0-TESTO COMPLETO.pdf - Fondazione Santa Lucia

AFM.1 – A study on the effects of p66Shc on oxidative stress and mitochondrial damage…
chondria are also the main source of reactive oxygen species (ROS) and function
as gatekeepers in the intrinsic apoptotic processes. Thus, mitochondrial
dysfunction can result in cell death, either by bioenergetics failure, oxidative
stress or apoptosis.
Damage to mitochondria has emerged as a central feature that contributes
to neurodegeneration in Amyotrophic Lateral Sclerosis (ALS). Recent evidence
indicates that mitochondria are one of the primary location of damage inside
motor neurons, but also astrocytes and muscle cells, which both have been
involved in the disease, show deficit in mitochondria metabolism [Cassina et
al. 2008; Dobrowolny et al. 2008; Dupuis et al. 2003]. Dysfunction of mitochondria
is observed early in patients (and in experimental models for ALS) and
causes the death of neurons, which underlies onset of paralysis and death of
patients [Cozzolino et al. 2008b]. A large body of studies in cells and mice over
expressing mutSOD1s, which model many characteristics of the disease, has
addressed different aspects of mitochondrial dysfunction occurring in ALS,
ranging from altered morphology (swelling and fragmentation) [Higgins et al.
2003; Kong and Xu 1998], to impaired activity of respiratory chain complexes
[Mattiazzi et al. 2002], from weakened calcium buffering capacity [von Lewinski
and Keller 2005], to mitochondria-dependent execution of apoptosis [Cozzolino
et al. 2006; Guegan et al. 2001; Pasinelli et al. 2000]. Moreover, recent
investigations have drawn attention to the presence of a generalized energetic
imbalance both in patients and mice, suggesting that ubiquitous defects in
mitochondrial physiology might contribute to the disease process [Dupuis et
al. 2008; Dupuis et al. 2004].
Although compelling evidence has accumulated that uncontrolled accumulation
of mutSOD1 inside the mitochondria may be directly responsible
for mitochondrial impairment [Kawamata et al. 2008; Liu et al. 2004;
Takeuchi et al. 2002; Vande Velde et al. 2008], it has also been indicated that
mitochondrial localization might not be necessary for mutant SOD1 to damage
mitochondria [Bergemalm et al. 2006]. However, which are the signals
that mediate the transfer of the inherent toxic properties of mutSOD1 to mitochondria
is an issue still unsolved.
A novel signaling mechanism involving the 66-kilodalton isoform of the
growth factor adapter Shc (p66Shc), that is operative in the pathophysiological
condition of oxidative stress, has been recently identified. The protooncogenes
Shc were initially recognized as ‘adaptor’ proteins, which specifically
bind to phosphorylated tyrosines on the cytoplasmic motif of growth
factor receptors [Pelicci et al. 1992]. In mice (and humans as well), three
isoforms of Shc are expressed, of 46, 52 and 66 kD. All three isoforms of Shc
are tyrosine-phosphorylated after growth factor receptor activation, and
form stable complexes with Grb2, an adaptor protein for the Ras exchange
factor SOS [Rozakis-Adcock et al. 1992]. p66Shc has the same modular
structure as p52Shc/p46Shc and contains a unique N-terminal region; however,
it is not involved in Ras regulation [Bonfini et al. 1996]. Instead, upon
stress the protein p66Shc is phosphorylated on a critical serine residue
(S36) which is unique for this isoform. Once phosphorilated, p66Shc is isomerized
by the prolyl isomerase PIN1, and in this form it localizes to mito-
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