Kras and Lkb1 mutations synergistically induce intraductal papillary mucinous neoplasm derived from pancreatic duct cells.

OBJECTIVE: Pancreatic cancer can arise from precursor lesions called intraductal papillary mucinous neoplasms (IPMN), which are characterised by cysts containing papillae and mucus-producing cells. The high frequency of KRAS mutations in IPMN and histological analyses suggest that oncogenic KRAS drives IPMN development from pancreatic duct cells. However, induction of Kras mutation in ductal cells is not sufficient to generate IPMN, and formal proof of a ductal origin of IPMN is still missing. Here we explore whether combining oncogenic KrasG12D mutation with an additional gene mutation known to occur in human IPMN can induce IPMN from pancreatic duct cells. DESIGN: We created and phenotyped mouse models in which mutations in Kras and in the tumour suppressor gene liver kinase B1 (Lkb1/Stk11) are conditionally induced in pancreatic ducts using Cre-mediated gene recombination. We also tested the effect of ß-catenin inhibition during formation of the lesions. RESULTS: Activating KrasG12D mutation and Lkb1 inactivation synergised to induce IPMN, mainly of gastric type and with malignant potential. The mouse lesions shared several features with human IPMN. Time course analysis suggested that IPMN developed from intraductal papillae and glandular neoplasms, which both derived from the epithelium lining large pancreatic ducts. ß-catenin was required for the development of glandular neoplasms and subsequent development of the mucinous cells in IPMN. Instead, the lack of ß-catenin did not impede formation of intraductal papillae and their progression to papillary lesions in IPMN. CONCLUSION: Our work demonstrates that IPMN can result from synergy between KrasG12D mutation and inactivation of a tumour suppressor gene. The ductal epithelium can give rise to glandular neoplasms and papillary lesions, which probably both contribute to IPMN formation.

Liver and Pancreas: Do Similar Embryonic Development and Tissue Organization Lead to Similar Mechanisms of Tumorigenesis?

The liver and pancreas are closely associated organs that share a common embryological origin. They display amphicrine properties and have similar exocrine organization with parenchymal cells, namely, hepatocytes and acinar cells, secreting bile and pancreatic juice into the duodenum via a converging network of bile ducts and pancreatic ducts. Here we compare and highlight the similarities of molecular mechanisms leading to liver and pancreatic cancer development. We suggest that unraveling tumor development in an organ may provide insight into our understanding of carcinogenesis in the other organ.

High-throughput sequencing analysis reveals the genetic diversity of different regions of the murine norovirus genome during in vitro replication.

In this study, we report the genetic diversity and nucleotide mutation rates of five representative regions of the murine norovirus genome during in vitro passages. The mutation rates were similar in genomic regions encompassing partial coding sequences for non-structural (NS) 1-2, NS5, NS6, NS7 proteins within open reading frame (ORF) 1. In a region encoding a portion of the major capsid protein (VP1) within ORF2 (also including the ORF4 region) and a portion of the minor structural protein (VP2), the mutation rates were estimated to be at least one order of magnitude higher. The VP2 coding region was found to have the highest mutation rate.

Norovirus Polymerase Fidelity Contributes to Viral Transmission In Vivo.

Intrahost genetic diversity and replication error rates are intricately linked to RNA virus pathogenesis, with alterations in viral polymerase fidelity typically leading to attenuation during infections in vivo. We have previously shown that norovirus intrahost genetic diversity also influences viral pathogenesis using the murine norovirus model, as increasing viral mutation frequency using a mutagenic nucleoside resulted in clearance of a persistent infection in mice. Given the role of replication fidelity and genetic diversity in pathogenesis, we have now investigated whether polymerase fidelity can also impact virus transmission between susceptible hosts. We have identified a high-fidelity norovirus RNA-dependent RNA polymerase mutant (I391L) which displays delayed replication kinetics in vivo but not in cell culture. The I391L polymerase mutant also exhibited lower transmission rates between susceptible hosts than the wild-type virus and, most notably, another replication defective mutant that has wild-type levels of polymerase fidelity. These results provide the first experimental evidence that norovirus polymerase fidelity contributes to virus transmission between hosts and that maintaining diversity is important for the establishment of infection. This work supports the hypothesis that the reduced polymerase fidelity of the pandemic GII.4 human norovirus isolates may contribute to their global dominance. IMPORTANCE Virus replication fidelity and hence the intrahost genetic diversity of viral populations are known to be intricately linked to viral pathogenesis and tropism as well as to immune and antiviral escape during infection. In this study, we investigated whether changes in replication fidelity can impact the ability of a virus to transmit between susceptible hosts by the use of a mouse model for norovirus. We show that a variant encoding a high-fidelity polymerase is transmitted less efficiently between mice than the wild-type strain. This constitutes the first experimental demonstration that the polymerase fidelity of viruses can impact transmission of infection in their natural hosts. These results provide further insight into potential reasons for the global emergence of pandemic human noroviruses that display alterations in the replication fidelity of their polymerases compared to nonpandemic strains.