Regulation of HTLV-1 gene expression in primary versus secondary target cell population in the context of chromosomally integrated viral promoter

S Rahman; D Pandya; B Wigdahl; Z Khan; P Jain

HTLV-1 exhibits a broad cellular tropism due to the ubiquitous nature of its receptor. In addition to the CD4+/CD25+ T cells other cell populations, including the cells of the monocyte-macrophage lineage, are also susceptible to HTLV-1 infection. Viral-induced alterations in these cells and their trafficking to the brain may play important roles in the progression of HAM/TSP. However, very little information exists concerning the regulation of HTLV-1 promoter or long terminal repeat (LTR) in secondary target cell populations. Moreover, most of the studies of HTLV-1 gene expression have been performed using transiently transfected LTRs that differ physically from a chromosomally integrated provirus, which like eukaryotic DNA, is wrapped with histone and nonhistone proteins to form the nucleosome, the basic unit of chromatin. Hence it is important to understand how the viral promoter is regulated when formatted in the context of chromatin. To this end, we have generated a number of clones of CD4+ T cell line Jurkat and monocytic line U-937 (representative primary and secondary target cell type, respectively) stably integrated with an HTLV-1 LTR. The single cell clones from both the cell types were propagated and examined for LTR integration by a reporter gene (luciferase) assay. Selected clones with varying luciferase expression were analyzed for integrated LTR copy number by real time PCR with higher levels of LTR expression shown to correlate with higher LTR copy number. An equal number of cells from the clones with comparable copy numbers were pooled and transfected with a Tax-expressing plasmid and analyzed for the luciferase expression as well as for global microRNA profiling. Tax has demonstrated a clear differential pattern in the activation and suppression of the cellular miRNA pathway indicating that the differential interplay of viral and cellular factors in primary versus secondary target cell populations regulates viral activation post-integration. Our results also demonstrated, for the first time, that HTLV-1 Tax protein can interfere with miRNA pathway as shown previously with other viral transactivator proteins such as HIV-1 Tat. These observations are currently being confirmed in the primary T cells and monocytes and are being extended to the B cell (Raji), and bone marrow progenitor cell (TF-1) lines. Future investigations will analyze the role of individual miRNAs and potential transcription factors in regulating Tax-mediated integrated LTR activation in selected cell types.

Regulation of HTLV-1 gene expression in primary versus secondary target cell population in the context of chromosomally integrated viral promoter

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Regulation of HTLV-1 gene expression in primary versus secondary target cell population in the context of chromosomally integrated viral promoter

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Abstract

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