Expression and Function of Tob in T Lymphocytes

细胞静止是一种以细胞大小和代谢活动减少为特征的状态。幼稚淋巴细胞的静止减少了维持大量T和B细胞库所需的资源、能量和空间。静止也可能保护细胞免受可能导致恶性肿瘤的代谢损伤的积累。最近的研究表明，在没有信号的情况下，淋巴细胞的静止是一种积极维持的状态，而不是默认的状态。迄今为止发现的沉默因子代表潜在的肿瘤抑制基因，因为它们的表达或功能的改变有助于淋巴系统的进展 恶性肿瘤。因此，了解和加强淋巴细胞静止的策略可能对控制白血病和淋巴瘤有用。最近，我们发现Tob是一个调节T淋巴细胞静止的基因。我们的研究表明Tob基因在无能细胞中高表达。Tob mRNA在未经刺激的原代外周血T淋巴细胞中也有结构性表达，并在共刺激存在的情况下通过TCR/CD3激活而下调。Tob的强制表达抑制了细胞因子和细胞周期蛋白的转录，抑制了T细胞的增殖。相反，用反义寡核苷酸抑制Tob可以增强CDS介导的反应，并取消对最大增殖和细胞因子分泌的共刺激要求。为了了解Tob在完整宿主的免疫应答中的功能作用，我们建立了转基因小鼠，在其T细胞中结构性地表达Tob。在体外，Tob-Tg T细胞表现出增殖抑制和 细胞因子的产生。体内免疫后，Tob转基因小鼠对抗原攻击的原代反应减弱，Recall T细胞反应消失。这些结果提供了证据，证明T细胞静止不是一种默认状态，而是一种活跃维持的基因程序，必须被抑制才能发生T细胞激活。我们的发现表明，Tob在维持T细胞静止方面起着关键作用。因此，了解控制ToB表达的整合过程背后的生物化学和逻辑将有助于阐明更好地调节T细胞免疫反应的药物靶点和方法，无论是在自身免疫、移植和过敏中的免疫抑制，还是在疫苗、慢性感染和癌症中的增强。由于ToB代表一种潜在的肿瘤抑制因子，而ToB基因缺陷的小鼠会患上恶性淋巴瘤，这类研究也可能为淋巴系统恶性肿瘤的病理生理学提供见解。因此，调控Tob表达的策略可能在控制白血病和淋巴瘤方面有用。为了实现这些目标，我提出了三个具体目标：1)确定调控Tob mRNA表达的机制；2)确定参与Tob转录和翻译后调控的生化信号通路；3)通过以下方式确定Tob在调节完整宿主的T细胞免疫反应中的作用 使用转基因小鼠进行Tob。

Cellular quiescence is a state characterized by decreased cell size and metabolic activity. Quiescence in naive lymphocytes acts to reduce the resources, energy and space, required to maintain a vast repertoire of T and B cells. Quiescence might also protect cells from accumulating metabolic damage that could result in malignancy. Recent studies have shown that quiescence in lymphocytes is an actively maintained rather than a default state in the absence of a signal. Quiescence factors identified to date, represent potential tumor suppressor genes because alterations in their expression or function contributes to progression of lymphoid malignancies. Thus, strategies to understand and enforce lymphocyte quiescence might be useful in controlling leukemia and lymphoma. Recently, we identified Tob as a gene that mediates quiescence in T lymphocytes. Our studies showed that Tob mRNA is highly expressed in anergic cells. Tob mRNA is also constitutively expressed in unstimulated, primary, peripheral blood T lymphocytes and is downregulated during activation via TCR/CD3 in the presence of costimulation. Forced expression of Tob inhibits transcription of cytokines and cyclins and T cell proliferation. In contrast, suppression of Tob with antisense oligonucleotide augments CDS-mediated responses and abrogates the requirement of costimulation for maximal proliferation and cytokine secretion. In order to understand the functional role of Tob in the immune response of the intact host, we have generated transgenic mice, which constitutively express Tob in their T cells. In vitro, Tob-Tg T cells display reduced proliferation and cytokine production. After in vivo immunization, Tob-transgenic mice display reduced primary responses and abrogated recall T cells responses to antigenic challenge. These results provide evidence that T cell quiescence is not a default state, but an actively maintained gene program that must be suppressed for T cell activation to occur. Our findings indicate that Tob has a critical role in maintaining T cell quiescence. Thus, understanding the biochemistry and logic behind the integrative processes that control Tob expression will illuminate drug targets and approaches to better regulate T cell immune responses either for immunosuppression in autoimmunity, transplantation and allergy or for augmentation in vaccines, chronic infections and cancer. Because Tob represents a potential tumor suppressor and Tob deficient mice develop malignant lymphomas, such studies might also provide insights to the pathophysiology of lymphoid malignancies. Thus, strategies to regulate Tob expression might be useful in controlling leukemia and lymphoma. To achieve these objectives I propose three specific aims to: 1) Determine the mechanisms that regulate Tob mRNA expression; 2) Determine the biochemical signaling pathways involved in transcriptional and post-translational regulation of Tob; 3) Determine the role of Tob in regulating T cell immune responses in the intact host, by using transgenic mice for Tob.