Abstract 835: hRrp15, a ribosome RNA processing protein, has profound function on nucleoli construction, ribosome biogenesis and cell proliferation.

Abstract

Abstract Nucleolus is the sub-organelle that controls ribosome biogenesis in cells, and ribosome biogenesis is a highly regulated process that ensures cell growth (increase in biomass) coordinated with cell proliferation. In the nucleolus, ribosomal RNA precursor (47S rRNA) is initially transcribed from rDNA and then subsequently processes into 5.8S, 18S and 28S rRNAs, together with numerous ribosome proteins and nonribosomal factors, to form 60S and 40S pre-ribosomal particles before they are exported to the cytoplasm. A large body of evidence demonstrates that perturbation of rRNA synthesis, process and/or pre-ribosomal factor function impairs ribosome biogenesis and induces cell cycle arrest. This is attributed to nucleolar disruption and diffusion of ribosomal proteins, such as Rpl11 and Rpl5, into the nucleoplasm in which these ribosomal proteins bind to and inhibit MDM2 function, resulting in p53 induction and activation. In this study, we described the identification and characterization of a human protein, hRrp15, that has sequence homology with yeast pre-ribosomal factor, Rrp15p. Previous studies showed that Rrp15p is a ribosome RNA processing protein required for 60S pre-ribosomal particle formation and/or maturation in yeast. Using immunofluorescence and sucrose gradient centrifugation analyses, we demonstrated that hRrp15 was mainly localized at nucleoli in human cells. Depletion of hRrp15 expression disrupted nucleolar structure, inducing diffusion of nucleolar protein, nucleolin, in the nucleus. In contrast to Rrp15p, hRrp15 mainly associated with 60S pre-ribosomal particle but it also presented in 40S pre-ribosomal particle. Consistently, inhibition of hRrp15 expression perturbed nucleolar formation and impaired ribosomal biogenesis in both 60S and 40S pre-ribosomal subunits. In addition, depletion of hRrp15 in human non-transformed cells, RPE1, resulted in the induction of p53 and p21 proteins and cell cycle arrest at G1-G1/S whereas depletion of hRrp15 in human tumor cells, HeLa and MCF7, caused DNA damage response with detectable γ-H2AX and apoptosis. These results indicated that hRrp15 plays a critical role in regulating formation of both 60S and 40S pre-ribosomal particles, ribosome biogenesis, construction of nucleoli, cell growth and cell proliferation in human cells. Hence, hRrp15 may serve as a potential target for cancer therapy. Citation Format: Zhixiong Dong, Changjun Zhu, Wei Jiang. hRrp15, a ribosome RNA processing protein, has profound function on nucleoli construction, ribosome biogenesis and cell proliferation. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 835. doi:10.1158/1538-7445.AM2013-835