6-Hydroxydopamine but Not 1-Methyl-4-phenylpyridinium Abolishes α-Synuclein Anti-apoptotic Phenotype by Inhibiting Its Proteasomal Degradation and by Promoting Its Aggregation

Abstract

We established previously that α-synuclein displayed a protective anti-apoptotic phenotype in neurons, mainly by down-regulating p53-dependent caspase-3 activation (Alves da Costa, C., Ancolio, K., and Checler, F. (2000) J. Biol. Chem. 275, 24065-24069; Alves da Costa, C., Paitel, E., Vincent, B., and Checler, F. (2002) J. Biol. Chem. 277, 50980-50984). This function was abolished by Parkinson disease-linked pathogenic mutations and by the dopaminergic toxin, 6-hydroxydopamine (6OH-DOPA) (Alves da Costa, C., Paitel, E., Vincent, B., and Checler, F. (2002) J. Biol. Chem. 277, 50980-50984). However, the mechanisms by which 6OH-DOPA interfered with α-synuclein function remained unclear. Here we showed that 6OH-DOPA prevents α-synuclein-mediated anti-apoptotic function by altering its degradation. Thus, 6OH-DOPA treatment of TSM1 neurons and SH-SY5Y neuroblastoma cells enhances endogenous α-synuclein-like immunoreactivity and inhibits the catabolism of endogenous and recombinant α-synucleins by purified 20 S proteasome. Furthermore, we demonstrated that 6OH-DOPA directly inhibits endogenous proteasomal activity in TSM1 and SH-SY5Y cells and also blocks purified activity in This by the We also established that 6OH-DOPA the of recombinant α-synuclein in we that 6OH-DOPA α-synuclein anti-apoptotic phenotype by its proteasomal its and the directly by 6OH-DOPA of Parkinson α-synuclein protective function and of recombinant Furthermore, proteasomal and of the purified 20 S by a that of 6OH-DOPA and α-synuclein function with Parkinson and We established previously that α-synuclein displayed a protective anti-apoptotic phenotype in neurons, mainly by down-regulating p53-dependent caspase-3 activation (Alves da Costa, C., Ancolio, K., and Checler, F. (2000) J. Biol. Chem. 275, 24065-24069; Alves da Costa, C., Paitel, E., Vincent, B., and Checler, F. (2002) J. Biol. Chem. 277, 50980-50984). This function was abolished by Parkinson disease-linked pathogenic mutations and by the dopaminergic toxin, 6-hydroxydopamine (6OH-DOPA) (Alves da Costa, C., Paitel, E., Vincent, B., and Checler, F. (2002) J. Biol. Chem. 277, 50980-50984). However, the mechanisms by which 6OH-DOPA interfered with α-synuclein function remained unclear. Here we showed that 6OH-DOPA prevents α-synuclein-mediated anti-apoptotic function by altering its degradation. Thus, 6OH-DOPA treatment of TSM1 neurons and SH-SY5Y neuroblastoma cells enhances endogenous α-synuclein-like immunoreactivity and inhibits the catabolism of endogenous and recombinant α-synucleins by purified 20 S proteasome. Furthermore, we demonstrated that 6OH-DOPA directly inhibits endogenous proteasomal activity in TSM1 and SH-SY5Y cells and also blocks purified activity in This by the We also established that 6OH-DOPA the of recombinant α-synuclein in we that 6OH-DOPA α-synuclein anti-apoptotic phenotype by its proteasomal its and the directly by 6OH-DOPA of Parkinson α-synuclein protective function and of recombinant Furthermore, proteasomal and of the purified 20 S by a that of 6OH-DOPA and α-synuclein function with Parkinson and Parkinson Parkinson Parkinson the This by the of the dopaminergic neurons of the the treatment of the of the a and the of the a and of a a of and and by mutations of the and the of function a of the of the α-synuclein J. of the in mutations J. J. J. the of the J. J. J. J. J. J. J. J. of with the of the that the J. of dopaminergic by in the