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p53 is essential for developmental neuron death as regulated by the TrkA and p75 neurotrophin receptors.

Aloyz RS, Bamji SX, Pozniak CD, Toma JG, Atwal J, Kaplan DR, Miller FD - J. Cell Biol. (1998)

Bottom Line: NGF withdrawal also results in elevation of a known p53 target, the apoptotic protein Bax.Finally, when p53 levels are reduced or absent in p53+/- or p53-/- mice, naturally occurring sympathetic neuron death is inhibited.Thus, p53 is an essential common component of two receptor-mediated signal transduction cascades that converge on the MEKK-JNK pathway to regulate the developmental death of sympathetic neurons.

View Article: PubMed Central - PubMed

Affiliation: Center for Neuronal Survival, Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada H3A 2B4.

ABSTRACT
Naturally occurring sympathetic neuron death is the result of two apoptotic signaling events: one normally suppressed by NGF/TrkA survival signals, and a second activated by the p75 neurotrophin receptor. Here we demonstrate that the p53 tumor suppressor protein, likely as induced by the MEKK-JNK pathway, is an essential component of both of these apoptotic signaling cascades. In cultured neonatal sympathetic neurons, p53 protein levels are elevated in response to both NGF withdrawal and p75NTR activation. NGF withdrawal also results in elevation of a known p53 target, the apoptotic protein Bax. Functional ablation of p53 using the adenovirus E1B55K protein inhibits neuronal apoptosis as induced by either NGF withdrawal or p75 activation. Direct stimulation of the MEKK-JNK pathway using activated MEKK1 has similar effects; p53 and Bax are increased and the subsequent neuronal apoptosis can be rescued by E1B55K. Expression of p53 in sympathetic neurons indicates that p53 functions downstream of JNK and upstream of Bax. Finally, when p53 levels are reduced or absent in p53+/- or p53-/- mice, naturally occurring sympathetic neuron death is inhibited. Thus, p53 is an essential common component of two receptor-mediated signal transduction cascades that converge on the MEKK-JNK pathway to regulate the developmental death of sympathetic neurons.

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p53 and its transcriptional targets, p21 and Bax, are increased during NGF-withdrawal induced apoptosis of sympathetic neurons. (A–G) Western blot analysis of equal amounts of  protein derived from sympathetic neurons either maintained in  10 ng/ml NGF (NGF), or at various timepoints from 4 to 48 h after withdrawal of NGF (−NGF).Western blots were probed with  antibodies specific to p53 (A), p21 (B), p27 (C), Bad (D), Bcl-2  (E), Bax (F), or Bcl-xl (G). Note that p53, p21, p27, Bad, and Bax  all increase after NGF withdrawal, whereas Bcl-2 and Bcl-xl decrease. (H) Western blot analysis of equal amounts of protein derived from sympathetic neurons either maintained in 20 ng/ml  NGF, or withdrawn from NGF for 12 h (0 NGF). Western blots  were probed with antibodies specific to phosphorylated forms of  Akt (P AKT) or ERKS (P Erks). Note that phosphorylation of  these TrkA targets was significantly decreased after NGF withdrawal.
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Figure 1: p53 and its transcriptional targets, p21 and Bax, are increased during NGF-withdrawal induced apoptosis of sympathetic neurons. (A–G) Western blot analysis of equal amounts of protein derived from sympathetic neurons either maintained in 10 ng/ml NGF (NGF), or at various timepoints from 4 to 48 h after withdrawal of NGF (−NGF).Western blots were probed with antibodies specific to p53 (A), p21 (B), p27 (C), Bad (D), Bcl-2 (E), Bax (F), or Bcl-xl (G). Note that p53, p21, p27, Bad, and Bax all increase after NGF withdrawal, whereas Bcl-2 and Bcl-xl decrease. (H) Western blot analysis of equal amounts of protein derived from sympathetic neurons either maintained in 20 ng/ml NGF, or withdrawn from NGF for 12 h (0 NGF). Western blots were probed with antibodies specific to phosphorylated forms of Akt (P AKT) or ERKS (P Erks). Note that phosphorylation of these TrkA targets was significantly decreased after NGF withdrawal.

Mentions: Previously, we have demonstrated that an increase in p53 levels is sufficient to cause sympathetic neuron apoptosis in the presence of NGF (Slack et al., 1996). To determine whether endogenous p53 protein levels were ever similarly elevated during sympathetic neuron apoptosis, we cultured sympathetic neurons from neonatal animals, a time when developmental death of these neurons is ongoing. Initially, we examined p53 during sympathetic neuron apoptosis induced by NGF withdrawal; this apoptosis is relatively slow, taking ∼48 h, and is transcription-dependent (Deckwerth and Johnson, 1993; reviewed in Johnson and Deckwerth, 1993). Neurons were cultured for 5 d in the presence of 50 ng/ml NGF, NGF was withdrawn, and then the cellular levels of p53 were quantitated using Western blots with anti-p53 at various timepoints post-withdrawal (Fig. 1 A). This analysis revealed that p53 levels were elevated approximately threefold by 16 h after NGF withdrawal (Fig. 1 A). Elevation of p53 protein was first observed at 12 h (data not shown), and was maintained until at least 36 h post NGF-withdrawal (Fig. 1 A). Interestingly, this timecourse corresponds to the commitment point, after which NGF-withdrawn sympathetic neurons cannot be rescued from apoptotic death (Johnson and Deckwerth, 1993). Thus, NGF withdrawal leads to an increase in p53 levels that correlates with the timecourse of commitment to an apoptotic death.


p53 is essential for developmental neuron death as regulated by the TrkA and p75 neurotrophin receptors.

