The role of the transcriptional regulator Ptf1a in converting intestinal to pancreatic progenitors
TL;DR: Rec recombination-based lineage tracing in vivo is used to show that PTF1a is expressed at these early stages in the progenitors of pancreatic ducts, exocrine and endocrine cells, rather than being an exocrine-specific gene as previously described.
Abstract: Pancreas development begins with the formation of buds at specific sites in the embryonic foregut endoderm. We used recombination-based lineage tracing in vivo to show that Ptf1a (also known as PTF1-p48) is expressed at these early stages in the progenitors of pancreatic ducts, exocrine and endocrine cells, rather than being an exocrine-specific gene as previously described. Moreover, inactivation of Ptf1a switches the character of pancreatic progenitors such that their progeny proliferate in and adopt the normal fates of duodenal epithelium, including its stem-cell compartment. Consistent with the proposal that Ptf1a supports the specification of precursors of all three pancreatic cell types, transgene-based expression of Pdx1, a gene essential to pancreas formation, from Ptf1a cis-regulatory sequences restores pancreas tissue to Pdx1-null mice that otherwise lack mature exocrine and endocrine cells because of an early arrest in organogenesis. These experiments provide evidence that Ptf1a expression is specifically connected to the acquisition of pancreatic fate by undifferentiated foregut endoderm.
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TL;DR: It is found that physiological levels of Kras(G12D) induce ductal lesions that recapitulate the full spectrum of human pancreatic intraepithelial neoplasias (PanINs), putative precursors to invasive pancreatic cancer.
2,251 citations
Cites background from "The role of the transcriptional reg..."
..., 2001) and P48 mice (Kawaguchi et al., 2002) were previously described....
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...The risks and difficulties of The conditional LSL-KRASG12D mice (Jackson et al., 2001) and P48 /Cre mice pancreatic needle biopsy preclude its routine use to establish (Kawaguchi et al., 2002) were previously described....
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...P48/PTF1 is expressed slightly later and is required to commit cells to a pancreatic fate; when it is absent, cells of the developing pancreatic bud instead differentiate into duodenal epithelium (Kawaguchi et al., 2002) and into endocrine cells that migrate to the spleen (Krapp et al....
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...In lineage-tracing studies in P48 mice, rare P48-expressing cells were retained in the duodenum, the presumed result of insufficient levels of p48 to secure the pancreatic specification of this region of the developing foregut endoderm (Kawaguchi et al., 2002)....
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...…unlike other epithelial malignancies, ittously discovered at its earliest stages, and therefore amenable 438 CANCER CELL : DECEMBER 2003 appears that from its very inception, PDA is already a micro- (Kawaguchi et al., 2002) and into endocrine cells that migrate to the spleen (Krapp et al., 1998)....
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TL;DR: Oncogene-directed increased expression of Nrf2 is a new mechanism for the activation of the NRF2 antioxidant program, and is evident in primary cells and tissues of mice expressing K-RasG12D and B-RafV619E, and in human pancreatic cancer.
Abstract: Reactive oxygen species (ROS) are mutagenic and may thereby promote cancer. Normally, ROS levels are tightly controlled by an inducible antioxidant program that responds to cellular stressors and is predominantly regulated by the transcription factor Nrf2 (also known as Nfe2l2) and its repressor protein Keap1 (refs 2-5). In contrast to the acute physiological regulation of Nrf2, in neoplasia there is evidence for increased basal activation of Nrf2. Indeed, somatic mutations that disrupt the Nrf2-Keap1 interaction to stabilize Nrf2 and increase the constitutive transcription of Nrf2 target genes were recently identified, indicating that enhanced ROS detoxification and additional Nrf2 functions may in fact be pro-tumorigenic. Here, we investigated ROS metabolism in primary murine cells following the expression of endogenous oncogenic alleles of Kras, Braf and Myc, and found that ROS are actively suppressed by these oncogenes. K-Ras(G12D), B-Raf(V619E) and Myc(ERT2) each increased the transcription of Nrf2 to stably elevate the basal Nrf2 antioxidant program and thereby lower intracellular ROS and confer a more reduced intracellular environment. Oncogene-directed increased expression of Nrf2 is a new mechanism for the activation of the Nrf2 antioxidant program, and is evident in primary cells and tissues of mice expressing K-Ras(G12D) and B-Raf(V619E), and in human pancreatic cancer. Furthermore, genetic targeting of the Nrf2 pathway impairs K-Ras(G12D)-induced proliferation and tumorigenesis in vivo. Thus, the Nrf2 antioxidant and cellular detoxification program represents a previously unappreciated mediator of oncogenesis.
