Characterization of the inhibition of interleukin 2 mRNA accumulation by 12-O-tetradecanoylphorbol-13-acetate in primary lymphocytes

We found previously that bovine lymph node cells (LNC) incubated with 12- O-tetradecanoylphorbol-13-acetate (TPA) for 18 h proliferate only to a limited degree on subsequent stimulation with concanavalin A (Con A), or with the comitogenic combination of Con A plus TPA. The lack of proliferation was traced to a lack of secretion of interleukin 2 (IL-2). Lack of secretion was paralled by a decrease in IL-2 mRNA levels. In this study we further characterized how TPA pretreatment affected IL-2 mRNA production. We found that TPA depressed IL-2 mRNA accumulation in a dose-dependent manner after at least 10 h of pretreatment. In contrast, pretreatment from 4 to 6 h augmented IL-2 mRNA accumulation. Furthermore, LNC stimulated with ionomycin plus TPA were less susceptible to inhibition by pretreatment with TPA, most likely because this mitogenic combination caused a much greater amount of IL-2 mRNA than did Con A or Con A plus TPA. Finally, a protein synthesis inhibitor, cycloheximide, partially counteracted the negative effects of TPA on IL-2 mRNA accumulation and on proliferation. These results suggest that TPA, probably acting through protein kinase C, initially augments the production of IL-2 mRNA but subsequently induces mechanisms to decrease the level of mRNA.