Chia-Yen C Wu1, Eileen S Carpenter2, Kenneth K Takeuchi3, Christopher J Halbrook4, Louise V Peverley3, Harold Bien5, Jason C Hall6, Kathleen E DelGiorno7, Debjani Pal8, Yan Song2, Chanjuan Shi9, Richard Z Lin10, Howard C Crawford11. 1. Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York. 2. Department of Pharmacological Sciences, Stony Brook University, Stony Brook, New York. 3. Department of Cancer Biology, Mayo Clinic Florida, Jacksonville, Florida. 4. Department of Cancer Biology, Mayo Clinic Florida, Jacksonville, Florida; Department of Chemistry, Stony Brook University, Stony Brook, New York. 5. Division of Hematology/Oncology, Stony Brook University, Stony Brook, New York. 6. Department of Pharmacological Sciences, Stony Brook University, Stony Brook, New York; Department of Cancer Biology, Mayo Clinic Florida, Jacksonville, Florida. 7. Department of Cancer Biology, Mayo Clinic Florida, Jacksonville, Florida; Molecular Genetics and Microbiology Graduate Program, Stony Brook University, Stony Brook, New York. 8. Molecular and Cellular Biology Graduate Program, Stony Brook University, Stony Brook, New York. 9. Department of Pathology, Vanderbilt University Medical Center, Nashville, Tennessee. 10. Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York; Medical Service, Northport VA Medical Center, Northport, New York. Electronic address: richard.lin@stonybrook.edu. 11. Department of Pharmacological Sciences, Stony Brook University, Stony Brook, New York; Department of Cancer Biology, Mayo Clinic Florida, Jacksonville, Florida. Electronic address: crawford.howard@mayo.edu.
Abstract
BACKGROUND & AIMS: New drug targets are urgently needed for the treatment of patients with pancreatic ductal adenocarcinoma (PDA). Nearly all PDAs contain oncogenic mutations in the KRAS gene. Pharmacological inhibition of KRAS has been unsuccessful, leading to a focus on downstream effectors that are more easily targeted with small molecule inhibitors. We investigated the contributions of phosphoinositide 3-kinase (PI3K) to KRAS-initiated tumorigenesis. METHODS: Tumorigenesis was measured in the Kras(G12D/+);Ptf1a(Cre/+) mouse model of PDA; these mice were crossed with mice with pancreas-specific disruption of genes encoding PI3K p110α (Pik3ca), p110β (Pik3cb), or RAC1 (Rac1). Pancreatitis was induced with 5 daily intraperitoneal injections of cerulein. Pancreata and primary acinar cells were isolated; acinar cells were incubated with an inhibitor of p110α (PIK75) followed by a broad-spectrum PI3K inhibitor (GDC0941). PDA cell lines (NB490 and MiaPaCa2) were incubated with PIK75 followed by GDC0941. Tissues and cells were analyzed by histology, immunohistochemistry, quantitative reverse-transcription polymerase chain reaction, and immunofluorescence analyses for factors involved in the PI3K signaling pathway. We also examined human pancreas tissue microarrays for levels of p110α and other PI3K pathway components. RESULTS: Pancreas-specific disruption of Pik3ca or Rac1, but not Pik3cb, prevented the development of pancreatic tumors in Kras(G12D/+);Ptf1a(Cre/+) mice. Loss of transformation was independent of AKT regulation. Preneoplastic ductal metaplasia developed in mice lacking pancreatic p110α but regressed. Levels of activated and total RAC1 were higher in pancreatic tissues from Kras(G12D/+);Ptf1a(Cre/+) mice compared with controls. Loss of p110α reduced RAC1 activity and expression in these tissues. p110α was required for the up-regulation and activity of RAC guanine exchange factors during tumorigenesis. Levels of p110α and RAC1 were increased in human pancreatic intraepithelial neoplasias and PDAs compared with healthy pancreata. CONCLUSIONS: KRAS signaling, via p110α to activate RAC1, is required for transformation in Kras(G12D/+);Ptf1a(Cre/+) mice.
BACKGROUND & AIMS: New drug targets are urgently needed for the treatment of patients with pancreatic ductal adenocarcinoma (PDA). Nearly all PDAs contain oncogenic mutations in the KRAS gene. Pharmacological inhibition of KRAS has been unsuccessful, leading to a focus on downstream effectors that are more easily targeted with small molecule inhibitors. We investigated the contributions of phosphoinositide 3-kinase (PI3K) to KRAS-initiated tumorigenesis. METHODS: Tumorigenesis was measured in the Kras(G12D/+);Ptf1a(Cre/+) mouse model of PDA; these mice were crossed with mice with pancreas-specific disruption of genes encoding PI3K p110α (Pik3ca), p110β (Pik3cb), or RAC1 (Rac1). Pancreatitis was induced with 5 daily intraperitoneal injections of cerulein. Pancreata and primary acinar cells were isolated; acinar cells were incubated with an inhibitor of p110α (PIK75) followed by a broad-spectrum PI3K inhibitor (GDC0941). PDA cell lines (NB490 and MiaPaCa2) were incubated with PIK75 followed by GDC0941. Tissues and cells were analyzed by histology, immunohistochemistry, quantitative reverse-transcription polymerase chain reaction, and immunofluorescence analyses for factors involved in the PI3K signaling pathway. We also examined human pancreas tissue microarrays for levels of p110α and other PI3K pathway components. RESULTS: Pancreas-specific disruption of Pik3ca or Rac1, but not Pik3cb, prevented the development of pancreatic tumors in Kras(G12D/+);Ptf1a(Cre/+) mice. Loss of transformation was independent of AKT regulation. Preneoplastic ductal metaplasia developed in mice lacking pancreaticp110α but regressed. Levels of activated and total RAC1 were higher in pancreatic tissues from Kras(G12D/+);Ptf1a(Cre/+) mice compared with controls. Loss of p110α reduced RAC1 activity and expression in these tissues. p110α was required for the up-regulation and activity of RAC guanine exchange factors during tumorigenesis. Levels of p110α and RAC1 were increased in humanpancreatic intraepithelial neoplasias and PDAs compared with healthy pancreata. CONCLUSIONS:KRAS signaling, via p110α to activate RAC1, is required for transformation in Kras(G12D/+);Ptf1a(Cre/+) mice.
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