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Human T cell leukemia virus type I (HTLV-I) is the etiologic agent of adult T cell leukemia (1). The HTLV-I-encoded tax gene has been implicated in leukemo-genesis. This gene encodes a 40-kD protein that causes transcriptional transactivation of viral gene expression and also activates expression of such cellular promoters as the interleukin-2 receptor (IL-2R) alpha chain, granulocyte-macrophage colony-stimulating factor (GM-CSF), fos, platelet-derived growth factor, IL-6, nerve growth factor, and transforming growth factor-Beta (2). There are two independent pathways for the action of Tax on transcription (2). The first affects the c-rel-related family of nuclear transcription factors that bind to NF-kappaB sites and are important for the normal activation of lymphocytes. NF-kappaB response sequences occur in a number of genes, including the HIV long terminal repeat (LTR) and the IL-6 promoter (3-5). The other effect of Tax, whereby Tax activates its own promoter through three Tax-responsive elements (TREs), is thought to occur independently of NF-kappaB. Similar sequence motifs have been identified in fos (6).
Transgenic mice that express Tax develop fibrosarcomas by 9 months of age (7). We have established cloned cell lines from fibroblastic mouse tumors derived from transgenic C57Bl/6 mice. Transfer of these cell lines to syngeneic mice resulted in rapid growth in situ of fibroblastic tumors (8). These tumors are well established (approximately 7 mm in diameter) by 10 days after injection, and the mice die from localized effects of the tumor by 2 months after injection. All of these cell lines expressed high levels of growth-related genes, similar to the expression in tumors from which they were derived. Analysis of a prototype malignant cell line (B line) is shown in Fig. 1A, lane 1. (Figure 1A omitted) Expression of these genes was at least ten times greater than those found in unstimulated Balb/3T3 cells (lane 4). In contrast, these cells do not express the T cell-specific factors IL-2 receptor (8), IL-2, or gamma interferon (IFN-gamma) (9).
To compare the importance of Tax and NF-kappaB proteins in the activation and maintenance of cell transformation, we used 3' terminal phosphorothioate (PS)-modified antisense oligodeoxynucleotides (ODNs) (10, 11) to inactivate expression of these proteins in transformed cell lines. The ODNs were modified with PS and purified according to published procedures (12). The ODNs extended over the...