regulation of genes that promote the mature acinar cell fate is required to reduce injury associated with pancreatitis, the factors that promote this repression are unknown. Activating transcription factor 3 (ATF3) is a key mediator of the unfolded protein response, a pathway rapidly activated during pancreatic insult. Using chromatin immunoprecipitation followed by next-generation sequencing, we show that ATF3 is bound to the transcriptional regulatory regions of >30% of differentially expressed genes during the initiation of pancreatitis. Of importance, ATF3-dependent regulation of these genes was observed only upon induction of pancreatitis, with pathways involved in inflammation, acinar cell differentiation, and cell junctions being specifically targeted. Characterizing expression of transcription factors that affect acinar cell differentiation suggested that acinar cells lacking ATF3 maintain a mature cell phenotype during pancreatitis, a finding supported by maintenance of junctional proteins and polarity markers. As a result, Atf3-/- pancreatic tissue displayed increased tissue damage and inflammatory cell infiltration at early time points during injury but, at later time points, showed reduced acinar-to-duct cell metaplasia. Thus our results reveal a critical role for ATF3 as a key regulator of the acinar cell transcriptional response during injury and may provide a link between chronic pancreatitis and PDAC.

GATA6 regulates EMT and tumour dissemination, and is a marker of response to adjuvant chemotherapy in pancreatic cancer

BACKGROUND AND AIMS

The role of GATA factors in cancer has gained increasing attention recently, but the function of GATA6 in pancreatic ductal adenocarcinoma (PDAC) is controversial. GATA6 is amplified in a subset of tumours and was proposed to be oncogenic, but high GATA6 levels are found in well-differentiated tumours and are associated with better patient outcome. By contrast, a tumour-suppressive function of GATA6 was demonstrated using genetic mouse models. We aimed at clarifying GATA6 function in PDAC.

DESIGN

We combined GATA6 silencing and overexpression in PDAC cell lines with GATA6 ChIP-Seq and RNA-Seq data, in order to understand the mechanism of GATA6 functions. We then confirmed some of our observations in primary patient samples, some of which were included in the ESPAC-3 randomised clinical trial for adjuvant therapy.

RESULTS

GATA6 inhibits the epithelial-mesenchymal transition (EMT) in vitro and cell dissemination in vivo. GATA6 has a unique proepithelial and antimesenchymal function, and its transcriptional regulation is direct and implies, indirectly, the regulation of other transcription factors involved in EMT. GATA6 is lost in tumours, in association with altered differentiation and the acquisition of a basal-like molecular phenotype, consistent with an epithelial-to-epithelial (ET2) transition. Patients with basal-like GATA6low tumours have a shorter survival and have a distinctly poor response to adjuvant 5-fluorouracil (5-FU)/leucovorin. However, modulation of GATA6 expression in cultured cells does not directly regulate response to 5-FU.

CONCLUSIONS

We provide mechanistic insight into GATA6 tumour-suppressive function, its role as a regulator of canonical epithelial differentiation, and propose that loss of GATA6 expression is both prognostic and predictive of response to adjuvant therapy.

Acinar cell plasticity and development of pancreatic ductal adenocarcinoma

Acinar cells in the adult pancreas show high plasticity and can undergo transdifferentiation to a progenitor-like cell type with ductal characteristics. This process, termed acinar-to-ductal metaplasia (ADM), is an important feature facilitating pancreas regeneration after injury. Data from animal models show that cells that undergo ADM in response to oncogenic signalling are precursors for pancreatic intraepithelial neoplasia lesions, which can further progress to pancreatic ductal adenocarcinoma (PDAC). As human pancreatic adenocarcinoma is often diagnosed at a stage of metastatic disease, understanding the processes that lead to its initiation is important for the discovery of markers for early detection, as well as options that enable an early intervention. Here, the critical determinants of acinar cell plasticity are discussed, in addition to the intracellular and extracellular signalling events that drive acinar cell metaplasia and their contribution to development of PDAC.