of and by that a function that in also by a with in previously the of TSM1 neurons and cells caspase-3 activation da F. J. Biol. Chem. This phenotype was with a of the da F. J. Biol. Chem. the protective was abolished by mutations da F. J. Biol. Chem. by 6-hydroxydopamine (6OH-DOPA) da F. J. Biol. Chem. a dopaminergic J. of the anti-apoptotic phenotype by and that protective a function of the with the in the of 6OH-DOPA function was the mechanisms by which the protective phenotype in neurons Furthermore, the of function was by 6OH-DOPA and by dopaminergic neurons remained we that with the anti-apoptotic phenotype by its proteasomal and its and and and and TSM1 was and previously da F. J. Biol. Chem. SH-SY5Y neuroblastoma cells TSM1 and of was in the and purified by by previously J. was and a was by and of the 20 S and 20 S activity of of was in activity was was with of the purified in a of of and in the in the of was and and previously F. in and cells in of and with of 6OH-DOPA in cells by and in and activity of the was of and by 20 S neurons in and with of the with of 20 S purified activity in the in the of was by was with purified 20 S and was with and with the and caspase-3 with the and that of that immunoreactivity that of the and neurons in a in in a of and in the and of of activity was previously da F. J. Biol. Chem. activity was da F. neurons in a in and in the and of 6OH-DOPA of was by of the was with by the of the previously established that the activation of caspase-3 in cells and in TSM1 neurons da F. J. Biol. Chem. This anti-apoptotic phenotype was abolished by the 6OH-DOPA da F. J. Biol. Chem. TSM1 neurons, the enhances caspase-3 and was of by the of with 6OH-DOPA also caspase-3 in and by by of Thus, TSM1 neurons displayed caspase-3 activity cells and This phenotype was by of the phenotype caspase-3 immunoreactivity in neurons caspase-3 activity abolished protective a the protective of a TSM1 neurons a TSM1 by was by a was and of TSM1 the of of the of by a the we the of in and we that by Thus, 6OH-DOPA a of the of TSM1 cells 6OH-DOPA abolished protective the that abolished the protective activity TSM1 We the mechanisms by which 6OH-DOPA the TSM1 neurons TSM1 neurons with the of and was by TSM1 neurons with 6OH-DOPA and was by the of and in and of cells of and by in and SH-SY5Y 6OH-DOPA in TSM1 neurons and SH-SY5Y neuroblastoma TSM1 neurons, 6OH-DOPA and its Furthermore, a proteasomal also immunoreactivity 6OH-DOPA and its in the of 6OH-DOPA also immunoreactivity in SH-SY5Y cells and that 6OH-DOPA and the that by of the of the the 6OH-DOPA the we 6OH-DOPA directly the function of endogenous and purified immunoreactivity in TSM1 neurons with and with with 6OH-DOPA immunoreactivity and SH-SY5Y cells with of of by of cells with 6OH-DOPA immunoreactivity and and in the of 20 S and in TSM1 and SH-SY5Y a of 20 and 20 S S S 20 S the in the and in J. Biol. Chem. of the of the S and its activity This purified of the 20 S purified 20 S and and the TSM1 endogenous proteasomal activity displayed the of endogenous purified 20 S that the was the of the endogenous activity in TSM1 6OH-DOPA endogenous TSM1 activity the in SH-SY5Y cells 6OH-DOPA endogenous proteasomal activity the of 6OH-DOPA the we the of purified 20 S proteasome. 6OH-DOPA the 20 S in a and of proteasomal activity of endogenous and purified 20 S proteasome. purified 20 S was the and activity was of 20 S was in the in the of the of and proteasomal activity was of endogenous proteasome. TSM1 cells with the of and cells and of activity in by the of in and and of inhibits endogenous proteasomal activity in TSM1 and SH-SY5Y TSM1 neurons with the of 6OH-DOPA and endogenous proteasomal activity was in TSM1 the of in and of SH-SY5Y cells with 6OH-DOPA and endogenous proteasomal activity was in the of in and of and of 6OH-DOPA and purified 20 S proteasome. 