Bid Function in Myeloid Homeostasis and Leukemogenesis

描述（由申请人提供）：BCL-2家族在细胞死亡途径中构成一个关键的检查点。BID是该家族“仅限BH3”子集的成员，其促凋亡功能需要其保守的BH3结构域。BID在TNF - RI和Fas等死亡受体下游的凋亡通路中发挥重要作用（1-7）。caspase 8和肉豆蔻酰化的切割作为一个激活分子开关，促进BID靶向线粒体(8)，激活多结构域的促凋亡成员，如BAK或BAX，介导细胞色素c的释放和下游效应caspase的激活(9)。bid缺陷小鼠可以存活并正常发育，然而肝细胞对抗fas诱导的肝细胞凋亡具有抗性（10）。因此，在某些细胞类型（如肝细胞）中，BID在介导死亡受体下游的线粒体扩增环中起重要作用。然而，在体外实验中，许多其他细胞，包括活化淋巴细胞，被Fas杀死，直接激活下游效应半胱天冬酶，促进细胞凋亡（11）。然而，随着BID缺陷小鼠衰老或受到慢性病毒感染的挑战，我们发现，在体内，BID也是维持所谓的I型细胞（包括B细胞、T细胞和骨髓单核细胞谱系）的稳态所必需的（12）。随着bid缺陷小鼠年龄的增长，它们表现出骨髓增生，然后高发发展为慢性髓细胞白血病。创始家族成员BCL-2是在t（14:18）染色体断点克隆的，这是滤泡性B细胞淋巴瘤的分子标志，建立了一类新的癌基因，其中畸变是细胞死亡而不是增殖（13-15）。在骨髓细胞中过度表达BCL-2的转基因小鼠会出现骨髓增生性疾病，当与Fas受体突变的小鼠杂交时，会进展为AML，这表明Fas途径和BCL-2在骨髓谱系的肿瘤抑制中具有协同作用（16）。促凋亡成员在正常骨髓稳态中的作用尚未得到很好的表征。我们认为BID是关键的促凋亡中间体，在髓系谱系中介导死亡受体信号传导，它的失活通过延长这些脆弱细胞的寿命来促进髓系白血病的发生，从而允许额外突变的积累。因此，这种单一的“仅bh3”蛋白有可能在维持正常骨髓稳态和抑制肿瘤方面发挥强有力的作用。为此，我提出以下具体目标：明确Bid在骨髓稳态中的作用。2. 明确Bid在髓性白血病发生中的作用。3. 确定在白血病发生中与Bid丧失合作的继发性遗传变化。

DESCRIPTION (provided by applicant): The BCL-2 family constitutes a crucial checkpoint in the cell death pathway. BID is a member of the "BH3-only" subset of this family and requires its conserved BH3 domain for its pro-apoptotic function. BID plays an important role in the apoptotic pathway downstream of death receptors such as TNF RI and Fas (1-7). Cleavage by caspase 8 and myristoylation serves as an activating molecular switch which facilitates targeting of BID to mitochondria(8) where it activates multidomain proapoptotic members such as BAK or BAX, mediating the release of cytochrome c and activation of downstream effector caspases (9). Bid-deficient mice are viable and develop normally, however hepatocytes are resistant to anti-Fas-induced hepatocellular apoptosis(10). BID thus plays an important role in mediating a mitochondrial amplification loop downstream of death receptors in certain cell types such as hepatocytes. Yet many other cells, including activated lymphocytes, are killed by Fas in in vitro assays, directly activating downstream effector caspases for the promotion of apoptosis(11). However, as Bid-deficient mice age or are challenged by chronic viral infection, we've discovered that BID is also singularly required in vivo to maintain homeostasis in so-called Type I cells including B cells, T cells, and the myelomonocytic lineage(12). As Bid-deficient mice age, they display a myeloid hyperplasia and then progress to Chronic myelomonocytic leukemia at high incidence. The founding family member, BCL-2 was cloned at the t(14:18) chromosomal breakpoint, the molecular hallmark of follicular B cell lymphoma establishing a new class of oncogenes in which the aberration is in cell death rather than proliferation(13-15). Transgenic mice over expressing BCL-2 in myeloid cells develop a myeloproliferative disorder, and when crossed with mice harboring a mutation in the Fas receptor, progress to AML, implicating a synergistic role for the Fas pathway and Bcl-2 in tumor suppression of the myeloid lineage(16). The role of pro-apoptotic members in normal myeloid homeostasis has not been well characterized. We propose that BID is the critical proapoptotic intermediate that mediates death receptor signaling in the myeloid lineage and that its inactivations promotes myeloid leukemogenesis by prolonging the life of these vulnerable cells, allowing accumulation of additional mutations. This single "BH3-only" protein therefore has potential to play a potent role in maintenance of normal myeloid homeostasis as well as tumor suppression. In this context, I propose the following specific aims: 1. Define the role of Bid in myeloid homeostasis. 2. Define the role of Bid in myeloid leukemogenesis. 3. Identify the secondary genetic changes that cooperate with loss of Bid in leukemogenesis.