Binding of hnRNP I-vRNA Regulates Sindbis Virus Structural Protein Expression to Promote Particle Infectivity

The leader RNA of SARS-CoV-2 sequesters polypyrimidine tract binding protein (PTBP1) and influences pre-mRNA splicing in infected cells

The large amount of viral RNA produced during infections has the potential to interact with and effectively sequester cellular RNA binding proteins, thereby influencing aspects of post-transcriptional gene regulation in the infected cell. Here we demonstrate that the abundant 5' leader RNA region of SARS-CoV-2 viral RNAs can interact with the cellular polypyrimidine tract binding protein (PTBP1). Interestingly, the effect of a knockdown of PTBP1 protein on cellular gene expression is also mimicked during SARS-CoV-2 infection, suggesting that this protein may be functionally sequestered by viral RNAs. Consistent with this model, the alternative splicing of mRNAs that is normally controlled by PTBP1 is dysregulated during SARS-CoV-2 infection. Collectively, these data suggest that the SARS-CoV-2 leader RNA sequesters the cellular PTBP1 protein during infection, resulting in significant impacts on the RNA biology of the host cell. These alterations in post-transcriptional gene regulation may play a role in SARS-CoV-2 mediated molecular pathogenesis.

Dancing with the Devil: A Review of the Importance of Host RNA-Binding Proteins to Alphaviral RNAs during Infection

Alphaviruses are arthropod-borne, single-stranded positive sense RNA viruses that rely on the engagement of host RNA-binding proteins to efficiently complete the viral lifecycle. Because of this reliance on host proteins, the identification of host/pathogen interactions and the subsequent characterization of their importance to viral infection has been an intensive area of study for several decades. Many of these host protein interaction studies have evaluated the Protein:Protein interactions of viral proteins during infection and a significant number of host proteins identified by these discovery efforts have been RNA Binding Proteins (RBPs). Considering this recognition, the field has shifted towards discovery efforts involving the direct identification of host factors that engage viral RNAs during infection using innovative discovery approaches. Collectively, these efforts have led to significant advancements in the understanding of alphaviral molecular biology; however, the precise extent and means by which many RBPs influence viral infection is unclear as their specific contributions to infection, as per any RNA:Protein interaction, have often been overlooked. The purpose of this review is to summarize the discovery of host/pathogen interactions during alphaviral infection with a specific emphasis on RBPs, to use new ontological analyses to reveal potential functional commonalities across alphaviral RBP interactants, and to identify host RBPs that have, and have yet to be, evaluated in their native context as RNA:Protein interactors.

Cell-Type-Dependent Role for nsP3 Macrodomain ADP-Ribose Binding and Hydrolase Activity during Chikungunya Virus Infection

Chikungunya virus (CHIKV) causes outbreaks of rash, arthritis, and fever associated with neurologic complications, where astrocytes are preferentially infected. A determinant of virulence is the macrodomain (MD) of nonstructural protein 3 (nsP3), which binds and removes ADP-ribose (ADPr) from ADP-ribosylated substrates and regulates stress-granule disruption. We compared the replication of CHIKV 181/25 (WT) and MD mutants with decreased ADPr binding and hydrolase (G32S) or increased ADPr binding and decreased hydrolase (Y114A) activities in C8-D1A astrocytic cells and NSC-34 neuronal cells. WT CHIKV replication was initiated more rapidly with earlier nsP synthesis in C8-D1A than in NSC-34 cells. G32S established infection, amplified replication complexes, and induced host-protein synthesis shut-off less efficiently than WT and produced less infectious virus, while Y114A replication was close to WT. However, G32S mutation effects on structural protein synthesis were cell-type-dependent. In NSC-34 cells, E2 synthesis was decreased compared to WT, while in C8-D1A cells synthesis was increased. Excess E2 produced by G32S-infected C8-D1A cells was assembled into virus particles that were less infectious than those from WT or Y114A-infected cells. Because nsP3 recruits ADP-ribosylated RNA-binding proteins in stress granules away from translation-initiation factors into nsP3 granules where the MD hydrolase can remove ADPr, we postulate that suboptimal translation-factor release decreased structural protein synthesis in NSC-34 cells while failure to de-ADP-ribosylate regulatory RNA-binding proteins increased synthesis in C8-D1A cells.