20 S was with the and of 6OH-DOPA and the proteasomal activity was purified 20 S was the with the of the of in and the of the of 20 S and in SH-SY5Y the of purified 20 S proteasome. was by the of the 20 S activity in a of 20 S remained also the of endogenous proteasomal activity in SH-SY5Y cells endogenous activity in SH-SY5Y and treatment with a proteasomal activity that with of of purified 20 S and endogenous proteasomal activity in SH-SY5Y purified 20 S was with and with 6OH-DOPA of and proteasomal activity was SH-SY5Y cells with and with 6OH-DOPA and proteasomal activity was the of in and the of by the of and by 20 S directly the of 6OH-DOPA purified and endogenous with the 6OH-DOPA and of in TSM1 neurons, we the of endogenous and recombinant by purified 20 S and the of 6OH-DOPA purified 20 S of in a and was by 6OH-DOPA by proteasomal was by the of purified 20 S recombinant of 6OH-DOPA and the catabolism of endogenous and recombinant by purified 20 S proteasome. TSM1 neurons was the with purified 20 S in the in the of 6OH-DOPA and immunoreactivity was recombinant was with purified 20 S 6OH-DOPA the and immunoreactivity was of the of recombinant by purified 20 S we the of immunoreactivity recombinant was 6OH-DOPA 6OH-DOPA and 20 S However, was with that J. and J. Biol. Chem. we that in its directly altering the of was in with 6OH-DOPA the of 6OH-DOPA the of which with of of recombinant was the with 6OH-DOPA and and and by of of with a with the of and by of the and the J. and and of a of dopaminergic of dopaminergic neurons and F. J. that with of the p53-dependent J. J. a of and was the with a J. of in in of its by dopaminergic by da F. J. Biol. Chem. da F. J. Biol. Chem. and the of J. Biol. Chem. J. J. J. that anti-apoptotic that abolished by pathogenic mutations da F. J. Biol. Chem. which F. J. J. Biol. Chem. J. J. J. Biol. Chem. anti-apoptotic phenotype was abolished by 6OH-DOPA da F. J. Biol. Chem. a dopaminergic a in J. immunoreactivity by treatment with 6OH-DOPA da F. J. Biol. Chem. the mechanisms by which the function remained This that 6OH-DOPA that directly 6OH-DOPA prevents and its of 6OH-DOPA was demonstrated in and in by the of 6OH-DOPA the proteasome. Thus, 6OH-DOPA inhibits endogenous F. J. and purified 20 S and prevents by Furthermore, 6OH-DOPA and a the of in a that the 6OH-DOPA inhibits proteasomal activity and in This and a the of Parkinson a dopaminergic J. J. J. This also that the 6OH-DOPA in the of that by J. Biol. Chem. J. J. Biol. Chem. was that recombinant by the purified 20 S in that the S in the of the 20 S mainly in the of a of which J. with the that of the dopaminergic neurons by the of and α-synuclein J. J. J. Biol. Chem. by which 6OH-DOPA of the its Thus, 6OH-DOPA the of and the of 6OH-DOPA purified 20 S by the the of and activity in SH-SY5Y neuroblastoma also of recombinant in also its that J. J. that the proteasomal and a of the of cells by 6OH-DOPA of that 6OH-DOPA enhances of the proteasome. that of its and that by the of 6OH-DOPA in with the of in and the that 6OH-DOPA of the of that of of the 6OH-DOPA and J. Biol. Chem. and with However, that dopaminergic J. J. Furthermore, showed that in the dopaminergic cells in of the the of J. J. and in with the the of α-synuclein-mediated that was a of the and of activity and 6OH-DOPA was and in and with of the of purified 20 S proteasome. However, was by the