TY - JOUR

T1 - Ras-inducible immortalized fibroblasts: focus formation without cell cycle deregulation.

AU - Jacobsen, Kivin

AU - Groth, Anja

AU - Willumsen, Berthe Marie

N1 - Keywords: 3T3 Cells; Animals; Cell Cycle; Cell Division; Cell Line, Transformed; Cell Transformation, Viral; Colony-Forming Units Assay; Culture Media, Serum-Free; Cyclin D1; Genes, Viral; Genes, ras; MAP Kinase Signaling System; Mice; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinases; Oncogene Protein p21(ras); Phosphorylation; Protein Processing, Post-Translational; Recombinant Fusion Proteins; Signal Transduction; Transfection

PY - 2002

Y1 - 2002

N2 - The Ras oncogene transforms cultured murine fibroblasts into malignant, focus-forming cells, whose lack of contact inhibition is evidenced by high saturation densities. In order to investigate the reversibility of Ras transformation, as well as the kinetics of Ras-induced changes, cell lines that conditionally express oncogenic Ras were constructed. Both focus formation and increased saturation density were inducible and fully reversible. In exponentially growing cells, oncogenic Ras-expression had no effect on proliferation rates, Erk phosphorylation, or the level of cyclin D1, and Ras-induction did not confer serum-independent growth. As expected, growth to high density in uninduced cells led to quiescence with a low level of cyclin D1 and no active Erk; in this setting, Ras induction prevented full downregulation of cyclin D1 and inactivation of Erk. Our results show that Ras expression to a level sufficient for transformation leads to relatively subtle effects on known downstream targets, and that the focus formation and increased saturation density growth induced by Ras is not a result of growth factor independence.

AB - The Ras oncogene transforms cultured murine fibroblasts into malignant, focus-forming cells, whose lack of contact inhibition is evidenced by high saturation densities. In order to investigate the reversibility of Ras transformation, as well as the kinetics of Ras-induced changes, cell lines that conditionally express oncogenic Ras were constructed. Both focus formation and increased saturation density were inducible and fully reversible. In exponentially growing cells, oncogenic Ras-expression had no effect on proliferation rates, Erk phosphorylation, or the level of cyclin D1, and Ras-induction did not confer serum-independent growth. As expected, growth to high density in uninduced cells led to quiescence with a low level of cyclin D1 and no active Erk; in this setting, Ras induction prevented full downregulation of cyclin D1 and inactivation of Erk. Our results show that Ras expression to a level sufficient for transformation leads to relatively subtle effects on known downstream targets, and that the focus formation and increased saturation density growth induced by Ras is not a result of growth factor independence.

U2 - 10.1038/sj.onc.1205423

DO - 10.1038/sj.onc.1205423

M3 - Journal article

C2 - 12082537

VL - 21

SP - 3058

EP - 3067

JO - Oncogene

JF - Oncogene

SN - 0950-9232

IS - 19

ER -