Regulation of HTLV-1 and cellular gene transcription by the viral protein HBZ

描述（由申请人提供）：人类t细胞白血病病毒1型（HTLV-1）是一种复杂的逆转录病毒，是多种临床疾病的病原体，包括成人t细胞白血病（ATL），一种成熟活化t细胞的侵袭性且通常致命的恶性肿瘤。ATL通常在感染数十年后才被诊断出来，这表明长时间的病毒潜伏期有助于该病的发展。HTLV-1碱性亮氨酸拉链因子（HBZ）被认为在病毒潜伏期和t细胞增殖中起作用。该蛋白定位于细胞核中，携带碱性亮氨酸拉链（bZIP）结构域，通过与其他蛋白质中合适的亮氨酸拉链相互作用促进蛋白质二聚化。与HBZ结合的细胞bZIP因子包括某些AP-1转录因子组分（c-Jun, JunB, JunD）和ATF/CREB家族成员（ATF-1， CREB， CREM和CREB-2）。总的来说，与HBZ的相互作用被认为通过阻止因子结合DNA来抑制转录，这种作用与HBZ bZIP结构域的非典型碱性区相关。我们发现HBZ还直接结合细胞共激活因子p300和CBP，这是通过病毒蛋白bZIP结构域外的区域介导的。在HTLV-1启动子的背景下，我们发现HBZ与CREB和p300/CBP的结合对于实现转录的完全抑制至关重要。由于HBZ基因在原病毒3‘端负链上唯一编码，因此其表达不受针对5’ LTR（正常病毒启动子）的抑制机制的影响。HBZ与细胞bZIP因子和p300/CBP的结合可能是其解除许多细胞基因表达调控能力的基础。为了深入了解HBZ影响转录的机制，我们评估了它与细胞转录调节因子的相互作用，并确定了它所针对的基因。我们已经获得证据表明HBZ与ATF/CREB因子之间形成的配合物在结构上不同于与AP-1因子形成的配合物。此外，我们发现HBZ直接作用于p300/CBP的多个结构域，包括KIX、ZZ和TAZ2结构域。在本建议中，我们将讨论这些相互作用的功能后果。在Aim 1中，我们建议解剖HBZ和p300/CBP之间的相互作用，并确定这种相互作用的下游效应，包括共激活物与特定细胞蛋白相互作用和/或乙酰化能力的改变。在Aim 2中，我们将比较HBZ与ATF/CREB和AP-1蛋白的相互作用。在Aim 3中，我们将描述hbz介导的细胞基因表达失调的机制。我们将测试特定基因的异常表达是否与HTLV-1感染的某些生物学方面有关，这些生物学方面可能与ATL的发展或临床表现有关。

DESCRIPTION (provided by applicant): Human T-cell leukemia virus type 1 (HTLV-1) is a complex retrovirus that is the causative agent of a variety of clinical disorders including adult T-cell leukemia (ATL), an aggressive and often fatal malignancy of mature activated T-cells. ATL is frequently diagnosed after several decades of infection, suggesting that a long period of viral latency contributes to the development of this disease. The HTLV-1 basic leucine zipper factor (HBZ) is believed to play a role in viral latency and T-cell proliferation. This protein is localized in the nucleus and carries a basic leucine zipper (bZIP) domain that promotes protein dimerization through interactions with appropriate leucine zippers in other proteins. Cellular bZIP factors that are bound by HBZ include certain AP-1 transcription factor components (c-Jun, JunB, JunD) and members of the ATF/CREB family (ATF-1, CREB, CREM and CREB-2). Overall, interactions with HBZ are believed to repress transcription by preventing factors from binding the DNA, an effect that is correlated with the atypical basic region in the HBZ bZIP domain. We found that HBZ also binds directly to the cellular coactivators p300 and CBP, which is mediated through regions of the viral protein outside its bZIP domain. In the context of the HTLV-1 promoter, we found that binding of HBZ to both CREB and p300/CBP is essential to achieve full repression of transcription. As the HBZ gene is uniquely encoded on the minus strand at the 3' end of the provirus, its expression is not affected by this and other mechanisms of repression targeting the 5' LTR (the normal viral promoter). It is likely that the binding of HBZ to cellular bZIP factors and p300/CBP underlie its ability to deregulate expression of many cellular genes. To gain insight into the mechanisms by which HBZ affects transcription, we have evaluated its interactions with cellular transcriptional regulators and we have identified genes that it targets. We have obtained evidence that complexes formed between HBZ and ATF/CREB factors are structurally distinct from complexes formed with AP-1 factors. In addition, we found that HBZ directly targets multiple domains of p300/CBP, including the KIX, ZZ and TAZ2 domains. In this proposal we will address the functional consequences of these interactions. In Aim 1, we propose to dissect the interaction between HBZ and p300/CBP, and determine downstream effects of this interaction, including alterations in the abilities of the coactivator to interact with and/or acetylate specific cellular proteins. In Aim 2, we will compare the interaction of HBZ with ATF/CREB and AP-1 proteins. In Aim 3, we will characterize mechanisms of HBZ-mediated deregulation of cellular gene expression. We will test whether abnormal expression of specific genes underlies certain biological aspects of HTLV-1 infection that may relate to development or clinical presentations of ATL. PUBLIC HEALTH RELEVANCE: Human T-cell leukemia virus type 1 (HTLV-1) is a retrovirus associated with an aggressive leukemia and a neurodegenerative disease. This virus encodes a viral protein, HTLV-1 bZIP factor (HBZ), which is uniquely encoded on the minus strand of the provirus and is not transcribed from the 5' LTR (the normal viral promoter). This proposal investigates how HBZ is involved in regulating viral and cellular transcription by targeting bZIP transcription factors and key coactivators required for viral and cellular transcription.