Re also modified by SUMOs, implying that SUMOylation of these disease-related proteins may participate in the regulation of their functions and thereby be associated with their pathogenic role. Tau, an Alzheimer’s disease associated protein, has been reported to be SUMOylated by SUMO-1, and to a much lesser extent by SUMO-2 or SUMO-3 simultaneously [36]. Many substrates were reported to be multi-SUMOylated by SUMO-1 on several residues, for example, ataxin-1 modified atSUMO-1 modification did not affect ataxin-3 ubiquitination or aggregate formation, but partially increased ataxin-3-68Q stabilityIt has been reported that SUMOylation alters the function or subcellular localization of some proteins, and the competitionThe Title Loaded From File Effect of SUMOylation on Ataxin-Figure 1. Identification of the SUMO-1 modification sites in ataxin-3. (A) HEK293 cells were used to co-express ataxin-3, Comparisons), total protein with dexamethasone treatment (2-way ANOVA). Count data was ataxin-3K8R, ataxin3K166R, or ataxin-3K206R with SUMO-1. 10 lysates were precipitated by TCA and 25331948 subjected to immunoblotting. #ataxin-3 main bands, ## ataxin-3 relative levels of modified and unmodified (whole-cell CA precipitates). (B) The tagged proteins were enriched with NTA magnetic nickel columns and detected by immunoblotting with SUMO-1 antibody. **, ataxin-3-20Q modified by SUMO-1, ##, ataxin-3-68Q modified by SUMO-1. doi:10.1371/journal.pone.0054214.gleast on five and huntingtin on three lysine residues [26?7]. SCA3/MJD is the most common spinocerebellar ataxia diseases. In our previous research, we found that ataxin-3 was also a substrate of SUMO-1 [32]. In order to identify the motif residue, mutagenesis analyses were carried out to converse lysine 166 residues to arginine, which lies within a SUMO consensus sequence, VKGD, in ataxin-3. This conversion completely blocked the SUMOylation of ataxin-3. However, the conversion of other lysines, K8 and K206, which also lie within the SUMO consensus sequence in ataxin-3, did not affect SUMOylation of ataxin-3. These data suggest that K166 in ataxin-3 is the major SUMOylation binding site. Modification by SUMO has been shown to play critical roles in subcellular localization, and protein degradation, which ultimately contribute to regulation of the cell cycle, cell growth, and apoptosis [37]. In order to examine whether SUMOylation of ataxin-3 affects 10457188 its subcellular localization, we compared the localization of ataxin-3 in transiently transfected HEK293 cells. In agreementwith previous studies, we found that the wild-type ataxin-3 protein was diffusively distributed in both nucleus and cytoplasm, while mutant-type ataxin-3 protein formed aggregates in nucleus. However, when we compared ataxin-3 and its SUMOylation deficient variant, we could not detect any difference in the subcellular localization of ataxin-3 in both immunofluorescent staining and immunoblot analysis, which indicates SUMOylation of ataxin-3 does not change its subcellular distribution. The similar result was also observed in SCA7, that SUMOylation on K257 of ataxin-7 does not influence its subcellular localization [28]. As we know, abnormal accumulation of mutant ataxin-3 in affected neurons reflexes that mutant protein may not be properly degraded. We found the insoluble fraction of ataxin-3-68Q was more than that of ataxin-3-20Q, which supported that mutanttype ataxin-3 protein was stable and easy to form aggregates. As SUMO modification of proteins is involved in protein degradation, it is possible that sumoylation of ataxin-3 may regulate it.Re also modified by SUMOs, implying that SUMOylation of these disease-related proteins may participate in the regulation of their functions and thereby be associated with their pathogenic role. Tau, an Alzheimer’s disease associated protein, has been reported to be SUMOylated by SUMO-1, and to a much lesser extent by SUMO-2 or SUMO-3 simultaneously [36]. Many substrates were reported to be multi-SUMOylated by SUMO-1 on several residues, for example, ataxin-1 modified atSUMO-1 modification did not affect ataxin-3 ubiquitination or aggregate formation, but partially increased ataxin-3-68Q stabilityIt has been reported that SUMOylation alters the function or subcellular localization of some proteins, and the competitionThe Effect of SUMOylation on Ataxin-Figure 1. Identification of the SUMO-1 modification sites in ataxin-3. (A) HEK293 cells were used to co-express ataxin-3, ataxin-3K8R, ataxin3K166R, or ataxin-3K206R with SUMO-1. 10 lysates were precipitated by TCA and 25331948 subjected to immunoblotting. #ataxin-3 main bands, ## ataxin-3 relative levels of modified and unmodified (whole-cell CA precipitates). (B) The tagged proteins were enriched with NTA magnetic nickel columns and detected by immunoblotting with SUMO-1 antibody. **, ataxin-3-20Q modified by SUMO-1, ##, ataxin-3-68Q modified by SUMO-1. doi:10.1371/journal.pone.0054214.gleast on five and huntingtin on three lysine residues [26?7]. SCA3/MJD is the most common spinocerebellar ataxia diseases. In our previous research, we found that ataxin-3 was also a substrate of SUMO-1 [32]. In order to identify the motif residue, mutagenesis analyses were carried out to converse lysine 166 residues to arginine, which lies within a SUMO consensus sequence, VKGD, in ataxin-3. This conversion completely blocked the SUMOylation of ataxin-3. However, the conversion of other lysines, K8 and K206, which also lie within the SUMO consensus sequence in ataxin-3, did not affect SUMOylation of ataxin-3. These data suggest that K166 in ataxin-3 is the major SUMOylation binding site. Modification by SUMO has been shown to play critical roles in subcellular localization, and protein degradation, which ultimately contribute to regulation of the cell cycle, cell growth, and apoptosis [37]. In order to examine whether SUMOylation of ataxin-3 affects 10457188 its subcellular localization, we compared the localization of ataxin-3 in transiently transfected HEK293 cells. In agreementwith previous studies, we found that the wild-type ataxin-3 protein was diffusively distributed in both nucleus and cytoplasm, while mutant-type ataxin-3 protein formed aggregates in nucleus. However, when we compared ataxin-3 and its SUMOylation deficient variant, we could not detect any difference in the subcellular localization of ataxin-3 in both immunofluorescent staining and immunoblot analysis, which indicates SUMOylation of ataxin-3 does not change its subcellular distribution. The similar result was also observed in SCA7, that SUMOylation on K257 of ataxin-7 does not influence its subcellular localization [28]. As we know, abnormal accumulation of mutant ataxin-3 in affected neurons reflexes that mutant protein may not be properly degraded. We found the insoluble fraction of ataxin-3-68Q was more than that of ataxin-3-20Q, which supported that mutanttype ataxin-3 protein was stable and easy to form aggregates. As SUMO modification of proteins is involved in protein degradation, it is possible that sumoylation of ataxin-3 may regulate it.
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