Reduction in sphingosine kinase 1 influences the susceptibility to dengue virus infection by altering antiviral responses

Abstract

Sphingosine kinase (SK) 1 is a host kinase that enhances some viral infections. Here we investigated the ability of SK1 to modulate dengue virus (DENV) infection in vitro. Overexpression of SK1 did not alter DENV infection; however, targeting SK1 through chemical inhibition resulted in reduced DENV RNA and infectious virus release. DENV infection of SK1 2/2 murine embryonic fibroblasts (MEFs) resulted in inhibition of infection in an immortalized line (iMEF) but enhanced infection in primary MEFs (18MEFs). Global cellular gene expression profiles showed expected innate immune mRNA changes in DENV-infected WT but no induction of these responses in SK1 2/2 iMEFs. Reverse transciption PCR demonstrated a low-level induction of IFN-b and poor induction of mRNA for the interferon-stimulated genes (ISGs) viperin, IFIT1 and CXCL10 in DENV-infected SK1 2/2 compared with WT iMEFs. Similarly, reduced induction of ISGs was observed in SK1 2/2 18MEFs, even in the face of high-level DENV replication. In both iMEFs and 18MEFs, DENV infection induced production of IFN-b protein. Additionally, higher basal levels of antiviral factors (IRF7, CXCL10 and OAS1) were observed in uninfected SK1 2/2 iMEFs but not 18MEFs. This suggests that, in this single iMEF line, lack of SK1 upregulates the basal levels of factors that may protect cells against DENV infection. More importantly, regardless of the levels of DENV replication, all cells that lacked SK1 produced IFN-b but were refractory to induction of ISGs such as viperin, IFIT1 and CXCL10. Based on these findings, we propose new roles for SK1 in affecting innate responses that regulate susceptibility to DENV infection.

Investigation of sphingosine kinase 1 in interferon responses during dengue virus infection

“…Our prior studies have demonstrated reduced DENV induction of ISGs in HEK293 cells treated with the SK1‐I 30 . This, however, is accompanied by a reduced DENV infection, and thus this system is not useful to discriminate effects on ISGs that are due to reduced SK1 activity compared with reduced induction by DENV replication per se .…”

“…Our prior data have suggested that the induction of ISGs are reduced in DENV‐infected SK1 −/− pMEF, 30 so to assess the type I IFN signalling pathways in SK1 −/− pMEF following DENV infection we measured IFNAR1 protein by flow cytometry and IFNAR2 mRNA by reverse transcriptase polymerase chain reaction (RT‐PCR). Cell‐surface IFNAR1 was significantly reduced at 24 h pi in both DENV‐infected WT and SK1 −/− pMEF (Figures 1a and b).…”

“…We have previously focused on IFIT1, viperin, CXCL10 and IRF7 mRNA changes following DENV infection, 30 while there is prior evidence for a linkage of SK1 with IRF1‐mediated CXCL10 induction 26 . Therefore, we defined the changes in IRF1 and IRF7 mRNA in WT and SK1 −/− pMEF following DENV infection.…”

“…In response to infection, overexpression of SK1 reduces the capacity of influenza A virus (IAV) to induce p‐STAT1, and these authors have proposed a role for SK1 in negatively regulating IFN signalling 27 , 28 . Our previous work has defined changes in SK1 activity during DENV infection 20 , 29 but discrepant effects of modulating SK1 on DENV infection; overexpression of SK1 has no effect, chemical inhibition of SK1 or infection of an immortalised SK1 −/− murine embryonic fibroblast line reduces infection, but infection of multiple isolates of SK1 −/− primary (p)MEF are enhanced 30 . Studying the induction of ISGs is confounded in models such as immortalised SK1 −/− murine embryonic fibroblast and SK1 drug inhibition, since DENV replication is concurrently reduced.…”

In silico study on anti-Chikungunya virus activity of hesperetin

“…Previous studies have shown close association between SPK/S1P pathway and important cellular processes such as cell growth, inflammation and immune responses, with both types of SPKs having the opposing effects (Maceyka et al, 2005; Okada et al, 2005; Olivera et al, 1999; Snider, Alexa Orr Gandy & Obeid, 2010). Interestingly, in addition to its contribution towards the development of degenerative diseases in humans, SPKs also play important roles in several viral infections, including Dengue and Influenza A viruses for SPK1 as well as Hepatitis C virus, Kaposi’s sarcoma-associated herpes virus, and most importantly for our study, CHIKV for SPK2 (Clarke et al, 2016; Couttas et al, 2014; Dai et al, 2014; Reid et al, 2015; Seo et al, 2013; Yamane et al, 2014). …”