Differential activation and inhibition of lymphocyte proliferation by phorbol esters, mezerein, teleocidin, and okadaic acid.

Abstract

Lymphocytes can be stimulated to proliferate in vitro by mitogens such as concanavalin A. The tumor-promoting phorbol ester 12-O-tetradecanoyl phorbol-13-acetate (TPA) can enhance this proliferation, partly because of an increase in interleukin 2 (IL-2) production. However, if lymphocytes are treated with TPA for 24 h before concanavalin A exposure, IL-2 production and proliferation are depressed. The target of the action of TPA is protein kinase C, which is activated after a short exposure but down-regulated after a longer one. This study was designed to determine if the modulation of IL-2 was separable from the modulation of protein kinase C. When phorbol esters phorbol 12-retinoate-13-acetate, phorbol 12,13-dibutyrate, 12-deoxyphorbol 13-phenylacetate, and 12-deoxyphorbol 13-phenylacetate-20-acetate, as well as nonphorbol tumor promoters mezerein, telocidin, and okadaic acid, were tested, all but okadaic acid reproduced the effects of TPA. However, 12-deoxyphorbol 13-phenylacetate and 12-deoxyphorbol 13-phenylacetate-20-acetate were required at nearly 100-fold higher concentrations than TPA to suppress IL-2 production, suppress mitogenesis, and cause down-regulation of protein kinase C. A comparison of structures indicated that an R group at the 12-position was less important for IL-2 production and mitogenesis than for down-regulation of protein kinase C and the suppression of mitogenesis. In no case was the modulation of protein kinase C separated from the effects on IL-2 production and proliferation.