Project description:How the relatively evolutionarily conserved spliceosome is able to manage the enormously expanded number of splicing events that occur in humans (~200,000 vs. ~400 reported for yeast) is not well understood. Here, we show deposition of one RNA modification-N2-methylguanosine (m2G)-on the G72 nucleoside of U6 snRNA (known to function as the catalytic center of the spliceosome) results in profoundly increased pre-mRNA splicing activity in human cells. This U6 m2G72 modification is conserved among vertebrates. Further, we demonstrate that THUMPD2 is the methyltransferase responsible for U6 m2G72 and show that it interacts with an auxiliary protein (TRMT112) to specifically recognize both sequence and structural elements of U6. THUMPD2 KO blocks U6 m2G72 and down-regulates the pre-mRNA splicing activity of major spliceosome, yielding thousands of changed alternative splicing events of endogenous pre-mRNAs. Notably, the aberrantly spliced pre-mRNA population of the THUMPD2 KO cells elicits the nonsense-mediated mRNA decay (NMD) pathway and restricts cell proliferation. We also show that THUMPD2-mediated control of the U6 m2G72 modification is associated with age-related macular degeneration and retinal function. Our study thus demonstrates how an RNA epigenetic modification of the major spliceosome differentially regulates global mRNA splicing and impacts physiology and disease.
Project description:Maintenance of the intracellular levels of the methyl donor S-adenosylmethionine (SAM) is essential for a wide variety of biological processes. We demonstrate that the N6-adenosine methyltransferase METTL16 regulates expression of MAT2A, which encodes the only SAM synthetase expressed in most cells. Upon SAM depletion by methionine starvation, cells induce MAT2A expression by enhanced splicing of a retained intron. Induction requires METTL16 and its methylation substrate, a vertebrate conserved hairpin (hp1) in the MAT2A 3´ UTR. Increasing METTL16 occupancy on the MAT2A 3´ UTR is sufficient to induce efficient splicing. We propose that under SAM-limiting conditions, METTL16 occupancy on hp1 increases due to inefficient enzymatic turnover, which in turn promotes MAT2A splicing. Interestingly, human and S. pombe METTL16 methylate the U6 spliceosomal snRNA at a sequence identical to hp1. These observations suggest that the conserved U6 snRNA methyltransferase evolved an additional function in vertebrates to regulate SAM homeostasis.
Project description:Modified nucleotides in non-coding RNAs, such as tRNAs and snRNAs, represent an important layer of gene expression regulation through their ability to fine-tune mRNA maturation and translation. Dysregulation of such modifications and the enzymes installing them have been linked to various human pathologies including neurodevelopmental disorders and cancers. Several methyltransferases (MTases) are regulated allosterically by human TRMT112 (Trm112 in Saccharomyces cerevisiae), but the interactome of this regulator and targets of its interacting MTases remain incompletely characterized. Here, we have investigated the interaction network of human TRMT112 in intact cells and identify three poorly characterized putative MTases (TRMT11, THUMPD3 and THUMPD2) as direct partners. We demonstrate that these three proteins are active N2-methylguanosine (m2G) MTases and that TRMT11 and THUMPD3 methylate positions 10 and 6 of tRNAs, respectively. For THUMPD2, we discovered that it directly associates with the U6 snRNA, a core component of the catalytic spliceosome, and is required for the formation of m2G, the last “orphan” modification in U6 snRNA. Furthermore, our data reveal the combined importance of TRMT11 and THUMPD3 for optimal protein synthesis and cell proliferation as well as a role for THUMPD2 in fine-tuning pre-mRNA splicing.
