The N6-methyladenosine mRNA methylase METTL14 promotes renal ischemic reperfusion injury via suppressing YAP1

Renal ischemia-reperfusion injury (IRI) is one of the most common causes of acute kidney injury (AKI), which is closely related to high morbidity and mortality. However, the pathogenesis underlying renal IRI is complex and not fully defined. N6-methyladenosine (m6A) was recently found to be an abundant modification in mammalian messenger RNAs. It is implicated in various biological processes, while the role of m6A in IRI is not illustrated. Here we show that the m6A-methylated RNA level and its methyltransferase METTL14 are elevated in human AKI renal tissues and IRI HK-2 cells. Moreover, METTL14 knockdown protects the kidney against IRI in vitro and in vivo. Mechanistically, we identified that YAP1 is a direct target of METTL14 in AKI progression. Inhibition of YAP1-TEAD signaling by peptide 17 abrogates the protective effect of METTL14 against IRI in vitro and in vivo. Taken together, these results reveal that the N6-methyladenosine mRNA methylase METTL14 promotes the renal IRI via suppressing YAP1. The discovery of the METTL14-YAP1 pathway provides an important new perspective for understanding AKI and is conducive to revealing new therapeutic strategies and targets.     

Gsdma3 is required for hair follicle differentiation in mice

Apoptosis can result from activation of three major pathways: the extrinsic, the intrinsic, and the most recently identified endoplasmic reticulum (ER) stress-mediated pathway. While the two former pathways are known to be operational in human polymorphonuclear neutrophils (PMNs), the existence of the ER stress-mediated pathway, generally involving caspase-4, has never been reported in these cells. Recently, we have documented that arsenic trioxide (ATO) induced apoptosis in human PMNs by a mechanism that needs to be further investigated. In this study, using immunofluorescence and electron microscopy, we present evidence of ER alterations in PMNs activated by the ER stress inducer arsenic trioxide (ATO). Several key players of the unfolded protein response, including GRP78, GADD153, ATF6, XBP1 and eIF2α are expressed and activated in PMNs treated with ATO or other ER stress inducers. Although caspase-4 is expressed and activated in neutrophils, treatment with a caspase-4 inhibitor did not attenuate the pro-apoptotic effect of ATO at a concentration that reverses caspase-4 processing and activation. Our results demonstrate for the first time that the ER stress-mediated apoptotic pathway operates in human neutrophils.     

The METTL5-TRMT112 N6-methyladenosine methyltransferase complex regulates mRNA translation via 18S rRNA methylation

Ribosomal RNAs (rRNAs) have long been known to carry chemical modifications, including 2′O-methylation, pseudouridylation, N⁶-methyladenosine (m⁶A), and N^6,6-dimethyladenosine. While the functions of many of these modifications are unclear, some are highly conserved and occur in regions of the ribosome critical for mRNA decoding. Both 28S rRNA and 18S rRNA carry single m⁶A sites, and while the methyltransferase ZCCHC4 has been identified as the enzyme responsible for the 28S rRNA m⁶A modification, the methyltransferase responsible for the 18S rRNA m⁶A modification has remained unclear. Here, we show that the METTL5-TRMT112 methyltransferase complex installs the m⁶A modification at position 1832 of human 18S rRNA. Our work supports findings that TRMT112 is required for METTL5 stability and reveals that human METTL5 mutations associated with microcephaly and intellectual disability disrupt this interaction. We show that loss of METTL5 in human cancer cell lines and in mice regulates gene expression at the translational level; additionally, Mettl5 knockout mice display reduced body size and evidence of metabolic defects. While recent work has focused heavily on m⁶A modifications in mRNA and their roles in mRNA processing and translation, we demonstrate here that deorphanizing putative methyltransferase enzymes can reveal previously unappreciated regulatory roles for m⁶A in noncoding RNAs.     

