Biology subjects

Taoka, M.

Publications and source records attributed to Taoka, M..

5 recordsLinked to original sources

bioRxiv2023

Structure of mitoribosome reveals mechanism of mRNA binding, tRNA interactions with L1 stalk, roles of cofactors and rRNA modifications

The mitoribosome translates mitochondrial mRNAs and regulates energy conversion that is a signature of aerobic life forms. We present a 2.2 [A] resolution structure of human mitoribosome together with validated mitoribosomal RNA (rRNA) modifications, including aminoacylated CP-tRNAVal. The structure shows how mitoribosomal proteins stabilise binding of mRNA and tRNA helping to align it in the decoding center, whereas the GDP-bound mS29 stabilizes intersubunit communication. Comparison between different states, with respect to tRNA position, allowed to characterize a non-canonical L1 stalk, and molecular dynamics simulations revealed how it facilitates tRNA transition in a way that does not require interactions with rRNA. We also report functionally important polyamines that are depleted when cells are subjected to an antibiotic treatment. The structural, biochemical, and computational data illuminate the principal functional components of the translation mechanism in mitochondria and provide the most complete description so far of the structure and function of the human mitoribosome.

biochemistry↗

bioRxiv2023

Microbiome ssRNA as an environmental cue to activate TLR13-dependent tissue-protective programs in CD5Lhi hepatic macrophages

Hepatic macrophages maintain liver homeostasis, but little is known about the signals that activate the hepatoprotective programs within macrophages. Here, we show that toll-like receptor 13 (TLR13), a sensor of bacterial 23S ribosomal RNA (rRNA), senses microbiome RNAs to drive tissue-protective responses in CD5Lhi hepatic macrophages. Splenomegaly and hepatomegaly developed in the absence of the endosomal RNase, RNaseT2, via TLR13-dependent macrophage proliferation. Furthermore, TLR13 in hepatic Ly6Clo macrophages activated the transcription factors LXR and MafB, leading to expression of tissue-clearance molecules, such as CD5L, C1qb, and Axl. Consequently, Rnaset2-/- mice developed resistance to acute liver injury caused by challenges with acetaminophen and lipopolysaccharide + D-galactosamine. TLR13 responses in Rnaset2-/- mice were impaired by antibiotics, suggesting that TLR13 were activated by microbiome rRNAs, which was detected in the sera and hepatic macrophages. Repeated administration of wild-type mice with the TLR13 ligand, rather than other TLR ligands, selectively increased the number of Kupffer cells, which expressed immunoregulatory and tissue-clearance genes as hepatic macrophages in Rnaset2-/- mice did. Our results suggest that microbiome ssRNA serves as an environmental cue for initiating tissue-protective TLR13 responses in hepatic macrophages. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=192 SRC="FIGDIR/small/540294v1_ufig1.gif" ALT="Figure 1"> View larger version (51K): org.highwire.dtl.DTLVardef@69614eorg.highwire.dtl.DTLVardef@737c69org.highwire.dtl.DTLVardef@1ecd9eforg.highwire.dtl.DTLVardef@d7e10d_HPS_FORMAT_FIGEXP M_FIG In the absence of an endosomal RNase, RNase T2, microbiome RNAs circulating in the vasculature activate TLR13 in hepatic macrophages to drive hepatoprotective responses through expression of immunoregulatory and tissue-clearance molecules. Consequently, mice lacking RNase T2 are resistant against acute liver injuries caused by acetaminophen and LPS + D-galactosamine. C_FIG

