title: Pharmacologic inhibition of RAF-->MEK-->ERK signaling elicits pancreatic cancer cell cycle arrest through induced expression of p27Kip1.
abstract: Expression of mutationally activated RAS is a feature common to the vast majority of human pancreatic adenocarcinomas. RAS elicits its effects through numerous signaling pathways including the RAF-->mitogen-activated protein (MAP)/extracellular signal-regulated kinase (ERK) kinase [MEK]-->ERK MAP kinase pathway. To assess the role of this pathway in regulating cell proliferation, we tested the effects of pharmacologic inhibition of MEK on human pancreatic cancer cell lines. In eight cell lines tested, MEK inhibition led to a cessation of cell proliferation accompanied by G0-G1 cell cycle arrest. Concomitant with cell cycle arrest, we observed induced expression of p27Kip1, inhibition of cyclin/cyclin-dependent kinase 2 (cdk2) activity, accumulation of hypophosphorylated pRb, and inhibition of E2F activity. Using both antisense and RNA interference techniques, we assessed the role of p27Kip1 in the observed effects of MEK inhibition on pancreatic cancer cell proliferation. Inhibition of p27Kip1 expression in Mia PaCa-2 cells restored the activity of cyclin/cdk2, phosphorylation of pRb, and E2F activity and partially relieved the effects of U0126 on pancreatic cancer cell cycle arrest. Consistent with the effects of p27Kip1 on cyclin/cdk2 activity, inhibition of CDK2 expression by RNA interference also led to G0-G1 cell cycle arrest. These data suggest that the expression of p27Kip1 is downstream of the RAF-->MEK-->ERK pathway and that the regulated expression of this protein plays an important role in promoting the proliferation of pancreatic cancer cells. Moreover, these data suggest that pharmacologic inhibition of the RAF-->MEK-->ERK signaling pathway alone might tend to have a cytostatic, as opposed to a cytotoxic, effect on pancreatic cancer cells.
authors.affiliation: Cancer Research Institute and Department of Cellular and Molecular Pharmacology, University of California, San Francisco Comprehensive Cancer Center, San Francisco, California 94115, USA.
authors.forename: Stephan
authors.initials: S
authors.lastname: Gysin
authors.forename: Sang-Hyun
authors.initials: SH
authors.lastname: Lee
authors.forename: Nicholas M
authors.initials: NM
authors.lastname: Dean
authors.forename: Martin
authors.initials: M
authors.lastname: McMahon
mesh_terms: D002070:Butadienes / Q000494:pharmacology*; D042846:CDC2-CDC28 Kinases / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology; D018797:Cell Cycle Proteins / Q000096:biosynthesis* / Q000235:genetics; D048708:Cell Growth Processes / Q000502:physiology; D045744:Cell Line, Tumor; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors*; D006801:Humans; D020930:MAP Kinase Kinase Kinases / Q000037:antagonists & inhibitors*; D020935:MAP Kinase Signaling System / Q000187:drug effects; D009570:Nitriles / Q000494:pharmacology*; D010190:Pancreatic Neoplasms / Q000188:drug therapy / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D010766:Phosphorylation; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D034622:RNA Interference; D016372:RNA, Antisense / Q000235:genetics; D016160:Retinoblastoma Protein / Q000378:metabolism; D014162:Transfection; D025521:Tumor Suppressor Proteins / Q000096:biosynthesis* / Q000235:genetics; D048490:raf Kinases / Q000037:antagonists & inhibitors*
chemical_list: D002070:Butadienes; D018797:Cell Cycle Proteins; D004791:Enzyme Inhibitors; D009570:Nitriles; D011518:Proto-Oncogene Proteins; D016372:RNA, Antisense; D016160:Retinoblastoma Protein; D025521:Tumor Suppressor Proteins; C113580:U 0126; D050760:Cyclin-Dependent Kinase Inhibitor p27; D048490:raf Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; C495900:CDK4 protein, human; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D020930:MAP Kinase Kinase Kinases