title: Comparison of transformation by manganese sulfate and 5-azacytidine in Rat 6 cells overexpressing the c-myc oncogene.
abstract: Rat 6 cells are not transformed by treatment with the well-known carcinogens benzo[a]pyrene (BP) or N-methyl-N-nitro-N'-nitrosoguanidine (MNNG). Upon retroviral transduction of the mouse c-myc gene, Rat 6 cells showed mildly altered morphology and formed microcolonies in soft agar; furthermore, they could be transformed by BP and MNNG to form large colonies in agar (Hsiao et al. (1992) Mol. Carcinogenesis, 5, 140-154). In the current report, we tested the sensitivity of the c-myc-overexpressing cells (Rat 6/c-myc) to two additional chemicals: 5-azacytidine and MnSO4. These chemicals differ from the direct-acting mutagens tested previously. 5-Azacytidine, a potent DNA methylation inhibitor, induced growth of large colonies in soft agar cultures of Rat 6 or Rat 6/c-myc cells. On the other hand, MnSO4 only induced transformation in Rat 6/c-myc cells, but not the parental Rat 6 cells. Transformants induced by 5-azacytidine lost c-myc-induced apoptotic cell death, whereas MnSO4-induced transformants showed a higher degree of apoptosis than the parental Rat 6/c-myc cells. These results suggest that MnSO4 co-operates with overexpressed c-myc in inducing transformation, while 5-azacytidine transformation is independent of c-myc overexpression and may involve alterations in the regulation of apoptosis.
authors.affiliation: Dept. of Molecular Biology and Biochemistry, and Cancer Research Institute, University of California, Irvine, USA.
authors.forename: W L
authors.initials: WL
authors.lastname: Hsiao
authors.forename: G
authors.initials: G
authors.lastname: Mendosa
authors.forename: N H
authors.initials: NH
authors.lastname: Kothari
authors.forename: H
authors.initials: H
authors.lastname: Fan
mesh_terms: D000818:Animals; D001374:Azacitidine / Q000633:toxicity*; D002460:Cell Line; D002471:Cell Transformation, Neoplastic / Q000139:chemically induced*; D016259:Genes, myc; D017895:Manganese Compounds; D020149:Manganese Poisoning; D051381:Rats; D011916:Rats, Inbred F344; D013431:Sulfates / Q000633:toxicity*
chemical_list: D017895:Manganese Compounds; D013431:Sulfates; D001374:Azacitidine; C039798:manganese sulfate