This that the mechanisms of by 6OH-DOPA and activity and that the of purified by of of and proteasomal 6OH-DOPA directly of the and of This the in in with with 6OH-DOPA that which by a dopaminergic in the the of the that 6OH-DOPA the the of and by a p53-dependent da F. J. Biol. Chem. anti-apoptotic function the of caspase-3 activation da F. J. Biol. Chem. 6OH-DOPA inhibits by of da F. J. Biol. Chem. that a of the also the protective in the of 6OH-DOPA da F. J. Biol. Chem. Furthermore, 6OH-DOPA da F. J. Biol. Chem. in with the of of its in J. J. J. the in the of in and the of by its and 6OH-DOPA the the of the in Thus, the the its anti-apoptotic However, the dopaminergic neurons the of the endogenous and its This the of the in also the that a by by with by its Parkinson Parkinson Parkinson the This by the of the dopaminergic neurons of the the treatment of the of the a and the of the a and Parkinson of a a of and and by mutations of the and the of function a of the of the α-synuclein J. of the in mutations J. J. J. the of the J. J. J. J. J. J. J. J. of with the of the that the J. of dopaminergic by in the of and by that a function that in also by a with in We previously the of TSM1 neurons and cells caspase-3 activation da F. J. Biol. Chem. This phenotype was with a of the da F. J. Biol. Chem. the protective was abolished by mutations da F. J. Biol. Chem. by 6-hydroxydopamine (6OH-DOPA) da F. J. Biol. Chem. a dopaminergic J. of the anti-apoptotic phenotype by and that protective a function of the with the in the of 6OH-DOPA function was the mechanisms by which the protective phenotype in neurons Furthermore, the of function was by 6OH-DOPA and by dopaminergic neurons remained we that with the anti-apoptotic phenotype by its proteasomal and its and and and and TSM1 was and previously da F. J. Biol. Chem. SH-SY5Y neuroblastoma cells TSM1 and of was in the and purified by by previously J. was and a was by and of the 20 S and 20 S activity of of was in activity was was with of the purified in a of of and in the in the of was and and previously F. in and cells in of and with of 6OH-DOPA in cells by and in and activity of the was of and by 20 S neurons in and with of the with of 20 S purified activity in the in the of was by was with purified 20 S and was with and with the and caspase-3 with the and that of that immunoreactivity that of the and neurons in a in in a of and in the and of of activity was previously da F. J. Biol. Chem. activity was da F. neurons in a in and in the and of 6OH-DOPA of was by of the was with by the of and and and and TSM1 was and previously da F. J. Biol. Chem. SH-SY5Y neuroblastoma cells TSM1 and of was in the and purified by by previously J. was and a was by and of the 20 S and 20 S activity of of was in activity was was with of the purified in a of of and in the in the of was and and previously F. in and cells in of and with of 6OH-DOPA in cells by and in and activity of the was of and by 20 S neurons in and with of the with of 20 S purified activity in the in the of was by was with purified 20 S and was with and with the and caspase-3 with the and that of that immunoreactivity that of the and neurons in a in in a of and in the and of of activity was previously da F. J. Biol. Chem. activity was da F. neurons in a in and in the and of 6OH-DOPA of was by of the was with by the of the previously established that the activation of caspase-3 in cells and in TSM1 neurons da F. J. Biol. Chem. This anti-apoptotic phenotype was abolished by the 6OH-DOPA da F. J. Biol. Chem. TSM1 neurons, the enhances caspase-3 and was of by the of with 6OH-DOPA also caspase-3 