FEBS 29707 FEBS Letters 579 (2005) 3913–3919 Parkin interacts with the proteasome subunit a4 J.C. Da¨chsela,1, C.B. Lu¨ckinga,*,1, S. Deega,1, E. Schultzb, M. Lalowskic, E. Casademunta, O. Cortid, C. Hamped, N. Patengee, K. Vaupela, A. Yamamotof, M. Dichgansa, A. Briced, E.E. Wankerc, P.J. Kahlee,f, T. Gassere a Labor fu¨r Molekulare Neurogenetik, Neurologische Klinik der Ludwig-Maximilians-Universita¨t, Marchioninistr. 15, 81377 Mu¨nchen, Germany b Deutsches Ressourcenzentrum fu¨r Genomforschung, Heidelberg, Germany c Max-Delbru¨ck-Centrum fu¨r Molekulare Medizin, Berlin, Germany d INSERM U679, Hop. de la Salpeˆtrie`re, Paris, France e Hertie-Institut fu¨r klinische Hirnforschung am Zentrum fu¨r Neurologie der Universita¨tTu¨bingen, Germany f Labor fu¨r Alzheimer- und Parkinson-Forschung, Abteilung fu¨r Stoffwechselbiochemie, Ludwig-Maximilians-Universita¨t, Mu¨nchen, Germany Received 25 May 2005; accepted 3 June 2005 Available online 16 June 2005 Edited by Barry Halliwell main at the N-terminus, followed by an in-between RING re- Abstract Mutations in the parkin gene encoding an E3 ligase are responsible for autosomal recessive ParkinsonÕs disease. gion (IBR) and two RING-finger domains at the C-terminus Putative parkin substrates and interacting partners have been [3] (Fig. 1A). Parkin has E3 ubiquitin-protein ligase activity identified, but the molecular mechanism underlying parkin-re- [4], and conjugates activated ubiquitin to proteins for further lated neurodegeneration is still unclear. We have identified the degradation by the 26S proteasome. Known interacting 20S proteasomal subunit a4 (synonyms: PSMA7, XAPC7, sub- partners, which also serve as substrates for parkin-mediated unit alpha type 7) as a new interacting partner of parkin. The C- ubiquitylation, include CDCrel, synphilin, the Pael-receptor, terminal IBR-RING domain of parkin and the C-terminal part an O-glycosylated form of a-synuclein, the p38 subunit of of a4 were essential for the interaction. Biochemical studies re- the aminoacyl-tRNA synthetase complex, synaptogamin XI vealed that a4 was not a substrate for parkin-dependent ubiqui- and tubulin (for reviews see [5] and [6]). These highly divergent tylation. Putative functions of the interaction might therefore be ubiquitylation substrates do not evoke, however, a unifying substrate presentation to the proteasome or regulation of prote- asomal activity. Full-length parkin and parkin lacking the N- cellular response. Thus, the exact mechanism by which parkin terminal ubiquitin-like domain slightly increased the proteasomal plays a role in cell survival, homeostasis, intracellular inclusion activity in HEK 293T cells, in line with the latter hypothesis. formation and neuroprotection remains to be elucidated. Ó 2005 Federation of European Biochemical Societies. Published In order to shed more light on the function of parkin, we by Elsevier B.V. All rights reserved. performed yeast two-hybrid (Y2H) screens to find new interac- tors and to link the protein to intracellular pathways. Keywords: Parkin; Proteasome subunit a4; PSMA7; Interaction; Proteasomal activity 2. Materials and methods 2.1. Yeast-two-hybrid screen cDNAs encoding full-length (FL) parkin and the parkin mutants 1. Introduction C289G, C418R were subcloned into the two-hybrid vector pBTM116-D9 and used as baits to screen a human fetal brain cDNA library (Clontech). The screening procedure was performed according ParkinsonÕs disease (PD) is a common neurodegenerative to [7]. Briefly, the plasmids encoding parkin and its mutants were disorder affecting approximately 1–2% of the population over transformed into the L40ccua yeast strain, tested for the absence of re- 60 years of age. It is characterized by resting tremor, rigidity porter gene activity, and co-transformed with a human fetal brain and bradykinesia caused by progressive degeneration of dopa- cDNA library, subcloned into pACT2. For each transformation, 1 · 106 independent transformants were plated onto minimal medium minergic neurons in the substantia nigra pars compacta. lacking amino acids Trp, Leu, His, and Ura (SD4 medium) and incu- Although the majority of PD cases are sporadic, mutations bated at 30 °C for 5–10 days. Clones were picked into microtiter plates, in several genes have been linked to familial forms of PD [1]. grown overnight in liquid minimal medium lacking Trp and Leu (SD2 Among those, parkin mutations are responsible for up to medium) and spotted onto nylon membranes placed on SD4 agar 50% of hereditary, autosomal recessive, early onset PD cases, plates. The membranes were subjected to a b-galactosidase (b-GAL) assay after 4 days of incubation. Plasmids obtained from positive characterized by early manifestation, relatively slow progres- clones were sequence verified. For interaction mapping the assays were sion, and a good long-term response to levodopa therapy [2]. performed with plasmids encoding baits and preys co-transformed into The parkin gene possesses 12 exons encoding 465 amino L40ccua strain and plated onto SD4 medium. The efficiency of co- acids. The protein is composed of a ubiquitin-like (UBL) do- transformations was tested on SD2 selective medium. The membranes were subjected to a b-GAL assay as above. 