Regulated nucleo-cytoplasmic shuttling of human aci-reductone dioxygenase (hADI1) and its potential role in mRNA processing
Regulated nucleo-cytoplasmic shuttling of human aci-reductone dioxygenase (hADI1) and its potential role in mRNA processing
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DOI：
10.1111/j.1365-2443.2006.01035.x
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发表时间：
2007-01-01
期刊：
影响因子：
2.1
通讯作者：
Seiki, Motoharu
中科院分区：
文献类型：
--
作者：
Gotoh, Isamu;Uekita, Takamasa;Seiki, Motoharu
细菌酸性还原酮双加氧酶（ARD）是cupin超家族的成员，具有进化上原始的蛋白质折叠和蛋氨酸循环途径中的功能。最近，已经鉴定了人ARD直向同源物（人ADI 1，hADI 1），其表现出除ARD活性之外的功能。hADI 1主要定位于细胞质，但相当大的一部分是核，这表明在两个细胞隔室的功能。在这项研究中，我们报告说，核质转运的hADI 1的非经典核输出信号（内斯）位于N-末端区域的hADI 1的调节。内斯由多个碱性氨基酸残基组成，而不是典型的富含亮氨酸的序列。hADI 1的核输出不受CRM 1介导，CRM 1是一种与富含亮氨酸的内斯结合的主要转运蛋白。用丙氨酸取代碱性残基可消除内斯活性。突变体hADI 1聚集在细胞核中，并形成斑点，经常与剪接因子和一些转录因子一起观察。事实上，hADI 1特异性地与剪接因子U1- 70 K共定位于细胞核，但不与另一个剪接因子SC 35共定位。U1- 70 K过表达诱导hADI 1的核积聚。细胞核hADI 1表达显着改变了腺病毒E1 A迷你基因的剪接模式，从而产生多种选择性剪接转录本。因此，hADI 1可能通过调节U1- 70 K相关功能（一种受非经典内斯序列负调控的活性）在核mRNA加工中发挥新作用。
Bacterial aci-reductone dioxygenase (ARD), a member of the cupin superfamily, has evolutionarily primitive protein folding and functions in the methionine recycling pathway. Recently, a human ARD orthologue (human ADI1, hADI1) has been identified and exhibits functions other than ARD activity. The hADI1 localizes mainly to the cytoplasm, but a substantial fraction is nuclear, suggesting functions in both cellular compartments. In this study, we report that nucleo-cytoplasmic transport of hADI1 is regulated by a non-canonical nuclear export signal (NES) located in the N-terminal region of hADI1. The NES is composed of multiple basic amino-acid residues instead of the canonical leucine-rich sequence. Nuclear export of hADI1 was not mediated by CRM1, a major transporter that binds to leucine-rich NES. Substitution of the basic residues with alanines abolished NES activity. Mutant hADI1 accumulated in the nucleus and formed speckles frequently observed with splicing factors and some transcription factors. Indeed, hADI1 specifically co-localized with the splicing factor U1-70K to the nucleus but not with another splicing factor, SC35. U1-70K over-expression induced nuclear accumulation of hADI1. Nuclear hADI1 expression significantly altered the splicing pattern of the adenovirus E1A mini-gene, which generates multiple alternatively spliced transcripts. Thus, hADI1 may have acquired a novel role in nuclear mRNA processing possibly by modulating U1-70K-related functions, an activity negatively regulated by a non-classical NES sequence.