title: Pleiotropic action of AP-1 in v-Src-transformed cells.
abstract: The activation of AP-1 is a hallmark of cell transformation by tyrosine kinases. In this study, we characterize the role of AP-1 proteins in the transformation of chicken embryo fibroblasts (CEF) by v-Src. In normal CEF, the expression of a dominant negative mutant of c-Jun (TAM67) induced senescence. In contrast, three distinct phenotypes were observed when TAM67 was expressed in v-Src-transformed CEF. While senescent cells were also present, the inhibition of AP-1 caused apoptosis in a fraction of the v-Src-transformed cells. In addition, cells containing lipid-rich vesicles accumulated, suggesting that a subpopulation of the v-Src-transformed cells underwent differentiation in response to the inhibition of AP-1. JunD and Fra-2 were the main components of this factor, while c-Jun accounted for a minor fraction of AP-1 in v-Src-transformed CEF. The downregulation of c-Jun expression by short hairpin RNA (shRNA) induced senescence in normal and v-Src-transformed cells. In contrast, a high incidence of apoptosis was caused by the downregulation of JunD, suggesting that it is required for the survival of v-Src-transformed CEF. Levels of the p53 tumor suppressor were elevated under conditions of JunD inhibition. Repression of p53 by shRNA enhanced the survival and anchorage-independent proliferation of v-Src-transformed CEF with JunD/AP-1 inhibition. The inhibition of Fra-2 had no visible phenotype in normal CEF but caused the appearance of lipid-rich vesicles in v-Src-transformed CEF. Therefore, AP-1 facilitated transformation by acting as a survival factor, by inhibiting premature entry into senescence, and by blocking the differentiation of v-Src-transformed CEF.
authors.affiliation: Department of Biology, McMaster University, 1280 Main St. West, Hamilton, Ontario L8S 4K1, Canada.
authors.forename: Lizhen
authors.initials: L
authors.lastname: Wang
authors.forename: Natalie A
authors.initials: NA
authors.lastname: Rodrigues
authors.forename: Ying
authors.initials: Y
authors.lastname: Wu
authors.forename: Bart M
authors.initials: BM
authors.lastname: Maslikowski
authors.forename: Nishi
authors.initials: N
authors.lastname: Singh
authors.forename: Samantha
authors.initials: S
authors.lastname: Lacroix
authors.forename: Pierre-André
authors.initials: PA
authors.lastname: Bédard
mesh_terms: D000818:Animals; D002461:Cell Line, Transformed; D002472:Cell Transformation, Viral; D002642:Chick Embryo; D004789:Enzyme Activation; D005347:Fibroblasts / Q000378:metabolism / Q000502:physiology / Q000821:virology*; D051921:Fos-Related Antigen-2; D005786:Gene Expression Regulation; D016391:Genes, src; D058685:Genetic Pleiotropy / Q000235:genetics / Q000502:physiology*; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics / Q000378:metabolism; D052736:Rous sarcoma virus / Q000502:physiology*; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism*
chemical_list: D051921:Fos-Related Antigen-2; D016755:Proto-Oncogene Proteins c-jun; D018808:Transcription Factor AP-1