Stress proteins (SPs) including heat-shock proteins (HSPs), RNA chaperones, and ER associated stress proteins are molecular chaperones essential for cellular homeostasis. The major functions of HSPs include chaperoning misfolded or unfolded polypeptides, protecting cells from toxic stress, and presenting immune and inflammatory cytokines. Regarded as a double-edged sword, HSPs also cooperate with numerous viruses and cancer cells to promote their survival. RNA chaperones are a group of heterogeneous nuclear ribonucleoproteins (hnRNPs), which are essential factors for manipulating both the functions and metabolisms of pre-mRNAs/hnRNAs transcribed by RNA polymerase II. hnRNPs involve in a large number of cellular processes, including chromatin remodelling, transcription regulation, RNP assembly and stabilization, RNA export, virus replication, histonelike nucleoid structuring, and even intracellular immunity. Dysregulation of stress proteins is associated with many human diseases including human cancer, cardiovascular diseases, neurodegenerative diseases (e.g., Parkinson's diseases, Alzheimer disease), stroke and infectious diseases. In this review, we summarized the biologic function of stress proteins, and current progress on their mechanisms related to virus reproduction and diseases caused by virus infections. As SPs also attract a great interest as potential antiviral targets (e.g., COVID-19), we also discuss the present progress and challenges in this area of HSP-based drug development, as well as with compounds already under clinical evaluation.

No abstract

Enterovirus 71 (EV-A71) is a human pathogen that causes hand, foot, and mouth disease (HFMD) and fatal neurological diseases, and no effective treatment is available. Characterization of key host factors is important for understanding its pathogenesis and developing antiviral drugs. Here we report that Hsp27 is one of the most upregulated proteins in response to EV-A71 infection, as revealed by two-dimensional gel electrophoresis-based proteomics studies. Depletion of Hsp27 by small interfering RNA or CRISPR/Cas9-mediated knockout significantly inhibited viral replication, protein expression, and reproduction, while restoration of Hsp27 restored such virus activities. Furthermore, we show that Hsp27 plays a crucial role in regulating viral internal ribosome entry site (IRES) activities by two different mechanisms. Hsp27 markedly promoted 2Apro-mediated eukaryotic initiation factor 4G cleavage, an important process for selecting and initiating IRES-mediated translation. hnRNP A1 is a key IRES trans-acting factor (ITAF) for enhancing IRES-mediated translation. Surprisingly, knockout of Hsp27 differentially blocked hnRNP A1 but not FBP1 translocation from the nucleus to the cytoplasm and therefore abolished the hnRNP A1 interaction with IRES. Most importantly, the Hsp27 inhibitor 1,3,5-trihydroxy-13,13-dimethyl-2H-pyran [7,6-b] xanthone (TDP), a compound isolated from a traditional Chinese herb, significantly protected against cytopathic effects and inhibited EV-A71 infection. Collectively, our results demonstrate new functions of Hsp27 in facilitating virus infection and provide novel options for combating EV-A71 infection by targeting Hsp27. IMPORTANCE Outbreaks of infections with EV-A71, which causes hand, foot, and mouth disease, severe neurological disorders, and even death, have been repeatedly reported worldwide in recent decades and are a great public health problem for which no approved treatments are available. We show that Hsp27, a heat shock protein, supports EV-A71 infection in two distinct ways to promote viral IRES-dependent translation. A small-molecule Hsp27 inhibitor isolated from a traditional Chinese medicinal herb effectively reduces virus yields. Together, our findings demonstrate that Hsp27 plays an important role in EV-A71 infection and may serve as an antiviral target.

Summary Enterovirus A71 (EV-A71) infection causes hand-foot-and-mouth disease (HFMD) and fatal neurological diseases, and there are no effective treatments. Host factors play key roles in establishing viral infection and determining the disease progression and outcome of antiviral therapies. In this study, we found that the expression of Pim1 was significantly upregulated in EV-A71 infection. Ectopic expression or silencing of Pim1 promoted or inhibited EV-A71 replication through two distinct mechanisms. Pim1 enhanced viral IRES activity by increasing viral 2A protease-mediated eIF4G cleavage and blocked AUF1, a suppressor of IRES, translocation from the nucleus to cytosol. More importantly, we discovered that Pim1 inhibitors (SGI-1776, AZD-1208, and CX-6258) reduced EV-A71 reproduction. Particularly, CX-6258 remarkably reduced EV-A71 reproduction more than 1,000 times, providing a potential therapeutic agent for EV-A71 treatment.

Increasingly recognized importance has been assumed for microRNA (miRNA) in the regulation of the delicate balance of gene expression. In our study, we aimed to explore the regulation role of miR181c towards Six2 in metanephric mesenchyme (MM) cells. Bioinformatics analysis, luciferase assay and semi-quantitative real-time (RT) PCR, subsequently RT PCR, Western blotting, 5-ethynyl-2'-deoxyuridine cell proliferation assay, Cell Counting Kit-8 assay, immunofluorescence and flow cytometry, were employed to verify the modulation function of miR181c on Six2 in the mK3 MM cell line that is one kind of MM cells. miR181c was predicted to bind the 3' untranslated region of Six2 by bioinformatics analysis, which was subsequently validated by the in vitro luciferase reporter assay. Moreover, transfection of miR181c mimic can decrease the expression of Six2 both in mRNA and protein levels in mK3 cells. Still, ectopic expression of miR181c inhibits the proliferation, promotes the apoptosis and even makes the nephron progenitor phenotype lose mK3 cells. These results revealed the ability of a single miRNA-miR181c to downregulate the expression of Six2, restrain the proliferation and promote the apoptosis that even makes the nephron progenitor phenotype lose MM cells, suggesting a potential role of miR181c during the kidney development.