Identification of Interferon-Stimulated Gene Proteins That Inhibit Human Parainfluenza Virus Type 3

Abstract

A major arm of cellular innate immunity is type I interferon (IFN), represented by IFN-␣ and IFN-␤. Type I IFN transcriptionally induces a large number of cellular genes, collectively known as IFN-stimulated gene (ISG) proteins, which act as antivirals. The IFIT (interferon-induced proteins with tetratricopeptide repeats) family proteins constitute a major subclass of ISG proteins and are characterized by multiple tetratricopeptide repeats (TPRs). In this study, we have interrogated IFIT proteins for the ability to inhibit the growth of human parainfluenza virus type 3 (PIV3), a nonsegmented negative-strand RNA virus of the Paramyxoviridae family and a major cause of respiratory disease in children. We found that IFIT1 significantly inhibited PIV3, whereas IFIT2, IFIT3, and IFIT5 were less effective or not at all. In further screening a set of ISG proteins we discovered that several other such proteins also inhibited PIV3, including IFITM1, IDO (indoleamine 2,3-dioxygenase), PKR (protein kinase, RNA activated), and viperin (virus inhibitory protein, endoplasmic reticulum associated, interferon inducible)/Cig5. The antiviral effect of IDO, the enzyme that catalyzes the first step of tryptophan degradation, could be counteracted by tryptophan. These results advance our knowledge of diverse ISG proteins functioning as antivirals and may provide novel approaches against PIV3. IMPORTANCE The innate immunity of the host, typified by interferon (IFN), is a major antiviral defense. IFN inhibits virus growth by inducing a large number of IFN-stimulated gene (ISG) proteins, several of which have been shown to have specific antiviral functions.Parainfluenza virus type 3 (PIV3) is major pathogen of children, and no reliable vaccine or specific antiviral against it currently exists. In this article, we report several ISG proteins that strongly inhibit PIV3 growth, the use of which may allow a better antiviral regimen targeting PIV3. P arainfluenza virus type 3 (PIV3) is a nonsegmented, negativestrand RNA virus belonging to the Paramyxoviridae family and a major cause of lower respiratory tract infection in humans and cattle (1-3). Human PIV3 is a particularly serious pathogen in young children, second in clinic importance only to respiratory syncytial virus (RSV), another member of the same family (3). There is currently no specific treatment or approved vaccine for PIV3. However, RNA viruses in general, and paramyxoviruses in particular, induce type I interferon (IFN), a major arm of host innate immunity, mainly by activating a cytoplasmic RNA helicase of the RIG-I family, which is followed by a signaling cascade ultimately leading to transcriptional induction of IFN genes (4-6). Early reports showed that PIV3 is highly sensitive to IFN (7), suggesting that this natural antiviral mechanism holds the potential to be harnessed. Type I IFN by itself has no antiviral activity, but upon binding to its cognate receptor on the cell surface, it triggers the so-called IFN response pathway, in which transcription factors STAT...

5-Hydroxytryptophan, a major product of tryptophan degradation, is essential for optimal replication of human parainfluenza virus

“…These have been described previously (Rabbani et al, 2016). In brief, all experiments were performed in A549 cells, which are human alveolar carcinoma type II-like and of epithelial origin.…”

“…of 1.0. Recombinant human IFN-γ (BD Biosciences; cat# 554616) and its use in cell culture (at a final concentration of 60 ng/ml) were described previously (Rabbani et al, 2016). …”

“…However, IDO was originally shown to inhibit the replication of the unicellular protozoan parasite Toxoplasma gondii in immune cells (Dai et al, 1994; Mehraj and Routy, 2016; Mellor and Munn, 2003). It is only recently that the relationship of IDO with viral pathogenesis and the antiviral role of IDO have been appreciated, notably with measles virus, herpes simplex virus, hepatitis B virus, influenza virus and respiratory syncytial virus (Adams et al, 2004; Huang et al, 2013; Mao et al, 2011; Obojes et al, 2005; Rabbani et al, 2016; Sage et al, 2014). The majority of these studies were conducted in cells of immune origin, such as macrophages and dendritic cells (DC), or in the live animal, which indicated a role of IDO in regulating adaptive immunity (Mellor and Munn, 2003; Schmidt and Schultze, 2014).…”

“…Our laboratory has recently shown that the parainfluenza virus type 3 (HPIV3), an agent of acute respiratory disease, is also strongly inhibited by IDO in lung epithelial A549 cells (Rabbani et al, 2016), suggesting a nonimmune mechanism. Here, we pursue the mechanism of this inhibition through the use of various catabolic products of Trp degradation and inhibitors of the degradative enzymes.…”

“…1) (Berger et al, 2009). Since the antiviral effect of IDO could be overcome by addition of Trp to the medium (Adams et al, 2004; Mao et al, 2011; Obojes et al, 2005; Rabbani et al, 2016), depletion of intracellular Trp levels has been considered the major reason of the antiviral effect of IDO, although the mechanism has remained unknown. In this communication, we show that the antiviral effect of IDO on PIV3 can be counteracted not only by Trp but also by 5-HTP (Fig.…”