in and by by of Thus, TSM1 neurons displayed caspase-3 activity cells and This phenotype was by of the phenotype caspase-3 immunoreactivity in neurons caspase-3 activity abolished protective a the protective of a TSM1 neurons a TSM1 by was by a was and of TSM1 the of of the of by a the we the of in and we that by Thus, 6OH-DOPA a of the of TSM1 cells 6OH-DOPA abolished protective the that abolished the protective activity TSM1 We the mechanisms by which 6OH-DOPA the in and SH-SY5Y 6OH-DOPA in TSM1 neurons and SH-SY5Y neuroblastoma TSM1 neurons, 6OH-DOPA and its Furthermore, a proteasomal also immunoreactivity 6OH-DOPA and its in the of 6OH-DOPA also immunoreactivity in SH-SY5Y cells and that 6OH-DOPA and the that by of the of the the 6OH-DOPA the we 6OH-DOPA directly the function of endogenous and purified immunoreactivity in TSM1 neurons with and with with 6OH-DOPA immunoreactivity and SH-SY5Y cells with of of by of cells with 6OH-DOPA immunoreactivity and and in the of 20 S and in TSM1 and SH-SY5Y a of 20 and 20 S S S 20 S the in the and in J. 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TSM1 cells with the of and cells and of activity in by the of in and and of inhibits endogenous proteasomal activity in TSM1 and SH-SY5Y TSM1 neurons with the of 6OH-DOPA and endogenous proteasomal activity was in TSM1 the of in and of SH-SY5Y cells with 6OH-DOPA and endogenous proteasomal activity was in the of in and of and of 6OH-DOPA and purified 20 S proteasome. 20 S was with the and of 6OH-DOPA and the proteasomal activity was purified 20 S was the with the of the of in and the of the of 20 S and in SH-SY5Y the of purified 20 S proteasome. was by the of the 20 S activity in a of 20 S remained also the of endogenous proteasomal activity in SH-SY5Y cells endogenous activity in SH-SY5Y and treatment with a proteasomal activity that with of of purified 20 S and endogenous proteasomal activity in SH-SY5Y purified 20 S was with and with 6OH-DOPA of and proteasomal activity was SH-SY5Y cells with and with 6OH-DOPA and proteasomal activity was the of in and the of by the of and by 20 S directly the of 6OH-DOPA purified and endogenous with the 6OH-DOPA and of in TSM1 neurons, we the of endogenous and recombinant by purified 20 S and the of 6OH-DOPA purified 20 S of in a and was by 6OH-DOPA by proteasomal was by the of purified 20 S recombinant of 6OH-DOPA and the catabolism of endogenous and recombinant by purified 20 S proteasome. TSM1 neurons was the with purified 20 S in the in the of 6OH-DOPA and immunoreactivity was recombinant was with purified 20 S 6OH-DOPA the and immunoreactivity was of the of recombinant by purified 20 S we the of immunoreactivity recombinant was 6OH-DOPA 6OH-DOPA and 20 S However, was with that J. and J. Biol. Chem. we that in its directly altering the of was in with 6OH-DOPA the of 6OH-DOPA the of which with of of recombinant was the with 6OH-DOPA and and and by 6OH-DOPA the previously established that the activation of caspase-3 in cells and in TSM1 neurons da F. J. Biol. Chem. This anti-apoptotic phenotype was abolished by the 6OH-DOPA da F. J. Biol. Chem. TSM1 neurons, the enhances caspase-3 and was of by the of with 6OH-DOPA also caspase-3 in and by by of Thus, TSM1 neurons displayed caspase-3 activity cells and This phenotype was by of the phenotype caspase-3 immunoreactivity in neurons caspase-3 activity abolished protective a We the protective of a TSM1 neurons a TSM1 by was by a was and of TSM1 the of of the of by a the we the of in and we that by Thus, 6OH-DOPA a of the of TSM1 cells 6OH-DOPA abolished protective the that abolished the protective activity TSM1 We the mechanisms by which 6OH-DOPA the 6OH-DOPA in and SH-SY5Y 6OH-DOPA in TSM1 neurons and SH-SY5Y neuroblastoma TSM1 neurons, 6OH-DOPA and its Furthermore, a proteasomal also immunoreactivity 6OH-DOPA and its in the of 6OH-DOPA also immunoreactivity in SH-SY5Y cells and that 6OH-DOPA and the that by of the of the the 6OH-DOPA the we 6OH-DOPA directly the function of endogenous and purified proteasome. 