Roles of the Ras-MEK-mitogen-activated protein kinase and phosphatidylinositol 3-kinase-Akt-mTOR pathways in Jaagsiekte sheep retrovirus-induced transformation of rodent fibroblast and epithelial cell lines.
Jaagsiekte sheep retrovirus (JSRV) is the causative agent of ovine pulmonary adenocarcinoma (OPA), a transmissible lung cancer of sheep. The virus can induce tumors rapidly, and we previously found that the JSRV envelope protein (Env) functions as an oncogene, because it can transform mammalian and avian fibroblast cell lines. (N. Maeda, Proc. Natl. Acad. Sci. USA 98:4449-4454, 2001). The molecular mechanisms of JSRV Env transformation are of considerable interest. Several reports suggested that the phosphatidylinositol 3-kinase/Akt pathway is important for transformation of mammalian fibroblasts but not for chicken fibroblasts. In this study, we found that Akt/mTOR is involved in JSRV transformation of mouse NIH 3T3 fibroblasts, because treatment with the mTOR inhibitor rapamycin reduced transformation. We also found that H/N-Ras inhibitor FTI-277 and MEK1/2 inhibitors PD98059 and U0126 strongly inhibited JSRV transformation of NIH 3T3 fibroblasts, suggesting that the H/N-Ras-MEK-mitogen-activated protein kinase (MAPK) p44/42 pathway is necessary for the transformation. In RK3E epithelial cells, the MEK1/2 inhibitors also eliminated transformation, but FTI-277 only partially inhibited transformation. It was noteworthy that p38 MAPK inhibitors enhanced JSRV transformation in both fibroblasts and epithelial cells. Treatment of transformed cells with p38 inhibitors both increased levels of phospho-MEK1/2 and phospho-p44/42 and induced rapid enhancement of the transformed phenotype. Immunohistochemical staining of tumor tissues from naturally and experimentally induced OPA and naturally occurring enzootic nasal adenocarcinoma revealed strong activation of MAPK p44/42 in all cases examined. However, p38 activation was not generally observed. These results indicate that signaling through two pathways (in particular, H/N-Ras-MEK-MAPK and, to a lesser extent, Akt-mTOR) is important for JSRV-induced transformation and that p38 MAPK has a negative regulatory effect on transformation, perhaps via MEK1/2 and p44/42.
Maeda
Naoyoshi
N
Cancer Research Institute, University of California, Irvine, Irvine, CA 92697-3900, USA.
Fu
Wuxia
W
Ortin
Aurora
A
de las Heras
Marcelo
M
Fan
Hung
H
D000818:Animals; D002070:Butadienes / Q000494:pharmacology; D002472:Cell Transformation, Viral; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000821:virology*; D005347:Fibroblasts / Q000821:virology*; D005419:Flavonoids / Q000494:pharmacology; D022141:Jaagsiekte sheep retrovirus / Q000472:pathogenicity*; D048369:MAP Kinase Kinase 1 / Q000502:physiology; D048370:MAP Kinase Kinase 2 / Q000502:physiology; D008715:Methionine / Q000031:analogs & derivatives* / Q000494:pharmacology; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D009570:Nitriles / Q000494:pharmacology; D011494:Protein Kinases / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D015398:Signal Transduction / Q000502:physiology*; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D048051:p38 Mitogen-Activated Protein Kinases / Q000502:physiology; D018631:ras Proteins / Q000502:physiology
D002070:Butadienes; D004791:Enzyme Inhibitors; C096856:FTI 277; D005419:Flavonoids; D009570:Nitriles; D011518:Proto-Oncogene Proteins; C113580:U 0126; D008715:Methionine; D011494:Protein Kinases; C546843:mTOR protein, mouse; C546845:mTOR protein, rat; C494920:Akt1 protein, rat; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048051:p38 Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; D018631:ras Proteins; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D020123:Sirolimus