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Human SAMD9 is a Virus-Activatable Anticodon Nuclease Inhibiting Codon-Specific Protein Synthesis

ABSTRACT: Transfer RNAs (tRNAs) are one of the most conserved components of protein synthesis machinery. An effective strategy for microbes to defend against viruses or competitors is to employ anticodon nucleases (ACNases) to deplete essential tRNAs and thereby shut off global protein synthesis, but this strategy has not been observed in multicellular eukaryotes. Here, we report that human SAMD9 is a virus-activatable ACNase that specifically depletes phenylalanine tRNA (tRNAPhe), causing codon-specific ribosomal pausing and inducing stress signaling. SAMD9 ACNase can be activated by poxvirus infection or by SAMD9 mutations associated with a spectrum of developmental or immunological disorders, implicating tRNAPhe deficiency as a major toxic effect in these human diseases and suggesting a new therapeutic strategy. The specificity of the ACNase, located to an N-terminal effector domain of SAMD9, is largely determined by a eukaryotic tRNAPhe specific 2’-O-methylation at the wobble position, making eukaryotic tRNAPhe a universal but specific target for SAMD9. The SAMD9 ACNase differs from the microbial ACNases in structure and substrate specificity, suggesting convergent evolution resulted in a universal immune defense strategy targeting tRNAs.

ORGANISM(S): Homo sapiens

PROVIDER: GSE230043 | GEO | 2023/06/07

REPOSITORIES: GEO

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Project description:Evolutionarily successful poxviruses presented effective and diverse strategies to circumvent or overcome host defense mechanisms. Poxviruses encode many immunoregulatory proteins to evade host immunity for a productive infection and unique means of inhibiting DNA-sensing dependent type 1 interferon (IFN-I) responses is anticipated due to the biology of its dsDNA genome in nature and an exclusive cytoplasmic life cycle. We found the key DNA sensing inhibition by poxvirus infection was dominant during the early stage of poxvirus infection independent from DNA replication. In an effort of identifying poxvirus novel means to subdue antiviral proinflammatory responses e.g., IFN-I response, we focused on the function of one early gene that is the known host range determinant from the highly conserved poxvirus host range C7L superfamily, myxoma virus (MYXV) M062. Host range factors are unique features of poxviruses that determine the species and cell type tropism. Almost all sequenced mammalian poxviruses retain at least one homologue of the poxvirus host range C7L superfamily. In MYXV, a rabbit specific poxvirus, the dominant and broad-spectrum host range determinant of the C7L superfamily is the M062R gene. M062R gene product is essential for MYXV infection in almost all cells tested from different mammalian species and specifically inhibits the function of host Sterile α Motif Domain-containing 9 (SAMD9), as M062R-null (ΔM062R) MYXV causes abortive infection in a SAMD9-dependend manner. In this study we investigated the immunostimulatory property of the ΔM062R. We found that the replication-defective ΔM062R infection activated host DNA sensing pathway in the cGAS dependent fashion and knocking down SAMD9 expression attenuated proinflammatory responses. Moreover, transcriptomic analyses showed a unique feature of host gene expression landscape that is different from dsDNA stimulated inflammatory state. This study built a link between the anti-neoplastic SAMD9 and the regulation of the innate immune responses.

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Human SAMD9 is a Virus-Activatable Anticodon Nuclease Inhibiting Codon-Specific Protein Synthesis

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