Hypoxia-inducible factor-2α stabilizes the von Hippel-Lindau (VHL) disease suppressor, Myb-related protein 2

Ubiquitin ligase von Hippel–Lindau tumor suppressor (pVHL) negatively regulates protein levels of hypoxia-inducible factor-α (HIF-α). Loss of pVHL causes HIF-α accumulation, which contributes to the pathogenesis of von Hippel-Lindau (VHL) disease. In contrast, v-Myb avian myeloblastosis viral oncogene homolog–like 2 (MYBL2; B-Myb), a transcription factor, prevents VHL pathogenesis by regulating gene expression of HIF-independent pathways. Both HIF-α and B-Myb are targets of pVHL-mediated polyubiquitination and proteasomal degradation. Here, we show that knockdown of HIF-2α induces downregulation of B-Myb in 786-O cells, which are deficient in pVHL, and this downregulation is prevented by proteasome inhibition. In the presence of pVHL and under hypoxia-like conditions, B-Myb and HIF-2α are both upregulated, and the upregulation of B-Myb requires expression of HIF-2α. We also show that HIF-2α and B-Myb interact in the nucleus, and this interaction is mediated by the central region of HIF-2α and the C-terminal region of B-Myb. These data indicate that oncogenic HIF-2α stabilizes B-Myb to suppress VHL pathogenesis.

Icaritin enhances mESC self-renewal through upregulating core pluripotency transcription factors mediated by ERα

Utilization of small molecules in modulation of stem cell self-renewal is a promising approach to expand stem cells for regenerative therapy. Here, we identify Icaritin, a phytoestrogen molecule enhances self-renewal of mouse embryonic stem cells (mESCs). Icaritin increases mESCs proliferation while maintains their self-renewal capacity in vitro and pluripotency in vivo. This coincides with upregulation of key pluripotency transcription factors OCT4, NANOG, KLF4 and SOX2. The enhancement of mESCs self-renewal is characterized by increased population in S-phase of cell cycle, elevation of Cylin E and Cyclin-dependent kinase 2 (CDK2) and downregulation of p21, p27 and p57. PCR array screening reveals that caudal-related homeobox 2 (Cdx2) and Rbl2/p130 are remarkably suppressed in mESCs treated with Icaritin. siRNA knockdown of Cdx2 or Rbl2/p130 upregulates the expression of Cyclin E, OCT4 and SOX2, and subsequently increases cell proliferation and colony forming efficiency of mESCs. We then demonstrate that Icaritin co-localizes with estrogen receptor alpha (ERα) and activates its nuclear translocation in mESCs. The promotive effect of Icaritin on cell cycle and pluripotency regulators are eliminated by siRNA knockdown of ERα in mESCs. The results suggest that Icaritin enhances mESCs self-renewal by regulating cell cycle machinery and core pluripotency transcription factors mediated by ERα.

The molecular and morphogenetic basis of pancreas organogenesis

The pancreas is an essential endoderm-derived organ that ensures nutrient metabolism via its endocrine and exocrine functions. Here we review the essential processes governing the embryonic and early postnatal development of the pancreas discussing both the mechanisms and molecules controlling progenitor specification, expansion and differentiation. We elaborate on how these processes are orchestrated in space and coordinated with morphogenesis. We draw mainly from experiments conducted in the mouse model but also from investigations in other model organisms, complementing a recent comprehensive review of human pancreas development (Jennings et al., 2015) [1]. The understanding of pancreas development in model organisms provides a framework to interpret how human mutations lead to neonatal diabetes and may contribute to other forms of diabetes and to guide the production of desired pancreatic cell types from pluripotent stem cells for therapeutic purposes.

Transcriptional Maintenance of Pancreatic Acinar Identity, Differentiation, and Homeostasis by PTF1A

Maintenance of cell type identity is crucial for health, yet little is known of the regulation that sustains the long-term stability of differentiated phenotypes. To investigate the roles that key transcriptional regulators play in adult differentiated cells, we examined the effects of depletion of the developmental master regulator PTF1A on the specialized phenotype of the adult pancreatic acinar cell in vivo Transcriptome sequencing and chromatin immunoprecipitation sequencing results showed that PTF1A maintains the expression of genes for all cellular processes dedicated to the production of the secretory digestive enzymes, a highly attuned surveillance of unfolded proteins, and a heightened unfolded protein response (UPR). Control by PTF1A is direct on target genes and indirect through a ten-member transcription factor network. Depletion of PTF1A causes an imbalance that overwhelms the UPR, induces cellular injury, and provokes acinar metaplasia. Compromised cellular identity occurs by derepression of characteristic stomach genes, some of which are also associated with pancreatic ductal cells. The loss of acinar cell homeostasis, differentiation, and identity is directly relevant to the pathologies of pancreatitis and pancreatic adenocarcinoma.