1,840 citations
TL;DR: In vivo mechanistic insights are provided into how oncogenic Kras promotes metabolic reprogramming in native tumors and illuminates potential metabolic targets that can be exploited for therapeutic benefit in PDAC.
1,559 citations
Cites background from "The role of the transcriptional reg..."
...These mice were crossed to ROSA26-LSL-rtTA-IRES-GFP (ROSA_rtTA) (Belteki et al., 2005) and p48-Cre (Kawaguchi et al., 2002) mice to enable pancreas-specific and doxycycline (doxy)-inducible expression of KrasG12D (Figure S1B)....
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TL;DR: The path to meaningful clinical progress has never been clearer to improve PDAC patient survival and a deeper understanding of cancer cell biology, particularly altered cancer cell metabolism and impaired DNA repair processes, is providing novel therapeutic strategies that show strong preclinical activity.
Abstract: With 5-year survival rates remaining constant at 6% and rising incidences associated with an epidemic in obesity and metabolic syndrome, pancreatic ductal adenocarcinoma (PDAC) is on track to become the second most common cause of cancer-related deaths by 2030. The high mortality rate of PDAC stems primarily from the lack of early diagnosis and ineffective treatment for advanced tumors. During the past decade, the comprehensive atlas of genomic alterations, the prominence of specific pathways, the preclinical validation of such emerging targets, sophisticated preclinical model systems, and the molecular classification of PDAC into specific disease subtypes have all converged to illuminate drug discovery programs with clearer clinical path hypotheses. A deeper understanding of cancer cell biology, particularly altered cancer cell metabolism and impaired DNA repair processes, is providing novel therapeutic strategies that show strong preclinical activity. Elucidation of tumor biology principles, most notably a deeper understanding of the complexity of immune regulation in the tumor microenvironment, has provided an exciting framework to reawaken the immune system to attack PDAC cancer cells. While the long road of translation lies ahead, the path to meaningful clinical progress has never been clearer to improve PDAC patient survival.
1,220 citations
Cites background from "The role of the transcriptional reg..."
...The Pdx1 and Ptf1-p48 promoters are active in the common progenitors of all pancreatic cell types with relatively restricted expression outside of the pancreas (Pdx1 is also expressed in the developing duodenum and stomach, and Ptf1-p48 is expressed in the cerebellum) (Kawaguchi et al. 2002; Gu et al. 2003)....
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TL;DR: It is reported that selective expression of an endogenous K-Ras(G12V) oncogene in embryonic cells of acinar/centroacinar lineage results in pancreatic intraepithelial neoplasias (PanINs) and invasive PDA, suggesting that PDA originates by differentiation of acINs or their precursors into ductal-like cells.
1,074 citations
Cites background from "The role of the transcriptional reg..."
..., 2001) is turned on during the early stages of embryonic pancreatic development by expressing a Cre recombinase under the control of the Pdx1 or P48 promoters (Kawaguchi et al., 2002; Kim and MacDonald, 2002)....
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...In this model, an endogenous K-RasG12D oncogene (Jackson et al., 2001) is turned on during the early stages of embryonic pancreatic development by expressing a Cre recombinase under the control of the Pdx1 or P48 promoters (Kawaguchi et al., 2002; Kim and MacDonald, 2002)....
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References
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4,950 citations
TL;DR: The findings show that IPF1 is needed for the formation of the pancreas and suggest that it acts to determine the fate of common pancreatic precursor cells and/ or to regulate their propagation.
Abstract: The mammalian pancreas is a mixed exocrine and endocrine gland that, in most species, arises from ventral and dorsal buds which subsequently merge to form the pancreas. In both mouse and rat the first histological sign of morphogenesis of the dorsal pancreas is a dorsal evagination of the duodenum at the level of the liver at around the 22-25-somite stage, and shortly thereafter a ventral evagination appears as a derivative of the liver diverticulum. Low levels of insulin gene transcripts are already present and restricted to the dorsal foregut endoderm at 20 somites, suggesting that pancreas- or insulin gene-specific transcriptional factors are present in this region before the onset of morphogenesis. Insulin-promoter-factor 1 (IPF1) is a homeodomain protein which, in the adult mouse pancreas, is selectively expressed in the beta-cells and binds to and transactivates the insulin promoter. In mouse embryos, IPF1 expression is restricted to the developing pancreatic anlagen and is initiated when the foregut endoderm is committed to a pancreatic fate. We now show that mice homozygous for a targeted mutation in the Ipf1 gene selectively lack a pancreas. The mutant pups survive fetal development but die within a few days after birth. The gastrointestinal part and all other internal organs were normal in appearance. No pancreatic tissue and no ectopic expression of insulin or pancreatic amylase could be detected in mutant embryos and neonates. These findings show that IPF1 is needed for the formation of the pancreas and suggest that it acts to determine the fate of common pancreatic precursor cells and/or to regulate their propagation.
