title: TGF-beta enforces senescence in Myc-transformed hematopoietic tumor cells through induction of Mad1 and repression of Myc activity.
abstract: Inhibition of tumor growth factor (TGF)-beta-mediated cell cycle exit is considered an important tumorigenic function of Myc oncoproteins. Here we found that TGF-beta1 enforced G(1) cell cycle arrest and cellular senescence in human U-937 myeloid tumor cells ectopically expressing v-Myc, which contains a stabilizing mutation frequently found in lymphomas. This correlated with induced expression of the Myc antagonist Mad1, resulting in replacement of Myc for Mad1 at target promoters, reduced histone acetylation and strong repression of Myc-driven transcription. The latter was partially reversed by histone deacetylase (HDAC) inhibitors, consistent with involvement of Mad1. Importantly, knockdown of MAD1 expression prevented TGF-beta1-induced senescence, underscoring that Mad1 is a crucial component of this process. Enforced Mad1 expression sensitized U-937-myc cells to TGF-beta and restored phorbol ester-induced cell cycle exit, but could not alone induce G(1) arrest, suggesting that Mad1 is required but not sufficient for cellular senescence. Our results thus demonstrate that TGF-beta can override Myc activity despite a stabilizing cancer mutation and induce senescence in myeloid tumor cells, at least in part by induction of Mad1. TGF-beta-induced senescence, or signals mimicking this pathway, could therefore potentially be explored as a therapeutic principle for treating hematopoietic and other tumors with deregulated MYC expression.
authors.affiliation: Department of Plant Biology and Forest Genetics, Uppsala Genetic Center, Swedish University of Agricultural Sciences, Box 7080, 750 07 Uppsala, Sweden.
authors.forename: Siqin
authors.initials: S
authors.lastname: Wu
authors.forename: Anne
authors.initials: A
authors.lastname: Hultquist
authors.forename: Per
authors.initials: P
authors.lastname: Hydbring
authors.forename: Cihan
authors.initials: C
authors.lastname: Cetinkaya
authors.forename: Fredrik
authors.initials: F
authors.lastname: Oberg
authors.forename: Lars-Gunnar
authors.initials: LG
authors.lastname: Larsson
mesh_terms: D002453:Cell Cycle / Q000502:physiology; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D016922:Cellular Senescence; D055785:Gene Knockdown Techniques; D019337:Hematologic Neoplasms / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D022423:Myeloid Cells / Q000378:metabolism / Q000502:physiology*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D053773:Transforming Growth Factor beta1 / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; C501384:MAD1L1 protein, human; D009687:Nuclear Proteins; D016271:Proto-Oncogene Proteins c-myc; D034741:RNA, Small Interfering; D053773:Transforming Growth Factor beta1