Combined Effects of Tumor Promoters and Serum on Proliferin mRNA Induction: A Biomarker Sensitive to Saccharin, 2,3,7,8-Tcdd, and Other Compounds at Minimal Concentrations Promoting C3H/10T1/2 Cell Transformation

Abstract

Increases in proliferin (PLF) gene family mRNA abundance and promotional effects in cell transformation assays are paired responses that follow exposures to diverse chemical and physical agents in the C3H/10T1/2 in vitro model of multi-stage carcinogenesis. This study measured PLF mRNA abundance changes over 1 to 3 d in response to several types of promoters that were previously unassessed for this effect. Saccharin is a known promoter of cell transformation in C3H/10T1/2 cell cultures, but unlike 12-O-tetradecanoylphorbol 13-acetate (TPA) or mezerein, PLF mRNA abundance increases were inconsistently detected following simple addition of saccharin to the culture medium. Consistent effects occurred when pretreatments with promoting concentrations of saccharin or sodium saccharin (1-13 mM) were combined with subsequent additions of serum or complete medium changes. When added at or near their lowest observed effect levels (LOELs) for transformation, other promoters of 10T1/2 cells such as formaldehyde (50-100 w M), diethylstilbesterol (DES) (0.5-30 w M), and 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) (4-40 pM) were shown to be inducers of both basal and serum-induced PLF mRNA levels. Acetaldehyde (300-900 w M) was comparable to formaldehyde as an inducer. In contrast to these various promoters, pretreatment with phenobarbital or methanol, both non-promoters in these cells, did not affect serum-induced PLF mRNA levels at concentrations up to 3 mM and 2 M, respectively. The published values for the LOELs of 17 promoters of cell transformation and the LOELs determined to date for PLF mRNA induction were highly correlated over a 1 billion -- fold concentration range. The response of PLF mRNA is a short-term marker sensitive to the active concentration ranges of diverse chemical agents with promotional activity in C3H/10T1/2 cell transformation system.