title: Evidence that mirex promotes a unique population of epidermal cells that cannot be distinguished by their mutant Ha-ras genotype.
abstract: Mirex is a potent tumor promoter in 7,1 2-dimethylbenz[a]anthracene (DMBA)-initiated female CD-1 mouse skin. Like 12-O-tetradecanoylphorbol-13-acetate (TPA), mirex promotes papillomas that have a Ha-ras mutation; however, unlike TPA promotion, mirex promotion does not involve a general hyperplastic response. We used proliferating cell nuclear antigen (PCNA) and 5-bromo-2'-deoxyuridine (BrdU) immunohistochemical staining to further examine the proliferative capacity of mirex. The numbers of PCNA- and BrdU-positive epidermal S-phase cells were highly concordant in all treatment groups. Unlike a single application of TPA, a single application of mirex had little or no effect on the number of S-phase epidermal cells, and chronic application of mirex to mouse skin produced only minimal increases in S-phase cells. Moreover, mirex did not significantly alter the growth of BALB/MK-2 keratinocytes in media containing either 0.05 or 1.2 mM Ca++. These results suggest that mirex may have highly specific effects on the proliferation of initiated cells and support the existence of a unique mirex mechanism and/or distinct population of mirex-promotable mutant Ha-ras epidermal cells. To begin to address this issue of a distinct population of mirex-promotable mutant Ha-ras cells, we conducted a tandem experiment in which DMBA-initiated mice were treated twice weekly with a maximal promoting dose of mirex. Then, when the number of papillomas reached a plateau, these same mice were treated twice weekly with a maximal promoting dose of TPA. Mice treated with mirex developed a maximum of 6.4 papillomas/mouse. These mice were then promoted with TPA, which produced 8.9 additional papillomas/mouse for a total of 15.3 papillomas/mouse. The maximum tumor yields from other groups of mice treated with only TPA or mirex were 9.8 and 7.3 papillomas/mouse, respectively. Therefore, under these tandem conditions, tumor yields were additive, indicating that there are at least two distinct populations of mutant Ha-ras cells: one promoted by mirex and the other by TPA.
authors.affiliation: Molecular and Cellular Toxicology, Department of Toxicology, North Carolina State University, Raleigh 27695-7633, USA.
authors.forename: T W
authors.initials: TW
authors.lastname: Kim
authors.forename: K L
authors.initials: KL
authors.lastname: Porter
authors.forename: J F
authors.initials: JF
authors.lastname: Foley
authors.forename: R R
authors.initials: RR
authors.lastname: Maronpot
authors.forename: R C
authors.initials: RC
authors.lastname: Smart
mesh_terms: D015127:9,10-Dimethyl-1,2-benzanthracene / Q000633:toxicity; D000818:Animals; D001973:Bromodeoxyuridine / Q000032:analysis; D002273:Carcinogens / Q000633:toxicity*; D002294:Carcinoma, Squamous Cell / Q000139:chemically induced* / Q000235:genetics; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D003043:Cocarcinogenesis; D005260:Female; D011905:Genes, ras; D005838:Genotype; D007150:Immunohistochemistry; D015603:Keratinocytes / Q000187:drug effects* / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D008917:Mirex / Q000633:toxicity*; D009154:Mutation; D009607:Nitrosourea Compounds / Q000032:analysis; D010212:Papilloma / Q000139:chemically induced* / Q000235:genetics; D016196:S Phase / Q000187:drug effects / Q000502:physiology; D012878:Skin Neoplasms / Q000139:chemically induced* / Q000235:genetics; D013755:Tetradecanoylphorbol Acetate / Q000633:toxicity
chemical_list: D002273:Carcinogens; D009607:Nitrosourea Compounds; D015127:9,10-Dimethyl-1,2-benzanthracene; C018627:1-(2-chloroethyl)-3-(2,6-dioxo-3-piperidinyl)-1-nitrosourea; D001973:Bromodeoxyuridine; D013755:Tetradecanoylphorbol Acetate; D008917:Mirex