immunology↗

bioRxiv2022

TLR7/8 stress response drives histiocytosis in SLC29A3 disorders

SLC29A3, also known as ENT3, is a lysosomal transmembrane protein that transports nucleosides from the lysosomes to the cytoplasm1. Loss-of-function mutations in SLC29A3 cause lysosomal nucleoside storage and histiocytosis: phagocyte accumulation in multiple organs2,3. However, little is known about the mechanism through which lysosomal nucleoside storage drives histiocytosis. Herein, histiocytosis in Slc29a3-/- mice was demonstrated to depend on TLR7, which senses a combination of nucleosides and oligoribonucleotides4,5. TLR7 responded to lysosomal nucleoside storage and enhanced proliferation of Ly6Chi CX3CR1low immature monocytes and their maturation into Ly6Clow phagocytes in Slc29a3-/- mice. Because accumulated nucleosides primarily originated from cell corpse phagocytosis, TLR7 in immature monocytes recognized nucleoside storage as lysosomal stress and increased phagocyte numbers. This non-inflammatory compensatory response is referred to as the TLR7 stress response where Syk, GSK3{beta}, {beta}-catenin, and mTORC1 serve as downstream signalling molecules. In SLC29A3 disorders, histiocytosis accompanies inflammation6,7. Nucleoside storage failed to induce pro-inflammatory cytokine production in Slc29a3-/- mice, but enhanced ssRNA-dependent pro-inflammatory cytokine production in Ly6Chi classical monocytes and peripheral macrophages, not proliferating immature monocytes. Patient-derived monocytes harbouring G208R SLC29A3 mutation showed higher survival and proliferation in the presence of M-CSF and produced larger amounts of IL-6 upon ssRNA stimulation than did those derived from healthy subjects. A TLR8 antagonist inhibited the survival/proliferation of patient-derived macrophages. These results demonstrated that TLR7/8 responses to lysosomal nucleoside stress drive SLC29A3 disorders.

immunology↗

bioRxiv2019

Nucleosides drive histiocytosis in SLC29A3 disorders by activating TLR7

A lysosomal transmembrane protein SLC29A3 transports nucleosides from lysosomes to the cytoplasm. Loss-of-function mutations of the SLC29A3 gene cause lysosomal nucleoside storage in monocyte/macrophages, leading to their accumulation called histiocytosis in humans and mice. Little is known, however, about a mechanism behind nucleoside-dependent histiocytosis. TLR7, an innate immune sensors for single stranded RNA, bind and respond to nucleosides. We here show that they drive nucleoside-mediated histiocytosis. Patrolling monocyte/macrophages accumulate in the spleen of Slc29a3-/- mice but not Slc29a3-/- Tlr7-/- mice. Accumulated patrolling monocyte/macrophages stored nucleosides derived from cell corpse. TLR7 was recruited to phagosomes and activated as evidenced by TLR7-dependent phagosomal maturation. TLR7 induced hyper-responsiveness to M-CSF in Slc29a3-/- monocyte/macrophages. These results suggest that TLR7 drives histiocytosis in SLC29A3 disorders. One Sentence SummarySLC29A3 disorders are caused by activation of TLR7 with accumulated nucleosides in lysosomes.

immunology↗

bioRxiv2019

SCAP promotes CARTS biogenesis at endoplasmic reticulum-Golgi contact sites

In response to cholesterol deprivation, SCAP escorts SREBP transcription factors from the endoplasmic reticulum (ER) to the Golgi complex for their proteolytic activation, leading to gene expression for cholesterol synthesis and uptake. Here we show that in cholesterol-fed cells ER-localized SCAP interacts through Sac1 phosphoinositide 4-phosphate (PI4P) phosphatase with a VAP/OSBP complex, which mediates counter-transport of ER cholesterol and Golgi PI4P at ER-Golgi contact sites. SCAP knockdown inhibited the turnover of PI4P perhaps due to a cholesterol transport defect and altered the subcellular distribution of the VAP/OSBP complex. As in the case of perturbation of lipid transfer complexes at ER-Golgi contact sites, SCAP knockdown inhibited the biogenesis of the trans-Golgi network-derived transport carriers CARTS, which was reversed by expression of wild-type SCAP but not cholesterol sensing-defective mutants. Altogether, our findings reveal a new role of SCAP under cholesterol-fed conditions in the facilitation of CARTS biogenesis at ER-Golgi contact sites, depending on the ER cholesterol. SummarySCAP is the key regulatory protein in cholesterol metabolism. Wakana et al. describe a new role of SCAP in controlling Golgi PI4P turnover and the biogenesis of the Golgi-derived transport carries CARTS via cholesterol/PI4P exchange machinery at ER-Golgi contact sites.

cell biology↗