β-Synuclein Displays an Antiapoptotic p53-dependent Phenotype and Protects Neurons from 6-Hydroxydopamine-induced Caspase 3 Activation

Abstract

We have established stable transfectants expressing ␤-synuclein in TSM1 neurons. We show that in basal and staurosporine-induced conditions the number of terminal deoxynucleotidyltransferase-mediated dUTP nick end-labeling (TUNEL)-positive ␤-synuclein-expressing neurons was drastically lower than in mock-transfected TSM1 cells. This was accompanied by a lower DNA fragmentation as evidenced by the reduction of propidium iodide incorporation measured by fluorescence-activated cell sorter analysis. ␤-Synuclein strongly reduces staurosporine-induced caspase 3 activity and immunoreactivity. We establish that ␤-synuclein triggers a drastic reduction of p53 expression and transcriptional activity. This was accompanied by increased Mdm2 immunoreactivity while p38 expression appeared enhanced, indicating that ␤-synuclein-induced p53 downregulation likely occurs at a post-transcriptional level. We showed previously that ␣-synuclein displays an antiapoptotic function that was abolished by the dopaminergic derived toxin 6-hydroxydopamine (6OHDA). Interestingly, ␤-synuclein retains its ability to protect TSM1 neurons even after 6OHDA treatment. Furthermore, ␤-synuclein restores the antiapoptotic function of ␣-synuclein in 6OHDA-treated neurons. Altogether, our data document for the first time that ␤-synuclein protects neurons from staurosporine and 6OHDA-stimulated caspase activation in a p53-dependent manner. Our observation that ␤-synuclein contributes to restoration of the ␣-synuclein antiapoptotic function abolished by 6OHDA may have direct implications for Parkinson's disease pathology. In this context, the cross-talk between these two parent proteins is discussed.Parkinson's disease (PD) 1 is one of the most common and devastating diseases in the elderly (1, 2). This pathology is characterized by intracellular aggregates, called Lewy bodies (LB) (3, 4) that are thought to be responsible for final dementia occurring not only in PD but also in Lewy body diseases. The main component of LB was identified as ␣-synuclein (5), a 140-amino acid-long synaptic protein (6) that accumulates within these neuropathological hallmarks (7-9). The central role of ␣-synuclein in PD pathology has been emphasized by the observation that familial forms of PD were due to two mutations borne by ␣-synuclein (10, 11). Interestingly, these mutations trigger alterations of the biophysical properties of ␣-synuclein, leading to an exacerbation of misfolding and aggregation (12). Therefore, as with many other neurodegenerative diseases such as Alzheimer's and prion diseases, among others (13-15), PD can be documented as a disease associated with protein misfolding. The fact that such aggregates of proteins were recently shown to exhibit an intrinsic toxic potential (16) could lead to a reunifying theory linking misfolding and neurodegeneration.Interestingly, we have shown that ␣-synuclein displays an antiapoptotic phenotype that was abolished by PD-related mutations (17). This antiapoptotic function was also prevented when neuronal cells were expo...

Caspase-3-derived C-terminal Product of Synphilin-1 Displays Antiapoptotic Function via Modulation of the p53-dependent Cell Death Pathway

“…Thus, both synphilin-1 and ␤-synuclein remain protective toward 6OH-DOPA (55) and lower the p53 pathway. Furthermore, ␤-synuclein restores the protective activity of ␣-synuclein, even in the presence of 6OH-DOPA (55). Whether synphilin-1 restores the antiapoptotic potential of ␣-synuclein in the presence of the dopaminergic derivative remains to be established.…”

“…It should be noted that this type of regulation has already been documented for other proteins. Thus, presenilins (54,55) and ␤-amyloid precursor protein (56 -60) undergo caspase-derived cleavages, generating proteolytic fragments controlling cell death. More related to PD, parkin, another binding partner of synphilin-1 (18,61) displaying an antiapoptotic phenotype (62,63), is also cleaved by caspases, but unlike for synphilin-1, this endoproteolysis leads to a loss of function of this protein (64).…”

An antiaggregation gene therapy strategy for Lewy body disease utilizing β-synuclein lentivirus in a transgenic model

“…30 The mechanisms of neuroprotection appear to be independent of upstream effects such as phosphatidylinositol 3-kinase (PI3-K) and phosphoinositide-dependent kinase (PDK)-1 and involve direct binding of b-synuclein to Akt, resulting in increased stability of the kinase and phosphorylation of downstream signaling molecules such as glycogen synthase kinase 3b (GSK3b) 30 and p53. 41 In regard to the latter signaling pathway, a recent study showed that b-synuclein protects from the toxic effects of 6-hydroxydopamine by decreasing the expression of the proapoptotic gene p53. 41 The mechanisms linking the effects of b-synuclein to the Akt and p53 signaling pathways are not completely clear.…”

“…41 In regard to the latter signaling pathway, a recent study showed that b-synuclein protects from the toxic effects of 6-hydroxydopamine by decreasing the expression of the proapoptotic gene p53. 41 The mechanisms linking the effects of b-synuclein to the Akt and p53 signaling pathways are not completely clear. However, recent studies have shown that p53 expression and activity are regulated by Mdm2, 42 an oncoprotein that under normal conditions is restricted to the cytoplasm but when phosphorylated by activated Akt is translocated to the nucleus.…”

Expression of α-, β- and γ-synuclein in colorectal cancer, and potential clinical significance in progression of the disease

“…·-, ß-, and Á-synuclein differ considerably in their acidic C-terminal domains, which is presumably where their functional differences arise, while share a characteristically conserved N-terminal domain, which arises presumably similar biological effects such as the chaperone activity and reversible binding to phospholipid membranes (4). All of these suggest that the relationship between ·-, ß-, and Á-synuclein may be restriction or complementation, for instance, ·-synuclein is the major pathological component of Parkinson's disease and Alzheimer's disease, and ß-, and Á-synuclein levels could reflect a neuroprotective role to inhibit the aggregation of ·-synuclein proteins (7,8,(28)(29)(30). On the other hand, the following situation might exist.…”