title: Unfolded protein response (UPR) gene expression during antibody-dependent enhanced infection of cultured monocytes correlates with dengue disease severity.
abstract: DENV (dengue virus) induces UPR (unfolded protein response) in the host cell, which strikes a balance between pro-survival and pro-apoptotic signals. We previously showed that Salubrinal, a drug that targets the UPR, inhibits DENV replication. Here, we examine the impact on UPR after direct or ADE (antibody-dependent enhanced) infection of cells with DENV clinical isolates. THP-1 cells in the presence of subneutralizing concentration of humanized antibody 4G2 (cross-reactive with flavivirus envelope protein) or HEK-293 cells (human embryonic kidney 293 cells) were infected with DENV-1-4 serotypes. UPR gene expression was monitored under these infection conditions using real-time RT-PCR (reverse transcription-PCR) and Western blots to analyse serotype-dependent variations. Subsequently, in a blinded study, strain-specific differences were compared between DENV-2 clinical isolates obtained from a single epidemic. Results showed that THP-1 cells were infected efficiently and equally by DENV-1-4 in the ADE mode. At 48 hpi (h post infection), DENV-1 and -3 showed a higher replication rate and induced higher expression of several UPR genes such as BiP (immunoglobulin heavy-chain-binding protein), GADD34 (growth arrest DNA damage-inducible protein 34) and CHOP [C/EBP (CCAAT/enhancer-binding protein)-homologous protein]. The ADE infection of THP-1 cells with epidemic DENV-2 high-UPR-gene-expressing strains appears to correlate with severe disease; however, no such correlation could be made when the same viruses were used to infect HEK-293 cells. Our finding that UPR gene expression in THP-1 cells during ADE infection correlates with dengue disease severity is consistent with a previous study [Morens, Marchette, Chu and Halstead (1991) Am. J. Trop. Med. Hyg. 45, 644-651] that showed that the growth of DENV 2 isolates in human peripheral blood leucocytes correlated with severe and mild dengue diseases.
authors.affiliation: Program in Emerging Infectious Diseases, Duke-NUS Graduate Medical School, 8 College Road, Singapore 169857, Singapore.
authors.forename: Prasad N
authors.initials: PN
authors.lastname: Paradkar
authors.forename: Eng Eong
authors.initials: EE
authors.lastname: Ooi
authors.forename: Brendon J
authors.initials: BJ
authors.lastname: Hanson
authors.forename: Duane J
authors.initials: DJ
authors.lastname: Gubler
authors.forename: Subhash G
authors.initials: SG
authors.lastname: Vasudevan
mesh_terms: D019067:Antibody-Dependent Enhancement; D002460:Cell Line; D003715:Dengue / Q000276:immunology*; D003716:Dengue Virus / Q000276:immunology*; D015870:Gene Expression; D006801:Humans; D009000:Monocytes / Q000821:virology*; D056811:Unfolded Protein Response