Project description:Mpn1 proteins are evolutionarily conserved exonucleases that modify spliceosomal U6 small nuclear RNAs (snRNAs) post-transcriptionally. Mutations in the human MPN1 gene are associated to the genodermatosis Clericuzio-type poikiloderma with neutropenia (PN). Mpn1 deficiency leads to aberrant U6 3M-bM-^@M-^Y end processing and accelerated U6 decay through unknown molecular mechanisms. Here we show that in mpn1M-NM-^T fission yeast cells U6 is barely bound by the protective Lsm2-8 complex, undergoes extensive oligoadenylation and is degraded by the nuclear RNA exonuclease Rrp6 independently of the poly(A) polymerase Cid14/Trf4. Mpn1 processes U6 in a spliceosome-dependent manner, as mutant U6 molecules that fail to join the spliceosome are not substrates for Mpn1. Moreover, human U6atac, the U6-like snRNA of the minor spliceosome, is a novel substrate for hMpn1. We unveil mechanistic details of a new U6 degradation pathway and further corroborate the notion that inefficient canonical and minor pre-mRNA splicing promotes PN. the 3' termini of U6 or tagged-U6 species from the indicated mutant cells were compared to wt yeast strain
Project description:Mpn1 proteins are evolutionarily conserved exonucleases that modify spliceosomal U6 small nuclear RNAs (snRNAs) post-transcriptionally. Mutations in the human MPN1 gene are associated to the genodermatosis Clericuzio-type poikiloderma with neutropenia (PN). Mpn1 deficiency leads to aberrant U6 3’ end processing and accelerated U6 decay through unknown molecular mechanisms. Here we show that in mpn1Δ fission yeast cells U6 is barely bound by the protective Lsm2-8 complex, undergoes extensive oligoadenylation and is degraded by the nuclear RNA exonuclease Rrp6 independently of the poly(A) polymerase Cid14/Trf4. Mpn1 processes U6 in a spliceosome-dependent manner, as mutant U6 molecules that fail to join the spliceosome are not substrates for Mpn1. Moreover, human U6atac, the U6-like snRNA of the minor spliceosome, is a novel substrate for hMpn1. We unveil mechanistic details of a new U6 degradation pathway and further corroborate the notion that inefficient canonical and minor pre-mRNA splicing promotes PN.
Project description:miRNAs are regulatory transcripts established as repressors of mRNA stability and translation. Here we demonstrate that an oncomiR-10b binds to U6 snRNA, a core component of the spliceosomal machinery. We provide evidence of direct binding between miR-10b and U6, in situ visualizations of miR-10b and U6 co-localization in glioma cells and tumor tissues, and biochemical co-isolation of miR-10b with the components of the spliceosome. We further demonstrate that miR-10b modulates U6 N-6-adenosine methylation and pseudouridylation, U6 binding to splicing factors SART3 and PRPF8, and regulates U6 stability, conformation, and levels. The effects on U6 result in splicing alterations, illustrated by the altered ratio of the isoforms of a small GTPase CDC42, reduced overall CDC42 levels, and downstream CDC42 -mediated effects on cell viability. We, therefore, present an unexpected intersection of the miRNA and splicing machineries and a new nuclear function for a cancer-associated miRNA.
Project description:miRNAs are regulatory transcripts established as repressors of mRNA stability and translation. Here we demonstrate that an oncomiR-10b binds to U6 snRNA, a core component of the spliceosomal machinery. We provide evidence of direct binding between miR-10b and U6, in situ visualizations of miR-10b and U6 co-localization in glioma cells and tumor tissues, and biochemical co-isolation of miR-10b with the components of the spliceosome. We further demonstrate that miR-10b modulates U6 N-6-adenosine methylation and pseudouridylation, U6 binding to splicing factors SART3 and PRPF8, and regulates U6 stability, conformation, and levels. The effects on U6 result in splicing alterations, illustrated by the altered ratio of the isoforms of a small GTPase CDC42, reduced overall CDC42 levels, and downstream CDC42 -mediated effects on cell viability. We, therefore, present an unexpected intersection of the miRNA and splicing machineries and a new nuclear function for a cancer-associated miRNA.
Project description:Modified nucleotides in non-coding RNAs, such as tRNAs and snRNAs, represent an important layer of gene expression regulation through their ability to fine-tune mRNA maturation and transla-tion. Growing evidences support important roles of tRNA/snRNAs modifications and hence the enzymes that install them, in eukaryotic cell development and their dysregulation has been linked to various human pathologies including neurodevelopmental disorders and cancers. Human TRMT112 (Trm112 in Saccharomyces cerevisiae) functions as an allosteric regulator of several methyltransfer-ases (MTases) targeting molecules (tRNAs, rRNAs and proteins) involved in protein synthesis. Here, we have investigated the interaction network of human TRMT112 in intact cells and identify three poorly characterized putative MTases (TRMT11, THUMPD3 and THUMD2) as direct part-ners. We demonstrate that these three proteins are active N2-methylguanosine (m2G) MTases and that TRMT11 and THUMPD3 methylate positions 10 and 6 of tRNAs, respectively. In contrast, we discovered that THUMPD2 directly associates with the U6 snRNA and is required for the for-mation of m2G in this core component of the catalytic spliceosome. Consistently, our data reveal the combined importance of TRMT11 and THUMPD3 for optimal protein synthesis and cancer cell proliferation as well as a role for THUMPD2 in fine-tuning pre-mRNA splicing.