Formation of stress granules (SGs), cytoplasmic condensates of stalled translation initiation complexes, is regulated by post-translational protein modification. Alphaviruses interfere with SG formation in response to inhibition of host protein synthesis through the activities of nonstructural protein 3 (nsP3). nsP3 has a conserved N-terminal macrodomain that binds and can remove ADP-ribose from ADPribosylated proteins and a C-terminal hypervariable domain that binds essential SG component G3BP1.We showed that the hydrolase activity of chikungunya virus nsP3 macrodomain removed ADPribosylation of G3BP1 and suppressed SG formation. ADP-ribosylhydrolase-deficient nsP3 mutants allowed stress-induced cytoplasmic condensation of translation initiation factors. nsP3 also disassembled SG-like aggregates enriched with translation initiation factors that are induced by the expression of FUS mutant R495X linked to amyotrophic lateral sclerosis. Therefore, our data indicate that regulation of ADP-ribosylation controls the localization of translation initiation factors during virus infection and other pathological conditions. All rights reserved. No reuse allowed without permission.
INTRODUCTIONNon-membranous structures are prevalent in cells and critical for cellular functions, including RNA metabolism, embryonic cell fate specification, and neuronal activities [1][2][3]. Although the components of these non-membranous structures are often dynamically exchanged with the surrounding milieu, the compositions of these cellular structures remain distinct [4]. It is, however, unclear how individual components are selectively retained in these non-membranous structures.Stress granules (SGs), one of the best characterized dynamic non-membranous structures, are RNAprotein assemblies formed in response to a variety of environmental cues [3]. In most cases, these environmental cues activate stress-responsive protein kinases that phosphorylate the eukaryotic initiation factor 2 alpha (eIF2α), resulting in the stalling of translation initiation [3]. The sudden influx of untranslated mRNAs is proposed to seed the formation of SGs, where the polynucleotide promotes local concentration of proteins through non-covalent binding [5]. These RNA-binding proteins are highly enriched with low-complexity regions, and emergent data indicate that the nonspecific, weak interactions between these regions are responsible for the condensation of proteins to form higherorder structures, such as microscopically visible SGs [6][7][8]. Depending on the type of stress, the composition of SGs could vary [9], but certain common components, such as Ras GTP-activating protein-binding proteins G3BP1/2, are essential for SG formation [10,11]. Dysregulation of SG assembly/disassembly and mutations in the low-complexity region of specific SG proteins are implicated in the pathogenesis of diseases such as viral infection, cancer and neurodegeneration [1,[12][13][14]. Therefore, understanding the regulatory mechanisms of SG assembly is critical for designing novel th...