The Importin-Alpha/Nucleophosmin Switch Controls Taspase1 Protease Function
The Importin-Alpha/Nucleophosmin Switch Controls Taspase1 Protease Function
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DOI：
10.1111/j.1600-0854.2011.01191.x
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发表时间：
2011-06-01
期刊：
影响因子：
4.5
通讯作者：
Stauber, Roland H.
中科院分区：
文献类型：
--
作者：
Bier, Carolin;Knauer, Shirley K.;Stauber, Roland H.
Taspase1是一种苏氨酸蛋白酶，被怀疑处理(病理)生物学上相关的核底物和细胞质底物，如混合血统白血病蛋白。然而，调控Taspase1‘S在细胞内定位的机制及其功能后果尚不清楚。对内源性和异位表达的Taspase1进行分析，发现其主要分布在细胞核中，聚集在核仁中。显微注射和异位表达研究证实了与Importin-α相互作用的进化保守的二分体核输入信号(NLS)(氨基酸197KRKRKLELA ERVDTDFMQLKRR220)。值得注意的是，NLS突变、进口缺陷的Taspase1在生物学上是不活跃的。尽管NLS已经提供了酶原的核转运，但Taspase1的S核仁定位需要它的自我蛋白分解过程，触发它与核仁穿梭蛋白核磷蛋白的相互作用。相反，(自动)催化失活的Taspase1突变体既不积累在核仁上，也不结合核磷蛋白。研究发现，活跃的核进口和与核磷蛋白的相互作用是形成具有蛋白分解活性的Taspase1所必需的，以确保有效地处理其核靶标。有趣的是，共表达的病理性核磷脂变异体增加了细胞质Taspase1的数量。因此，Taspase1似乎利用核磷蛋白的核出口活性来获得瞬时进入细胞质的途径，该细胞质也需要裂解其细胞质底物。总而言之，我们在这里描述了一种迄今未知的调节这种蛋白酶的生物活性的机制。
Taspase1 is a threonine protease suspected to process (patho)biologically relevant nuclear and cytoplasmic substrates, such as the mixed lineage leukemia protein. However, neither the mechanisms regulating Taspase1's intracellular localization nor their functional consequences are known. Analysis of endogenous and ectopically expressed Taspase1 detected the protease predominantly in the nucleus accumulating at the nucleolus. Microinjection and ectopic expression studies identified an evolutionarily conserved bipartite nuclear import signal (NLS) (amino acids 197KRNKRKLELA ERVDTDFMQLKKRR220) interacting with importin-alpha. Notably, an NLS-mutated, import-deficient Taspase1 was biologically inactive. Although the NLS conferred nuclear transport already of the proenzyme, Taspase1's nucleolar localization required its autoproteolytic processing, triggering its interaction with the nucleolar shuttle protein nucleophosmin. In contrast, (auto)catalytically inactive Taspase1 mutants neither accumulated at the nucleolus nor bound nucleophosmin. Active nuclear import and interaction with nucleophosmin was found to be required for the formation of proteolytically active Taspase1 ensuring to efficiently process its nuclear targets. Intriguingly, coexpression of pathological nucleophosmin variants increased the amount of cytoplasmic Taspase1. Hence, Taspase1 appears to exploit the nuclear export activity of nucleophosmin to gain transient access to the cytoplasm required to also cleave its cytoplasmic substrates. Collectively, we here describe a hitherto unknown mechanism regulating the biological activity of this protease.