Lack of a role for Jun kinase and AP-1 in Fas-induced apoptosis

Cross-linking of Fas (CD95) induces apoptosis, a response that has been reported to depend upon the Ras activation pathway. Since man?; examples of apoptosis have been reported to involve AP-1 and/or the AP-1-activating enzyme Jun kinase (JNK), downstream effecters of Pas or Ras-like small GTP-binding proteins, we evaluated the role of these molecules in Fas-mediated apoptosis. Although cross-linking of Pas an Jurkat T cells did result in JNK activation, increased activity was observed relatively late, being detectable only after 60 min of stimulation. Expression of a dominant negative form of SEK1 that blocked Pas-mediated induction of JNK activity had no effect on Pas-mediated apoptosis, Furthermore, maximally effective concentrations of anti-Pas did not cause JNK activation if apoptosis was blocked by a cysteine protease inhibitor, suggesting that under these conditions, activation of JNK may be secondary to the stress of apoptosis rather than a direct result of Fas engagement, Despite the activation of JNK, there was no induction of AP-I activity as determined by gel shift assay or induction of an AP-1-responsive reporter, The lack of a requirement for AP-1 induction in Pas-mediated death was further substantiated with Jurkat cells that were stably transfected with a dominant negative cJun, TAM-67. While TAM-67 effectively prevented AP-1-dependent transcription of both the interleukin-2 and cJun genes, it had no effect on Pas-induced cell death, even at limiting levels of Pas signaling, Thus, induction of JNK activity in Jurkat cells hy ligation of Pas at levels sufficient to cause cell death is likely a result, rather than a cause, of the apoptotic response, and AP-1 function is not required for Pas-induced apoptosis.