Abstract
The nucleolus is the site of ribosomal DNA (rDNA) transcription and ribosome production. In exploring the role of nucleolar protein MCRS1 (microspherule protein1)/MSP58 (58-kDa microspherule protein), we found that Mi-2beta, a component of a nucleosome remodeling and deacetylase (NuRD) complex, RET finger protein (RFP), and upstream binding factor (UBF) were associated with MCRS1. Yeast two-hybrid assays revealed that MCRS1 bound to the ATPase/helicase region of Mi-2beta and the coiled-coil region of RFP. Interestingly, confocal microscopic analyses revealed the co-localization of MCRS1, Mi-2beta, RFP, and the rRNA transcription factor UBF in the nucleoli. We also found that MCRS1, Mi-2beta, and RFP were associated with rDNA using a chromatin immunoprecipitation assay. Finally, we showed that MCRS1, Mi-2beta, and RFP up-regulated transcriptional activity of the rDNA promoter and that ribosomal RNA transcription was repressed when MCRS1, Mi-2beta, and RFP expression was reduced using siRNA. These results indicated that Mi-2beta and RFP, known to be involved in transcriptional repression in the nucleus, co-localize with MCRS1 in the nucleolus and appear to activate the rRNA transcription.
Highlights
With DNA methyltransferases, histone deacetylases, histone methyltransferases, and TTF-I [11,12,13,14]
Our results indicated that Mi-2, RET finger protein (RFP), and nucleolar protein MCRS1 were involved in ribosomal gene transcription and suggested that Mi-2 may be a candidate for the unidentified chromatin remodeling protein that establishes the euchromatin structure of ribosomal genes
In a survey of MCRS1-interacting proteins by immunoprecipitation of lysates from human embryo kidney (HEK) 293 cells transfected with FLAG-MCRS1 (Fig. 1A), we repeatedly identified a 220-kDa protein that co-precipitated with FLAG-MCRS1
Summary
With DNA methyltransferases, histone deacetylases, histone methyltransferases, and TTF-I (transcription terminator factor) [11,12,13,14]. NuRD complex and Mi-2 have been associated with the transcriptional repressive activities of KAP-1, RET finger protein (RFP), Trk (Tram-track69), and ROR␥ [21,22,23,24]. MTA-3, another component of the NuRD complex, was reported to repress Snail expression, and the estrogen-dependent transcriptional control of MTA3, Snail, and E-cadherin was associated with breast cancer progression [25]. Ribosomal Gene Regulation by MCRS1, Mi-2, and RFP repressive activity and that it was associated and co-localized with Enhancer of Polycomb 1 and Mi-2 in the nucleus [24, 32]. Binding and stabilization of MSP58 by transcription factor STRA13 has been observed [40] These findings suggest that MCRS1 may have several distinct functions, its transcriptional role in the nucleolus has not yet been fully characterized
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