MIST1 and PTF1 Collaborate in Feed-Forward Regulatory Loops That Maintain the Pancreatic Acinar Phenotype in Adult Mice

Much remains unknown regarding the regulatory networks formed by transcription factors in mature, differentiated mammalian cells in vivo, despite many studies of individual DNA-binding transcription factors. We report a constellation of feed-forward loops formed by the pancreatic transcription factors MIST1 and PTF1 that govern the differentiated phenotype of the adult pancreatic acinar cell. PTF1 is an atypical basic helix-loop-helix transcription factor complex of pancreatic acinar cells and is critical to acinar cell fate specification and differentiation. MIST1, also a basic helix-loop-helix transcription factor, enhances the formation and maintenance of the specialized phenotype of professional secretory cells. The MIST1 and PTF1 collaboration controls a wide range of specialized cellular processes, including secretory protein synthesis and processing, exocytosis, and homeostasis of the endoplasmic reticulum. PTF1 drives Mist1 transcription, and MIST1 and PTF1 bind and drive the transcription of over 100 downstream acinar genes. PTF1 binds two canonical bipartite sites within a 0.7-kb transcriptional enhancer upstream of Mist1 that are essential for the activity of the enhancer in vivo MIST1 and PTF1 coregulate target genes synergistically or additively, depending on the target transcriptional enhancer. The frequent close binding proximity of PTF1 and MIST1 in pancreatic acinar cell chromatin implies extensive collaboration although the collaboration is not dependent on a stable physical interaction.

Early pancreatic islet fate and maturation is controlled through RBP-Jκ

Notch signaling is known to control early pancreatic differentiation through Ngn3 repression. In later stages, downstream of Notch, the Presenilins are still required to maintain the endocrine fate allocation. Amongst their multiple targets, it remains unclear which one actually controls the maintenance of the fate of the early islets. Conditional deletions of the Notch effector RBP-Jκ with lineage tracing in Presenilin-deficient endocrine progenitors, demonstrated that this factor is central to the control of the fate through a non-canonical Notch mechanism. RBP-Jκ mice exhibit normal islet morphogenesis and function, however, a fraction of the progenitors fails to differentiate and develop into disorganized masses resembling acinar to ductal metaplasia and chronic pancreatitis. A subsequent deletion of RBP-Jκ in forming β-cells led to the transdifferentiation into the other endocrine cells types, indicating that this factor still mediates the maintenance of the fate within the endocrine lineage itself. These results highlight the dual importance of Notch signaling for the endocrine lineage. Even after Ngn3 expression, Notch activity is required to maintain both fate and maturation of the Ngn3 progenitors. In a subset of the cells, these alterations of Notch signaling halt their differentiation and leads to acinar to ductal metaplasia.

The acinar regulator Gata6 suppresses KrasG12V-driven pancreatic tumorigenesis in mice

BACKGROUND AND AIMS

Gata6 is required to complete and maintain acinar differentiation in the mouse pancreas. Pancreas-specific Gata6 ablation during development causes extensive and persistent acinar-ductal metaplasia, which is considered an initial step of mutant KRas-driven carcinogenesis. Therefore, the Gata6-null pancreas might represent a tumour-prone environment. We investigated whether Gata6 plays a role during pancreatic tumorigenesis.

DESIGN

We analysed genetically engineered mouse models and human pancreatic ductal adenocarcinoma (PDAC) cell lines, using a combination of histopathological studies, genome-wide expression and chromatin immunoprecipitation experiments to understand the role of Gata6 in the initiation and progression of KRas(G12V)-driven tumours

RESULTS

We show that Gata6 maintains the acinar differentiation programme, both directly and indirectly, and it concomitantly suppresses ectopic programmes in the pancreas. Gata6 ablation renders acinar cells more sensitive to KRas(G12V), thereby accelerating tumour development. Gata6 expression is spontaneously lost in a mouse model of KRas(G12V)-driven PDAC, in association with altered cell differentiation. Using a combination of ChIP-Seq and RNA-Seq, we show that Gata6 exerts its tumour-suppressive effect through the promotion of cell differentiation, the suppression of inflammatory pathways, and the direct repression of cancer-related pathways. Among them is the epidermal growth factor receptor (EGFR) pathway, the activity of which is upregulated in the normal and preneoplastic Gata6-null pancreas. Accordingly, GATA6-silencing in human PDAC cells leads to an upregulation of EGFR.

