RESUMO
Ribosomal RNAs (rRNAs) act as scaffolds and ribozymes in ribosomes, and these functions are modulated by post-transcriptional modifications. However, the biological role of base methylation, a well-conserved modification of rRNA, is poorly understood. Here, we demonstrate that a nucleolar factor, nucleomethylin (NML; also known as RRP8), is required for the N(1)-methyladenosine (m(1)A) modification in 28S rRNAs of human and mouse cells. NML also contributes to 60S ribosomal subunit formation. Intriguingly, NML depletion increases 60S ribosomal protein L11 (RPL11) levels in the ribosome-free fraction and protein levels of p53 through an RPL11-MDM2 complex, which activates the p53 pathway. Consequently, the growth of NML-depleted cells is suppressed in a p53-dependent manner. These observations reveal a new biological function of rRNA base methylation, which links ribosomal subunit formation to p53-dependent inhibition of cell proliferation in mammalian cells.
Assuntos
Metiltransferases/metabolismo , Proteínas Nucleares/metabolismo , RNA Ribossômico/metabolismo , Proteína Supressora de Tumor p53/metabolismo , Animais , Sequência de Bases , Proliferação de Células , Técnicas de Silenciamento de Genes , Células HCT116 , Células HeLa , Humanos , Metilação , Camundongos Endogâmicos C57BL , Proteínas de Ligação a RNA , Proteínas Ribossômicas/metabolismo , Subunidades Ribossômicas Maiores de Eucariotos/metabolismoRESUMO
RNAs are post-transcriptionally modified in all kingdoms of life. Of these modifications, base methylations are highly conserved in eukaryote ribosomal RNA (rRNA). Recently, rRNA processing protein 8 (Rrp8) and nucleomethylin (NML) were identified as factors of N1-methyladenosine (m1A) modification in yeast 25 S and mammalian 28 S rRNA, respectively. However, m1A modification of rRNA is still poorly understood in Caenorhabditis elegans (C. elegans). Here, using the liquid chromatography/tandem mass spectrometry analysis and RNA immunoprecipitation assay, we have identified that the m1A modification is located around position 674 (A674) of 26 S rRNA in C. elegans. Furthermore, quantitative PCR-based analysis revealed that T07A9.8, a C. elegans homolog of yeast Rrp8 and human NML, is responsible for m1A modification at A674 of 26 S rRNA. This m1A modification site in C. elegans corresponds to those in yeast 25 S rRNA and human 28 S rRNA. Intriguingly, T07A9.8 is not associated with pre-rRNA transcription under normal nutrient conditions. Since the m1A modification of 26 S rRNA requires T07A9.8 in C. elegans, we designated the gene as rRNA adenine methyltransferase-1 (rram-1).