6OH-DOPA 20 S and in TSM1 and SH-SY5Y a of 20 and 20 S S S 20 S the in the and in J. Biol. Chem. of the of the S and its activity This purified of the 20 S purified 20 S and and the TSM1 endogenous proteasomal activity displayed the of endogenous purified 20 S that the was the of the endogenous activity in TSM1 6OH-DOPA endogenous TSM1 activity the in SH-SY5Y cells 6OH-DOPA endogenous proteasomal activity the of 6OH-DOPA the we the of purified 20 S proteasome. 6OH-DOPA the 20 S in a and of proteasomal activity the of 20 S and in SH-SY5Y the of purified 20 S proteasome. was by the of the 20 S activity in a of 20 S remained also the of endogenous proteasomal activity in SH-SY5Y cells endogenous activity in SH-SY5Y and treatment with a proteasomal activity that with 6OH-DOPA the of and by 20 S directly the of 6OH-DOPA purified and endogenous with the 6OH-DOPA and of in TSM1 neurons, we the of endogenous and recombinant by purified 20 S and the of 6OH-DOPA purified 20 S of in a and was by 6OH-DOPA by proteasomal was by the of purified 20 S recombinant 6OH-DOPA of the of recombinant by purified 20 S we the of immunoreactivity recombinant was 6OH-DOPA 6OH-DOPA and 20 S However, was with that J. and J. Biol. Chem. we that in its directly altering the of was in with 6OH-DOPA the of 6OH-DOPA the of which with of of of with a with the of and by of the and the J. and and of a of dopaminergic of dopaminergic neurons and F. J. that with of the p53-dependent J. J. a of and was the with a J. of in in of its by dopaminergic by da F. J. Biol. Chem. da F. J. Biol. Chem. and the of J. Biol. Chem. J. J. J. that anti-apoptotic that abolished by pathogenic mutations da F. J. Biol. Chem. which F. J. J. Biol. Chem. J. J. J. Biol. Chem. anti-apoptotic phenotype was abolished by 6OH-DOPA da F. J. Biol. Chem. a dopaminergic a in J. immunoreactivity by treatment with 6OH-DOPA da F. J. Biol. Chem. the mechanisms by which the function remained This that 6OH-DOPA that directly 6OH-DOPA prevents and its of 6OH-DOPA was demonstrated in and in by the of 6OH-DOPA the proteasome. Thus, 6OH-DOPA inhibits endogenous F. J. and purified 20 S and prevents by Furthermore, 6OH-DOPA and a the of in a that the 6OH-DOPA inhibits proteasomal activity and in This and a the of Parkinson a dopaminergic J. J. J. This also that the 6OH-DOPA in the of that by J. Biol. Chem. J. J. Biol. Chem. was that recombinant by the purified 20 S in that the S in the of the 20 S mainly in the of a of which J. with the that of the dopaminergic neurons by the of and α-synuclein J. J. J. Biol. Chem. by which 6OH-DOPA of the its Thus, 6OH-DOPA the of and the of 6OH-DOPA purified 20 S by the the of and activity in SH-SY5Y neuroblastoma also of recombinant in also its that J. J. that the proteasomal and a of the of cells by 6OH-DOPA of that 6OH-DOPA enhances of the proteasome. that of its and that by the of 6OH-DOPA in with the of in and the that 6OH-DOPA of the of that of of the 6OH-DOPA and J. Biol. Chem. and with However, that dopaminergic J. J. Furthermore, showed that in the dopaminergic cells in of the the of J. J. and in with the the of α-synuclein-mediated that was a of the and of activity and 6OH-DOPA was and in