Abstract
Nucleolin is an RNA binding protein that is involved in many post-transcriptional regulation steps of messenger RNAs in addition to its nucleolar role in ribosomal RNA transcription and assembly in pre-ribosomes. Acetylated nucleolin was found to be associated with nuclear speckles and to co-localize with the splicing factor SC35. Previous nuclear pull down of nucleolin identified several splicing components and factors involved in RNA polymerase II transcription associated with nucleolin. In this report, we show that these splicing components are specifics of the pre-catalytic A and B spliceosomes, while proteins recruited in the Bact, C and P complexes are absent from the nucleolin interacting proteins. Furthermore, we show that acetylated nucleolin co-localized with P-SF3B1, a marker of co-transcriptional active spliceosomes. P-SF3B1 complexes can be pulled down with nucleolin specific antibodies. Interestingly, the alternative splicing of Fibronectin at the IIICS and EDB sites was affected by nucleolin depletion. These data are consistent with a model where nucleolin could be a factor bridging RNA polymerase II transcription and assembly of pre-catalytic spliceosome similarly to its function in the co-transcriptional maturation of pre-rRNA.
Highlights
Nucleolin (Ncl) is one of the most abundant protein of the nucleolus, and it has been implicated in many molecular and cellular processes, its functions remain poorly understood [1,2]
We have previously shown that Ncl could be acetylated (Ac-Ncl) on several lysines, which are present exclusively within the first 150 N-terminal residues of nucleolin [16]
To gain more insight into the potential implication of Ncl in spliceosome assembly/function, in this work, we studied the subcellular co-localization and interaction of acetylated nucleolin nucleolin (Ac-Ncl) with a component of catalytically activated/active spliceosome, P-SF3b155
Summary
Nucleolin (Ncl) is one of the most abundant protein of the nucleolus, and it has been implicated in many molecular and cellular processes, its functions remain poorly understood [1,2]. Ncl is remarkable due to the fact that it is present in many different cellular localization [1]. Historically, it was found as an abundant nucleolar protein (which gave it its name, Nucleolin) [7], it has been shown to be present in the nucleoplasm, cytoplasm and on the cell surface of many cell types. It is likely that for each of these cellular localizations, Ncl is associated with a specific set of proteins that give to Ncl a localization-dependent specific function
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