Effects of tumor promoters and extracellular calcium on the growth of normal, transformed and temperature sensitive rat liver epithelial cells.

We have compared the effect of extracellular Ca2+ concentration and of phorbol ester tumor promoters on the growth of normal rat liver epithelial cells, a chemically transformed derivative of these cells and a mutant of the latter cells that is temperature sensitive in the expression of transformation. The normal K16 or K22 cells grew considerably better in 1.25 mM Ca2+ than in 0.01 mM Ca2+, whereas their transformed counterpart, W8, grew equally well in 1.25 and 0.01 mM Ca2+. The temperature-sensitive mutant TS 223 exhibited an intermediate phenotype. When grown at either 36 degrees C or 39.5 degrees C, these cells were less Ca2+ dependent than K16 or K22 cells; but they were more Ca2+ dependent than W8 cells. The phorbol ester tumor promoters TPA (12-O-tetradecanoyl-phorbol-13-acetate), PDD (phorbol-12, 13-didecanoate) and PDB (phorbol-12,13-dibenzoate) enhanced the growth of K16 or K22 cells in 0.01 mM Ca2+. On the other hand, the same agents markedly inhibited the growth of W8 and TS 223 cells, at 36 degrees C and 39.5 degrees C, in both low (0.01 mM0 and normal (1.25 mM) Ca2+ concentrations. Two structurally related diterpenes which lack tumor promoting activity on mouse skin, phorbol and 4 alpha PDD, did not alter the growth properties of any of these cell lines, at either low or normal Ca2+ concentrations. Our results indicate, therefore, differences in the responses between normal and transformed rat liver epithelial cells to growth control by extracellular Ca2+ and tumor promoters.