Phosphoinositide signaling pathways in nuclei are associated with nuclear speckles containing pre-mRNA processing factors
Phosphoinositide signaling pathways in nuclei are associated with nuclear speckles containing pre-mRNA processing factors
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DOI：
10.1091/mbc.9.12.3547
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发表时间：
1998-12-01
影响因子：
3.3
通讯作者：
Anderson, RA
中科院分区：
文献类型：
--
作者：
Boronenkov, IV;Loijens, JC;Anderson, RA
细胞核中的磷酸肌醇信号转导途径使用与其胞质类似物难以区分的酶。我们证明，不同的磷脂酰肌醇磷酸激酶（PIPKs），I型和II型亚型，集中在哺乳动物细胞的细胞核。胞质和核PIPKs显示出对底物磷脂酰肌醇4-磷酸和磷脂酰肌醇S-磷酸的相当的活性。间接免疫荧光显示，这些激酶与不同的亚核结构域，确定为“核斑点”，其中还包含前mRNA加工因子。一个池的核磷脂酰肌醇二磷酸（PIP 2），这些激酶的产品，也检测到在这些相同的网站通过单克隆抗体染色。PIPKs和PIP 2在斑点上的定位是动态的，因为在mRNA转录受到抑制时，PIPKs和PIP 2都与其他斑点组分一起沿着重组。由于PIPKs在大多数磷脂酰肌醇第二信使的产生中起作用，这些发现表明磷脂酰肌醇信号通路定位于核斑点。令人惊讶的是，PIPK和PIP 2与核膜或任何核膜结构的内陷无关。假定在这些网站的膜的情况下，提出了新的机制，在这些结构内产生的磷酸肌醇。
Phosphoinositide signal transduction pathways in nuclei use enzymes that are indistinguishable from their cytosolic analogues. We demonstrate that distinct phosphatidylinositol phosphate kinases (PIPKs), the type I and type II isoforms, are concentrated in nuclei of mammalian cells. The cytosolic and nuclear PIPKs display comparable activities toward the substrates phosphatidylinositol 4-phosphate and phosphatidylinositol S-phosphate. Indirect immunofluorescence revealed that these kinases were associated with distinct subnuclear domains, identified as "nuclear speckles," which also contained pre-mRNA processing factors. A pool of nuclear phosphatidylinositol bisphosphate (PIP2), the product of these kinases, was also detected at these same sites by monoclonal antibody staining. The localization of PIPKs and PIP2 to speckles is dynamic in that both PIPKs and PIP2 reorganize along with other speckle components upon inhibition of mRNA transcription. Because PIPKs have roles in the production of most phosphatidylinositol second messengers, these findings demonstrate that phosphatidylinositol signaling pathways are localized at nuclear speckles. Surprisingly, the PIPKs and PIP2 are not associated with invaginations of the nuclear envelope or any nuclear membrane structure. The putative absence of membranes at these sites suggests novel mechanisms for the generation of phosphoinositides within these structures.