Aloyz RS, Bamji SX, Pozniak CD, Toma JG, Atwal J, Kaplan DR, Miller FD - J. Cell Biol. (1998)

p53 and its transcriptional targets, p21 and Bax, are increased during NGF-withdrawal induced apoptosis of sympathetic neurons. (A–G) Western blot analysis of equal amounts of  protein derived from sympathetic neurons either maintained in  10 ng/ml NGF (NGF), or at various timepoints from 4 to 48 h after withdrawal of NGF (−NGF).Western blots were probed with  antibodies specific to p53 (A), p21 (B), p27 (C), Bad (D), Bcl-2  (E), Bax (F), or Bcl-xl (G). Note that p53, p21, p27, Bad, and Bax  all increase after NGF withdrawal, whereas Bcl-2 and Bcl-xl decrease. (H) Western blot analysis of equal amounts of protein derived from sympathetic neurons either maintained in 20 ng/ml  NGF, or withdrawn from NGF for 12 h (0 NGF). Western blots  were probed with antibodies specific to phosphorylated forms of  Akt (P AKT) or ERKS (P Erks). Note that phosphorylation of  these TrkA targets was significantly decreased after NGF withdrawal.
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Figure 1: p53 and its transcriptional targets, p21 and Bax, are increased during NGF-withdrawal induced apoptosis of sympathetic neurons. (A–G) Western blot analysis of equal amounts of protein derived from sympathetic neurons either maintained in 10 ng/ml NGF (NGF), or at various timepoints from 4 to 48 h after withdrawal of NGF (−NGF).Western blots were probed with antibodies specific to p53 (A), p21 (B), p27 (C), Bad (D), Bcl-2 (E), Bax (F), or Bcl-xl (G). Note that p53, p21, p27, Bad, and Bax all increase after NGF withdrawal, whereas Bcl-2 and Bcl-xl decrease. (H) Western blot analysis of equal amounts of protein derived from sympathetic neurons either maintained in 20 ng/ml NGF, or withdrawn from NGF for 12 h (0 NGF). Western blots were probed with antibodies specific to phosphorylated forms of Akt (P AKT) or ERKS (P Erks). Note that phosphorylation of these TrkA targets was significantly decreased after NGF withdrawal.
Mentions: Previously, we have demonstrated that an increase in p53 levels is sufficient to cause sympathetic neuron apoptosis in the presence of NGF (Slack et al., 1996). To determine whether endogenous p53 protein levels were ever similarly elevated during sympathetic neuron apoptosis, we cultured sympathetic neurons from neonatal animals, a time when developmental death of these neurons is ongoing. Initially, we examined p53 during sympathetic neuron apoptosis induced by NGF withdrawal; this apoptosis is relatively slow, taking ∼48 h, and is transcription-dependent (Deckwerth and Johnson, 1993; reviewed in Johnson and Deckwerth, 1993). Neurons were cultured for 5 d in the presence of 50 ng/ml NGF, NGF was withdrawn, and then the cellular levels of p53 were quantitated using Western blots with anti-p53 at various timepoints post-withdrawal (Fig. 1 A). This analysis revealed that p53 levels were elevated approximately threefold by 16 h after NGF withdrawal (Fig. 1 A). Elevation of p53 protein was first observed at 12 h (data not shown), and was maintained until at least 36 h post NGF-withdrawal (Fig. 1 A). Interestingly, this timecourse corresponds to the commitment point, after which NGF-withdrawn sympathetic neurons cannot be rescued from apoptotic death (Johnson and Deckwerth, 1993). Thus, NGF withdrawal leads to an increase in p53 levels that correlates with the timecourse of commitment to an apoptotic death.

Bottom Line: NGF withdrawal also results in elevation of a known p53 target, the apoptotic protein Bax.Finally, when p53 levels are reduced or absent in p53+/- or p53-/- mice, naturally occurring sympathetic neuron death is inhibited.Thus, p53 is an essential common component of two receptor-mediated signal transduction cascades that converge on the MEKK-JNK pathway to regulate the developmental death of sympathetic neurons.

View Article: PubMed Central - PubMed

Affiliation: Center for Neuronal Survival, Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada H3A 2B4.

ABSTRACT
Naturally occurring sympathetic neuron death is the result of two apoptotic signaling events: one normally suppressed by NGF/TrkA survival signals, and a second activated by the p75 neurotrophin receptor. Here we demonstrate that the p53 tumor suppressor protein, likely as induced by the MEKK-JNK pathway, is an essential component of both of these apoptotic signaling cascades. In cultured neonatal sympathetic neurons, p53 protein levels are elevated in response to both NGF withdrawal and p75NTR activation. NGF withdrawal also results in elevation of a known p53 target, the apoptotic protein Bax. Functional ablation of p53 using the adenovirus E1B55K protein inhibits neuronal apoptosis as induced by either NGF withdrawal or p75 activation. Direct stimulation of the MEKK-JNK pathway using activated MEKK1 has similar effects; p53 and Bax are increased and the subsequent neuronal apoptosis can be rescued by E1B55K. Expression of p53 in sympathetic neurons indicates that p53 functions downstream of JNK and upstream of Bax. Finally, when p53 levels are reduced or absent in p53+/- or p53-/- mice, naturally occurring sympathetic neuron death is inhibited. Thus, p53 is an essential common component of two receptor-mediated signal transduction cascades that converge on the MEKK-JNK pathway to regulate the developmental death of sympathetic neurons.

Show MeSH
Related in: MedlinePlus