title: Colony size, cell density and nature of the tumor promoter are critical variables in expression of a transformed phenotype (focus formation) in co-cultures of UV-TDTx and C3H10T1/2 cells.
abstract: UV-TDTx cells are cloned from foci arising after C3H10T1/2 cells are sequentially exposed to u.v. irradiation followed by tetradecanoylphorbol acetate (TPA). When grown in pure culture, UV-TDTx cells appear transformed. Co-culture with C3H10T1/2 cells suppresses focus formation by the UV-TDTx cells. In the presence of TPA, however, focus formation by UV-TDTx cells occurs in C3H10T1/2 co-cultures. We now demonstrate that only tumor promoters that activate protein kinase C (TPA, teleocidin) can reverse C3H10T1/2 suppression of UV-TDTx focus formation in co-culture; other promoters (diethyl stilbestrol, dioxin, saccharin, cadmium) are inactive. Retinoic acid, a potent inhibitor of many biological effects of TPA, blocks the action of TPA in UV-TDTx:C3H10T1/2 co-cultures. Focus formation by UV-TDTx cells in co-culture is dependent on the size of the UV-TDTx colony at confluence; if the UV-TDTx colony is below a minimal size when the co-cultures reach density-dependent growth arrest, suppression of focus formation by C3H10T1/2 cells occurs even in the presence of TPA. Finally, TPA must be present prior to confluence to relieve suppression of focus formation. If TPA is added to co-cultures after density arrest, UV-TDTx cells will not subsequently form foci.
mesh_terms: D002452:Cell Count; D002471:Cell Transformation, Neoplastic / Q000187:drug effects / Q000473:pathology*; D002478:Cells, Cultured; D002999:Clone Cells; D006801:Humans; D010641:Phenotype; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014212:Tretinoin / Q000494:pharmacology
chemical_list: D014212:Tretinoin; D013755:Tetradecanoylphorbol Acetate