Role of cytosine-5 methylation of ribosomal RNA in cell cycle control

Abstract

5-methylcytosine (m5C) is a widespread modification in DNA and RNA. However, while the functions of m5C in DNA have been extensively studied, its role in RNA is emerging to be elucidated (1)we focus on the occurrence of 5-methylcytosine (m5C deposition is found mainly in transfer RNA (tRNA) and ribosomal RNA (rRNA) and is mediated by DNMT2 and NSUN family members (1–4). Recently it has been shown that m5C on tRNAs regulates stem cell functions and stress responses in normal epidermis and skin cancer (5–7), and its inhibition specifically eliminates cancer initiating cells (5), suggesting that RNA-methylation may regulate essential cellular and physiological processes and its dysregulation may lead to critical pathological consequences such as cancer. By analysing cancer expression databases we have found that the cytosine-5 methylase NSUN5 is overexpressed in advanced metastatic prostate cancer (PCa), one of the most frequent form of cancer Worldwide in men. In vitro analysis using NSUN5-silenced cell lines showed that NSUN5 depletion leads to impaired proliferation and migration capacity. Flow cytometry analysis showed that NSUN5 silencing results in decreased cell size and arrest in G2/M phase, suggesting an impairment in cell cycle progression through G2/M phase transition. We find that NSUN5 expression fluctuates along the cell cycle, further confirming its role in regulating this process. NSUN5 is a rRNA m5C methyltransferase that methylates position C3872, located at the interphase of the small and large ribosome subunits. Whether rRNA m5C methylation is regulated along the cell cycle and whether m5C deposition at rRNA regulates protein translation in G2/M and migration capacity needs to be determined.