A NOVEL MECHANISM OF TCL1 TUMORIGENESIS

描述（由申请人提供）：我们提出了一种新的TCL 1（T细胞白血病-1）诱导淋巴癌的机制。 假设是异常的TCL 1表达促进不适当的AKT（蛋白激酶-B）活化以引起转化。 然而，TCL 1增强的AKT活化程度与B细胞中靶向缺失PTEN肿瘤抑制因子诱导的增强的AKT活化程度相当。 最值得注意的是，我们的TCL 1转基因小鼠迅速发展成熟的B细胞恶性肿瘤，而条件性PTEN缺失小鼠从不形成B细胞癌。这些观察结果使我们假设TCL 1介导的AKT增强最多具有轻微的致瘤作用。 然而，我们不能排除TCL 1改变AKT靶特异性的可能性，我们在本提案中简要讨论了这个问题。 以前，我们表明，细胞质膜因子增强TCL 1/AKT的相互作用。 随后，我们在标记的TCL 1 co-IP反应中寻找新的TCL 1相互作用伙伴。 令人惊讶的是，我们确定了RNA降解酶多核苷酸磷酸化酶（PNIPs）作为淋巴细胞中唯一的TCL 1结合伴侣。 我们将确定PNDT是否是TCL 1/AKT相互作用增强因子。 我们支持这样的观点，即PNTR/TCL 1相互作用通过TCL 1稳定PNTR靶mRNA介导TCL 1诱导的肿瘤发生，而不是通过影响AKT/TCL 1相互作用。 检验这一假设是本提案的主要目的。 我们提供的初步证据表明，TCL 1/PNTR的相互作用阻止特定的mRNA的加工。因此，TCL 1可能是一种天然的PNIPs配体，通过改变PNIPs的mRNA周转来调节发育基因的表达。 当失调时，我们预测TCL 1不适当地稳定了特定的mRNA注定降解，提供了一种新的机制，导致转化的异常基因表达。 最引人注目的候选靶mRNA是AID，因为持续的AID超突变可以解释我们的TCL 1转基因小鼠模型中的广泛的生发中心来源的B细胞癌。 本提案的具体目标是对TCL 1介导的转化机制进行研究，重点关注TCL 1、PND 3和AKT在体外和体内较小程度上相互作用的功能后果。

DESCRIPTION (provided by applicant): We propose a new mechanism for TCL1 (T cell leukemia-1) induction of lymphoid cancers. The assumption has been that aberrant TCL1 expression promotes inappropriate AKT (protein kinase-B) activation to cause transformation. However, the extent of TCL1-augmented AKT activation is comparable to the degree of enhanced AKT activation induced by targeted deletion of the PTEN tumor suppressor in B cells. Most notably, our TCL1 transgenic mice rapidly develop mature B cell malignancies while conditional PTEN-null mice never form B cell cancers. These observations lead us to hypothesize that TCL1-mediated AKT augmentation has, at most, a minor tumorigenic effect. We cannot, however, exclude the possibility that TCL1 alters the target specificity of AKT and we address this issue briefly in this proposal. Previously, we showed that a cytoplasmic membrane factor augmented TCL1/AKT interactions. We subsequently searched for new TCL1-interacting partners in flag-tagged TCL1 co-IP reactions. Surprisingly, we identified the RNA degrading enzyme polynucleotide phosphorylase (PNPase) as the sole TCL1 binding partner in lymphoid cells. We will determine whether or not PNPase is the TCL1/AKT interaction-augmenting factor. We favor the idea that PNPase/TCL1 interactions mediate TCL1-induced tumorigenesis through TCL1 stabilization of PNPase target mRNAs rather than by effecting AKT/TCL1 interactions. Testing this hypothesis is the main aim of this proposal. We provide preliminary evidence that TCL1/PNPase interactions block the processing of specific mRNAs. As such, TCL1 may be a natural PNPase ligand that regulates developmental gene expression by altering mRNA turnover by PNPase. When dysregulated, we predict TCL1 inappropriately stabilizes specific mRNAs destined for degradation, providing a novel mechanism of aberrant gene expression resulting in transformation. The most compelling candidate target mRNA is AID, since persistent AID hypermutation could account for the broad spectrum of germinal center-derived B cell cancers in our TCL1 transgenic mouse model. The specific aims in this proposal form an investigation of the mechanism of TCL1-mediated transformation, focusing on functional consequences of interactions between TCL1, PNPase and to a lesser extent AKT in vitro and in vivo.