EFFECTS OF SERUM CONCENTRATION ON EXPRESSION OF CARCINOGEN-INDUCED TRANSFORMATION IN C3H-10T1/2 CL8 CELL LINE

Abstract

The C3H/10T 1/2 CL8 [mouse embryo fibroblast] cell line (10T 1/2) is being widely used as a quantitative assay system for chemical and physical carcinogens. 10T 1/2 cells, but not their transformed counterparts, exhibit a decreased final saturation density with decreasing serum concentration. Exposure of carcinogen treated cultures to 5% serum 8 days posttreatment led to a 2- to 6-fold enhancement in transformation frequency in comparison with cultures maintained in 10% serum throughout. Exposure 14, 21 or 28 days posttreatment also caused enhancement of transformation frequency, provided a sufficient time for expression of the malignant phenotype was allowed. Exposure to 5% serum 1 or 2 days posttreatment did not lead to significant enhancement of transformation frequency. Exposure to 15 or 20% serum after 8 days abolished the expression of malignancy. This inhibition could be reversed by 5% serum. Morphologically transformed foci isolated from cultures exposed to 5% serum produced clones in agarose with the same frequency as foci isolated from cultures exposed to 10% serum. Reconstruction experiments, utilizing confluent monolayers of 10T 1/2 cells overlaid with transformed cells, demonstrated that the growth of transformed cells decreased proportionally with the log of serum concentration. This effect was not caused by depletion of medium and was dependent on the presence of 10T 1/2 cells. The expression of malignancy in this system is governed by the serum-modulated cell density of the mass of nontransformed cells in culture.