Nuclear Protein Quality Is Regulated by the Ubiquitin-Proteasome System through the Activity of Ubc4 and San1 in Fission Yeast

Yuzy Matsuo,Hayafumi Kishimoto,Katsuhiro Tanae,Kenji Kitamura,Satoshi Katayama,Makoto Kawamukai

doi:10.1074/jbc.m110.169953

Yuzy Matsuo, Hayafumi Kishimoto + Show 4 more

Open Access

https://doi.org/10.1074/jbc.m110.169953

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Abstract

Eukaryotic cells monitor and maintain protein quality through a set of protein quality control (PQC) systems whose role is to minimize the harmful effects of the accumulation of aberrant proteins. Although these PQC systems have been extensively studied in the cytoplasm, nuclear PQC systems are not well understood. The present work shows the existence of a nuclear PQC system mediated by the ubiquitin-proteasome system in the fission yeast Schizosaccharomyces pombe. Asf1-30, a mutant form of the histone chaperone Asf1, was used as a model substrate for the study of the nuclear PQC. A temperature-sensitive Asf1-30 protein localized to the nucleus was selectively degraded by the ubiquitin-proteasome system. The Asf1-30 mutant protein was highly ubiquitinated at higher temperatures, and it remained stable in an mts2-1 mutant, which lacks proteasome activity. The E2 enzyme Ubc4 was identified among 11 candidate proteins as the ubiquitin-conjugating enzyme in this system, and San1 was selected among 100 candidates as the ubiquitin ligase (E3) targeting Asf1-30 for degradation. San1, but not other nuclear E3s, showed specificity for the mutant nuclear Asf1-30, but did not show activity against wild-type Asf1. These data clearly showed that the aberrant nuclear protein was degraded by a defined set of E1-E2-E3 enzymes through the ubiquitin-proteasome system. The data also show, for the first time, the presence of a nuclear PQC system in fission yeast.

Highlights

Triggering the covalent attachment of a polyubiquitin chain to the target protein
The present work only addresses the instability of Asf1-30, other nuclear located mutant proteins, such as Mis12537, Orc-H37, Cnp1-1, Pim1-46, and Sad1-1, have been reported to be unstable at high temperatures (40 – 44), suggesting that these proteins could be processed by the ubiquitin-proteasome system (UPS)
The results of the present study show that the selective degradation of nuclear aberrant proteins mediates nuclear protein quality control (PQC) in the fission yeast S. pombe

Summary

Introduction

Triggering the covalent attachment of a polyubiquitin chain to the target protein. Polyubiquitinated proteins are recognized and degraded by the 26 S proteasome. For example, the accumulation of aberrant proteins is thought to be associated with diseases such as Alzheimer, Huntington, Parkinson, and Creutzfeldt-Jakob diseases [5] The removal of these harmful proteins and the maintenance of homeostasis are accomplished through the selective degradation of aberrant or misfolded proteins by the UPS. The lack of activity of the autophagy-lysosome system in the nucleus [9] suggests that nuclear PQC depends entirely on the UPS. Supporting this hypothesis, studies demonstrated that the San E3 ligase, which shows specificity for nuclear aberrant proteins, plays a pivotal role in nuclear PQC in the budding yeast Saccharomyces cerevisiae [10, 11]. L972 PR110 UMP0 SKP561-15 SKP593-30 SKP593-33 SKP634-1 UMP1 UMP2 UMP3 UMP4 ⌬ubc2(1331) ts ubc ts ubc KSP1346 KSP1347 KSP1348 KSP1307 KSP1309 KSP1310 KSP1349 KSP1350 UMP5 UMP6 HY95 HYY184 UMP7 UMP8 UMP9 UMP10 UMP11 UMP12 UMP13 UMP14 UMP15 UMP16 UMP17 UMP18 UMP19 UMP20 UMP21 UMP22 UMP23 MY2354 Orc5-H37 MY566 MY3517 MY3285 UMP24 UMP25 UMP26 UMP27 UMP28 MY624 MY3236 MY3280 UMP29 UMP30

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