Shh is required for Tabby hair follicle development

In embryonic Eda mutant (“Tabby”) mice, the development of one of the two major types of hair, “primary” hair fails, but other “secondary” hairs develop in normal numbers, though shorter and slightly aberrant. In Tabby mice, Shh is undetectable in skin early on, but is activated during secondary hair formation. We inferred that Shh may be involved in primary hair formation, activated normally by Eda, and also possibly in secondary hair formation, activated by an Eda-independent pathway. Varying the dosage of Shh now supports these inferences. In Shh knockout mice, mice were totally hairless: primary and secondary hair follicle germs were formed, but further progression failed. Consistent with these findings, when Shh loss was restricted to the skin, secondary hair follicle germs were initiated on time in Tabby mice, but their subsequent development (down-growth) failed. An Shh transgene expressed in Tabby skin could not restore induction of primary hair follicles, but restored normal length to the somewhat aberrant secondary hair that was formed and prolonged the anagen phase of hair cycling. Thus, Shh is required for primary and secondary hair downgrowth and full secondary hair length, but is not itself sufficient to replace Eda or make fully normal secondary hair.Key words: Eda, Shh, Wnt, hair follicle subtypes, Tabby     

Shh is required for Tabby hair follicle development

In embryonic Eda mutant ("Tabby") mice, the development of one of the two major types of hair, "primary" hair fails, but other "secondary" hairs develop in normal numbers, though shorter and slightly aberrant. In Tabby mice, Shh is undetectable in skin early on, but is activated during secondary hair formation. We inferred that Shh may be involved in primary hair formation, activated normally by Eda, and also possibly in secondary hair formation, activated by an Eda-independent pathway. Varying the dosage of Shh now supports these inferences. In Shh knockout mice, mice were totally hairless: primary and secondary hair follicle germs were formed, but further progression failed. Consistent with these findings, when Shh loss was restricted to the skin, secondary hair follicle germs were initiated on time in Tabby mice, but their subsequent development (down-growth) failed. An Shh transgene expressed in Tabby skin could not restore induction of primary hair follicles, but restored normal length to the somewhat aberrant secondary hair that was formed and prolonged the anagen phase of hair cycling. Thus, Shh is required for primary and secondary hair down-growth and full secondary hair length, but is not itself sufficient to replace Eda or make fully normal secondary hair.     

RNA N6-methyladenosine modification promotes auxin biosynthesis required for male meiosis in rice

1. Download : Download high-res image (230KB)
2. Download : Download full-size image

     

Drosophila PI4KIIIalpha is required in follicle cells for oocyte polarization and Hippo signaling

In a genetic screen we isolated mutations in CG10260, which encodes a phosphatidylinositol 4-kinase (PI4KIIIalpha), and found that PI4KIIIalpha is required for Hippo signaling in Drosophila ovarian follicle cells. PI4KIIIalpha mutations in the posterior follicle cells lead to oocyte polarization defects similar to those caused by mutations in the Hippo signaling pathway. PI4KIIIalpha mutations also cause misexpression of well-established Hippo signaling targets. The Merlin-Expanded-Kibra complex is required at the apical membrane for Hippo activity. In PI4KIIIalpha mutant follicle cells, Merlin fails to localize to the apical domain. Our analysis of PI4KIIIalpha mutants provides a new link in Hippo signal transduction from the cell membrane to its core kinase cascade.     

N6-methyladenosine (m6A) is an endogenous A3 adenosine receptor ligand

1. Download : Download high-res image (217KB)
2. Download : Download full-size image

     

Methyltransferase METTL8 is required for 3-methylcytosine modification in human mitochondrial tRNAs

A subset of eukaryotic tRNAs is methylated in the anticodon loop, forming 3-methylcytosine (m³C) modifications. In mammals, the number of tRNAs containing m³C modifications has been expanded to include mitochondrial (mt) tRNA-Ser-UGA and mt-tRNA-Thr-UGU. However, whereas the enzymes catalyzing m³C formation in nuclear-encoded tRNAs have been identified, the proteins responsible for m³C modification in mt-tRNAs are unknown. Here, we show that m³C formation in human mt-tRNAs is dependent upon the methyltransferase-Like 8 (METTL8) enzyme. We find that METTL8 is a mitochondria-associated protein that interacts with mitochondrial seryl-tRNA synthetase, as well as with mt-tRNAs containing m³C. We demonstrate that human cells deficient in METTL8 exhibit loss of m³C modification in mt-tRNAs, but not nuclear-encoded tRNAs. Consistent with the mitochondrial import of METTL8, the formation of m³C in METTL8-deficient cells could be rescued by re-expression of WT METTL8, but not by a METTL8 variant lacking the N-terminal mitochondrial localization signal. Notably, we found METTL8-deficiency in human cells causes alterations in the native migration pattern of mt-tRNA-Ser-UGA, suggesting a role for m³C in tRNA folding. Altogether, these findings demonstrate that METTL8 is required for m³C formation in mt-tRNAs and uncover a potential function for m³C modification in mitochondrial tRNA structure.     

