Pancreatic ductal adenocarcinoma (PDA) has a dismal prognosis and insights into both disease etiology and targeted intervention are needed. A total of 109 micro-dissected PDA cases were subjected to whole-exome sequencing. Microdissection enriches tumour cellularity and enhances mutation calling. Here we show that environmental stress and alterations in DNA repair genes associate with distinct mutation spectra. Copy number alterations target multiple tumour suppressive/oncogenic loci; however, amplification of MYC is uniquely associated with poor outcome and adenosquamous subtype. We identify multiple novel mutated genes in PDA, with select genes harbouring prognostic significance. RBM10 mutations associate with longer survival in spite of histological features of aggressive disease. KRAS mutations are observed in >90% of cases, but codon Q61 alleles are selectively associated with improved survival. Oncogenic BRAF mutations are mutually exclusive with KRAS and define sensitivity to vemurafenib in PDA models. High-frequency alterations in Wnt signalling, chromatin remodelling, Hedgehog signalling, DNA repair and cell cycle processes are observed. Together, these data delineate new genetic diversity of PDA and provide insights into prognostic determinants and therapeutic targets.

Whole-exome sequencing of pancreatic cancer defines genetic diversity and therapeutic targets

International experts met to discuss recent advances and to revise the 2004 recommendations for assessing and reporting precursor lesions to invasive carcinomas of the pancreas, including pancreatic intraepithelial neoplasia (PanIN), intraductal papillary mucinous neoplasm (IPMN), mucinous cystic neoplasm, and other lesions. Consensus recommendations include the following: (1) To improve concordance and to align with practical consequences, a 2-tiered system (low vs. high grade) is proposed for all precursor lesions, with the provision that the current PanIN-2 and neoplasms with intermediate-grade dysplasia now be categorized as low grade. Thus, "high-grade dysplasia" is to be reserved for only the uppermost end of the spectrum ("carcinoma in situ"-type lesions). (2) Current data indicate that PanIN of any grade at a margin of a resected pancreas with invasive carcinoma does not have prognostic implications; the clinical significance of dysplasia at a margin in a resected pancreas with IPMN lacking invasive carcinoma remains to be determined. (3) Intraductal lesions 0.5 to 1 cm can be either large PanINs or small IPMNs. The term "incipient IPMN" should be reserved for lesions in this size with intestinal or oncocytic papillae or GNAS mutations. (4) Measurement of the distance between an IPMN and invasive carcinoma and sampling of intervening tissue are recommended to assess concomitant versus associated status. Conceptually, concomitant invasive carcinoma (in contrast with the "associated" group) ought to be genetically distinct from an IPMN elsewhere in the gland. (5) "Intraductal spread of invasive carcinoma" (aka, "colonization") is recommended to describe lesions of invasive carcinoma invading back into and extending along the ductal system, which may morphologically mimic high-grade PanIN or even IPMN. (6) "Simple mucinous cyst" is recommended to describe cysts >1 cm having gastric-type flat mucinous lining at most minimal atypia without ovarian-type stroma to distinguish them from IPMN. (7) Human lesions resembling the acinar to ductal metaplasia and atypical flat lesions of genetically engineered mouse models exist and may reflect an alternate pathway of carcinogenesis; however, their biological significance requires further study. These revised recommendations are expected to improve our management and understanding of precursor lesions in the pancreas.

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A Revised Classification System and Recommendations From the Baltimore Consensus Meeting for Neoplastic Precursor Lesions in the Pancreas.

Lgr5 was originally discovered as a common Wnt target gene in adult intestinal crypts and colon cancer. It was subsequently identified as an exquisite marker of multiple Wnt-driven adult stem cell types. Lgr5 and its homologs, Lgr4 and Lgr6, constitute the receptors for R-spondins, potent Wnt signal enhancers and stem cell growth factors. The Lgr5/R-spondin complex acts by neutralizing Rnf43 and Znrf3, two transmembrane E3 ligases that remove Wnt receptors from the stem cell surface. Rnf43/Znrf3 are themselves encoded by Wnt target genes and constitute a negative Wnt feedback loop. Thus, adult stem cells are controlled by an intricate interplay of potent Wnt agonists, antagonists, and anti-antagonists.