CONCLUSIONS

We propose that, in the pancreas, Gata6 acts as a tumour suppressor by enforcing acinar cell differentiation, by directly and indirectly repressing ectopic differentiation programmes, and by regulating crucial cancer-related gene expression pathways.

Transcription factor regulation of pancreatic organogenesis, differentiation and maturation

Lineage tracing studies have revealed that transcription factors play a cardinal role in pancreatic development, differentiation and function. Three transitions define pancreatic organogenesis, differentiation and maturation. In the primary transition, when pancreatic organogenesis is initiated, there is active proliferation of pancreatic progenitor cells. During the secondary transition, defined by differentiation, there is growth, branching, differentiation and pancreatic cell lineage allocation. The tertiary transition is characterized by differentiated pancreatic cells that undergo further remodeling, including apoptosis, replication and neogenesis thereby establishing a mature organ. Transcription factors function at multiple levels and may regulate one another and auto-regulate. The interaction between extrinsic signals from non-pancreatic tissues and intrinsic transcription factors form a complex gene regulatory network ultimately culminating in the different cell lineages and tissue types in the developing pancreas. Mutations in these transcription factors clinically manifest as subtypes of diabetes mellitus. Current treatment for diabetes is not curative and thus, developmental biologists and stem cell researchers are utilizing knowledge of normal pancreatic development to explore novel therapeutic alternatives. This review summarizes current knowledge of transcription factors involved in pancreatic development and β-cell differentiation in rodents.

Silencing Mist1 Gene Expression Is Essential for Recovery from Acute Pancreatitis

Acinar cells of the exocrine pancreas are tasked with synthesizing, packaging and secreting vast quantities of pro-digestive enzymes to maintain proper metabolic homeostasis for the organism. Because the synthesis of high levels of hydrolases is potentially dangerous, the pancreas is prone to acute pancreatitis (AP), a disease that targets acinar cells, leading to acinar-ductal metaplasia (ADM), inflammation and fibrosis—events that can transition into the earliest stages of pancreatic ductal adenocarcinoma. Despite a wealth of information concerning the broad phenotype associated with pancreatitis, little is understood regarding specific transcriptional regulatory networks that are susceptible to AP and the role these networks play in acinar cell and exocrine pancreas responses. In this study, we examined the importance of the acinar-specific maturation transcription factor MIST1 to AP damage and organ recovery. Analysis of wild-type and Mist1 conditional null mice revealed that Mist1 gene transcription and protein accumulation were dramatically reduced as acinar cells underwent ADM alterations during AP episodes. To test if loss of MIST1 function was primarily responsible for the damaged status of the organ, mice harboring a Cre-inducible Mist1 transgene (iMist1) were utilized to determine if sustained MIST1 activity could alleviate AP damage responses. Unexpectedly, constitutive iMist1 expression during AP led to a dramatic increase in organ damage followed by acinar cell death. We conclude that the transient silencing of Mist1 expression is critical for acinar cells to survive an AP episode, providing cells an opportunity to suppress their secretory function and regenerate damaged cells. The importance of MIST1 to these events suggests that modulating key pancreas transcription networks could ease clinical symptoms in patients diagnosed with pancreatitis and pancreatic cancer.

The acinar differentiation determinant PTF1A inhibits initiation of pancreatic ductal adenocarcinoma

Understanding the initiation and progression of pancreatic ductal adenocarcinoma (PDAC) may provide therapeutic strategies for this deadly disease. Recently, we and others made the surprising finding that PDAC and its preinvasive precursors, pancreatic intraepithelial neoplasia (PanIN), arise via reprogramming of mature acinar cells. We therefore hypothesized that the master regulator of acinar differentiation, PTF1A, could play a central role in suppressing PDAC initiation. In this study, we demonstrate that PTF1A expression is lost in both mouse and human PanINs, and that this downregulation is functionally imperative in mice for acinar reprogramming by oncogenic KRAS. Loss of Ptf1a alone is sufficient to induce acinar-to-ductal metaplasia, potentiate inflammation, and induce a KRAS-permissive, PDAC-like gene expression profile. As a result, Ptf1a-deficient acinar cells are dramatically sensitized to KRAS transformation, and reduced Ptf1a greatly accelerates development of invasive PDAC. Together, these data indicate that cell differentiation regulators constitute a new tumor suppressive mechanism in the pancreas.

