Loss of Activin Receptor Type 1B Accelerates Development of Intraductal Papillary Mucinous Neoplasms in Mice With Activated KRAS.

BACKGROUND & AIMS: Activin, a member of the transforming growth factor-ß (TGFB) family, might be involved in pancreatic tumorigenesis, similar to other members of the TGFB family. Human pancreatic ductal adenocarcinomas contain somatic mutations in the activin A receptor type IB (ACVR1B) gene, indicating that ACVR1B could be a suppressor of pancreatic tumorigenesis. METHODS: We disrupted Acvr1b specifically in pancreata of mice (Acvr1b(flox/flox);Pdx1-Cre mice) and crossed them with LSL-KRAS(G12D) mice, which express an activated form of KRAS and develop spontaneous pancreatic tumors. The resulting Acvr1b(flox/flox);LSL-KRAS(G12D);Pdx1-Cre mice were monitored; pancreatic tissues were collected and analyzed by histology and immunohistochemical analyses. We also analyzed p16(flox/flox);LSL-Kras(G12D);Pdx1-Cre mice and Cre-negative littermates (controls). Genomic DNA, total RNA, and protein were isolated from mouse tissues and primary pancreatic tumor cell lines and analyzed by reverse-transcription polymerase chain reaction, sequencing, and immunoblot analyses. Human intraductal papillary mucinous neoplasm (IPMN) specimens were analyzed by immunohistochemistry. RESULTS: Loss of ACVR1B from pancreata of mice increased the proliferation of pancreatic epithelial cells, led to formation of acinar to ductal metaplasia, and induced focal inflammatory changes compared with control mice. Disruption of Acvr1b in LSL-KRAS(G12D);Pdx1-Cre mice accelerated the growth of pancreatic IPMNs compared with LSL-KRAS(G12D);Pdx1-Cre mice, but did not alter growth of pancreatic intraepithelial neoplasias. We associated perinuclear localization of the activated NOTCH4 intracellular domain to the apical cytoplasm of neoplastic cells with the expansion of IPMN lesions in Acvr1b(flox/flox);LSL-KRAS(G12D);Pdx1-Cre mice. Loss of the gene that encodes p16 (Cdkn2a) was required for progression of IPMNs to pancreatic ductal adenocarcinomas in Acvr1b(flox/flox);LSL-Kras(G12D);Pdx1-Cre mice. We also observed progressive loss of p16 in human IPMNs of increasing grades. CONCLUSIONS: Loss of ACVR1B accelerates growth of mutant KRAS-induced pancreatic IPMNs in mice; this process appears to involve NOTCH4 and loss of p16. ACVR1B suppresses early stages of pancreatic tumorigenesis; the activin signaling pathway therefore might be a therapeutic target for pancreatic cancer.

Pancreatic DCLK1+ cells originate distinctly from PDX1+ progenitors and contribute to the initiation of intraductal papillary mucinous neoplasm in mice.

PanINs and IPMNs are the two most common precursor lesions that can progress to invasive pancreatic ductal adenocarcinoma (PDA). DCLK1 has been identified as a biomarker of progenitor cells in PDA progressed from PanINs. To explore the potential role of DCLK1-expressing cells in the genesis of IPMNs, we compared the incidence of DCLK1-positive cells in pancreatic tissue samples from genetically-engineered mouse models (GEMMs) for IPMNs, PanINs, and acinar to ductal metaplasia by immunohistochemistry and immunofluorescence. Mouse lineage tracing experiments in the IPMN GEMM showed that DCLK1+ cells originated from a cell lineage distinct from PDX1+ progenitors. The DCLK1+ cells shared the features of tuft cells but were devoid of IPMN tumor biomarkers. The DCLK1+ cells were detected in the earliest proliferative acinar clusters prior to the formation of metaplastic ductal cells, and were enriched in the "IPMN niches". In summary, DCLK1 labels a unique pancreatic cellular lineage in the IPMN GEMM. The clustering of DCLK1+ cells is an early event in Kras-induced pancreatic tumorigenesis and may contribute to IPMN initiation.

PIK3CA mutations in mucinous cystic neoplasms of the pancreas.

OBJECTIVES: Mucinous cystic neoplasms (MCNs) are rare, potentially curable, mucin-producing neoplasms of the pancreas. We have previously reported PIK3CA (phosphoinositide-3-kinase catalytic subunit, p110α) mutations in intraductal papillary mucinous neoplasms, another mucin-producing neoplasm of the pancreas. In this study, we analyzed the presence of PIK3CA and AKT1/PKB (V-akt murine thymoma viral oncogene homolog 1) hot-spot mutations in MCN specimens. METHODS: Using the genomic DNA sequencing of tumor tissues isolated by laser capture microdissection, we evaluated 15 well-characterized MCNs for the E542K, E545K (exon 9), and H1047R (exon 20) hot-spot mutations in the PIK3CA gene and the E17K mutation in the AKT1 gene. RESULTS: A hot-spot mutation (E545K) of the PIK3CA gene was detected in 1 of the 15 MCNs and further confirmed by a mutant-enriched method. Interestingly, this mutation was found to be present only in the high-grade but not in low-grade dysplastic epithelium obtained from this neoplasm and coexisted with a KRAS mutation. No mutations were identified in the AKT1 gene. CONCLUSIONS: Our data, when combined with previous reports on intraductal papillary mucinous neoplasms, indicate that oncogenic activation of the PI3K pathway involving PIK3CA gene mutations can contribute to the progression of mucin-producing neoplasms but not pancreatic intraepithelial neoplasia. PIK3CA status could be useful for understanding their progression to malignancy.