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The R-spondin/Lgr5/Rnf43 module: regulator of Wnt signal strength

Aberrant expression and activity of G proteins and G-protein-coupled receptors (GPCRs) are frequently associated with tumorigenesis. Deep sequencing studies show that 4.2% of tumours carry activating mutations in GNAS (encoding Gαs), and that oncogenic activating mutations in genes encoding Gαq family members (GNAQ or GNA11) are present in ~66% and ~6% of melanomas arising in the eye and skin, respectively. Furthermore, nearly 20% of human tumours harbour mutations in GPCRs. Many human cancer-associated viruses also express constitutively active viral GPCRs. These studies indicate that G proteins, GPCRs and their linked signalling circuitry represent novel therapeutic targets for cancer prevention and treatment.

/pdf/the-emerging-mutational-landscape-of-g-proteins-and-g-5emwt4h3ml.pdf

The emerging mutational landscape of G proteins and G-protein-coupled receptors in cancer

Human Pancreatic Tumor Organoids Reveal Loss of Stem Cell Niche Factor Dependence during Disease Progression

Intraductal papillary mucinous neoplasm (IPMN) is a common pancreatic cystic neoplasm that is often invasive and metastatic, resulting in a poor prognosis. Few molecular alterations unique to IPMN are known. We performed whole-exome sequencing for a primary IPMN tissue, which uncovered somatic mutations in KCNF1, DYNC1H1, PGCP, STAB1, PTPRM, PRPF8, RNASE3, SPHKAP, MLXIPL, VPS13C, PRCC, GNAS, KRAS, RBM10, RNF43, DOCK2, and CENPF. We further analyzed GNAS mutations in archival cases of 118 IPMNs and 32 pancreatic ductal adenocarcinomas (PDAs), which revealed that 48 (40.7%) of the 118 IPMNs but none of the 32 PDAs harbored GNAS mutations. G-protein alpha-subunit encoded by GNAS and its downstream targets, phosphorylated substrates of protein kinase A, were evidently expressed in IPMN; the latter was associated with neoplastic grade. These results indicate that GNAS mutations are common and specific for IPMN, and activation of G-protein signaling appears to play a pivotal role in IPMN.

/pdf/whole-exome-sequencing-uncovers-frequent-gnas-mutations-in-2bywg9avld.pdf

Whole-exome sequencing uncovers frequent GNAS mutations in intraductal papillary mucinous neoplasms of the pancreas

Intraductal papillary mucinous neoplasm (IPMN), the most common pancreatic cystic neoplasm, is known to progress to invasive ductal adenocarcinoma. IPMNs commonly harbor activating somatic mutations in GNAS and KRAS, primarily GNAS(R201H) and KRAS(G12D). GNAS encodes the stimulatory G-protein α subunit (Gsα) that mediates a stimulatory signal to adenylyl cyclase to produce cyclic adenosine monophosphate (cAMP), subsequently activating cAMP-dependent protein kinase A. The GNAS(R201H) mutation results in constitutive activation of Gsα. To study the potential role of GNAS in pancreatic tumorigenesis in vivo, we generated lines of transgenic mice in which the transgene consisted of Lox-STOP-Lox (LSL)-GNAS(R201H) under the control of the CAG promoter (Tg(CAG-LSL-GNAS)). These mice were crossed with pancreatic transcription factor 1a (Ptf1a)-Cre mice (Ptf1a(Cre/+)), generating Tg(CAG-LSL-GNAS);Ptf1a(Cre/+) mice. This mouse line showed elevated cAMP levels, small dilated tubular complex formation, loss of acinar cells and fibrosis in the pancreas; however, no macroscopic tumorigenesis was apparent by 2 months of age. We then crossed Tg(CAG-LSL-GNAS);Ptf1a(Cre/+) mice with LSL-Kras(G12D) mice, generating Tg(CAG-LSL-GNAS);LSL-Kras(G12D);Ptf1a(Cre/+) mice. We used these mice to investigate a possible cooperative effect of GNAS(R201H) and Kras(G12D) in pancreatic tumorigenesis. Within 5 weeks, Tg(CAG-LSL-GNAS);LSL-Kras(G12D);Ptf1a(Cre/+) mice developed a cystic tumor consisting of marked dilated ducts lined with papillary dysplastic epithelia in the pancreas, which closely mimicked the human IPMN. Our data strongly suggest that activating mutations in GNAS and Kras cooperatively promote murine pancreatic tumorigenesis, which recapitulates IPMN. Our mouse model may serve as a unique in vivo platform to find biomarkers and effective drugs for diseases associated with GNAS mutations.

