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Mol. Cell. Biol., 01 1997, 170-181, Vol 17, No. 1
JM Lenczowski, L Dominguez, AM Eder, LB King, CM Zacharchuk and JD Ashwell
Cross-linking of Fas (CD95) induces apoptosis, a response that has been
reported to depend upon the Ras activation pathway. Since many examples of
apoptosis have been reported to involve AP-1 and/or the AP-1- activation
pathway. Since many examples of apoptosis have been reported to involve
AP-1 and/or the AP-1-activating enzyme Jun kinase (JNK), downstream
effectors of Ras or Ras-like small GTP-binding proteins, we evaluated the
role of these molecules in Fas-mediated apoptosis. Although cross-linking
of Fas on 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
Fas-mediated induction of JNK activity had no effect on Fas-mediated
apoptosis. Furthermore, maximally effective concentrations of anti-Fas 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- 1
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
Fas-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 Fas-induced cell death,
even at limiting levels of Fas signaling. Thus, induction of JNK activity
in Jurkat cells by ligation of Fas 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 Fas-induced apoptosis.
Copyright © 1997, American Society for Microbiology
Lack of a role for Jun kinase and AP-1 in Fas-induced apoptosis
Laboratory of Immune Cell Biology, National Institutes of Health, Bethesda, Maryland 20892-1152, USA.
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