P54nrb Forms a Heterodimer with PSP1 That Localizes to Paraspeckles in an RNA-dependent Manner

Division of Gene Regulation and Expression, Wellcome Trust Biocentre, University of Dundee, Dundee DD1 5EH, United Kingdom.
Molecular Biology of the Cell (Impact Factor: 4.55). 12/2005; 16(11):5304-15. DOI: 10.1091/mbc.E05-06-0587
Source: PubMed

ABSTRACT P54nrb is a protein implicated in multiple nuclear processes whose specific functions may correlate with its presence at different nuclear locations. Here we characterize paraspeckles, a subnuclear domain containing p54nrb and other RNA-binding proteins including PSP1, a protein with sequence similarity to p54nrb that acts as a marker for paraspeckles. We show that PSP1 interacts in vivo with a subset of the total cellular pool of p54nrb. We map the domain within PSP1 that is mediating this interaction and show it is required for the correct localization of PSP1 to paraspeckles. This interaction is necessary but not sufficient for paraspeckle targeting by PSP1, which also requires an RRM capable of RNA binding. Blocking the reinitiation of RNA Pol II transcription at the end of mitosis with DRB prevents paraspeckle formation, which recommences after removal of DRB, indicating that paraspeckle formation is dependent on RNA Polymerase II transcription. Thus paraspeckles are the sites where a subset of the total cellular pool of p54nrb is targeted in a RNA Polymerase II-dependent manner.

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Available from: Charles S Bond, Aug 24, 2015
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    • "In addition, a number of proteins were identified that were unique to this study including paraspeckle protein 1 (PSPC1), symplekin, FIP1, and nucleophosmin. PSPC1 is a component of a novel subnuclear compartment named paraspeckle and was previously shown to interact with NONO via its coiled-coil domain (Fox et al. 2005). PSPC1 and SFPQ and have also been shown to be coexpressed and interact with Sertoli cells (Kuwahara et al. 2006). "
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    • "However, drug treatment and fluorescence loss in photobleaching (FLIP) experiments confirmed that this protein interacted dynamically with the nucleoplasm and nucleolus in a transcriptional-dependent manner (Fox et al., 2005). To fully confirm the presence of a protein in the nucleolus, therefore, it is therefore necessary to take this into consideration and perform FLIP experiments on the transfected cells. "
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    • "Individual paraspeckles begin to form in early G1 phase until approximately 1 hour after RNA transcription is initiated (Fox et al. 2005). Importantly, blocking the initiation of RNA polymerase II transcription by the inhibitor DRB at the end of mitosis prevents formation of paraspeckles, suggesting that these structures are dependent on ongoing transcription (Fox et al. 2005; Clemson et al. 2009). The earliest paraspeckles are often positioned next to the NEAT1 gene locus and an increase in NEAT1 expression by ectopic plasmids leads to a corresponding increase in the number of paraspeckles, which is essentially unchanged upon PSP1 overexpression (Clemson et al. 2009). "
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