Parkin directly modulates 26S proteasome activity.

Parkinson's disease (PD) is a common neurodegenerative disease that involves the deterioration of dopaminergic neurons in the substantia nigra pars compacta. Although the etiology of PD remains poorly understood, recent genetic, postmortem, and experimental evidence shows that abnormal protein accumulation and subsequent aggregate formation are prominent features of both sporadic and familial PD. While proteasome dysfunction is observed in PD, diverse mutations in the parkin gene are linked to early-onset autosomal-recessive forms of familial PD. We demonstrate that parkin, an E3 ubiquitin ligase, activates the 26S proteasome in an E3 ligase activity-independent manner. Furthermore, an N-terminal ubiquitin-like domain within parkin is critical for the activation of the 26S proteasome through enhancing the interaction between 19S proteasomal subunits, whereas the PD-linked R42P mutant abolishes this action. The current findings point to a novel role for parkin for 26S proteasome assembly and suggest that parkin mutations contribute to the proteasomal dysfunction in PD.

Molecular interaction between parkin and PINK1 in mammalian neuronal cells.

Parkinson's disease (PD) is characterized by the deterioration of dopaminergic neurons in the pars compacta of substantia nigra and the formation of intraneuronal protein inclusions. The etiology of PD is not known, but the recent identification of several mutation genes in familial PD has provided a rich understanding of the molecular mechanisms of PD pathology. Mutations in PTEN-induced putative kinase 1 (PINK1) and parkin are linked to early-onset autosomal recessive forms of familial PD. Here we show molecular and functional interactions between parkin and PINK1. Parkin selectively binds to PINK1 and upregulates PINK1 levels. In addition, PINK1 reduces the solubility of parkin, which induces the formation of microtubule-dependent cytoplasmic aggresomes. Our findings reveal that parkin and PINK1 affect each other's stability, solubility and tendency to form aggresomes, and have important implications regarding the formation of Lewy bodies.

Neuroprotective effects of rotigotine in the acute MPTP-lesioned mouse model of Parkinson's disease.

Dopamine agonists used to manage Parkinsonian motor symptoms have been suggested to be neuroprotective. The study was designed to assess the neuroprotective potential of the D(3)/D(2)/D(1) dopamine receptor agonist rotigotine in the acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned (MPTP) mouse model of Parkinson's disease by measuring mesencephalic degenerating neurons using FluoroJade staining and the remaining dopaminergic nerve endings in the striatum using dopamine transporter binding. Continuous administration of rotigotine at a dose of 3mg/kg significantly attenuated MPTP-induced acute cell degeneration in the FluoroJade-staining paradigm. Rotigotine (0.3-3mg/kg) partially protected dopamine nerve endings from MPTP-induced degeneration in a dose-dependent manner. These data suggest that rotigotine, at the doses employed, significantly protected dopamine neurons from degeneration in an acute mouse model of MPTP intoxication.

Endogenous alkaloids in man. XXXVIII. "Chiral" and "achiral" determination of the neurotoxin TaClo (1-trichloromethyl-1,2,3,4-tetrahydro-beta-carboline) from blood and urine samples by high-performance liquid chromatography--electrospray ionization tandem mass spectrometry.

An improved sensitive assay for the determination of the dopaminergic and serotonergic neurotoxin 1-trichloromethyl-1,2,3,4-tetrahydro-beta-carboline (TaClo) is presented, based upon on-line coupling of high-performance liquid chromatography with electrospray ionization tandem mass spectrometry (HPLC-ESI-MS-MS). Applying synthetic [D4]TaClo as a fourfold deuterated internal standard, TaClo was detected and reliably quantified as a trace constituent of blood samples (0.5 up to 70 ng g(-1) of clot) obtained from six patients orally treated with the hypnotic chloral hydrate. Unambiguous identification of this tricyclic "endogenous alkaloid" was achieved by selected reaction monitoring (SRM) experiments. The molecular ion peaks of TaClo, m/z 289 (for [35Cl3]TaClo) and m/z 291 (for its [37Cl35Cl2]isotopomer), were both monitored to undergo a retro-Diels-Alder fragmentation by loss of a CH2=NH portion (-29 u) as typical of a tetrahydropyrido ring system of tetrahydro-beta-carbolines. Detection of the resulting fragments, m/z 260 and m/z 262, with the expected statistical chlorine isotopic intensities of 100:96 confirmed the identity of the TaClo molecule. In addition, an enantiomer-specific device was developed for TaClo, by employing a chiral reversed-phase HPLC column in combination with circular dichroism (CD) spectroscopy and MS-MS analysis (LC-CD and LC-MS-MS coupling). In a human clot sample, both TaClo enantiomers were found in equimolar concentration (i.e., as a racemate) corroborating a spontaneous, non-enzymatic formation of TaClo from biogenic tryptamine and therapeutically administered chloral. In urine samples of TaClo-treated rats, by contrast, the (S)-antipode was found to predominate, hinting at an enantiomer-differentiating metabolism of the compound.