Parkin Facilitates the Elimination of Expanded Polyglutamine Proteins and Leads to Preservation of Proteasome Function

Abstract

Parkin, the most commonly mutated gene known to result in familial Parkinson's disease (PD), 1 encodes an E3 ubiquitin ligase (1). Several substrates for parkin have been identified including CDCrel-1, an o-glycosylated form of ␣-synuclein ␣Sp22, Pael-R (2), and synphilin-1 (3-5). These parkin substrates have little sequence or functional similarities; however, Pael-R and ␣-synuclein have a propensity to misfold and aggregate (2, 4). This common property of known parkin substrates suggests that parkin may play a general role in the degradation of misfolded proteins, which might otherwise overwhelm the ubiquitin-proteasome system (UPS).Parkin has been demonstrated to function in the endoplasmic reticulum-associated degradation (ERAD) of misfolded ER proteins (2, 6). Parkin is up-regulated during the unfolded protein response (6). Pael-R overexpression results in ER accumulation of the protein, causing ER stress-induced cell death; parkin overexpression ameliorates these effects (2). Proteasome function is also important for normal ERAD and proteasomal dysfunction can cause ER stress (7, 8). Whereas ERAD is an important pathway for eliminating misfolded proteins in the ER, there are many misfolded aggregation-prone proteins that are translated in the cytosol including most of the polyglutamine (poly(Q)) containing proteins. Accumulation of misfolded cytosolic and ER-translated proteins can ultimately inhibit proteasomal activity (9 -11).Whereas the cytotoxicity of expanded poly(Q) proteins may be because of a variety of mechanisms (12-16), expanded poly(Q) proteins impair proteasome function (9 -11). Proteasomal dysfunction has also been demonstrated in PD brain and may play a role in the accumulation of aberrant proteins and neuronal loss that characterize several of the adult neurodegenerative diseases (17). Accumulation of aberrant proteins is a hallmark of both PD and the poly(Q) expansion diseases, which include Huntington's disease (HD) and several spinocerebellar ataxias. Overexpression of aberrant proteins has been very useful for identifying genes and proteins capable of modifying their accumulation or toxicity. Molecular chaperones such as Hsp70 improve cell viability (18 -20) and facilitate the elimination of poly(Q) proteins in cellular models and ameliorate disease phenotype in transgenic Drosophila models (18,(21)(22)(23)(24)(25). Hsp70 also improves the phenotype in a Drosophila PD model in which human ␣-synuclein is overexpressed (26). Parkin appears to interact with Hsp70 along with the ubiquitinating factor CHIP (27). The N terminus of parkin contains a domain homologous to ubiquitin called the ubiquitin-like (Ubl) domain. A similar domain in the human homologue of the yeast DNA repair factor (hhRad23) has been shown to interact with expanded poly(Q) proteins (28) and bind the proteasome (29,30). Other Ubl domain containing proteins such as Dsk2 (31, 32) and Ubp6 (33) also bind the proteasome. These findings suggest that parkin may also bind expanded poly(Q) proteins and proteasomes via its Ubl ...

Structure of the Parkin in-between-ring domain provides insights for E3-ligase dysfunction in autosomal recessive Parkinson's disease

“…A total of 95.9% of the proton, nitrogen, and carbon chemical shifts were assigned and used to calculate the three-dimensional structure of IBR . This resulted in a total of 1,263 distance restraints derived from 13 C-edited, 15 N-edited, and 1 H-1 H NOESY spectra (SI Table 1). Initial structures were calculated in the absence of Zn 2ϩ ion restraints to determine the overall fold of the domain.…”

The E3 Ubiquitin Ligase Parkin Is Recruited to the 26 S Proteasome via the Proteasomal Ubiquitin Receptor Rpn13

“…Similarly to Ubp6, parkin requires its Ubl domain to interact with the 26 S proteasomes, at least in vitro (31). However, the exact protein(s) within the proteasome involved in parkin binding, as well as the physiological relevance of this interaction, have not been completely elucidated.…”

“…We have previously shown that the Ubl functions as a key interaction module allowing parkin to interact with proteins containing ubiquitin-binding domains, such as Eps15, Ataxin-3, and endophilin-A (8,10,30). Interestingly, Tsai et al (31) showed that the Ubl domain of parkin is necessary for its direct interaction with purified 26 S proteasomes in vitro. Additionally, two independent groups found that parkin could interact with the 26 S proteasome by binding the 19 S proteasome subunit Rpn10/S5a (32) or the 20 S subunit ␣4/PSMA7 (33).…”

Familial Parkinson's Disease-associated L166P Mutation Disrupts DJ-1 Protein Folding and Function

“…The nature of such signals is unknown, but it has been proposed that exposed hydrophobic domains normally buried in the interior of the protein or in the protein-protein interaction interfaces may serve as recognition signals for the ubiquitination machinery (42,43,51). Interestingly recent evidence indicates that the PD-associated E3 ubiquitin-protein ligase parkin may facilitate the ubiquitination and degradation of misfolded proteins such as Pael-R and the polyglutamine-containing proteins in conjunction with the molecular chaperone Hsp70 and its binding partner carboxyl terminus of Hsp70-interacting protein (52)(53)(54). It would be worthwhile to determine whether parkin has a role in facilitating the ubiquitination of the L166P mutant DJ-1 protein.…”