The E3 ubiquitin ligase thyroid hormone receptor-interacting protein 12 targets pancreas transcription factor 1a for proteasomal degradation

Pancreas transcription factor 1a (PTF1a) plays a crucial role in the early development of the pancreas and in the maintenance of the acinar cell phenotype. Several transcriptional mechanisms regulating expression of PTF1a have been identified. However, regulation of PTF1a protein stability and degradation is still unexplored. Here, we report that inhibition of proteasome leads to elevated levels of PTF1a and to the existence of polyubiquitinated forms of PTF1a. We used the Sos recruitment system, an alternative two-hybrid system method to detect protein-protein interactions in the cytoplasm and to map the interactome of PTF1a. We identified TRIP12 (thyroid hormone receptor-interacting protein 12), an E3 ubiquitin-protein ligase as a new partner of PTF1a. We confirmed PTF1a/TRIP12 interaction in acinar cell lines and in co-transfected HEK-293T cells. The protein stability of PTF1a is significantly increased upon decreased expression of TRIP12. It is reduced upon overexpression of TRIP12 but not a catalytically inactive TRIP12-C1959A mutant. We identified a region of TRIP12 required for interaction and identified lysine 312 of PTF1a as essential for proteasomal degradation. We also demonstrate that TRIP12 down-regulates PTF1a transcriptional and antiproliferative activities. Our data suggest that an increase in TRIP12 expression can play a part in PTF1a down-regulation and indicate that PTF1a/TRIP12 functional interaction may regulate pancreatic epithelial cell homeostasis.

The nuclear hormone receptor family member NR5A2 controls aspects of multipotent progenitor cell formation and acinar differentiation during pancreatic organogenesis

The orphan nuclear receptor NR5A2 is necessary for the stem-like properties of the epiblast of the pre-gastrulation embryo and for cellular and physiological homeostasis of endoderm-derived organs postnatally. Using conditional gene inactivation, we show that Nr5a2 also plays crucial regulatory roles during organogenesis. During the formation of the pancreas, Nr5a2 is necessary for the expansion of the nascent pancreatic epithelium, for the subsequent formation of the multipotent progenitor cell (MPC) population that gives rise to pre-acinar cells and bipotent cells with ductal and islet endocrine potential, and for the formation and differentiation of acinar cells. At birth, the NR5A2-deficient pancreas has defects in all three epithelial tissues: a partial loss of endocrine cells, a disrupted ductal tree and a >90% deficit of acini. The acinar defects are due to a combination of fewer MPCs, deficient allocation of those MPCs to pre-acinar fate, disruption of acinar morphogenesis and incomplete acinar cell differentiation. NR5A2 controls these developmental processes directly as well as through regulatory interactions with other pancreatic transcriptional regulators, including PTF1A, MYC, GATA4, FOXA2, RBPJL and MIST1 (BHLHA15). In particular, Nr5a2 and Ptf1a establish mutually reinforcing regulatory interactions and collaborate to control developmentally regulated pancreatic genes by binding to shared transcriptional regulatory regions. At the final stage of acinar cell development, the absence of NR5A2 affects the expression of Ptf1a and its acinar specific partner Rbpjl, so that the few acinar cells that form do not complete differentiation. Nr5a2 controls several temporally distinct stages of pancreatic development that involve regulatory mechanisms relevant to pancreatic oncogenesis and the maintenance of the exocrine phenotype.

