STIMULATION OF DNA-SYNTHESIS IN CALCIUM-DEPRIVED T51B LIVER-CELLS BY THE TUMOR PROMOTERS PHENOBARBITAL, SACCHARIN, AND 12-O-TETRADECANOYLPHORBOL-13-ACETATE

Abstract

Extracellular Ca deprivation arrested the proliferative development of T51B rat liver cells in late G1 or S phases. These arrested cells initiated DNA synthesis within 1 h after addition of Ca or tumor promoter such as phorbol-12, 13-didecanoate, phenobarbital, saccharin or 12-O-tetradecanoylphorbol-13-acetate. Nonpromoting relatives of 12-O-tetradecanoylphorbol-13-acetate such as phorbol, 4-O-methyl-12-O-tetradencanoylphorbol-13-acetate, and 4.alpha.-phorbol-12, 13-didecanoate were unable to significantly induce the Ca-deprived cells to initiate DNA synthesis. An ability to elicit a prompt DNA-synthetic response from Ca-deprived cells might be a useful in vitro indicator of tumor- promoting potential.