Divergent roles for Ras and Rap in the activation of p38 mitogen-activatedprotein kinase by interleukin-1

We have found that lethal toxin from Clostridiam sordellii, which specifica lly inactivates the low molecular weight G proteins Ras, Rap, and Rac, inhi bits the activation of p38 mitogen-activated protein kinase (MAPK) by inter leukin-1 (IL-1) in EL4.NOB-1 cells and primary fibroblasts. The target prot ein involved appeared to be Ras, because transient transfections with domin ant negative RasN17 inhibited p38 MAPK activation by IL-1. Furthermore, tra nsfections of cells with constitutively active RasVHa-activated p38 MASH. F urther evidence for Ras involvement came from the observation that IL-1 cau sed a rapid activation of Ras in the cells and from the inhibitory effects of the Ras inhibitors manumycin A and damnacanthal. Toxin B from Clostridiu m difficile, which inactivates Rac, Cdc42, and Rho, was without effect. Dom inant negative versions of Rac (RacN17) or Bap (Rap1AN17) did not inhibit t he response. Intriguingly, transfection of cells with dominant negative Rap 1AN17 activated p38 MAPK, Furthermore, constitutively active Rap1AV12 inhib ited p38 MAPK activation by IL-1, consistent with Rap antagonizing Ras func tion. IL-1 also activated Rap in the cells, but with slower kinetics than R as. Our studies therefore provide clear evidence using multiple approaches for Ras as a signaling component in the activation of p38 MAPK by IL-1, wit h Rap having an inhibitory effect.