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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 levels increase during  apoptosis of sympathetic neurons as  induced by BDNF-mediated activation of p75NTR. (A) Western blot  analysis for p53 in equal amounts of  protein derived from sympathetic  neurons that were cultured in 50 ng/ ml NGF for 4 d, and then were  washed free of NGF and switched  into 50 mM KCl (KCL), 50 mM  KCl plus 100 ng/ml BDNF (KCL +  BDNF), or media containing no  NGF or KCl (0 NGF) for 24 or 36 h.  Note that p53 levels in the neurons  treated with KCl and BDNF are  similar to those in 0 NGF, and are  greater than those maintained in  KCl alone. (B) The same blot as in  A reprobed for the neurotransmitter enzyme, tyrosine hydroxylase  (TH) to demonstrate that equal  amounts of protein were present in  each of the lanes.
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Figure 4: p53 levels increase during apoptosis of sympathetic neurons as induced by BDNF-mediated activation of p75NTR. (A) Western blot analysis for p53 in equal amounts of protein derived from sympathetic neurons that were cultured in 50 ng/ ml NGF for 4 d, and then were washed free of NGF and switched into 50 mM KCl (KCL), 50 mM KCl plus 100 ng/ml BDNF (KCL + BDNF), or media containing no NGF or KCl (0 NGF) for 24 or 36 h. Note that p53 levels in the neurons treated with KCl and BDNF are similar to those in 0 NGF, and are greater than those maintained in KCl alone. (B) The same blot as in A reprobed for the neurotransmitter enzyme, tyrosine hydroxylase (TH) to demonstrate that equal amounts of protein were present in each of the lanes.

Mentions: We have previously demonstrated that the immediate early protein, c-jun, is hyperphosphorylated in sympathetic neurons after p75NTR activation (Bamji et al., 1998) as it is after NGF withdrawal (Estus et al., 1994; Ham et al., 1995). To determine whether p53 elevation was also a common downstream component of these two apoptotic signaling cascades, we examined p53 levels in sympathetic neurons in conditions where p75NTR activation leads to apoptosis. Specifically, for these experiments, sympathetic neurons were cultured for 5 d in 50 ng/ml NGF and then were switched to KCl, which maintains sympathetic neuron survival in the absence of TrkA activation (Franklin et al., 1995). We then added the neurotrophin BDNF, which selectively binds p75NTR but not Trk receptors on sympathetic neurons (Bamji et al., 1998), and determined cellular p53 levels (Fig. 4 A). As seen with NGF withdrawal, p53 levels were increased at 24 and 36 h in neurons maintained in KCl plus BDNF relative to those in KCl alone. Reprobing of the same blot with an antibody to tyrosine hydroxylase revealed that equal amounts of protein were present in all of the samples (Fig. 4 B). This increase was already apparent at 12 h, a timepoint when p53 levels were only first starting to increase after NGF withdrawal (data not shown). Thus, p53 elevation is downstream of both p75NTR activation and NGF withdrawal.


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 levels increase during  apoptosis of sympathetic neurons as  induced by BDNF-mediated activation of p75NTR. (A) Western blot  analysis for p53 in equal amounts of  protein derived from sympathetic  neurons that were cultured in 50 ng/ ml NGF for 4 d, and then were  washed free of NGF and switched  into 50 mM KCl (KCL), 50 mM  KCl plus 100 ng/ml BDNF (KCL +  BDNF), or media containing no  NGF or KCl (0 NGF) for 24 or 36 h.  Note that p53 levels in the neurons  treated with KCl and BDNF are  similar to those in 0 NGF, and are  greater than those maintained in  KCl alone. (B) The same blot as in  A reprobed for the neurotransmitter enzyme, tyrosine hydroxylase  (TH) to demonstrate that equal  amounts of protein were present in  each of the lanes.
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Related In: Results  -  Collection

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Figure 4: p53 levels increase during apoptosis of sympathetic neurons as induced by BDNF-mediated activation of p75NTR. (A) Western blot analysis for p53 in equal amounts of protein derived from sympathetic neurons that were cultured in 50 ng/ ml NGF for 4 d, and then were washed free of NGF and switched into 50 mM KCl (KCL), 50 mM KCl plus 100 ng/ml BDNF (KCL + BDNF), or media containing no NGF or KCl (0 NGF) for 24 or 36 h. Note that p53 levels in the neurons treated with KCl and BDNF are similar to those in 0 NGF, and are greater than those maintained in KCl alone. (B) The same blot as in A reprobed for the neurotransmitter enzyme, tyrosine hydroxylase (TH) to demonstrate that equal amounts of protein were present in each of the lanes.
Mentions: We have previously demonstrated that the immediate early protein, c-jun, is hyperphosphorylated in sympathetic neurons after p75NTR activation (Bamji et al., 1998) as it is after NGF withdrawal (Estus et al., 1994; Ham et al., 1995). To determine whether p53 elevation was also a common downstream component of these two apoptotic signaling cascades, we examined p53 levels in sympathetic neurons in conditions where p75NTR activation leads to apoptosis. Specifically, for these experiments, sympathetic neurons were cultured for 5 d in 50 ng/ml NGF and then were switched to KCl, which maintains sympathetic neuron survival in the absence of TrkA activation (Franklin et al., 1995). We then added the neurotrophin BDNF, which selectively binds p75NTR but not Trk receptors on sympathetic neurons (Bamji et al., 1998), and determined cellular p53 levels (Fig. 4 A). As seen with NGF withdrawal, p53 levels were increased at 24 and 36 h in neurons maintained in KCl plus BDNF relative to those in KCl alone. Reprobing of the same blot with an antibody to tyrosine hydroxylase revealed that equal amounts of protein were present in all of the samples (Fig. 4 B). This increase was already apparent at 12 h, a timepoint when p53 levels were only first starting to increase after NGF withdrawal (data not shown). Thus, p53 elevation is downstream of both p75NTR activation and NGF withdrawal.

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