IL-1 STIMULATES A DIVERGING SIGNALING PATHWAY IN EL4-6.1 THYMOMA CELLS - IL-2 RELEASE, BUT NOT IL-2 RECEPTOR EXPRESSION, IS SENSITIVE TO PERTUSSIS TOXIN

We reassessed the involvement of Bordetella pertussis toxin (PTX)-sens itive proteins in the IL-1 signaling pathway on the responses induced by IL-1 on the murine thymoma cell line EL4 6.1. We demonstrate that t he ADP-ribosyltransferase activity of PTX, and not its cell-anchoring B oligomer part, is responsible for the inhibition of IL-1-induced IL- 2 release, since 1) the concentration of PTX (less than or equal to 1 ng/ml) required to block the secretion is 100 to 1000 times lower than the concentration needed with the B oligomer; and 2) the mutated PT-9 K/129G, devoid of ADP-ribosyltransferase activity, was inactive at 100 ng/ml. We found that partial ADP-ribosylation of the G(i2)/G(i3) prot eins before stimulation with IL-1 was sufficient to obtain full inhibi tion of IL-2 release. PTX did not however inhibit the appearance on th e cell surface of the high affinity IL-2 receptors or the IL-2 release induced by PMA. in addition, we show that PTX prevented the expressio n of the IL-2 mRNA induced by IL-1, without affecting the binding of I L-2 specific nuclear factors to the T cell distal element of the IL-2 promoter. Furthermore, PTX also inhibited IL-1-induced proliferation o f non-transformed thymocytes. In conclusion, our results demonstrate t hat IL-1-induced IL-2 release is sensitive to PTX-catalyzed ADP-ribosy lation and that IL-1 activates a diverging pathway on EL4 6.1 cells.