Biology subjects

Ricciardi-Jorge, T.

Publications and source records attributed to Ricciardi-Jorge, T..

3 recordsLinked to original sources

bioRxiv2025

IFIT3 controls IFIT1 accumulation and specificity preventing self mRNA targeting during the innate immune response.

IFIT1 is among the highest expressed proteins following virus detection and interferon (IFN) induction and binds the 5-end of non-self viral cap0-mRNAs lacking 2-O-methylation, blocking their translation. IFIT1 hetero-complexes with IFIT3, which enhances IFIT1 cap0-binding. Here, we demonstrate that IFIT3 is a master regulator of IFIT1, dictating its activity and stability. When expressed at high levels in the absence of IFIT3, IFIT1 can inhibit Semliki Forest virus replication, but can also inhibit translation of certain other self IFN-stimulated genes (ISGs), including the important innate immune proteins ISG15 and IFITM1 as exemplars. However, IFIT1:IFIT3 complexing rescues ISG15 and IFITM1 from IFIT1 translation inhibition. We demonstrate that IFIT1 is degraded by the proteasome in the absence of IFIT3, but that direct binding to IFIT3 protects IFIT1 from degradation, ensuring IFIT1 accumulation only occurs along with IFIT3, demonstrating a mechanism to control the fine balance between antiviral activity and self-targeting in the face of unrelenting viral evolution.

immunology↗

bioRxiv2025

Determinant host differences in ZIKV sfRNA accumulation.

Zika virus (Orthoflavivirus zikaese) is part of the Orthoflavivirus genus that contains several viral species posing major and expanding burdens to public health worldwide. Upon infection, orthoflaviviruses produce viral RNA fragments named sfRNAs (short flaviviral RNA), generated from viral genomic RNA incompletely degraded by Xrn1/Pcm, the major cellular 5-3 exonuclease. Several conserved elements in the orthoflavivirus 3 untranslated region (UTR) are responsible for XrnI-resistance, named xrRNA. The ubiquitous prevalence of xrRNA/sfRNA in flaviviruses indicate an important role of these structures in the viral life cycle, although their function is not completely understood. Here, we used in vitro reconstitution and infection models to examine the role of ZIKV xrRNA2 in mammalian and insect cells. SHAPE RNA structure probing revealed that disruption of ZIKV xrRNA2 does not affect xrRNA1 or dumbbell structure elsewhere in the 3UTR despite disrupting all sfRNA accumulation in mammalian cells. In vitro RNA degradation assays showed that xrRNA1 efficiently stalled human or mosquito Xrn1 independent of xrRNA2 integrity. Reversion in mammalian cells occurred at early passages in protein kinase R (PKR)-/- or IFN-receptor1 (IFAR1)-/-/PKR-/- knock out (KO) or double KO mammalian A549 cells, respectively, while wild-type virus outcompeted the xrRNA2 defective virus in RNAi-deficient mosquito cells. Together, our data reveals novel details of the mechanism of sfRNA accumulation in mammalian and insect cells We demonstrate a differential sensitivity to the absence of a functional xrRNA2 structure in mammalian and insect cells, with reversion to an active xrRNA2 occurring more rapidly in mammalian cells. Together, our work reveals new details on the requirements for ZIKV sfRNA accumulation in mammalian and mosquito cells.

microbiology↗

bioRxiv2021

PKR-MEDIATED STRESS RESPONSE ENHANCES DENGUE AND ZIKA VIRUS REPLICATION

The mechanisms by which flaviviruses use non-canonical translation to support their replication in host cells are largely unknown. Here we investigated how the integrated stress response (ISR), which promotes translational arrest by eIF2[a] phosphorylation (p-eIF2[a]), regulates flavivirus replication. During Dengue virus (DENV) and Zika virus (ZIKV) infection, eIF2[a] phosphorylation peaked at 24 hours post infection and was dependent on PKR but not type I interferon. The ISR is activated downstream of p-eIF2 during infection with either virus, but translation arrest only occurred following DENV4 infection. Despite this difference, both DENV4 and ZIKV replication was impaired in cells lacking PKR, independent of IFN-I/NF-kB signalling or cell viability. By using a ZIKV 5' UTR reporter system as a model, we found that this region of the genome is sufficient to promote an enhancement of viral mRNA translation in the presence of an active ISR. Together we provide evidence that flaviviruses escape ISR translational arrest and co-opt this response to increase viral replication.

immunology↗