1,776 citations
TL;DR: This work generated cells expressing insulin and other pancreatic endocrine hormones from mouse ES cells that self-assemble to form three-dimensional clusters similar in topology to normal pancreatic islets where pancreatic cell types are in close association with neurons.
Abstract: Although the source of embryonic stem (ES) cells presents ethical concerns, their use may lead to many clinical benefits if differentiated cell types can be derived from them and used to assemble functional organs. In pancreas, insulin is produced and secreted by specialized structures, islets of Langerhans. Diabetes, which affects 16 million people in the United States, results from abnormal function of pancreatic islets. We have generated cells expressing insulin and other pancreatic endocrine hormones from mouse ES cells. The cells self-assemble to form three-dimensional clusters similar in topology to normal pancreatic islets where pancreatic cell types are in close association with neurons. Glucose triggers insulin release from these cell clusters by mechanisms similar to those employed in vivo. When injected into diabetic mice, the insulin-producing cells undergo rapid vascularization and maintain a clustered, islet-like organization.
1,634 citations
TL;DR: The pdx-1/beta-galactosidase fusion allele is expressed in pancreatic and duodenal cells in the absence of functional PDX-1, with expression continuing into perinatal stages with similar boundaries and expression levels, and offers additional insight into the role of p dx-1 in the determination and differentiation of the posterior foregut.
Abstract: It has been proposed that the Xenopus homeobox gene, XlHbox8, is involved in endodermal differentiation during pancreatic and duodenal development (Wright, C.V.E., Schnegelsberg, P. and De Robertis, E.M. (1988). Development 105, 787–794). To test this hypothesis directly, gene targeting was used to make two different null mutations in the mouse XlHbox8 homolog, pdx-1. In the first, the second pdx-1 exon, including the homeobox, was replaced by a neomycin resistance cassette. In the second, a lacZ reporter was fused in-frame with the N terminus of PDX-1, replacing most of the homeodomain. Neonatal pdx-1 −/− mice are apancreatic, in confirmation of previous reports (Jonsson, J., Carlsson, L., Edlund, T. and Edlund, H. (1994). Nature 371, 606–609). However, the pancreatic buds do form in homozygous mutants, and the dorsal bud undergoes limited proliferation and outgrowth to form a small, irregularly branched, ductular tree. This outgrowth does not contain insulin or amylase-positive cells, but glucagon-expressing cells are found. The rostral duodenum shows a local absence of the normal columnar epithelial lining, villi, and Brunner's glands, which are replaced by a GLUT2-positive cuboidal epithelium resembling the bile duct lining. Just distal of the abnormal epithelium, the numbers of enteroendocrine cells in the villi are greatly reduced. The PDX-1/beta-galactosidase fusion allele is expressed in pancreatic and duodenal cells in the absence of functional PDX-1, with expression continuing into perinatal stages with similar boundaries and expression levels. These results offer additional insight into the role of pdx-1 in the determination and differentiation of the posterior foregut, particularly regarding the proliferation and differentiation of the pancreatic progenitors.
1,540 citations
TL;DR: The results provide direct evidence that NGN3+ cells are islet progenitors during embryogenesis and in adult mice, and suggest that lineages for exocrine, endocrine islet and duct progenitor are committed at mid-gestation.
Abstract: The location and lineage of cells that give rise to endocrine islets during embryogenesis has not been established nor has the origin or identity of adult islet stem cells. We have employed an inducible Cre-ER(TM)-LoxP system to indelibly mark the progeny of cells expressing either Ngn3 or Pdx1 at different stages of development. The results provide direct evidence that NGN3+ cells are islet progenitors during embryogenesis and in adult mice. In addition, we find that cells expressing Pdx1 give rise to all three types of pancreatic tissue: exocrine, endocrine and duct. Furthermore, exocrine and endocrine cells are derived from Pdx1-expressing progenitors throughout embryogenesis. By contrast, the pancreatic duct arises from PDX1+ progenitors that are set aside around embryonic day 10.5 (E9.5-E11.5). These findings suggest that lineages for exocrine, endocrine islet and duct progenitors are committed at mid-gestation.
1,507 citations