Inhibition of Protein Ubiquitination by Paraquat and 1-Methyl-4-Phenylpyridinium Impairs Ubiquitin-Dependent Protein Degradation Pathways

Abstract

Intracytoplasmic inclusions of protein aggregates in dopaminergic cells (Lewy bodies) are the pathological hallmark of Parkinson’s disease (PD). Ubiquitin (Ub), alpha [α]-synuclein, p62/sequestosome 1 and oxidized proteins are major components of Lewy bodies. However, the mechanisms involved in the impairment of misfolded/oxidized protein degradation pathways in PD are still unclear. PD is linked to mitochondrial dysfunction and environmental pesticide exposure. In this work, we evaluated the effect of the pesticide paraquat (PQ) and the mitochondrial toxin 1-methyl-4-phenylpyridinium (MPP+) on Ub-dependent protein degradation pathways. No increase in the accumulation of Ub-bound proteins or aggregates was observed in dopaminergic cells (SK-N-SH) treated with PQ or MPP+, or in mice chronically exposed to PQ. PQ decreased Ub protein content, but not its mRNA transcription. Protein synthesis inhibition with cycloheximide depleted Ub levels and potentiated PQ–induced cell death. Inhibition of proteasomal activity by PQ was found to be a late event in cell death progression, and had no effect on either the toxicity of MPP+ or PQ, or the accumulation of oxidized sulfenylated, sulfonylated (DJ-1/PARK7 and peroxiredoxins) and carbonylated proteins induced by PQ. PQ- and MPP+-induced Ub protein depletion prompted the dimerization/inactivation of the Ub-binding protein p62 that regulates the clearance of ubiquitinated proteins by autophagic. We confirmed that PQ and MPP+ impaired autophagy flux, and that the blockage of autophagy by the overexpression of a dominant-negative form of the autophagy protein 5 (dnAtg5) stimulated their toxicity, but there was no additional effect upon inhibition of the proteasome. PQ induced an increase in the accumulation of α-synuclein in dopaminergic cells and membrane associated foci in yeast cells. Our results demonstrate that inhibition of protein ubiquitination by PQ and MPP+ is involved in the dysfunction of Ub-dependent protein degradation pathways.

Exposure to selenomethionine causes selenocysteine misincorporation and protein aggregation in Saccharomyces cerevisiae

“…Paraquat and 1-methyl-4-phenylpyridinium (MPP+) are environmental toxicants associated with an increased risk of developing Parkinson’s disease, a neurodegenerative pathology characterized by an accumulation of insoluble protein deposits. Exposure of dopaminergic cells to paraquat or MPP+ was shown to decrease protein ubiquitination, leading to a dysfunction of protein degradation pathways 36 . The molecular target of radicicol is the heat-shock protein Hsp90p, the inhibition of which affects protein quality control 37 .…”

Yeast polyubiquitin gene UBI4 deficiency leads to early induction of apoptosis and shortened replicative lifespan

“…Another possible explanation is that PQ may, at least to some extent, impair the protein ubiquitination pathway. Previous studies also reported that PQ can induce ubiquitin/proteasome system dysfunction (Navarro-Yepes et al 2016;Yang et al 2007).…”

Cognitive-enhancing and antioxidant activities of the aqueous extract from Markhamia tomentosa (Benth.) K. Schum. stem bark in a rat model of scopolamine

“…The extent of protein oxidation in the hippocampus was assessed by measuring the content of protein carbonyl groups, using 2,4-dinitrophenylhydrazine (DNPH) derivatization as described by Oliver et al [38] and following the indications of Luo and Wehr [39, 40]. Basically, the supernatant fraction was divided into two equal aliquots containing approximately 2 mg of protein each.…”