Alteration of Rb in HTLV-1 transformed cells

HTLV-1 转化细胞中 Rb 的变化

• 批准号: 6901886
• 负责人: Fatah Kashanchi
• 金额: $ 19.13万
• 依托单位: GEORGE WASHINGTON UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-06-15 至 2007-05-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6901886
• 关键词: cell cycle; cell growth regulation; deltaretrovirus; gene expression; host organism interaction; human T cell leukemia; neoplastic transformation; oncoproteins; phenotype; posttranslational modifications; proteasome; protein protein interaction; proteolysis; retinoblastoma protein; tissue /cell culture; transfection; ubiquitin; viral leukemogenesis; virus protein

DESCRIPTION (provided by applicant): Human T-cell leukemia virus type I (HTLV-I) is the etiologic agent of adult T-cell leukemia (ATL). ATL is a complex and multi-faceted disease that evolves initially from viral-induced carcinogenic events and leads to multiple chromosomal abnormalities that are associated with the aggressive subtypes of ATL. Tax, the viral oncoprotein encoded within the pX region of the viral genome, is considered a major contributor to cell cycle deregulation in HTLV-I transformed cells by targeting such cellular factors as cyclin D2, p21/waf1, p16/INK4a, and p53. This concerted deregulation, especially at the G1 phase of the cell cycle, ensures continuous cellular progression via the loss of checkpoint control and insensitivity to anti-mitogens. The long-term goal of our research is to understand how Tax-dependent perturbation of restriction point regulators leads to leukemogenesis. A significant regulator of the G1 restriction point in eukaryotic cells is the tumor suppressor protein retinoblastoma (Rb). Rb, with p107 and p130, are part of a family of proteins involved in quiescence, cellular division, differentiation, senescence, and apoptosis. We have recently found that within both HTLV-I transformed cells and ATL patients there are a decrease of Rb protein as compared to uninfected controls. Specifically, this decrease is dependent on Tax expression and regulated at the posttranslational level. We have found that Tax is able to bind to Rb within the B domain through either a LXCXE or PENF homology motif within the C terminus of Tax. We further show, through in vitro degradation assays, that Rb degradation is dependent on Tax's ability to associate with the 26S proteasome. The proteasome degradation of Rb appears to be restricted to the hypophosphorylated (or active) Rb species, since the predominant Rb species remaining in HTLV-I transformed cells is the inactive form of Rb. Therefore, loss of the active species of Rb has led us to speculate that this results in a phenotype that is similar to cells that have lost Rb activity due to genetic/epigenetic alterations. Our hypothesis is that Rb degradation by Tax contributes to the immortalization of HTLV-I infected cells. Our rationale for these studies is based on data that shows the HTLV-I viral protein Tax destabilizes the Rb protein by targeting this protein to the 26S proteasome for degradation. We believe this mechanism is analogous to HPV's E7-dependent destabilization of Rb that results in the loss of the active form of Rb. Rb deregulation within the p16/INK4a/cyclin D pathway is an early event in HPV-16 immortalization by promoting cell cycle entry and proliferation of senescent primary cells. These phenotypes are also observed in HTLV-I transformed cells as shown by our preliminary data and may contribute to ATL malignancy. The following specific aims will address our hypothesis: (I) what is the mechanism of Tax-dependent proteolysis of Rb in HTLV-I transformed cells? (II) Is degradation of Rb an early event that contributes to Tax-dependent immortalization? Data obtained from these studies will shed light on how Tax and Rb interaction leads to the immortalization of HTLV-I infected ATL cells.

描述（由申请方提供）：人T细胞白血病病毒I型（HTLV-I）是成人T细胞白血病（ATL）的病原体。ATL是一种复杂且多方面的疾病，其最初从病毒诱导的致癌事件演变，并导致与ATL的侵袭性亚型相关的多种染色体异常。Tax是在病毒基因组pX区域内编码的病毒癌蛋白，被认为是HTLV-1转化细胞中细胞周期失调的主要贡献者，其靶向细胞因子如细胞周期蛋白D2、p21/waf 1、p16/INK 4a和p53。这种协调的失调，特别是在细胞周期的G1期，通过检查点控制的丧失和对抗有丝分裂原的不敏感性来确保连续的细胞进展。 我们研究的长期目标是了解限制点调节因子的税收依赖性扰动如何导致白血病发生。真核细胞中G1限制点的一个重要调节因子是肿瘤抑制蛋白视网膜母细胞瘤（Rb）。Rb与p107和p130是参与静止、细胞分裂、分化、衰老和凋亡的蛋白质家族的一部分。我们最近发现，在HTLV-I转化细胞和ATL患者中，与未感染的对照组相比，Rb蛋白减少。具体而言，这种减少依赖于Tax表达，并在翻译后水平进行调节。我们已经发现Tax能够通过Tax C末端的LXCXE或PENF同源基序与B结构域内的Rb结合。我们进一步表明，通过体外降解试验，Rb降解依赖于税收的能力，与26 S蛋白酶体。Rb的蛋白酶体降解似乎仅限于低磷酸化（或活性）Rb物种，因为HTLV-1转化细胞中剩余的主要Rb物种是Rb的非活性形式。因此，Rb活性物质的丢失使我们推测，这导致与由于遗传/表观遗传改变而失去Rb活性的细胞相似的表型。 我们的假设是Rb降解税有助于HTLV-I感染细胞的永生化。我们进行这些研究的基本原理是基于显示HTLV-I病毒蛋白Tax通过将Rb蛋白靶向26 S蛋白酶体进行降解而使Rb蛋白不稳定的数据。我们认为这种机制类似于HPV的E7依赖性Rb的不稳定，导致Rb活性形式的丧失。p16/INK 4a/cyclin D通路中Rb的失调是HPV-16永生化的早期事件，通过促进细胞周期进入和衰老原代细胞的增殖。如我们的初步数据所示，这些表型也在HTLV-I转化细胞中观察到，并且可能有助于ATL恶性肿瘤。以下具体目标将解决我们的假设：（一）在HTLV-Ⅰ转化细胞中Rb的Tax依赖性蛋白水解的机制是什么？(II)Rb的降解是导致税收依赖性永生化的早期事件吗？从这些研究中获得的数据将阐明Tax和Rb相互作用如何导致HTLV-I感染的ATL细胞的永生化。