SELF-RENEWAL IN LEUKEMIC STEM CELLS

描述(申请人提供)：我们的长期目标是促进对控制白血病干细胞(LSCs)自我更新特性的分子机制的理解(S)。LSCs是在移植模型中可能导致白血病的细胞，因此具有自我更新的特性。据推测，在目前的化疗方案下，这些细胞不是靶向的，因此是耐药和白血病复发的原因。识别与LSCs自我更新有关的基因或信号通路可能会促进白血病和其他癌症更有效的治疗方法的发展。Bmi-1是LSC自我更新的关键因子，在LSC中异常上调。LSC中Bmi-1基因解除调控的根本原因(S)尚不清楚。我们发现SALL4是一种新发现的多能因子和新的癌基因，在人类急性髓系白血病(AML)中异常表达。模拟SALL4亚型之一的SALL4B异常表达的转基因小鼠发展为AML.8对这些SALL4B小鼠的进一步研究导致了在SALL4B诱导的AML小鼠模型中LSCs的鉴定和特征。在功能获得研究的同时，抑制白血病细胞系中SALL4的表达会触发细胞凋亡和生长停滞。在SALL4B诱导的LSCs中，Bmi-1的表达上调，而SALL4的下调导致Bmi-1的表达减少。在SALL4基因敲除的白血病细胞系中恢复Bmi-1的表达可以挽救凋亡表型。更详细的研究表明，BMI-1是SALL4在骨髓细胞中的直接靶点。基于这些发现，我们假设SALL4B的解除调控在通过激活BMI-1促进LSC自我更新方面起着关键作用。为了证明这一假设，我建议1)确定SALL4在正常造血干细胞和LSCs自我更新中的功能作用(S)；2)确定SALL4促进HSCs和LSCs自我更新的机制，重点是其上调Bmi-1。这两组实验将有助于更好地理解白血病发生的关键机制(S)，并可能开发抗击白血病的新策略。与公共卫生相关：在美国，每年有3.3万新的白血病(血癌)病例，死亡率为2.3万。尽管有化疗和骨髓移植，但大多数白血病会复发，死亡率很高。最近一种降低复发率的方法是以白血病干细胞(LSC)为靶点，我们建议测试一种新的癌基因SALL4在LSC中的功能作用及其在治疗白血病方面的潜在用途。

DESCRIPTION (provided by applicant): Our long-term objectives are to advance the understanding of the molecular mechanism(s) that govern the self-renewal property of leukemic stem cells (LSCs). LSCs are cells that can give rise to leukemia in transplant models, and therefore have self-renewal properties. It is hypothesized that these cells are not targeted under current chemotherapy regimens and therefore account for drug resistance and leukemia relapse. Identifying genes or signaling pathways involved in the self-renewal of LSCs will likely promote the development of more effective treatments for leukemia and other cancers. Bmi-1 is a key element involved in LSC self-renewal, and is aberrantly upregulated in LSCs. The underlying cause(s) for deregulation of Bmi-1 in LSCs remain unknown. We have discovered that SALL4, a newly identified pluripotency factor and a novel oncogene, is aberrantly expressed in human acute myeloid leukemia (AML). Transgenic mice that mimic this aberrant expression of SALL4B, one of the SALL4 isoforms, develop AML.8 Further studies on these SALL4B mice have led to the identification and characterization of LSCs in the SALL4B-induced AML mouse model. Parallel to gain-of-function studies, knockdown of SALL4 expression in leukemic cell lines triggers cell apoptosis and growth arrest. While upregulation of Bmi-1 is found in the SALL4B-induced LSCs, downregulation of SALL4 leads to decreased expression of Bmi-1. Restoring Bmi-1 expression in SALL4 knockdown leukemic cell lines rescues the apoptotic phenotype. More detailed studies have demonstrates that Bmi-1 is a direct target of SALL4 in bone marrow cells. Based on these findings, we hypothesize that deregulation of SALL4B plays a key role in promoting self-renewal of LSCs by activation of Bmi-1. To prove this hypothesis, I propose to 1) Determine the functional role(s) of SALL4 in self-renewal of normal hematopoietic stem cell (HSCs) and LSCs; and 2) Define the mechanism of SALL4 enhancement of self-renewal of HSCs and LSCs with a focus on its up-regulation of Bmi-1. These two groups of experiments will serve to better understand the critical mechanism(s) in leukemogenesis, and potentially develop novel strategies to combat leukemia. PUBLIC HEALTH RELEVANCE: In United States, there are 33,000 new cases of leukemia (blood cancer) with a death rate of 23,000 every year. Despite chemotherapy and bone marrow transplantation, most leukemia relapses and has a high-mortality rate. One recent approach to decrease the incidence of relapse involves targeting "leukemic stem cell (LSC)", and we propose to test the functional role of a novel oncogene SALL4 in LSCs and its potential usage in treating leukemia.