2.2. Cell culture *Corresponding author. Fax: +49 89 7095 3677. PC12 cells, stably transfected to express FL human parkin under E-mail address: [email protected] (C.B. Lu¨cking). the control of the tetracyclin-dependent Tet-off promotor (Clontech), were maintained in DulbeccoÕs modified EagleÕs medium containing 1 These authors contributed equally to this work. 0.11 g/l sodium-pyruvate, pyridoxine (Gibco), 10% horse serum, 5% 0014-5793/$30.00 Ó 2005 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.febslet.2005.06.003 3914 J.C. Da¨chsel et al. / FEBS Letters 579 (2005) 3913–3919 Fig. 1. The proteasomal subunit a4 interacts with parkin in the Y2H assay. (A) Parkin protein structure and bait constructs used for human fetal brain cDNA library and interaction mapping Y2H screens. The black boxes represent parkin with mutations at positions C289G and C418R. (B) Results from reporter activity assay. Parkin C-terminal baits, which activated the HIS3, URA3 (SD4 minimal plates) and lacZ reporter genes (membranes) after co-transformation with empty pACT2 vector in the L40ccua strain, were excluded from further interaction mapping analysis. The membranes were spotted using 2 · 2 patterns. (C) The interaction between FL parkin and a C-terminal fragment of the proteasome subunit a4 (aa 179–248) could be confirmed in an independent co-transformation assay. UBL, ubiquitin-like; IBR, in-between-RING; FL, Full-length; NT, N-terminal; CT, C-terminal. tetracycline-free fetal calf serum (PAA Laboratories), 10 mM L-gluta- into the HA-pcDNA3 vector, as described elsewhere [8,9]. The plas- mine (Gibco), penicillin/streptomycin (Invitrogen, 100 units/ml and mids for the expression of the truncated parkin fragments HA- 100 lg/ml, respectively), and 100 lg/ml geneticin (Gibco) at 37 °C, in parkin(1–191) and HA-parkin(192–465) were generated by subcloning a chamber containing 5% CO2. Hygromycin B and doxycycline, a tet- of cDNA fragments into pTL1-HA1-D48. MYC-tagged parkin pro- racyclin analogue, were added to maintain stable transfection and sup- teins (FL, aa 1–144 and aa 294–465) were produced by expression of press parkin expression. subcloned cDNA fragments with pcDNA3.1 zeo(-) [10]. All constructs HEK 293 and HEK 293T cells were cultivated in DulbeccoÕsMEM were sequence verified. The plasmids for the expression of FLAG- with addition of Glutamax 1, sodium pyruvate, 4500 mg/l glucose, pyr- tagged parkin (N-FLAG-pcDNA3), HA-CDCrel (pRK-5-HA), and idoxine (Gibco), penicillin/streptomycin (100 units/ml and 100 lg/ml, p6HIS-ubiquitin (pMT107) were kindly provided by R. Takahashi, respectively) and 10% fetal calf serum. To maintain stable transfection, T. Dawson and G. Bossis, respectively. HEK 293 cells stably overexpressing parkin were supplemented with Zeocin (Invitrogen) (200 lg/ml). 2.4. Co-immunoprecipitation assays 2.3. Plasmids Tet-off PC12 cells were transfected with Lipofectamine 2000, as rec- The Y2H vectors pACT2 and pBTM116D-9 were described earlier ommended by the manufacturerÕs instructions. Two days after trans- [7]. The cDNA fragment encoding the FL a4 isoform 1 was amplified fection, the cells were harvested, washed with cold PBS and lysed in by PCR (based on NCBI_NM002792 accession number) from a mouse 50 mM Tris–HCl, 200 mM NaCl, 0.5% Nonidet 40 and protease inhib- brain cDNA library and subcloned into pFLAG-CMV-2 (Sigma). The itors (Complete Mini, Roche). Cell lysates were then rotated at 4 °C cDNAs encoding the last 70 amino acids of human a4 (aa 179–248) for 30 min and centrifuged for 10 min, at 5000 · g. The protein concen- were subcloned downstream of the HA-tag into the pTL1-HA-D48 tration of the supernatant was determined using the BCA Protein vector. Delta-UBL parkin was subcloned downstream of the HA-tag Assay Reagent Kit (Pierce). HEK 293 cells, which were more sensitive J.C. Da¨chsel et al. / FEBS Letters 579 (2005) 3913–3919 3915 to our transfection conditions, were harvested after 16 hours. For the fragments (aa 192–465) could not be used for mapping of mapping experiments in PC12 cells, 5 lg of purified human 20S protea- the binding region using the Y2H system. However, further some (Biotrend) was added to 300 lg of cell lysate proteins. two-hybrid studies revealed that, in contrast to FL parkin, Equal amounts of total protein were incubated with EZviewe Red Anti-FLAG M2 Affinity Gel (Sigma) or agarose-immobilized mouse the N-terminal parkin fragment (aa 1–191) did not interact monoclonal antibodies (Abs) to 20S proteasome subunit a4 (Biotrend), with the C-terminal a4 fragment (Fig. 1C), suggesting that previously equilibrated in TBS, for 3–6 h at 4 °C.