Rivera I, Harhaj E W, Sun S C
Department of Microbiology and Immunology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.
J Biol Chem. 1998 Aug 28;273(35):22382-8. doi: 10.1074/jbc.273.35.22382.
Human T-cell leukemia virus type I (HTLV-I)-infected T-cells constitutively express surface Fas ligand (FasL), which may serve as a mechanism of viral pathogenesis. HTLV-I induces transcription of FasL gene through the viral transactivator Tax, although the underlying molecular mechanism remains unclear. In the present study, we have analyzed both the cis-activating element and transactivating factors involved in Tax activation of the FasL promoter. We show that the 486-base pair upstream region of the human FasL gene is sufficient for Tax-mediated transactivation in Jurkat T-cells. Interestingly, a palindromic DNA sequence (GGAAACTTCC) covering the consensus NF-ATp binding site (GGAAA), is required for Tax activation of FasL promoter. The involvement of NF-AT in this transactivation event is suggested by the finding that Tax fails to activate the FasL promoter in a Jurkat T-cell line defective in capacitative calcium entry, a signaling mechanism involved in NF-AT activation. Furthermore, activation of FasL promoter by Tax is largely attenuated in the nonlymphoid F9 embryonal and COS kidney cells deficient in NF-ATp expression. DNA-protein interaction assays reveal that the NF-AT-like motif in the FasL promoter is bound by both NF-ATp and NF-AT4 in Jurkat T-cells expressing Tax. The binding of NF-ATp, although not NF-AT4, to this enhancer also occurs along with HTLV-I-mediated infection of human peripheral blood T-cells. Furthermore, exogenously transfected NF-ATp binds to the NF-AT-like enhancer and participates in Tax-mediated FasL promoter transactivation. These results suggest an important role for proteins of the NF-AT family in HTLV-I Tax-mediated FasL gene transactivation.
人类I型嗜T细胞白血病病毒（HTLV-I）感染的T细胞持续表达表面Fas配体（FasL），这可能是病毒发病机制之一。HTLV-I通过病毒反式激活因子Tax诱导FasL基因转录，但其潜在分子机制仍不清楚。在本研究中，我们分析了参与Tax激活FasL启动子的顺式激活元件和反式激活因子。我们发现人类FasL基因上游486个碱基对的区域足以在Jurkat T细胞中实现Tax介导的反式激活。有趣的是，覆盖共有NF-ATp结合位点（GGAAA）的回文DNA序列（GGAAACTTCC）是Tax激活FasL启动子所必需的。Tax无法在缺乏储存性钙内流（一种参与NF-AT激活的信号传导机制）的Jurkat T细胞系中激活FasL启动子，这一发现提示了NF-AT参与了这一反式激活事件。此外，在缺乏NF-ATp表达的非淋巴细胞F9胚胎细胞和COS肾细胞中，Tax对FasL启动子的激活作用大大减弱。DNA-蛋白质相互作用分析表明，在表达Tax的Jurkat T细胞中，FasL启动子中的NF-AT样基序与NF-ATp和NF-AT4都结合。NF-ATp而非NF-AT4与该增强子的结合也发生在HTLV-I介导的人类外周血T细胞感染过程中。此外，外源转染的NF-ATp与NF-AT样增强子结合并参与Tax介导的FasL启动子反式激活。这些结果表明NF-AT家族蛋白在HTLV-I Tax介导的FasL基因反式激活中起重要作用。
