Niki M, Ohtani K, Nakamura M, Sugamura K
Department of Microbiology, Tohoku University School of Medicine, Sendai, Japan.
J Virol. 1992 Jul;66(7):4348-57. doi: 10.1128/JVI.66.7.4348-4357.1992.
We examined the regulatory mechanisms of binding and transcriptional enhancement of the 21-bp core element of the enhancer of human T-cell leukemia virus type I (HTLV-I) in response to forskolin, 12-O-tetradecanoylphorbol-13-acetate (TPA), and a viral transactivator, p40tax. The 21-bp core element has been shown to bind to a cyclic AMP-responsive element binding protein (CREB)-like molecule at the site of an imperfect palindrome containing the TGAC motif. Experiments with oligonucleotides with mutations in the imperfect palindrome demonstrated that one TGAC motif is necessary and sufficient for both the binding of the CREB-related factor and transcriptional activity in response to forskolin in a human T-cell line, Jurkat. We also found that binding of the CREB-like factor to the 21-bp core element was enhanced by treatment with TPA, with little effect on transcriptional activity; in contrast, forskolin and p40tax did not facilitate binding, though they enhanced transcription. The combination of forskolin and TPA synergistically induced the transcription activity of the element, showing a hierarchical mechanism of regulation of the HTLV-I core enhancer element to levels sufficient for formation of the factor-enhancer complex and for activation of the complex. Added to those findings, our results indicate that the modes of activation by forskolin and p40tax are different from each other.
我们研究了人类I型T细胞白血病病毒（HTLV-I）增强子的21碱基核心元件在福司可林、12-O-十四酰佛波醇-13-乙酸酯（TPA）和病毒反式激活因子p40tax作用下的结合调控机制及转录增强作用。21碱基核心元件已被证明可在含有TGAC基序的不完全回文序列位点与环磷酸腺苷反应元件结合蛋白（CREB）样分子结合。对不完全回文序列中存在突变的寡核苷酸进行的实验表明，在人T细胞系Jurkat中，一个TGAC基序对于CREB相关因子的结合以及对福司可林的转录活性而言是必要且充分的。我们还发现，用TPA处理可增强CREB样因子与21碱基核心元件的结合，而对转录活性影响很小；相反，福司可林和p40tax虽能增强转录，但不促进结合。福司可林和TPA的组合协同诱导该元件的转录活性，显示出HTLV-I核心增强子元件的分级调控机制，可达到足以形成因子-增强子复合物并激活该复合物的水平。除了这些发现，我们的结果表明福司可林和p40tax的激活模式彼此不同。
