Redox control of Epstein-Barr virus replication by human thioredoxin/ATL-derived factor: differential regulation of lytic and latent infection

Thioredoxin-mediated redox control of human T cell lymphotropic virus type I (HTLV-I) gene expression

Thioredoxin (TRX) is a small ubiquitous protein with multiple biological functions, including the thiol-mediated redox-regulation of gene expression. We have previously demonstrated that human TRX is overexpressed as a major protein oxidoreductase in human T cell lymphotropic virus type I (HTLV-I)-infected cells. In the present study, we investigated the relationship between TRX and viral gene expression in HTLV-I infection. To study the mechanism that causes overexpression of TRX in HTLV-I-infected cells, we first examined the effect of the HTLV-I transactivator, Tax, on TRX expression. Induction of HTLV-I Tax protein increased the expression of TRX protein in a Tax-transfected Jurkat cell line, JPX-9. Moreover, chloramphenicol acetyltransferase (CAT) analysis with a reporter gene containing the TRX promoter revealed that Tax activates the transcription of TRX gene. To study the role of overexpressed TRX in HTLV-I infection, we next examined the effect of TRX on HTLV-I long terminal repeat (LTR)-mediated transcription using CAT analysis. In an HTLV-I-infected human T cell line MT-2, the HTLV-I LTR transactivation was suppressed by the overexpression of wild-type TRX, but activated by the introduction of inactive mutant TRX. Moreover, in HTLV-I negative Jurkat T cells, the HTLV-I LTR transactivation induced by Tax was also repressed by overexpression of wild-type TRX. Because cellular redox changes were shown to affect the HTLV-I gene expression, it is likely that TRX modulates the HTLV-I gene expression by regulating cellular redox state. Taken together, these findings suggest that overexpressed TRX, which is induced by HTLV-I Tax, may play an important role in HTLV-I infection through the negative regulation of viral gene expression.

Redox control of EBV infection: prevention by thiol-dependent modulation of functional CD21/EBV receptor expression

CD21 serves as a receptor for the Epstein-Barr virus (EBV). In this report, surface expression of CD21 on B and T cells was shown to be suppressed by a thiol-antioxidant, N-acetylcysteine (NAC), in a dose- and time-dependent manner. In contrast, expression of other surface markers, CD25 and CD4 for T cells and CD19 and surface IgM for B cells, was not affected by NAC. When an EBV-negative B-cell line B104 was treated with NAC, the cells were not susceptible to infection with B95-8-derived EBV. The effect of NAC was shown to be irrelevant to the transcriptional levels of CD21 mRNA and the intracellular glutathione levels. Immunoprecipitation study revealed that NAC causes a loss of anti-CD21 monoclonal antibody (HB5) binding to both membrane and soluble CD21, suggesting that NAC modulates the structure of CD21. Other thiol-antioxidants, such as 2-mercaptoethanol, pyrrolidine dithiocarbamate, and glutathione, showed similar effect to NAC on CD21 expression. These results suggest the possible modulation of EBV infection via thiol-dependent redox control of CD21, and thiol-antioxidants may be good candidates for controlling EBV infection.