Research Article: Human Subtilisin Kexin Isozyme-1 (SKI-1)/Site-1 Protease (S1P) regulates cytoplasmic lipid droplet abundance: A potential target for indirect-acting anti-dengue virus agents

Date Published: March 24, 2017

Publisher: Public Library of Science

Author(s): Anastasia Hyrina, Fanrui Meng, Steven J. McArthur, Sharlene Eivemark, Ivan R. Nabi, François Jean, Pierre Roques.

http://doi.org/10.1371/journal.pone.0174483

Abstract

Viral hijacking and manipulation of host-cell biosynthetic pathways by human enveloped viruses are shared molecular events essential for the viral lifecycle. For Flaviviridae members such as hepatitis C virus and dengue virus (DENV), one of the key subsets of cellular pathways that undergo manipulation is the lipid metabolic pathways, underlining the importance of cellular lipids and, in particular, lipid droplets (LDs) in viral infection. Here, we hypothesize that targeting cellular enzymes that act as key regulators of lipid homeostasis and LD formation could represent a powerful approach to developing a novel class of broad-spectrum antivirals against infection associated with all DENV serotypes (1–4) circulating around the world. Using PF-429242, an active-site-directed inhibitor of SKI-1/S1P, we demonstrate that inhibition of SKI-1/S1P enzymatic activity in human hepatoma Huh-7.5.1 cells results in a robust reduction of the LD numbers and LD-positive areas and provides a means of effectively inhibiting infection by DENV (1–4). Pre-treatment of Huh-7.5.1 cells with PF-429242 results in a dose-dependent inhibition of DENV infection [median inhibitory dose (EC50) = 1.2 microM; median cytotoxic dose (CC50) = 81 microM; selectivity index (SI) = 68)] and a ~3-log decrease in DENV-2 titer with 20 microM of PF-429242. Post-treatment of DENV-2 infected Huh-7.5.1 cells with PF-429242 does not affect viral RNA abundance, but it does compromise the assembly and/or release of infectious virus particles. PF-429242 antiviral activity is reversed by exogenous oleic acid, which acts as an inducer of LD formation in PF-429242-treated and non-treated control cells. Collectively, our results demonstrate that human SKI-1/S1P is a potential target for indirect-acting pan-serotypic anti-DENV agents and reveal new therapeutic opportunities associated with the use of lipid-modulating drugs for controlling DENV infection.

Partial Text

Dengue virus (DENV) represents a significant threat to global public health, with approximately 390 million cases annually and about 2.5 billion people living in endemic countries [1–3]. DENV is the causative agent of dengue fever (DF) and of life-threatening severe dengue, including dengue haemorrhagic fever (DHF) and dengue shock syndrome (DSS) [4]. Although DENV was first isolated more than 70 years ago, current treatment and prevention approaches are still limited to palliative relief of symptoms and vector control [4–7]. Currently, four DENV serotypes (DENV-1 to -4) transmitted by Aedes aegypti and Aedes albopictus mosquitoes are known to circulate in humans [3, 8]. All four DENV serotypes are considered to be hyper-endemic in most tropical and subtropical areas of the world, and they are poised to spread into new territories [3, 9]. A better understanding of host-DENV interactions and DENV pathogenesis is urgently needed to design broad-spectrum antivirals that will be effective against all four DENV serotypes.

In this study, using PF-429242, an active-site-directed inhibitor of SKI-1/S1P, we demonstrated that strategic manipulation of human SKI-1/S1P enzymatic activity in Huh-7.5.1 human hepatoma cells provides a means of interfering with the SKI-1/S1P-mediated proteolytic activation of the SREBP pathway. PF-429242 treatment in Huh-7.5.1 cells results in a robust inhibition of cytosolic LD formation and effectively inhibits viral infection of Huh-7.5.1 cells by all four DENV serotypes (1–4). Collectively, our results demonstrate that human SKI-1/S1P is a potential target for indirect-acting pan-serotypic anti-dengue virus agents, and these results reveal new therapeutic opportunities associated with the use of lipid-modulating drugs for controlling DENV infection.

 

Source:

http://doi.org/10.1371/journal.pone.0174483

 

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