| Research Abstract |
The human T-cell leukemia virus type I (HTLV-I) is the etiologic agent of an aggressive form of human malignancy, adult T-cell leukemia/lymphoma (ATLL) and is also associated with many inflammatory diseases including myelopathy/tropical spastic paraparesis (HAM/TSP), arthropathy (HAAP), bronchopneumonopathy (HAB), uveitis and Sjogren syndrome. HTLV-I infection is widely distributed among mammalian cells including B lymphocytes, monocyte/macrophage cells and fibroblasts. Monocyte/macrophage cells are versatile secretory cells able to release various kinds of cytokines which contribute substantially to host defence and inflammation. Recently, HTLV-I-infected monocyte/macrophage cells from patients with ATLL or HAM/TSP have been demonstrated to participate in various pathological events in ATLL and HTLV-I-associated inflammatory diseases. In addition, a recent paper has shown that IL-2 production by primary ATLL cells is macrophage-dependent.
In the present study, we clarified cell-type sp
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ecific transcriptional activation of the HTLV-I LTR in monocytes. CAT reporters containing the HTLV-I LTR were transfected into THP-1 monocytes. As a result, LPS as well as p40Tax dose-dependently activated the HTLV-I LTR in monocytes. The LTR possesses 3 GGAA motifs, PuB1, PET and PuB2. Mutation studies further showed that 2 GGAA motifs, PET and PuB2 are essential to the LPS induction of the LTR in monocytes. In contrast, Tax-induction of the LTR in T-cells did not require either PuB2 or PET. These results demonstrate that GGAAs within the LTR are monocyte-specific LPS-responsive elements. Our EMSA data using a PuB2 probe and LPS-stimulated THP-1 nuclear extracts revealed binding of PU.1 (Spi-1), an Ets family transcription factor to PuB2, showing the importance of PU.1 binding in LPS-induction of the LTR in monocytes. In vitro translated recombinant PU.1 also bound to PET. Moreover, any Ets proteins including PU.1 did not bind to the PuB2 sequence. Interestingly, the THP-1 nuclear extract/PuB2 complex migrated significantly slower than recombinant PU.1/PuB2 complex did. Anti-IRF-8 Ab supershifted the slow complex, showing IRF-8, a co-factor for PU.1 is involved in the slow complex. Based upon the results obtained in the present study, the LTR of the HTLV-I gene is a LPS-responsive element recognized by PU.1 in monocytes. We propose cell-type specific transcriptional regulation of the HTLV-I gene in monocytes and T-cells. Less
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