Interaction of nucleolin with ribosomal RNA genes and its role in RNA polymerase I transcription

Abstract

Nucleolin is a multi-functional nucleolar protein that is required for ribosomal RNA gene (rRNA) transcription in vivo, but the mechanism by which nucleolin modulates RNA polymerase I (RNAPI) transcription is not well understood. Nucleolin depletion results in an increase in the heterochromatin mark H3K9me2 and a decrease in H4K12Ac and H3K4me3 euchromatin histone marks in rRNA genes. ChIP-seq experiments identified an enrichment of nucleolin in the ribosomal DNA (rDNA) coding and promoter region. Nucleolin is preferentially associated with unmethylated rRNA genes and its depletion leads to the accumulation of RNAPI at the beginning of the transcription unit and a decrease in UBF along the coding and promoter regions. Nucleolin is able to affect the binding of transcription termination factor-1 on the promoter-proximal terminator T0, thus inhibiting the recruitment of TIP5 and HDAC1 and the establishment of a repressive heterochromatin state. These results reveal the importance of nucleolin for the maintenance of the euchromatin state and transcription elongation of rDNA.

Nucleolin and nucleophosmin: nucleolar proteins with multiple functions in DNA repair

“…NCL has been reported to support the eviction of H2A-H2B dimers from histone octamers, an important process for DNA transcription, replication and repair (Angelov et al 2006;Kobayashi et al D r a f t 2012). NCL can also act on the variant histone macro-H2A1, which is loaded onto transcriptionally silent rDNA repeats (Angelov et al 2006;Cong et al 2012). NCL has also been reported to possess protease activity responsible for phosphorylation-sensitive autoproteolysis under certain conditions (Chen et al 1991;Fang and Yeh 1993;Warrener and Petryshyn 1991), though others have attributed this proteolysis to other cellular proteases (Hsu et al 2015;Pasternack et al 1991).…”

“…NCL binds directly to rDNA in vivo and is required for the loading of general transcription factors (TFs) and, ultimately, progression of RNA Pol I along the gene (Cong et al 2012;Rickards et al 2007). In this context, NCL contributes extensively to the remodeling of rDNA chromatin in vivo, likely through its roles as a H2A-H2B and/or macro-H2A1 histone chaperone (Durut and SaezVasquez 2015;Cong et al 2012).…”

“…NCL binds directly to rDNA in vivo and is required for the loading of general transcription factors (TFs) and, ultimately, progression of RNA Pol I along the gene (Cong et al 2012;Rickards et al 2007). In this context, NCL contributes extensively to the remodeling of rDNA chromatin in vivo, likely through its roles as a H2A-H2B and/or macro-H2A1 histone chaperone (Durut and SaezVasquez 2015;Cong et al 2012). Independently, NCL binds directly to nascent 47S pre-rRNA transcripts at a cis motif in the 5' Externally Transcribed Spacer (5'ETS), where it cooperates with other trans-acting factors, in particular the U3 snoRNP, to promote the first endonucleolytic cleavage of the 47S pre-rRNA (Ginisty et al 2000;Turner et al 2009).…”

“…The histone chaperone activities of NCL and NPM1 have been known for at least 10 years (Angelov et al 2006;Okuwaki et al 2001), as have their ability to regulate activity on Pol II-transcribed loci (Angelov et al 2006). However, the widespread importance of these activities are only now becoming clear with the observations of their contribution to diverse processes including rDNA repeat silencing (Cong et al 2012), centrosome stability (Foltz et al 2009) and, most recently, chromatin remodeling during HR and/or NHEJ (Goldstein et al 2013;Kobayashi et al 2012). These observations suggest that histone chaperoning may be a common mechanism to many of NPM1 and NCL's functions;…”

Centrosomal nucleolin is required for microtubule network organization

“…WB 1/1000), 29 a rabbit polyclonal antibody raised against 3 peptides of human nucleolin (Covalab, pab0971-P / dil. WB 1/1000), 59,60 or a rabbit polyclonal antibody raised against the first hundred amino acids of human nucleolin (Abcam ab#22758 / dil. IF 1/300).…”