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Mol. Cell. Biol., Nov 1995, 6364-6376, Vol 15, No. 11
JD Woronicz, A Lina, BJ Calnan, S Szychowski, L Cheng and A Winoto
T-cell receptor (TCR)-mediated apoptosis in immature thymocytes and T- cell
hybridomas is calcium dependent and can be inhibited by cyclosporin A
(CsA). Induction of the orphan steroid receptor Nur77 (NGFI-B) is required
for activation-induced apoptosis. Here, we examined the regulation of Nur77
expression, in response to apoptotic TCR signals, which consists of kinase
C and calcium pathways. We show that the major control of Nur77 induction
is mediated by the calcium signaling pathway. In contrast, protein kinase C
signals induce only a low level of Nur77 activity. Nur77 promoter activity
parallels its protein levels. CsA decreases both Nur77 protein levels and
promoter activity, and the kinetics of CsA inhibition of apoptosis
correlates with a decrease in Nur77 protein levels. TCR signals and kinase
C signals result in a similar level of Nur77 protein phosphorylation but
mediate differential transactivation activity of Nur77. In addition, Nur77
promoter deletion analysis revealed two RSRF (related to serum- responsive
factor) binding sites, which can confer calcium and CsA sensitivity on a
heterologous promoter. Taken together, our data suggest that the levels of
transcriptional induction of Nur77 play an important role during
activation-induced apoptosis and that calcium signals regulate a novel
CsA-sensitive nuclear factor required for Nur77 transcription in T cells.
Copyright © 1995, American Society for Microbiology
Regulation of the Nur77 orphan steroid receptor in activation-induced apoptosis
Department of Molecular and Cell Biology, University of California, Berkeley 94720-3200, USA.
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