The nuclear mitotic apparatus protein NuMA controls rDNA transcription and mediates the nucleolar stress response in a p53-independent manner

Abstract

The nuclear mitotic apparatus protein, NuMA, is involved in major cellular events such as DNA damage response, apoptosis and p53-mediated growth-arrest, all of which are under the control of the nucleolus upon stress. Proteomic investigation has identified NuMA among hundreds of nucleolar proteins. Yet, the precise link between NuMA and nucleolar function remains undetermined. We confirm that NuMA is present in the nucleolus and reveal redistribution of NuMA upon actinomycin D or doxorubicin-induced nucleolar stress. NuMA coimmunoprecipitates with RNA polymerase I, with ribosomal proteins RPL26 and RPL24, and with components of B-WICH, an ATP-dependent chromatin remodeling complex associated with rDNA transcription. NuMA also binds to 18S and 28S rRNAs and localizes to rDNA promoter regions. Downregulation of NuMA expression triggers nucleolar stress, as shown by decreased nascent pre-rRNA synthesis, fibrillarin perinucleolar cap formation and upregulation of p27kip1, but not p53. Physiologically relevant nucleolar stress induction with reactive oxygen species reaffirms a p53-independent p27kip1 response pathway and leads to nascent pre-rRNA reduction. It also promotes the decrease in the amount of NuMA. This previously uncharacterized function of NuMA in rDNA transcription and p53-independent nucleolar stress response supports a central role for this nuclear structural protein in cellular homeostasis.

Diverse Regulators of Human Ribosome Biogenesis Discovered by Changes in Nucleolar Number

“…Additionally, although some studies have shown that both KAT5 and its yeast ortholog Esa1 function to downregulate rDNA transcription ( Koiwai et al, 2011 ; Clarke et al, 2006 ; Chang et al, 2012 ), our work provides evidence for the alternative hypothesis that KAT5 increases rDNA transcription ( Halkidou et al, 2004 ). Finally, a recent paper used different assays and experimental conditions to describe NUMA1 as an enhancer of rDNA transcription, contrary to the lack of effect on transcription reported here ( Jayaraman et al, 2017 ).…”

Deciphering MET‐dependent modulation of global cellular responses to DNA damage by quantitative phosphoproteomics

“…First, a few of the ATM‐dependent phosphorylations were upregulated by the prolonged MET inhibition combined with IR compared with IR alone, exemplified by NUMA1 S395 phosphorylation. NUMA1, such as ACIN1 and TP53BP1, is important in nuclear organization, and was shown to localize at several structures with key relevance to the DDR: NUMA1 localized with ATM at spindle poles during mitosis (Palazzo et al ., 2014), at DNA damage sites to facilitate repair (Vidi et al ., 2014), in the nucleolus to regulate rRNA transcription (Jayaraman et al ., 2017), and at camptothecin‐stalled replication forks (Ribeyre et al ., 2016). Furthermore, NUMA1 has also been demonstrated to have a role in apoptotic chromatin rearrangement in a caspase‐dependent manner (Dieker et al ., 2012).…”

The roles of nuclear focal adhesion kinase (FAK) on Cancer: a focused review

“…The nuclear mitotic apparatus protein (NuMA) is present in the nucleolus. NuMA can be involved in DNA damage as well as p53-mediated growth arrest and apoptosis [91]. Nuclear FAK binds to p53, reduce p53 levels and regulate the p53 signaling pathway in a kinase-independent manner.…”