2,3,7,8-Tetrachlorodibenzo-p-dioxin causes unbalanced growth in 5L rat hepatoma cells.

5L cells, dedifferentiated descendents of the rat hepatoma line H4IIEC3, constitute one of the rare continuous lines which are sensitive to the toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In the present study we investigated the nature of TCDD toxicity in these cells. The following results were obtained: (1) Exposure to 0.1 nM TCDD for 48 hr inhibits the proliferation of 5L cells by more than 50%, as determined by the increase in the number of cells and the amount of DNA per culture. (2) TCDD doubles the amount of protein and the uptake of neutral red per cell during the 48-hr exposure period. (3) TCDD restores neither constitutive levels of tyrosine aminotransferase, a marker of liver-specific functions, nor its inducibility by dexamethasone. (4) The effects of TCDD are reversible when TCDD-containing growth media are replaced by TCDD-free medium. (5) 5L cells grown at 2% of fetal bovine serum are considerably more sensitive to TCDD than those grown at 10% serum. These results indicate that TCDD inhibits the proliferation of 5L cells without retarding the rate of growth or overtly changing the status of differentiation. The dioxin possibly causes unbalanced cell growth by interfering with the action of hormones or factors contained in the growth medium.