ACTIVATION OF THE MOUSE IL-2 GENE BY OKADAIC ACID - SYNERGY WITH INTERLEUKIN-1

Interleukin-1 (IL-1) has potent immunoregulatory and inflammatory func tions. Its activity is mediated by an 80-kDa receptor on the cell surf ace and leads: to activation of other genes. The underlying molecular events are largely unknown. We investigated the role of phosphatases i n activation of the IL-2 gene in EL4 thymoma cells. We found that the protein phosphatase PP1 and PP2A inhibitor okadaic acid (OA) alone was able to significantly stimulate IL-2 production by the IL-1-responsiv e EL4 subline EL4 5D3 and also by the IL-1-nonresponsive EL4 subline E L4D6/76. In the IL-1-responsive cell line OA strongly synergized with phorbol myristate acetate (PMA) and IL-1. In the IL-1-nonresponsive ce ll line OA synergized with PMA but not with IL-1. Under suboptimal con ditions of PMA/OA synergy an additional synergistic effect of IL-1 was shown. This was true for IL-2 and IL-6 production. Sphingomyelinase o r sphingosine had no detectable effect. The kinetics of OA- and PMA-in duced expression of IL-2 mRNA and IL-2 protein was different. PMA indu ced maximal expression between 6 and 12 h and was almost undetectable at 24 h. OA-induced expression was first obvious at 12 h and continued longer than 36 h. In both cases IL-1 caused no shift in kinetics, but potentiated the effects of the different tumor promoters. Utilizing I L-2 promoter-CAT constructs we showed in transfection experiments that the synergistic effect was also evident on the transcriptional level. We conclude from the data that phosphatases play an important role fo r IL-2 expression and and that IL-1 can use additional pathways of act ivation that are different from events induced by PMA or OA.