King J A, Bridger J M, Löchelt M, Lichter P, Schulz T F, Schirrmacher V, Khazaie K
Department of Cellular Immunology, German Cancer Research Center, Heidelberg.
Oncogene. 1998 Jun 25;16(25):3309-16. doi: 10.1038/sj.onc.1201884.
Appropriate expression of HTLV-1 genes requires transcriptional transactivation by Tax and post-transcriptional regulation by Rex, both mediated by LTR encoded RNA sequences. Using a combination of deletion mutagenesis, Rex-reporter CAT assays, fluorescence in situ hybridization (FISH) and confocal laser scanning microscopy it was established that in the absence of Rex, CAT mRNAs harboring HTLV-1 LTR sequences were unable to leave the nucleus. Deletion of the known U5 encoded cis-acting repressing sequence (CRS) led to a partial release of nuclear retention. A novel regulatory element overlapping the 3' Rex responsive element (RxRE) region was shown to prevent export and expression of these transcripts. Deletion of both the 5' LTR encoded CRS and 3' LTR encoded downstream repressive sequence (3' CRS) led to constitutive mRNA nuclear export and gene expression, independently of Rex. The locations of the two regulatory elements indicate that while the 5' CRS selectively acts to hinder export of unspliced transcripts, the 3' CRS has the capacity to induce nuclear retention of all HTLV-1 transcripts, and therefore could potentially contribute to viral latency in infected cells.
HTLV-1基因的适当表达需要Tax介导的转录反式激活和Rex介导的转录后调控，两者均由LTR编码的RNA序列介导。通过缺失诱变、Rex报告基因CAT分析、荧光原位杂交（FISH）和共聚焦激光扫描显微镜相结合的方法，确定在没有Rex的情况下，携带HTLV-1 LTR序列的CAT mRNA无法离开细胞核。已知的U5编码顺式作用抑制序列（CRS）的缺失导致核滞留的部分释放。一个与3' Rex反应元件（RxRE）区域重叠的新型调控元件被证明可阻止这些转录本的输出和表达。5' LTR编码的CRS和3' LTR编码的下游抑制序列（3' CRS）的缺失导致组成型mRNA核输出和基因表达，与Rex无关。这两个调控元件的位置表明，虽然5' CRS选择性地阻碍未剪接转录本的输出，但3' CRS有能力诱导所有HTLV-1转录本的核滞留，因此可能有助于病毒在感染细胞中的潜伏。