GNAS R201H and Kras G12D cooperate to promote murine pancreatic tumorigenesis recapitulating human intraductal papillary mucinous neoplasm

Aberrant expression of microRNAs (miRNA) is associated with phenotypes of various cancers, including pancreatic cancer. However, the mechanism of the aberrant expression is largely unknown. Activation of the mitogen-activated protein kinase (MAPK) signaling pathway plays a crucial role in gene expression related to the malignant phenotype of pancreatic cancer. Hence, we studied the role of MAPK in the aberrant expression of miRNAs in pancreatic cancer cells. The alterations in expression of 183 miRNAs induced by activation or inactivation of MAPK were assayed in cultured pancreatic cancer cells and HEK293 cells by means of the quantitative real-time PCR method. We found that four miRNAs, namely, miR-7-3, miR-34a, miR-181d, and miR-193b, were preferentially associated with MAPK activity. Among these miRNAs, miR-7-3 was upregulated by active MAPK, whereas the others were downregulated. Promoter assays indicated that the promoter activities of the host genes of miR-7-3 and miR-34a were both downregulated by alteration in MAPK activity. Exogenous overexpression of the MAPK-associated miRNAs had the effect of inhibition of the proliferation of cultured pancreatic cancer cells; miR-193b was found to exhibit the most remarkable inhibition. A search for target genes of miR-193b led to identification of CCND1, NT5E, PLAU, STARD7, STMN1, and YWHAZ as the targets. Translational suppression of these genes by miR-193b was confirmed by reporter assay. These results indicate that activation of MAPK may play a significant role in aberrant expression of miRNAs and their associated phenotypes in pancreatic cancer.

https://mcr.aacrjournals.org/content/molcanres/10/2/259.full.pdf

MicroRNAs Associated with Mitogen-Activated Protein Kinase in Human Pancreatic Cancer

GNAS, a gene encoding G protein stimulating α subunit, is frequently mutated in intraductal papillary mucinous neoplasms (IPMNs), which are indolent and slow-growing pancreatic tumors that secrete abundant mucin. The GNAS mutation is not observed in conventional ductal adenocarcinomas of the pancreas. To determine the functional significance of the GNAS mutation in pancreatic ductal lineage cells, we examined in vitro phenotypes of cells of pancreatic ductal lineage, HPDE, PK-8, PCI-35, and MIA PaCa-2, with exogenous expression of either wild-type or mutated (R201H) GNAS. We found that exogenous GNAS upregulated intracellular cyclic adenine monophosphate (cAMP), particularly in mutated GNAS transfectants, and upregulated expression of MUC2 and MUC5AC in HPDE and PK-8 cells. By contrast, exogenous GNAS inhibited expression of mucin genes in PCI-35 and MIA PaCa-2 cells, despite upregulation of cAMP. We examined global gene expression profiles of some of the cells transfected with exogenous mutated GNAS (PK-8, PCI-35, and MIA PaCa-2), and found that PK-8 cells exhibited drastic alterations of the gene expression profile, which contrasted with modest alterations in PCI-35 and MIA PaCa-2 cells. To identify a cause of these different effects of exogenous mutated GNAS on phenotypes of the cells, we examined effects of interactions of the signaling pathways of G protein-coupled receptor (GPCR), mitogen-activated protein kinase (MAPK), and phosphatidylinositol 3-kinase (PI3K) on expression of mucin genes. The MAPK and PI3K pathways significantly influenced the expression of mucin genes. Exogenous GNAS did not promote cell growth but suppressed it in some of the cells. In conclusion, mutated GNAS found in IPMNs may extensively alter gene expression profiles, including expression of mucin genes, through the interaction with MAPK and PI3K pathways in pancreatic ductal cells; these changes may determine the characteristic phenotype of IPMN. PK-8 cells expressing exogenous mutated GNAS may be an ideal in vitro model of IPMN.

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A GNAS Mutation Found in Pancreatic Intraductal Papillary Mucinous Neoplasms Induces Drastic Alterations of Gene Expression Profiles with Upregulation of Mucin Genes

Etsuko Tanji

Papers

Whole-exome sequencing uncovers frequent GNAS mutations in intraductal papillary mucinous neoplasms of the pancreas

GNAS R201H and Kras G12D cooperate to promote murine pancreatic tumorigenesis recapitulating human intraductal papillary mucinous neoplasm

MicroRNAs Associated with Mitogen-Activated Protein Kinase in Human Pancreatic Cancer

A GNAS Mutation Found in Pancreatic Intraductal Papillary Mucinous Neoplasms Induces Drastic Alterations of Gene Expression Profiles with Upregulation of Mucin Genes

Feedback regulation of DUSP6 transcription responding to MAPK1 via ETS2 in human cells.