Human coronaviruses activate and hijack the proteostasis guardian HSF1 to enhance viral replication (preprint)

Organisms respond to proteotoxic stress by activating a cellular defense mechanism, known as the heat shock response (HSR), that triggers the expression of cytoprotective heat shock proteins (HSP) to counteract the damaging effects of proteostasis disruption. The HSR is regulated by a family of transcription factors (heat shock factors, HSFs); among six human HSFs, HSF1 acts as a proteostasis guardian regulating acute and severe stress-driven transcriptional responses. Seasonal coronaviruses HCoV-229E, HCoV-NL63, HCoV-OC43 and HCoV-HKU1 (sHCoV) are globally circulating in the human population. Although sHCoV generally cause only mild upper respiratory diseases in immunocompetent hosts, severe complications may occur in specific populations. There is no effective treatment for sHCoV infections, also due to the limited knowledge on sHCoV biology. We now show that both Alpha- and Beta- sHCoV are potent inducers of HSF1, selectively promoting HSF1 phosphorylation at serine-326 residue and nuclear translocation, and triggering a powerful HSF1-driven transcriptional response in infected cells at late stages of infection. Despite the coronavirus-mediated shut-down of the host cell translational machinery, high levels of selected canonical and non-canonical HSF1-target genes products, including HSP70, HSPA6 and the zinc-finger AN1-type domain-2a gene/AIRAP, were found in HCoV-infected cells. Interestingly, silencing experiments demonstrate that HSR activation does not merely reflect a cellular defense response to viral infection, but that sHCoV activate and hijack the HSF1-pathway for their own gain. Notably, nuclear HSF1 pools depletion via Direct-Targeted HSF1 inhibitor (DTHIB) treatment was highly effective in hindering sHCoV replication in lung cells. Altogether the results open new scenarios for the search of innovative antiviral strategies in the treatment of coronavirus infections.

Nitazoxanide is a potent inhibitor of human seasonal coronaviruses acting at postentry level: effect on viral spike glycoprotein (preprint)

Coronaviridae is recognized as one of the most rapidly evolving virus family as a consequence of the high genomic nucleotide substitution rates and recombination. The family comprises a large number of enveloped, positive-sense single-stranded RNA viruses, causing an array of diseases of varying severity in animals and humans. To date, seven human coronaviruses (HCoV) have been identified, namely HCoV-229E, HCoV-NL63, HCoV-OC43 and HCoV-HKU1, which are globally circulating in the human population (seasonal HCoV, sHCoV), and the highly pathogenic SARS-CoV, MERS-CoV and SARS-CoV-2. Seasonal HCoV are estimated to contribute to 15-30% of common cold cases in humans; although diseases are generally self-limiting, sHCoV can sometimes cause severe lower respiratory infections, as well as enteric and neurological diseases. No specific treatment is presently available for sHCoV infections. Herein we show that the anti-infective drug nitazoxanide has a potent antiviral activity against three human endemic coronaviruses, the Alpha-coronaviruses HCoV-229E and HCoV-NL63, and the Beta-coronavirus HCoV-OC43 in cell culture with IC50 ranging between 0.05 and 0.15 g/ml, and high selectivity indexes. We found that nitazoxanide does not affect HCoV adsorption, entry or uncoating, but acts at postentry level and interferes with the spike glycoprotein maturation, hampering its terminal glycosylation at an endoglycosidase H-sensitive stage. Altogether the results indicate that nitazoxanide, due to its broad-spectrum anti-coronavirus activity, may represent a readily available useful tool in the treatment of seasonal coronavirus infections.

Impairment of SARS-CoV-2 spike glycoprotein maturation and fusion activity by the broad-spectrum anti-infective drug nitazoxanide (preprint)

The emergence of the highly-pathogenic severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the causative agent of COVID-19 (coronavirus disease-2019), has caused an unprecedented global health crisis, as well as societal and economic disruption. The SARS-CoV-2 spike (S), a surface-anchored trimeric class-I fusion glycoprotein essential for entry into host cells, represents a key target for developing vaccines and therapeutics capable of blocking virus invasion. The emergence of several SARS-CoV-2 spike variants that facilitate virus spread and may affect the efficacy of recently developed vaccines, creates great concern and highlights the importance of identifying antiviral drugs to reduce SARS-CoV-2-related morbidity and mortality. Nitazoxanide, a thiazolide originally developed as an antiprotozoal agent with recognized broad-spectrum antiviral activity in-vitro and in clinical studies, was recently shown to be effective against several coronaviruses, including SARS-CoV-2. Using biochemical and pseudovirus entry assays, we now demonstrate that nitazoxanide interferes with the SARS-CoV-2 spike biogenesis, hampering its maturation at an endoglycosidase H-sensitive stage, and hindering its fusion activity in human cells. Besides membrane fusion during virus entry, SARS-CoV-2 S-proteins in infected cells can also trigger receptor-dependent formation of syncytia, observed in-vitro and in COVID-19 patients tissues, facilitating viral dissemination between cells and possibly promoting immune evasion. Utilizing two different quantitative cell-cell fusion assays, we show that nitazoxanide is effective in inhibiting syncytia formation mediated by different SARS-CoV-2 spike variants in human lung, liver and intestinal cells. The results suggest that nitazoxanide may represent a useful tool in the fight against COVID-19 infections, inhibiting SARS-CoV-2 replication and preventing spike-mediated syncytia formation.