Characterization of the morphological, growth, and steroidogenic effect of TPA on mouse Y-1 adrenal cortical tumor cells in culture.

The tumor-promoting agent 12-0-tetradecanoyl-phorbol-13-acetate (TPA) caused a time- and dose-dependent morphological change in Y-1 adrenocortical tumor cells. The morphological alteration was apparent 2 hr following addition of 1 microgram/ml TPA to cell cultures and became more striking with longer treatment times. Smaller doses of TPA took a longer time to produce an effect. Cultures grown in the presence of TPA exhibited more rounding and piling up of cells than similar cultures maintained in medium lacking TPA. These TPA-stimulated morphological changes were reversible, and after 24 hr in TPA-free media, the cultured cells began to flatten. After 96 hr in TPA-free media they resembled the control cultures. The reversibility of the morphological change was also dose dependent: cells treated with 1 microgram/ml TPA took a longer time to resume the typical control morphology than did cultures treated with 0.01 microgram/ml TPA. In addition, TPA treatment resulted in a decrease in cell growth rate, an increase in steroid production, and an increase in the localization of free catalytic units of cAMP-dependent protein kinase in the cytoplasm. The steroidogenic effect of ACTH on the cell population was inhibited in cultures maintained in TPA. The results of this study indicate that TPA induces morphological changes in the Y-1 adrenocortical tumor cell population while increasing steroidogenesis and the activation of cAMP-dependent protein kinase and decreasing cell growth rate.