METTL3-mediated m6A modification stabilizes TERRA and maintains telomere stability

Telomeric repeat-containing RNA (TERRA) is a type of long non-coding RNA transcribed from telomeres, and it forms R-loops by invasion into telomeric DNA. Since either an excessive or inadequate number of R-loops leads to telomere instability, the TERRA levels need to be delicately modulated. In this study, we found that m⁶A modification presents on the subtelomeric regions of TERRA and stabilizes it, and the loss of METTL3 impacts telomere stability. Mechanically, the m⁶A modification on TERRA is catalyzed by METTL3, recognized and stabilized by the m⁶A reader YTHDC1. Knockdown of either METTL3 or YTHDC1 enhances TERRA degradation. The m⁶A-modified TERRA forms R-loops and promotes homologous recombination which is essential for the alternative lengthening of telomeres (ALT) pathway in cancer cells. METTL3 depletion leads to R-loop reduction, telomere shortening and instability. Altogether, these findings reveal that METTL3 protects telomeres by catalyzing m⁶A modification on TERRA, indicating that inhibition or deletion of METTL3 is potentially a new avenue for ALT cancer therapy.     

Solution structure of the RNA recognition domain of METTL3-METTL14 N^6-methyladenosine methyltransferase

N^6-methyladenosine(m6A),a ubiquitous RNA modification,is installed by METTL3-METTL14 complex.The structure of the heterodimeric complex between the methyltransferase domains(MTDs)of METTL3 and METTL14 has been previously determined.However,the MTDs alone possess no enzymatic activity.Here we present the solution structure for the zinc finger domain(ZFD)of METTL3,the inclusion of which fulfills the methyltransferase activity of METTL3-METTL14.We show that the ZFD specifically binds to an RNA containing 5'-GGACU-3'consensus sequence,but does not to one without.The ZFD thus serves as the target recognition domain,a structural feature previously shown for DNA methyltransferases,and cooperates with the MTDs of METTL3-METTL14 for catalysis.However,the interaction between the ZFD and the specific RNA is extremely weak,with the binding affinity at several hundred micromolar under physiological conditions.The ZFD contains two CCCH-type zinc fingers connected by an anti-parallel P-sheet.Mutational analysis and NMR titrations have mapped the functional interface to a contiguous surface.As a division of labor,the RNA-binding interface comprises basic residues from zinc finger 1 and hydrophobic residues fromβ-sheet and zinc finger 2.Further we show that the linker between the ZFD and MTD of METTL3 is flexible but partially folded,which may permit the cooperation between the two domains during catalysis.Together,the structural characterization of METTL3 ZFD paves the way to elucidate the atomic details of the entire process of RNA m6A modification.     

Methyltransferase-like 3-mediated N6-methyladenosine modification of miR-7212-5p drives osteoblast differentiation and fracture healing

N6-methyladenosine (m6A) modification has been reported in various diseases and implicated in increasing numbers of biological processes. However, previous studies have not focused on the role of m6A modification in fracture healing. Here, we demonstrated that m6A modifications are decreased during fracture healing and that methyltransferase-like 3 (METTL3) is the main factor involved in the abnormal changes in m6A modifications. Down-regulation of METTL3 promotes osteogenic processes both in vitro and in vivo, and this effect is recapitulated by the suppression of miR-7212-5p maturation. Further studies have shown that miR-7212-5p inhibits osteoblast differentiation in MC3T3-E1 cells by targeting FGFR3. The present study demonstrated an important role of the METTL3/miR-7212-5p/FGFR3 axis and provided new insights on m6A modification in fracture healing.     

METTL9 mediated N1-histidine methylation of zinc transporters is required for tumor growth

Dear Editor, Histidine methylation has been known for many years(Searle and Westall,1951),but only a few proteins carrying such modifications have been studied ...