Background: GNAS, a gene encoding G-protein stimulating alpha subunit, is frequently mutated in pancreatic intraductal papillary mucinous neoplasms (IPMNs) that are indolent neoplasms secreting abundant mucin and are considered to be one of precursors of pancreatic cancer. GNAS mutation is not found in conventional ductal adenocarcinomas of the pancreas or pancreatic cystic neoplasms except IPMN. Mutated GNAS is supposed to upregulate intracellular cAMP and activate GPCR pathway, however, its phenotype in pancreatic ductal cells is unknown.
Methods: To determine the functional significance of GNAS mutation, 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. cAMP assay, real time PCR for mucin gene expressions, serial analysis of gene expression (SAGE) with pathway analysis using KEGG, colony formation assay and MTT assay for proliferation, and flow cytometry for cell cycle were performed. Interactions between GPCR, MAPK and PI3K pathways for expression of mucin genes were also determined.
Results: The exogenous GNAS induced increasing of intracellular cAMP, however, the degree of increasing appeared to be cell-type specific. The exogenous GNAS showed no obvious cell-growth promotion or cell cycle alterations but suppressions of proliferation and survival of some cells. In SAGE analysis, the exogenous GNAS induced varying degrees of alterations in global gene expression profiles. PK-8 exhibited drastic alterations in the gene expression profile, which indicated that it was most sensitive to the mutated GNAS among the cells examined. Moreover, the exogenous GNAS upregulated expression of MUC2 and MUC5AC in PK-8 and HPDE. On the other hand, PCI-35 and MIA PaCa-2 cells exhibited modest change of gene expression profiles and downregulation of mucin genes. Pathway analysis revealed that mutated GNAS altered expression of genes involved in PI3K and MAPK signaling pathways. Furthermore, the experiments using MAPK and PI3K inhibitors clarified that these signaling contributed mucin gene expressions as GPCR did, however, their roles for mucin gene expressions were diverse and cell-type specific.
Conclusion: Mutated GNAS found in IPMNs can extensively alter gene expression profiles, including expression of mucin genes, with the interaction with MAPK and PI3K pathways in pancreatic ductal-lineage cells, which may determine the characteristic phenotype of the neoplasm.
Citation Format: Hirotake Komatsu, Naoaki Sakata, Takeshi Aoki, Fuyuhiko Motoi, Takeshi Naitoh, Yu Katayose, Shinichi Egawa, Michiaki Unno, Toru Furukawa. A GNAS mutation found in pancreatic intraductal papillary mucinous neoplasms changes mucin gene expression and gene expression profiles. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4407. doi:10.1158/1538-7445.AM2014-4407