Inhibition of phorbol ester-accelerated amino acid transport in bovine lymphocytes

Abstract

12- O-Tetradecanoylphorbol-13-acetate, a highly active tumor-promoting agent and lymphocyte comitogen, rapidly accelerates the transport of α-aminoisobutyric acid in cultured bovine lymphocytes. Structure-activity studies show that the ability of phorbol diesters to accelerate α-aminoisobutyric acid uptake runs parallel to their potency as lymphocyte comitogens and as tumor promoters in mouse skin. This phorbol ester-accelerated, amino acid transport is largely insensitive to the inhibition of RNA and protein synthesis by actinomycin D and cycloheximide, respectively, and is insensitive to the inhibition of membrane movement by cytochalasin B and colchicine. Retinoic acid, an antagonist of the tumor-promoting and comitogenic actions of phorbol esters also inhibits the acceleration of amino acid uptake by 12- O-tetradecanoyl-phorbol-13-acetate; however, the epoxy derivatives of retinoic acid and structurally related analogs, which are potent antagonists of the other aspects of phorbol ester activation of lymphocytes, are inactive in blocking amino acid uptake. Comparative studies in lymphocytes show that this phorbol ester elicits a number of metabolic responses which appear to originate at the cell membrane and that these are differentially antagonized by retinoic acid, the 5,6-epoxide of retinoic acid, and related retinoid analogs.