and with of the of purified 20 S proteasome. However, was by the This that the mechanisms of by 6OH-DOPA and activity and that the of purified by of of and proteasomal 6OH-DOPA directly of the and of This the in in with with 6OH-DOPA that which by a dopaminergic in the the of the that 6OH-DOPA the the of and by a p53-dependent da F. J. Biol. Chem. anti-apoptotic function the of caspase-3 activation da F. J. Biol. Chem. 6OH-DOPA inhibits by of da F. J. Biol. Chem. that a of the also the protective in the of 6OH-DOPA da F. J. Biol. Chem. Furthermore, 6OH-DOPA da F. J. Biol. Chem. in with the of of its in J. J. J. the in the of in and the of by its and 6OH-DOPA the the of the in Thus, the the its anti-apoptotic However, the dopaminergic neurons the of the endogenous and its This the of the in also the that a by by with by its of of with a with the of and by of the and the J. and and of a of dopaminergic of dopaminergic neurons and F. J. that with of the p53-dependent J. J. a of and was the with a J. of in in of its by dopaminergic by da F. J. Biol. Chem. da F. J. Biol. Chem. and the of J. Biol. Chem. J. J. J. that anti-apoptotic that abolished by pathogenic mutations da F. J. Biol. Chem. which F. J. J. Biol. Chem. J. J. J. Biol. Chem. anti-apoptotic phenotype was abolished by 6OH-DOPA da F. J. Biol. Chem. a dopaminergic a in J. immunoreactivity by treatment with 6OH-DOPA da F. J. Biol. Chem. the mechanisms by which the function remained This that 6OH-DOPA that directly 6OH-DOPA prevents and its of 6OH-DOPA was demonstrated in and in by the of 6OH-DOPA the proteasome. Thus, 6OH-DOPA inhibits endogenous F. J. and purified 20 S and prevents by Furthermore, 6OH-DOPA and a the of in a that the 6OH-DOPA inhibits proteasomal activity and in This and a the of Parkinson a dopaminergic J. J. J. This also that the 6OH-DOPA in the of that by J. Biol. Chem. J. J. Biol. Chem. was that recombinant by the purified 20 S in that the S in the of the 20 S mainly in the of a of which J. with the that of the dopaminergic neurons by the of and α-synuclein J. J. J. Biol. Chem. by which 6OH-DOPA of the its Thus, 6OH-DOPA the of and the of 6OH-DOPA purified 20 S by the the of and activity in SH-SY5Y neuroblastoma 6OH-DOPA also of recombinant in also its that J. J. that the proteasomal and a of the of cells by 6OH-DOPA of that 6OH-DOPA enhances of the proteasome. that of its and that by the of 6OH-DOPA in with the of in and the that 6OH-DOPA of the of that of of the 6OH-DOPA and J. Biol. Chem. and with However, that dopaminergic J. J. Furthermore, showed that in the dopaminergic cells in of the the of J. J. and in with the the of α-synuclein-mediated that was a of the and of activity and 6OH-DOPA was and in and with of the of purified 20 S proteasome. However, was by the This that the mechanisms of by 6OH-DOPA and activity and that the of purified by of of and proteasomal 6OH-DOPA directly of the and of This the in in with with 6OH-DOPA that which by a dopaminergic in the the of the that 6OH-DOPA the the of and 6OH-DOPA by a p53-dependent da F. J. Biol. Chem. anti-apoptotic function the of caspase-3 activation da F. J. Biol. Chem. 6OH-DOPA inhibits by of da F. J. Biol. Chem. that a of the also the protective in the of 6OH-DOPA da F. J. Biol. Chem. Furthermore, 6OH-DOPA da F. J. Biol. Chem. in with the of of its in J. J. J. the in the of in and the of by its and 6OH-DOPA the the of the in Thus, the the its anti-apoptotic However, the dopaminergic neurons the of the endogenous and its This the of the in also the that a by by with by its α-synuclein anti-apoptotic phenotype by its proteasomal and by its of