Targeting the C/EBPalpha-Gfi-pathway in CML stem cells

描述（由申请人提供）：转录因子C/EBP¿在骨髓形成的早期阶段需要调节分化和增殖之间的平衡。在许多类型的髓性白血病中，C/EBP¿在遗传上或功能上失活，其中增殖和分化之间的稳态协调丧失，这一观察结果证明了这一功能的重要性。此外，它在髓性白血病细胞系和慢性髓性白血病(CML)-母细胞危象患者的原代母细胞中的异位表达可诱导粒细胞分化并抑制增殖；这表明，恢复功能性C/EBP¿的表达或调节C/EBP¿调节的白血病干细胞增殖和存活所需的效应物的活性可能是一种新的抗白血病治疗方法。我们发现，C/EBP¿的增殖抑制作用需要转录抑制因子Gfi-1，它对维持造血干细胞的静止很重要。过表达Gfi-1可抑制BCR/ abl转化细胞的增殖和集落形成，其抑制作用可通过恢复STAT 5和Mcl-1的表达而逆转，这两个转录抑制的Gfi-1靶点对正常和白血病干细胞的增殖和存活至关重要。这些发现支持C/EBP¿-Gfi-1-STAT5/Mcl-1调控通路的存在，该通路可用于治疗性地消除CML干细胞。因此，本文提出了两种替代方法来评估干扰CML干细胞中C/EBP调控通路的治疗潜力：i)使用C/EBP本身作为生物活性蛋白递送到原始CML细胞；ii) CML干细胞增殖/存活特异性所需的C/EBP¿- gfi -1调控基因的遗传和药理学靶向。

DESCRIPTION (provided by applicant): The transcription factor C/EBP¿ is required for regulation of the balance between differentiation and proliferation during the early stages of myelopoiesis. The importance of this function is demonstrated by the observation that C/EBP¿ is genetically or functionally inactivated in many types of myeloid leukemia in which the homeostatic coordination between proliferation and differentiation is lost. Moreover, its ectopic expression in myeloid leukemia lines and in primary blast cells from chronic myelogenous leukemia (CML)-blast crisis patients induces granulocytic differentiation and inhibits proliferation; this suggests that restoring the expression of functional C/EBP¿ or modulating the activity of C/EBP¿-regulated effectors required for proliferation and survival of leukemic stem cells may be a novel anti-leukemia therapy. We found that the transcription repressor Gfi-1, which is important for maintaining the quiescence of hematopoietic stem cells, is required for the proliferation inhibitory effects of C/EBP¿. Overexpression of Gfi-1 suppresses proliferation and colony formation of BCR/ABL-transformed cells and its inhibitory effects are reversed by restoring the expression of STAT 5 and Mcl-1, two transcriptionally repressed Gfi-1 targets important for proliferation and survival of normal and leukemic stem cells. These findings support the existence of a C/EBP¿-Gfi-1-STAT5/Mcl-1 regulatory pathway that could be exploited therapeutically for the elimination of CML stem cells. Thus, two alternative approaches are proposed here to assess the therapeutic potential of perturbing C/EBP¿-regulated pathways in CML stem cells: i) the use of C/EBP¿ itself delivered as a biologically active protein to primitive CML cells; ii) the genetic and pharmacological targeting of C/EBP¿ -Gfi-1-regulated genes specifically required for the proliferation/survival of CML stem cells.