Essential role of the 58-kDa microspherule protein in the modulation of Daxx-dependent transcriptional repression as revealed by nucleolar sequestration
Essential role of the 58-kDa microspherule protein in the modulation of Daxx-dependent transcriptional repression as revealed by nucleolar sequestration
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DOI：
10.1074/jbc.m200633200
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发表时间：
2002-07-12
影响因子：
4.8
通讯作者：
Shih, HM
中科院分区：
文献类型：
--
作者：
Lin, DY;Shih, HM
已报道Daxx介导细胞质中的Fas/JNK依赖性信号。然而，一些证据表明Daxx主要位于细胞核中，并作为转录调节因子发挥作用。最近的研究进一步表明，Daxx引起的转录抑制可以被核小体相关的早幼粒细胞白血病蛋白和凋亡信号调节激酶1通过将Daxx分别隔离到核小体和细胞质来抑制。在这里，我们进一步研究了Daxx功能通过蛋白质-蛋白质相互作用调节的协调分子机制。使用酵母双杂交筛选来鉴定Daxx相互作用蛋白，鉴定了编码58-kDa微球蛋白（MSP 58）片段的三个独立克隆。此外，我们已经证明，Daxx相互作用，在体外和体内与MSP 58通过其NH 2-末端片段，这是不同的Fas，凋亡信号调节激酶1，和早幼粒细胞白血病蛋白的结合区域，表明一个独特的调节作用的MSP 58 Daxx功能。瞬时转染实验表明，MSP 58以剂量依赖性方式在COS-1和293细胞中而不是在HeLa细胞中减轻Daxx的阻遏物活性，暗示MSP 58对Daxx功能的细胞类型特异性调节。此外，免疫荧光分析明确表明，MSP 58过表达的结果在易位的Daxx的扩大核仁COS-1或293细胞，而Daxx表现出弥漫性的核模式在HeLa细胞。总之，这些发现描绘了一个网络的调节信号通路，收敛于MSP 58/Daxx相互作用，因果关联Daxx核仁靶向与其转录激活功能。
Daxx has been reported to mediate the Fas/JNK-dependent signals in the cytoplasm. However, several lines of evidence have suggested that Daxx is located mainly in the nucleus and functions as a transcriptional regulator. Recent studies have further indicated that Daxx-elicited transcriptional repression can be inhibited by the nuclear body-associated promyelocytic leukemia protein and apoptosis signal-regulating kinase 1 by sequestering Daxx to the nuclear bodies and the cytoplasm, respectively. Here, we further investigated the coordinated molecular mechanism by which Daxx function is regulated through protein-protein interaction. Using yeast two-hybrid screens to identify Daxx-interacting protein(s), three independent clones encoding the 58-kDa microspherule protein (MSP58) fragments were identified. Furthermore, we have demonstrated that Daxx interacts in vitro and in vivo with MSP58 via its NH2-terminal segment, which is distinct from the binding region of Fas, apoptosis signal-regulating kinase 1, and promyelocytic leukemia protein, suggesting a unique modulatory role of MSP58 on Daxx function. Transient transfection experiments revealed that MSP58 relieves the repressor activity of Daxx in a dose-dependent manner in COS-1 and 293 cells but not in HeLa cells, implicating cell type-specific modulation of Daxx function by MSP58. Moreover, immunofluorescence analysis unequivocally demonstrated that MSP58 overexpression results in a translocation of Daxx to the enlarged nucleoli in COS-1 or 293 cells, whereas Daxx exhibited a diffuse nuclear pattern in HeLa cells. Taken together, these findings delineate a network of regulatory signaling pathways that converges on MSP58/Daxx interaction, causally associating Daxx nucleolus targeting with its transcriptional activation function.