Biology Reference
In-Depth Information
neuronal differentiation came from the evidence that p53 localization is, in-
deed, nuclear during differentiation of PC12 cells, whereas in mature differ-
entiating cells, it appears mainly cytoplasmic (
Eizenberg et al., 1996
).
Nerve growth factor (NGF), an important regulator of neuronal survival
and maturation, is also known to induce both differentiation and cell cycle
arrest of PC12 cells. NGF activates an intracellular phosphorylation signaling
cascade that fosters p53 nuclear accumulation and transcriptional activation,
and as a consequence blocks cell proliferation, enhances the expression of
neuronal markers, and promotes neurite extension (
Poluha et al., 1997
).
Indeed, p53 has been shown to be a key element for neurite outgrowth
as p53 gene silencing or overexpression of its dominant negative form
-p53DN, both block NGF-mediated neuronal outgrowth and differentiation
and inhibit neuronal maturation in primary cortical neurons (
Di Giovanni,
2006; Eizenberg et al., 1996; Tedeschi, Nguyen, Puttagunta, Gaub, & Di
Giovanni, 2009; Zhang et al., 2010
). Furthermore, p53 activation is
required for NGF-mediated neuronal differentiation of PC12 cells by
transcriptional regulation of TrkA constitutive levels via binding to p53-
responsive elements on TrkA promoter (Zhang et al., 2006). Along the
same lines, overexpression of p53DN is also able to block BDNF-
dependent neuronal outgrowth in cortical neurons, likely and at least
partially, via the transcriptional regulation of GAP-43, a growth cone
remodeling and neurotrophin-dependent protein, whose expression was
downregulated following p53 silencing or overexpression of p53DN
(
Eizenberg et al., 1996; Tedeschi, Nguyen, Puttagunta, et al., 2009
). p53
binds to specific and highly conserved p53-responsive elements on the
proximal promoter of GAP-43 as shown by both chromatin
immunoprecipitation experiments (ChIP) and luciferase assays. In fact,
mutations of single core elements of this promoter result in lack of
luciferase activity following overexpression of p53 in primary neurons
(
Tedeschi, Nguyen, Puttagunta, et al., 2009
;
Tedeschi, Nguyen, Steele,
et al., 2009
). These data obtained in both neurons and PC12 cells
strongly suggest a role for p53 in axonal outgrowth and growth cone
remodeling (
Di Giovanni et al., 2006; Tedeschi, Nguyen, Puttagunta,
et al., 2009; Tedeschi, Nguyen, Steele, et al., 2009
). Indeed, GAP-43
expression is classically associated with plasticity and is expressed during
development and following injury in regenerating axons and growth cones.
In addition to regulating GAP-43 expression, ChIP and luciferase assays
have shown that in both primary neurons and PC12 cells, p53 is active and
able to promote the transcription of several additional genes important for
