Human herpes virus-6 increases HIV-1 expression in co-infected T cells via nuclear factors binding to the HIV-1 enhancer

Abstract

Human herpes virus-6 (HHV-6) can co-infect with HIV-1 human CD4+ T-cells, leading to accelerated cell death, and factors in HHV-6-infected cells stimulate HIV-1 LTR directed gene expression. In this study, we have examined the mechanism of HIV-1 activation by HHV-6 and localized the cis-acting sequences of HIV-1 LTR responsive to trans-activation. Increased HIV-1 LTR directed gene expression is obtained in HIV-1 infected cells co-infected with HHV-6, or in HHV-6 infected cells co-transfected with the HIV-1 tat gene. Parallel increases of HIV-1-specific transcripts are seen by in situ hybridization in HHV-6/HIV-1 doubly infected cells as compared to single HIV-1 infection. Similarly, infection by HHV-6 increases the steady-state level of HIV-1 LTR mRNA that parallels CAT enzymatic activity, suggesting a transcriptional and/or post-transcriptional activation. Sequences necessary for HIV-1 LTR activation by HHV-6 are distinct from those required for the tat response and map to a region of the HIV-1 LTR from -103 to -48. The HIV-1 enhancer sequence (-105 to -80) is sufficient to confer HHV-6 inducibility to a heterologous promoter, and nuclear protein(s) activated or induced by HHV-6 infection specifically bind to the NFχB motifs of the HIV-1 enhancer region. Since HHV-6 and HIV-1 share similar cell tropism, our data suggest that HHV-6 infection may play an important role in the progression of HIV-1 infection to AIDS by increasing HIV-1 gene expression, viral replication and consequently accelerating the cytopathic effect in co-infected CD4+ T-cells.