The roles of RRP15 in nucleolar formation, ribosome biogenesis and checkpoint control in human cells

Abstract

The nucleolus controls ribosome biogenesis and its perturbation induces nucleolar stress that inhibits cell cycle progression and activates checkpoint responses. Here, we investigate the roles of ribosomal RNA processing protein, RRP15, in nucleolar formation, ribosome biogenesis, cell cycle progression and checkpoint control in human cells. RRP15 is localized in the nucleolus and required for nucleolar formation. In contrast to the budding yeast Rrp15p that was reported as a component of pre-60S subunits, RRP15 is found in both pre-40S and pre-60S subunits and involved in regulating rRNA transcription and ribosome biogenesis. Perturbation of RRP15 induces nucleolar stress that activates RPL5/RPL11/5S rRNA (RP)-Mdm2-p53 axis checkpoint response and arrests cells at G1-G1/S in p53-proficient non-transformed RPE1 cells but not in p53-deficient HeLa and MCF7 tumor cells. Instead, p53-deficient HeLa and MCF7 cells with RRP15-dependent nucleolar stress enter S-phase with S-phase perturbation that activates ATR-Chk1- γH2AX axis DNA replication/damage checkpoint response, delaying S-G2/M progression and, ultimately, causing cell death. The selective checkpoint response, cell cycle inhibition and/or cytotoxicity induced by RRP15-dependent nucleolar stress in p53-proficient non-transformed cells and p53-deficient tumor cells suggest that RRP15 might be a potential target for cancer therapy.

Mapping the nucleolar proteome reveals a spatiotemporal organization related to intrinsic protein disorder

“…A study shows that RRP15 is central for rRNA transcription and biogenesis. The authors further present evidence of it being a checkpoint protein as perturbations of RRP15 induce nucleolar stress triggering cell cycle arrest (Dong et al, 2017). Among the other highly disordered proteins is the uncharacterized protein PRR19, where we show experimental data for it being nucleolar in interphase and localized to the chromosomes during mitosis (Fig.…”

New Roles for the Nucleolus in Health and Disease

“…Other nucleolar proteins, including ARF, NS, and NPM1, also use a similar mechanism of modulating p53 abundance . As an additional layer of complexity, when perturbed, nucleolar proteins such as the rRNA processing protein RRP15, which is required for pre‐40S/SSU and pre‐60S/LSU ribosomal subunit formation and rDNA transcription, can promote 5SRNP excess which then outcompetes p53 for its interaction with MDM2 …”

Genomic analysis of small nucleolar RNAs identifies distinct molecular and prognostic signature in hepatocellular carcinoma

“…Indeed, snoRNAs often combine with ribonucleoproteins (RNPs) to form stable and functional snoRNP particles, which is necessary for the effective and accurate formation of ribosomes (22). Ribosomes are considered to be the processing plants for protein synthesis in cells, but in tumor cells, this molecular machinery is misaligned and cellular metabolism is deregulated (23). Upregulated cell proliferation is usually accompanied by changes in the ribosome production rate.…”