Transcriptional control of mammalian pancreas organogenesis

The field of pancreas development has markedly expanded over the last decade, significantly advancing our understanding of the molecular mechanisms that control pancreas organogenesis. This growth has been fueled, in part, by the need to generate new therapeutic approaches for the treatment of diabetes. The creation of sophisticated genetic tools in mice has been instrumental in this progress. Genetic manipulation involving activation or inactivation of genes within specific cell types has allowed the identification of many transcription factors (TFs) that play critical roles in the organogenesis of the pancreas. Interestingly, many of these TFs act at multiple stages of pancreatic development, and adult organ function or repair. Interaction with other TFs, extrinsic signals, and epigenetic regulation are among the mechanisms by which TFs may play context-dependent roles during pancreas organogenesis. Many of the pancreatic TFs directly regulate each other and their own expression. These combinatorial interactions generate very specific gene regulatory networks that can define the different cell lineages and types in the developing pancreas. Here, we review recent progress made in understanding the role of pancreatic TFs in mouse pancreas formation. We also summarize our current knowledge of human pancreas development and discuss developmental pancreatic TFs that have been associated with human pancreatic diseases.

Nr5a2 maintains acinar cell differentiation and constrains oncogenic Kras-mediated pancreatic neoplastic initiation

OBJECTIVES

Emerging evidence from mouse models suggests that mutant Kras can drive the development of pancreatic ductal adenocarcinoma (PDA) precursors from acinar cells by enforcing ductal de-differentiation at the expense of acinar identity. Recently, human genome-wide association studies have identified NR5A2, a key regulator of acinar function, as a susceptibility locus for human PDA. We investigated the role of Nr5a2 in exocrine maintenance, regeneration and Kras driven neoplasia.

DESIGN

To investigate the function of Nr5a2 in the pancreas, we generated mice with conditional pancreatic Nr5a2 deletion (PdxCre(late); Nr5a2(c/c)). Using this model, we evaluated acinar differentiation, regeneration after caerulein pancreatitis and Kras driven pancreatic neoplasia in the setting of Nr5a2 deletion.

RESULTS

We show that Nr5a2 is not required for the development of the pancreatic acinar lineage but is important for maintenance of acinar identity. Nr5a2 deletion leads to destabilisation of the mature acinar differentiation state, acinar to ductal metaplasia and loss of regenerative capacity following acute caerulein pancreatitis. Loss of Nr5a2 also dramatically accelerates the development of oncogenic Kras driven acinar to ductal metaplasia and PDA precursor lesions.

CONCLUSIONS

Nr5a2 is a key regulator of acinar plasticity. It is required for maintenance of acinar identity and re-establishing acinar fate during regeneration. Nr5a2 also constrains pancreatic neoplasia driven by oncogenic Kras, providing functional evidence supporting a potential role as a susceptibility gene for human PDA.

Let-7b and miR-495 stimulate differentiation and prevent metaplasia of pancreatic acinar cells by repressing HNF6

BACKGROUND & AIMS

Diseases of the exocrine pancreas are often associated with perturbed differentiation of acinar cells. MicroRNAs (miRNAs) regulate pancreas development, yet little is known about their contribution to acinar cell differentiation. We aimed to identify miRNAs that promote and control the maintenance of acinar differentiation.

METHODS

We studied mice with pancreas- or acinar-specific inactivation of Dicer (Foxa3-Cre/Dicer(loxP/-) mice), combined (or not) with inactivation of hepatocyte nuclear factor (HNF) 6 (Foxa3-Cre/Dicer(loxP/-)/Hnf6-/- mice). The role of specific miRNAs in acinar differentiation was investigated by transfecting cultured cells with miRNA mimics or inhibitors. Pancreatitis-induced metaplasia was investigated in mice after administration of cerulein.

RESULTS

Inhibition of miRNA synthesis in acini by inactivation of Dicer and pancreatitis-induced metaplasia were associated with repression of acinar differentiation and with induction of HNF6 and hepatic genes. The phenotype of Dicer-deficient acini depends on the induction of HNF6; overexpression of this factor in developing acinar cells is sufficient to repress acinar differentiation and to induce hepatic genes. Let-7b and miR-495 repress HNF6 and are expressed in developing acini. Their expression is inhibited in Dicer-deficient acini, as well as in pancreatitis-induced metaplasia. In addition, inhibiting let-7b and miR-495 in acinar cells results in similar effects to those found in Dicer-deficient acini and metaplastic cells, namely induction of HNF6 and hepatic genes and repression of acinar differentiation.

CONCLUSIONS

Let-7b, miR-495, and their targets constitute a gene network that is required to establish and maintain pancreatic acinar cell differentiation. Additional studies of this network will increase our understanding of pancreatic diseases.