© 1993 Oxford University Press
research-article |
Inactivation of a tumor suppressor function in immortal Syrian hamster cells by N-methyl-N'-nitro-N-nitrosoguanidine and by 5-aza-2'-deoxycytidine
Division of Biochemical Toxicology, National Center for Toxicological Research Jefferson, AR 72079-9502, USA
Laboratory of Molecular Carcinogenesis, National Institute for Environmental Health Sciences, National Institutes of Health PO Box 12233, Research Triangle Park, NC 27709, USA
Clonal lines of immortal Syrian hamster cells were previously isolated that either suppressed (supB+) tumorigenicity in hybrids with a malignant hamster cell line (BP6T) or had lost this suppression ability (supB–). Neither line was tumorigenic or showed anchorage-independent growth in normal growth medium. SupB– cells, but not supB+ cells, grew in agar supplemented with the growth factors EGF, PDGF and insulin (EPI), providing a selective assay for the supB–phenotype. After treatment of supB+ cells with either N-methyl-N'-nitro-N-nitrosoguanidine (10–300 ng/ml) or 5-aza-2'-deoxycytidine (25–250 ng/ml), and an expression period of 4–8 weeks, a dose-dependent increase in altered cells that grew in agar supplemented with EPI was observed. Cell lines derived from colonies in agar showed persistent EPI-stimulated growth in agar, and decreased suppression of growth in agar for hybrids with BP6T cells. Thus, carcinogen-induced loss of the tumor suppressor phenotype has been demonstrated.