5S Ribosomal RNA Is an Essential Component of a Nascent Ribosomal Precursor Complex that Regulates the Hdm2-p53 Checkpoint

Abstract

SUMMARY Recently, we demonstrated that RPL5 and RPL11 act in a mutually dependent manner to inhibit Hdm2 and stabilize p53 following impaired ribosome biogenesis. Given that RPL5 and RPL11 form a preribosomal complex with noncoding 5S ribosomal RNA (rRNA) and the three have been implicated in the p53 response, we reasoned they may be part of an Hdm2-inhibitory complex. Here, we show that small interfering RNAs directed against 5S rRNA have no effect on total or nascent levels of the noncoding rRNA, though they prevent the reported Hdm4 inhibition of p53. To achieve efficient inhibition of 5S rRNA synthesis, we targeted TFIIIA, a specific RNA polymerase III cofactor, which, like depletion of either RPL5 or RPL11, did not induce p53. Instead, 5S rRNA acts in a dependent manner with RPL5 and RPL11 to inhibit Hdm2 and stabilize p53. Moreover, depletion of any one of the three components abolished the binding of the other two to Hdm2, explaining their common dependence. Finally, we demonstrate that the RPL5/RPL11/5S rRNA preribosomal complex is redirected from assembly into nascent 60S ribosomes to Hdm2 inhibition as a consequence of impaired ribosome biogenesis. Thus, the activation of the Hdm2-inhibitory complex is not a passive but a regulated event, whose potential role in tumor suppression has been recently noted.

Sharing of mitotic pre-ribosomal particles between daughter cells

“…However, specific mechanisms might directly or indirectly inhibit specific steps of pre-rRNA processing. In particular, because 32S pre-rRNA processing depends on the presence of 5S rRNA (Dechampesme et al, 1999;Donati et al, 2013;Zhang et al, 2007), shutdown of 32S pre-rRNA processing might be linked to the regulation of Pol III transcription and/or any step involved in recruiting the RPL5-RPL11-5S rRNA precursor complex. In addition, as suggested by the presence of only 45S, 32S and 30S pre-rRNAs in mitotic cells (this study ;Carron et al, 2012;Dundr and Olson, 1998), inhibition operates in a targeted manner on these pre-rRNA processing steps and logically excludes most pre-rRNA processing factors (Tafforeau et al, 2013) as potential targets.…”

The NEDD8 inhibitor MLN4924 increases the size of the nucleolus and activates p53 through the ribosomal-Mdm2 pathway

“…Under these conditions, several RPs have been reported to block Mdm2 E3-ligase activity towards p53 through direct binding to Mdm2. In particular, for RPL11 and RPL5, a cooperation between the 2 RPs and 5S rRNA enhances Mdm2 inhibition under ribosomal stress conditions 26,27 . This causes p53 stabilisation, activation of the p53 response and cell cycle arrest 28, 29, 30 ,31 .…”

RNA polymerase III component Rpc9 regulates hematopoietic stem and progenitor cell maintenance in zebrafish

“…The major snRNAs transcribed by Pol III are implicated in protein synthesis. As a component of the large subunit of ribosomes, 5S rRNA binds the ribosome proteins RPL5 and RPL11 to initiate assembly of ribosome precursor complex (Donati et al, 2013). tRNAs, which are amino acid transporters indispensable for protein synthesis, are the other major transcripts of Pol III.…”