Regulation of Karyopherin α1 and Nuclear Import by Mammalian Target of Rapamycin
Regulation of Karyopherin α1 and Nuclear Import by Mammalian Target of Rapamycin
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DOI：
10.1074/jbc.m111.246785
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发表时间：
2012-04-27
影响因子：
4.8
通讯作者：
Kristof, Arnold S.
中科院分区：
文献类型：
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作者：
Fielhaber, Jill A.;Tan, Jason;Kristof, Arnold S.
在丝裂原或营养底物水平降低的条件下，雷帕霉素的丝氨酸/苏氨酸激酶靶标可以增加不同转录因子的核含量，促进胁迫反应基因的诱导。转录因子STAT1以其潜伏的(即非磷酸化的)形式，调节与免疫调节和细胞凋亡有关的基因的子集。在以往研究表明哺乳动物靶标雷帕霉素(MTOR)与潜伏的STAT1核含量之间存在功能关系的基础上，我们研究了mTOR控制STAT1核输入的机制。在荧光共聚焦显微镜下，雷帕霉素灭活mTOR可促进未磷酸化的STAT1的核转位，但不能促进不能与其核输入接头核粘附素-α1(KPNA1)结合的STAT1突变体的核转位。通过免疫沉淀，KPNA1与mTOR和STAT1在物理上结合在一个复合体中，该复合体对雷帕霉素做出反应而移位到细胞核。虽然mTOR不是KPNA1的一种激酶，但mTOR相关的磷酸酶蛋白磷酸酶2A催化直接与KPNA1相互作用，并调节mTOR-KPNA1复合体的核输入。KPNA1或其与STAT1的相互作用是潜在的STAT1的核输入、STAT1基因的转录诱导以及在mTOR活性降低的条件下(如雷帕霉素、葡萄糖饥饿、血清停用)激活caspase-3所必需的。因此，在低有丝分裂原或营养水平下，mTOR和蛋白磷酸酶2A通过KPNA1催化控制潜伏的STAT1的结构性核输入，而KPNA1是STAT1表达和凋亡的关键调控因子。
Under conditions of reduced mitogen or nutritional substrate levels, the serine/threonine kinase target of rapamycin can augment the nuclear content of distinct transcription factors and promote the induction of stress response genes. In its latent (i.e., unphosphorylated) form, the transcription factor STAT1 regulates a subset of genes involved in immune modulation and apoptosis. Based on previous work indicating a functional relationship between mammalian target of rapamycin (mTOR) and the nuclear content of latent STAT1, we investigated the mechanism by which mTOR controls STAT1 nuclear import. By fluorescence confocal microscopy, inactivation of mTOR with rapamycin promoted the nuclear translocation of unphosphorylated STAT1, but not that of a STAT1 mutant incapable of binding its nuclear import adaptor karyopherin-alpha 1 (KPNA1). By immunoprecipitation, KPNA1 was physically associated with mTOR and STAT1 in a complex that translocated to the nucleus in response to rapamycin. Although mTOR is not a kinase for KPNA1, the mTOR-associated phosphatase protein phosphatase 2A catalytic interacted directly with KPNA1 and regulated nuclear import of the mTOR-KPNA1 complex. KPNA1, or its interaction with STAT1, was required for the nuclear import of latent STAT1, transcriptional induction of the STAT1 gene, and caspase-3 activation under conditions of reduced mTOR activity (i.e. rapamycin, glucose starvation, serum withdrawal). Therefore, at low mitogen or nutrient levels, mTOR and protein phosphatase 2A catalytically control the constitutive nuclear import of latent STAT1 by KPNA1, which are key modulators of STAT1 expression and apoptosis.