The kinetics, mechanisms, and consequences of HTLV-1 plus-strand expression in naturally-infected T-cell clones

Abstract

HTLV-1 replication requires the expression of plus-strand-encoded transcriptional transactivator protein Tax. However, Tax protein, a surrogate for HTLV-1 plus-strand expression is seldom detected in freshly isolated infected blood. The kinetics and consequences of plus-strand expression remain poorly understood. I used two fluorescent protein-based Tax reporter systems to study the dynamics and consequences of plus-strand expression and the changes to the host gene expression during plus-strand expression in naturally HTLV-1-infected, non-malignant T-cell clones. Time-lapse live-cell imaging followed by single-cell analysis of two T-cell clones stably transduced with a short-lived enhanced green fluorescent protein Tax reporter system identified five patterns of Tax expression in both clones and the distribution of these patterns was different between the two clones. Mathematical modelling of the experimental data revealed that the mean duration of Tax expression differed between the two clones – 94 and 417 hours, respectively. Host cell transcriptome analysis during successive stages of plus-strand strand expression using a fluorescent timer protein-based Tax reporter system in naturally-infected T-cell clones identified dysregulation in the expression of genes related to multiple cellular processes, including cell cycle, DNA damage response, and apoptosis at the initiation of the plus-strand transcriptional burst. The plus-strand expression showed immediate but transient adverse effects, including reduced proliferation, increased apoptosis, upregulation of a DNA damage marker, and impaired cell cycle progression. In the longer term, the immediate negative consequences of Tax expression were offset by reduced apoptosis and increased proliferation as cells terminated plus-strand expression. Plus-strand expression was also associated with cell-to-cell adhesion and reduced motility. These findings show within and between clone variability in the patterns and duration of HTLV-1 plus-strand expression, changes to the host gene expression during successive stages of the plus-strand expression, and the balance between the beneficial and adverse effects on the host cell associated with the plus-strand expression.