Journal: Cell Death & Disease
Article Title: Parkin loss of function contributes to RTP801 elevation and neurodegeneration in Parkinson's disease
doi: 10.1038/cddis.2014.333
Figure Lengend Snippet: RTP801 is poly-ubiquitinated by parkin E3 ligase and degraded by the proteasome. ( a ) RTP801 is degraded by the proteasome. HEK293 cells were exposed for 4 h to 1 μ M epoxomycin or 50 μ M chloroquine, and cell lysates were analyzed by western immunoblotting for RTP801 and α -actin (loading control). ut = untreated. ( b ) RTP801 is poly-ubiquitinated by parkin prior to proteasomal degradation. HEK293 cells were co-transfected with pCMS-eGFP RTP801, HA-ubiquitin and one of the pRK5-myc constructs, either empty or containing parkin WT or parkin ΔR2. Twenty-four hours later, cultures were exposed to epoxomycin for 3 h prior to harvesting. RTP801 was immunoprecipitated (IP) and immunocomplexes along with whole-cell lysates were analyzed by western immunoblotting (IB). Membranes were probed for HA, myc and α -actin as a loading control. Membranes were reprobed with anti-RTP801 antibody to confirm that RTP801 was immunoprecipitated. Non-specific mouse immunoglobulins were used as negative controls (m IgG). (HMW Ub-RTP801, high molecular weight ubiquitinated RTP801) ( c ) Parkin ubiquitinates RTP801 in a cell-free in vitro system. Recombinant parkin E3 ligase (active full-length), truncated parkin (inactive), GST-RTP801, and UbcH7 E2 enzyme, were mixed and incubated as indicated along with biotinylated ubiquitin, E1 enzyme, and ATP. RTP801 was immunoprecipitated, and immunocomplexes resolved in a western blot. The membrane was incubated with Avidin/Biotin and then incubated with chemiluminiscent peroxidase substrate solution (upper panel). The same membrane was reprobed with an anti-RTP801 antibody (lower panel). (HMW Ub-RTP801, high molecular weight ubiquitinated RTP801) ( d ) Ectopic parkin physically interacts with ectopic RTP801. HEK293 cells were co-transfected either with the pCMS-eGFP and pEGFP-C2 empty vectors or pCMS-eGFP RTP801 along with pEGFP-C2-parkin. Twenty-four hours later, cultures were treated with the cross-linking agent DSP for 2 h at 4°C, prior to harvesting. After RTP801 immunoprecipitation, the samples were analyzed by western immunoblotting for parkin to detect the interaction, and for RTP801 as an IP control. ( e and f ) Reciprocal co-immunoprecipitation indicates interaction of endogenous parkin and RTP801 in cells. Neuronal PC12 cells were treated with or without MG132 for 5 h as indicated, lysed and subjected to immunoprecipitation (IP) with control antibody (GFP), and either ( e ) anti-parkin or ( f ) anti-RTP801 antibodies. Immunoprecipitates were analyzed by western immunoblotting with anti-parkin and anti-RTP801 as indicated. In ( e ) all samples were analyzed on the same blot, but irrelevant intervening lanes were removed. In the right panel ( f ), the membrane was probed with a light chain-specific secondary antibody to diminish overlap of signal with co-immunoprecipitated RTP801. In each panel ( a , b , c , d , e and f ), a representative western blot is shown from a pool of at least two independent experiments. Specific bands are pointed out by arrows
Article Snippet: Briefly, (20 mM Tris-HCl; pH 7.5, 1 mM dithiothreitol, 20 U/ml inorganic pyrophosphatase, 5 mM Mg-ATP, 0.1 μ M His 6 -tagged recombinant human ubiquitin-activating enzyme E1, 2.5 μ M biotinylated ubiquitin), His 6 -tagged recombinant human ubiquitin-conjugating enzyme UbcH7 E2 (Enzo Life Biosciences), His 6 -tagged recombinant human parkin full-lenght (Merck Millipore), N-terminal GST-tagged recombinant human RTP801 full-length (Novus Biologicals, Cambridge, UK), and GST-tagged recombinant human truncated and inactive parkin (1-387) (Novus Biologicals), were added to the reaction buffer, as referred in each condition, and then incubated at 37 °C for 90 min. RTP801 was immunoprecipitated as described above, and equal volumes of each sample were subjected to WB.
Techniques: Western Blot, Transfection, Construct, Immunoprecipitation, Molecular Weight, In Vitro, Recombinant, Incubation, Membrane, Avidin-Biotin Assay