title: Attenuation of ribosomal protein S6 phosphatase activity in chicken embryo fibroblasts transformed by Rous sarcoma virus.
abstract: In chicken embryo fibroblasts, phosphorylation of the 40S ribosomal protein S6 increases during G1 but returns to basal level by mitosis. In contrast, in Rous sarcoma virus (RSV)-transformed fibroblasts, S6 remains highly phosphorylated throughout mitosis. This study investigated the mechanism by which RSV alters the pattern of S6 phosphorylation. Pulse-chase experiments demonstrate that phosphate turnover in S6 is rapid in normal cells and in cells infected with an RSV transformation-defective virus. In contrast, phosphate turnover in S6 is severely reduced in cells infected with temperature-sensitive RSV at a temperature permissive for transformation, indicating a diminished S6 phosphatase activity. Fractionation of cell lysates by DEAE chromatography showed an almost threefold lower S6 phosphatase activity in RSV-transformed versus normal cells. The S6 phosphatase was sensitive to inhibitor 2 and specifically recognized by an antibody to type 1 phosphatase (PP1). The S6 phosphatase activity recovered by immunoprecipitation of PP1 was threefold lower in transformed cells, but the steady-state level of expression and the rate of synthesis of PP1 were not altered by oncogenic transformation. Together, the results show that transformation by RSV reduced the S6-PP1 activity.
authors.affiliation: Instituto de Investigaciones Biomédicas, Consejo Superior de Investigaciones Científicas, Madrid, Spain.
authors.forename: B
authors.initials: B
authors.lastname: Belandia
authors.forename: D
authors.initials: D
authors.lastname: Brautigan
authors.forename: J
authors.initials: J
authors.lastname: Martín-Pérez
mesh_terms: D000818:Animals; D001358:Avian Sarcoma Viruses; D002472:Cell Transformation, Viral; D002478:Cells, Cultured; D002642:Chick Embryo; D005347:Fibroblasts / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D038601:Ribosomal Protein S6; D019893:Ribosomal Protein S6 Kinases; D012269:Ribosomal Proteins / Q000378:metabolism
chemical_list: D038601:Ribosomal Protein S6; D012269:Ribosomal Proteins; D017346:Protein Serine-Threonine Kinases; D019893:Ribosomal Protein S6 Kinases; D010749:Phosphoprotein Phosphatases