Oncogenic KRAS activates hedgehog signaling pathway in pancreatic cancer cells.
Hedgehog (Hh) signaling is deregulated in multiple human cancers including pancreatic ductal adenocarcinoma (PDA). Because KRAS mutation represents one of the earliest genetic alterations and occurs almost universally in PDA, we hypothesized that oncogenic KRAS promotes pancreatic tumorigenesis in part through activation of the Hh pathway. Here, we report that oncogenic KRAS activates hedgehog signaling in PDA cells, utilizing a downstream effector pathway mediated by RAF/MEK/MAPK but not phosphatidylinositol 3-kinase (PI3K)/AKT. Oncogenic KRAS transformation of human pancreatic ductal epithelial cells increases GLI transcriptional activity, an effect that is inhibited by the MEK-specific inhibitors U0126 and PD98059, but not by the PI3K-specific inhibitor wortmannin. Inactivation of KRAS activity by a small interfering RNA specific for oncogenic KRAS inhibits GLI activity and GLI1 expression in PDA cell lines with activating KRAS mutation; the MEK inhibitors U0126 and PD98059 elicit a similar response. In addition, expression of the constitutively active form of BRAF(E600), but not myr-AKT, blocks the inhibitory effects of KRAS knockdown on Hh signaling. Finally, suppressing GLI activity leads to a selective attenuation of the oncogenic transformation activity of mutant KRAS-expressing PDA cells. These results demonstrate that oncogenic KRAS, through RAF/MEK/MAPK signaling, is directly involved in the activation of the hedgehog pathway in PDA cells and that collaboration between these two signaling pathways may play an important role in PDA progression.
Ji
Zhenyu
Z
Department of Pharmacology and Toxicology, Sealy Center for Cancer Cell Biology, School of Medicine, The University of Texas Medical Branch, Galveston, TX 77555, USA.
Mei
Fang C
FC
Xie
Jingwu
J
Cheng
Xiaodong
X
D021441:Carcinoma, Pancreatic Ductal / Q000378:metabolism*; D049109:Cell Proliferation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D053823:Hedgehog Proteins / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D008156:Luciferases / Q000378:metabolism; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D010190:Pancreatic Neoplasms / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D016283:Proto-Oncogene Proteins p21(ras); D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism; D014407:Tumor Cells, Cultured; D000071676:Zinc Finger Protein GLI1; D018631:ras Proteins / Q000502:physiology*
D004791:Enzyme Inhibitors; C400551:GLI1 protein, human; D053823:Hedgehog Proteins; C117307:KRAS protein, human; D011518:Proto-Oncogene Proteins; D014157:Transcription Factors; D000071676:Zinc Finger Protein GLI1; D008156:Luciferases; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D019908:Proto-Oncogene Proteins c-raf; D020928:Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins