Significance: Alphaviruses are mosquito-borne RNA viruses that cause rash, arthritis, and neurologic disease. Despite a continued risk of outbreaks, there are no licensed interventions for any alphavirus. For progress in control, an understanding of the molecular targets that affect virus replication and virulence is essential. This paper characterizes a conserved macrodomain in the virulence factor nonstructural protein 3 (nsP3). We discovered that the macrodomain ADP-ribosylhydrolase activity is critical for controlling the composition of cellular condensates, specifically through regulating the localization of translation factors, during viral infection. Given that this macrodomain is conserved across alphaviruses and coronaviruses and that the associated enzymatic activity is critical for virulence, our work may open avenues for developing a class of antiviral therapeutics.

Stress granules (SGs) harbour translationally stalled messenger ribonucleoproteins and play important roles in regulating gene expression and cell fate. Here we show that neddylation promotes SG assembly in response to arsenite-induced oxidative stress. Inhibition or depletion of key components of the neddylation machinery concomitantly inhibits stress-induced polysome disassembly and SG assembly. Affinity purification and subsequent mass-spectrometric analysis of Nedd8-conjugated proteins from translationally stalled ribosomal fractions identified ribosomal proteins, translation factors and RNA-binding proteins (RBPs), including SRSF3, a previously known SG regulator. We show that SRSF3 is selectively neddylated at Lys85 in response to arsenite. A non-neddylatable SRSF3 (K85R) mutant do not prevent arsenite-induced polysome disassembly, but fails to support the SG assembly, suggesting that the neddylation pathway plays an important role in SG assembly.

Viruses depend on host cellular resources to replicate. Interaction between viral and host proteins is essential for the pathogens to ward off immune responses as well as for virus propagation within the infected cells. While different viruses employ unique strategies to interact with diverse sets of host proteins, the multifunctional RNA-binding protein G3BP1 is one of the common targets for many viruses. G3BP1 controls several key cellular processes, including mRNA stability, translation, and immune responses. G3BP1 also serves as the central hub for the protein–protein and protein–RNA interactions within a class of biomolecular condensates called stress granules (SGs) during stress conditions, including viral infection. Increasing evidence suggests that viruses utilize distinct strategies to modulate G3BP1 function—either by degradation, sequestration, or redistribution—and control the viral life cycle positively and negatively. In this review, we summarize the pro-viral and anti-viral roles of G3BP1 during infection among different viral families.

Mitochondrial morphology is dynamically regulated by forming small, fragmented units or interconnected networks, and this is a pivotal process that is used to maintain mitochondrial homeostasis. Although dysregulation of mitochondrial dynamics is related to the pathogenesis of several human diseases, its molecular mechanism is not fully elucidated. In this study, we demonstrate the potential role of miR-27 in the regulation of mitochondrial dynamics. Mitochondrial fission factor (MFF) mRNA is a direct target of miR-27, whose ectopic expression decreases MFF expression through binding to its 3′-untranslated region. Expression of miR-27 results in the elongation of mitochondria as well as an increased mitochondrial membrane potential and mitochondrial ATP level. Our results suggest that miR-27 is a novel regulator affecting morphological mitochondrial changes by targeting MFF.

Twist1, a key transcription factor regulating epithelial–mesenchymal transition and cancer metastasis, is highly expressed in invasive cancers in contrast to the loss of BTG2^/TIS21expression. Based on our observation that forced expression of BTG2^/TIS21downregulated Twist1 protein expression without altering mRNA level, we investigated molecular mechanisms of the BTG2^/TIS21-inhibited Twist1 translation in the triple negative breast cancer (TNBC) cells and in vivo BTG2^/TIS21-knockout (KO) mice and human breast cancer tissues. (1) C-terminal domain of Twist1 and Box B of BTG2^/TIS21interacted with each other, which abrogated Twist1 activity. (2) BTG2^/TIS21inhibited translational initiation by depleting eIF4E availability via inhibiting 4EBP1 phosphorylation. (3) Expression of BTG2^/TIS21maintained p-eIF2α that downregulates initiation of protein translation, confirmed by eIF2α-AA mutant expression and BTG2^/TIS21knockdown in MEF cells. (4) cDNA microarray analysis revealed significantly higher expression of initiation factors-eIF2A, eIF3A, and eIF4G2-in the BTG2^/TIS21-KO mouse than that in the wild type. (5) BTG2^/TIS21-inhibited translation initiation lead to the collapse of polysome formation and the huge peak of 80s monomer in the BTG2^/TIS21expresser, but not in the control. (6) mRNAs and protein expressions of elongation factors were also downregulated by BTG2^/TIS21expression in TNBC cells, but much higher in both TIS21-KO mice and lymph node-positive human breast cancers. (7) BTG2^/TIS21-mediated Twist1 loss was not due to the protein degradation by ubiquitination and autophagy activation. (8) Twist1 protein level was significantly higher in various organs of TIS21-KO mice compared with that in the control, indicating the in vivo role ofBTG2^/TIS21gene in the regulation of Twist1 protein level. Altogether, the present study support our hypothesis that BTG2^/TIS21is a promising target to combat with metastatic cancers with high level of Twist1 without BTG2^/TIS21expression.