Novel Pathways for Bcr-Abl transformation

将Bcr蛋白的氨基末端序列融合到羧基的染色体重排 Abl酪氨酸激酶（p210 Bcr-Abl）的末端序列与几乎所有的慢性髓细胞性白血病（CML）病例相关。尽管Abl编码序列对Bcr-Abl介导的白血病发生的贡献相对较好理解，但Bcr编码序列的贡献尚不清楚。例如，几项体外研究已经鉴定了Bcr氨基末端内的催化活性，但这些活性与Bcr和Bcr-Abl的体内功能的关系尚不清楚。我们最近完成的两项研究表明，Bcr可能有助于Bcr-Abl的转化活性的方式，以前没有意识到。首先，我们已经确定了Bcr和 致癌转录因子c-Myc。这种相互作用的破坏可能是Bcr-Abl转化细胞中观察到的c-Myc表达水平升高的原因。与此一致，我们观察到c-Myc蛋白水平对CML衍生白血病细胞系中Bcr的剂量敏感。第二，我们已经证明Bcr的中心RhoGEF结构域（保留在Bcr-Abl中）含有体内催化、信号传导和转化活性。重要的是，在p210 Bcr-Abl的背景下观察到类似的催化活性。本提案的目的是表征这些新的活性，并确定它们在Bcr-Abl背景下的命运。具体而言，我们建议（1）确定Bcr与c-Myc转录因子的结合是否具有有助于Bcr-Abl介导的转化的功能后果，以及（2）确定我们已经定位到Bcr的RhoGEF结构域的转化和催化活性是否有助于Bcr-Abl介导的转化。这些研究的结果将大大有助于我们了解费城染色体阳性白血病的分子基础。

Chromosomal rearrangements that fuse amino terminal sequences of the Bcr protein to carboxyl terminal sequences of the Abl tyrosine kinase (p210 Bcr-Abl) are associated with virtually all cases of chronic myelogenous leukemia (CML). Whereas the contribution of Abl encoded sequences to Bcr-Abl-mediated leukemogenesis are relatively well understood, the contribution from the Bcr encoded sequences is unclear. For example, several in vitro studies have identified catalytic activities within the amino terminus of Bcr, yet the relationship of these activities to the in vivo functions of Bcr, and Bcr-Abl, are not known. We have recently completed two studies which suggest that Bcr may contribute to the transforming activity of Bcr-Abl in ways that were not previously realized. First, we have identified a functional interaction between Bcr and the oncogenic transcription factor c-Myc. The disruption of this interaction may account for the elevated levels of c-Myc expression that are observed in Bcr-Abl transformed cells. Consistent with this, we have observed that c-Myc protein levels are sensitive to the dosage of Bcr in a CML-derived leukemic cell line. Second, we have demonstrated that the central RhoGEF domain of Bcr (which is retained in Bcr-Abl) contains in vivo catalytic, signaling and transforming activity. Importantly, a similar catalytic activity is observed within the context of p210 Bcr-Abl. The objective of this proposal is to characterize these new activities, and determine their fates within the context of Bcr-Abl. Specifically, we propose to (1) determine if the association of Bcr with the c-Myc transcription factor has functional consequences that contribute to Bcr-Abl-mediated transformation, and (2) determine whether the transforming and catalytic activities that we have mapped to the RhoGEF domain of Bcr contribute to Bcr-Abl-mediated transformation. The results from these studies should contribute substantially to our knowledge of the molecular basis of Philadelphia chromosome positive leukemias.