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Neurodegenerative Dis 2012;10:49–51 DOI: 10.1159/000332803

Parkin: Much More than a Simple Ubiquitin Ligase

C. Alves da Costa F. Checler

Institut de Pharmacologie Moléculaire et Cellulaire et Institut de NeuroMédecine Moléculaire, Equipe Labellisée Fondation pour la Recherche Médicale, Sophia-Antipolis, Valbonne , France

Introduction

Parkinson’s disease (PD) is one of the most important neurodegenerative diseases [1–3] . It can be of sporadic origin or inherited depending on dominant or recessive transmissions [4, 5] . During the last few years, many studies led to the identification of the genes responsible for genetic cases of PD [6, 7] . Early-onset recessive cases of PD are mainly due to mutations located on genes cod-ing for PINK1, DJ-1 and parkin [8, 9] .

Several lines of evidence suggest that apoptosis con-tributes to the etiology of PD [10] . Interestingly, parkin, which is responsible for most of juvenile autosomal reces-sive (AR-JP) cases of PD [11] , was described as a negative modulator of apoptosis and that most of AR-JP-related mutations of parkin prevent this function [12, 13] . It has been suggested that parkin acts as a ubiquitin ligase, the activity of which is abolished by mutations. As a conse-quence, it has been proposed that AR-JP-associated par-kin mutations trigger a functional enzymatic deficit lead-ing to the accumulation and aggregation of a series of proteasome-resistant proteins [14] .

We have recently demonstrated that part of the parkin protective phenotype could be accounted for its ability to control the p53-dependent pathway [15, 16] . Here, we sum-marize our data showing that parkin downregulates p53

Key Words

Parkinson’s disease � Parkin � Mutations � Transcription factor � p53

Abstract

Parkin is mainly a cytosolic protein involved in a subset of Parkinson’s disease (PD) cases referred to as autosomal juve-nile recessive forms of PD. Most studies have established as a dogma that parkin function could be resumed as an ubiq-uitin ligase activity. Accordingly, several cellular functions as-cribed to parkin derive from its ability to ubiquitinate a series of proteins, thereby rendering them prone to proteasomal degradation. Several lines of data indicated that parkin could display antiapoptotic properties and we demonstrated that indeed, parkin could downregulate the p53-dependent pathway. However, we showed that such function remained independent of parkin’s ability to act as an ubiquitin ligase. Thus, we established that parkin repressed p53 transcription by physically interacting with its promoter. Here, we de-scribe this novel parkin-associated transcription factor func-tion and we speculate on putative additional transcriptional targets.

Copyright © 2011 S. Karger AG, Basel

Received: June 16, 2011 Accepted after revision: September 4, 2011 Published online: December 23, 2011 D i s e a s e s

F. Checler Institut de Pharmacologie Moléculaire et CellulaireEquipe Labellisée Fondation pour la Recherche Médicale, 660, route des Lucioles Sophia-Antipolis, FR–06560 Valbonne (France) Tel. +33 49 395 3460, E-Mail checler   @   ipmc.cnrs.fr

© 2011 S. Karger AG, Basel1660–2854/12/0104–0049$38.00/0

Accessible online at:www.karger.com/ndd

Alves da Costa   /Checler  

Neurodegenerative Dis 2012;10:49–51 50

mRNA and protein levels by interacting physically with the promoter of p53. This transcriptional parkin-related function is abolished by AR-JP-related mutations. Overall, our data document a novel function of parkin independent of its previously characterized ubiquitin ligase activity.

Materials and Methods

All methods including cell cultures, vectors and transfections, promoter transactivation, and statistical analyses of data have been extensively detailed elsewhere [15, 17] .

Results and Discussion

Parkin Downregulates Cell Death and p53 Pathway in Cells and in Mouse Brain: Effect of Mutations The overexpression of parkin in TSM1 neuronal cells

drastically reduces staurosporine- and 6-hydroxydopa-mine-induced caspase-3 activation [15] . Interestingly, parkin reduces p53 expression and lowers its transcrip-tional activity measured by both PG13 (a construct har-boring the consensus sequence targeted by p53 in frame with luciferase; a kind gift from Dr. B. Vogelstein) and transactivation of its downstream targets Bax and p21 [15] . Furthermore, parkin lowered both p53 mRNA levels and promoter transactivation. Parkin-associated down-regulation of 6-hydroxydopamine-induced caspase-3 ac-tivation was fully prevented by p53 depletion.

This set of data was reinforced by the examination of the influence of endogenous parkin on the p53 pathway. Thus, the depletion of endogenous parkin drastically en-hances 6-hydroxydopamine-induced caspase-3 activa-tion. This was accompanied by an upregulation of p53 expression, mRNA levels and promoter transactivation [15] . Of most interest, parkin-deficient mouse brains ex-hibit increased levels of p53 protein and mRNA.

We examined the influence of pathogenic mutations on parkin-associated protective function. The mutations chosen either inactivate (C418R and C441R) or leave in-tact (K161N and R256C) parkin ubiquitin ligase activity. All mutations abolish parkin-related control of caspase-3 and p53 pathway. Accordingly, unlike wild-type parkin, none of the mutated parkin was able to restore function-al deficiency observed in parkin null fibroblasts [15] . Overall, the above data indicated first, that the parkin protective phenotype was linked to parkin’s ability to control the tumor suppressor p53; second, that pathogen-ic mutations abolish parkin-dependent control of cell

death and p53, and third, that the ability of parkin to con-trol p53 was not related to its ubiquitin ligase properties.

Parkin Control of p53: How Does It Work? The control of p53 promoter transactivation and

mRNA levels by parkin led us to hypothesize that the pro-tein could modulate p53, either directly or indirectly, at a transcriptional level. Three lines of data indicated that parkin could act as a transcriptional repressor of p53. First, 5 � -deletion analysis of p53 promoter transactivation showed that the –312 to –196 region of the p53 promoter was required for parkin-induced luciferase activity; sec-ond, gel shift analysis showed that among three probes covering the –312 to –130 region, both endogenous and overexpressed parkin only functionally interacted with the –312 to –243 region of the p53 promoter; third, phys-ical interaction of parkin with p53 promoter was ob-served in wild-type fibroblasts but not in parkin-defi-cient cells [15] . Interestingly, pathogenic parkin muta-tions abolished both DNA binding to, and promoter transactivation of p53. Further characterization of par-kin-p53 promoter physical interaction was indicated by the identification of the parkin RING1 sequence as the functional domain that is required to repress p53 [15] .

The above data indicate that besides its well-character-ized ubiquitin ligase activity, parkin could harbor addi-tional functions including that of a transcription factor. This opens new avenues to better understand physiologi-cal roles of parkin and its modulation in physiopatho-logical situations. Current work in our laboratory is in progress that should lead to the future delineation of ad-ditional transcriptional targets of parkin.

Acknowledgements

We wish to thank Drs. C. Sunyach, E. Giaime, A. West, O. Cor-ti, A. Brice, S. Safe, P.M. Abou-Sleiman, N.W. Wood, H. Takahashi, M.W. Goldberg, and J. Shen for their contribution for the ini-tial study. This work was supported by the Fondation pour la Re-cherche Médicale and by the Conseil Général des Alpes Mari-times.

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