RIP1/RIP3-Calpain-Stat3 and NF-kappa B pathways in AML pathogenesis and treatment

白血病母细胞中NF-κB和STAT3的异常激活与耐药有关 预后不良，提示它们可能成为治疗的潜在靶点。我们发现两者的失活 NF-κB和STAT3信号通路协同抑制白血病干细胞的自我更新和耐药 细胞(LSCs)，提示这两个途径在白血病的发病机制中具有代偿作用。 STAT3α和STAT3β是两种主要的剪接异构体。激活的STAT3α通过调节促进肿瘤生长 靶基因表达(作为转录因子)和控制线粒体生产的ATP和 ROS(作为电子传输链的调节器)，而STAT3β缺乏反式激活结构域和 对STAT3α起显性-负性作用。目前使用的所有STAT3抑制剂仅抑制其转录 活性而不考虑其线粒体活性，这可能解释了为什么这些抑制剂失败 来抑制患者的白血病。据报道，从STAT3α到STAT3β的诱导提供了一个 两种异构体均有较好的抑瘤效果。我们发现，我们可以通过以下方式来诱导这种转变 抑制丝氨酸/苏氨酸蛋白激酶受体相互作用蛋白激酶1(RIP1)和RIP3。 RIP3和NF-κB是RIP1的平行下游信号通路，介导细胞因子诱导的激酶-2。 RIP1的依赖和非独立活性。我们发现中等水平的RIP1-RIP3激酶的激活 具有MLL1重排(MLL-r)或NPM1突变的急性髓系白血病(AML)细胞存在信号转导 (NPM1c+)。RIP1-RIP3信号在正常造血干/祖细胞(HSPC)和 急性髓系白血病细胞。在HSPC中，RIP1-RIP3信号介导肿瘤坏死因子α和IL1β诱导的坏死性下垂，而在急性髓系白血病细胞中， 适度激活这种信号是通过抑制钙蛋白来维持STAT3α水平所必需的 (CAPN)，一个蛋白水解酶家族。CAPN通过特异性切割降低STAT3α和增强STAT3β STAT3α蛋白和SFRS5，一种用于STAT3α选择性剪接的剪接调节因子。RIP1-RIP3激酶的抑制作用 信号转导导致STAT3α耗尽，STAT3β增加。我们的研究表明，就像共同抑制一样 在STAT3和NF-κB中，共同抑制RIP1-κ3信号和NF-RIPB也损害了LSC的自我更新和 使AML对标准化疗敏感。我们希望在初选阶段测试我们的新型联合治疗方案。 使用异种移植模型的人急性髓系白血病细胞。我们还打算阐明STAT3的分子机制 而NF-κB调节LSCs的自我更新和耐药，并探讨其分子机制 RIP3信号调节CAPN依赖的STAT3亚型开关。 这项研究的预期结果将使我们能够确定目前已知的 RIP1/RIP3和NF-kB信号通路抑制剂联合应用可改善MLL-r和NPM1c+AML的治疗 用标准的化疗。机理研究将提供详细的信息，使我们能够 有效靶向RIP3-CAPN-STAT3通路治疗AML。

Both NF-κB and Stat3 are abnormally activated in leukemic blasts and are implicated in drug-resistance and poor prognosis, suggesting they could be potential targets for therapy. We found that inactivation of both NF-κB and Stat3 signaling pathways synergistically represses self-renewal and drug-resistance in leukemia stem cells (LSCs), suggesting a compensatory role for these two pathways in the pathogenesis of leukemia. Stat3α and Stat3β are two major splicing isoforms. Active Stat3α promotes tumor growth by regulating target gene expression (functions as a transcription factor) and controlling mitochondrial production of ATP and ROS (functions as a regulator of the electron transport chain), while Stat3β lacks a transactivation domain and functions as a dominant-negative to Stat3α. All currently used inhibitors of Stat3 only repress its transcriptional activity without taking consideration of its mitochondrial activity, which might explain why these inhibitors failed to repress leukemia in patients. It was reported that induction of the switch from Stat3α to Stat3β provides a better tumor repressive effect than inhibition of both isoforms. We found that we can induce such a switch by inhibiting the serine/threonine-protein kinases receptor-interacting protein kinase 1 (Rip1) and Rip3. Rip3 and NF-κB are parallel downstream signaling pathways of Rip1, mediating cytokine-induced kinase- dependent and -independent activities of Rip1. We found that a moderate level of activation of Rip1-Rip3 kinase signaling exists in acute myeloid leukemia (AML) cells with MLL1-rearrangement (MLL-r) or NPM1 mutation (NPM1c+). Rip1-Rip3 signaling plays distinct roles in normal hematopoietic stem/progenitor cells（HSPCs）and AML cells. In HSPCs, Rip1-Rip3 signaling mediates TNFα and IL1β-induced necroptosis, while in AML cells, the moderate activation of such signaling is required for maintaining the levels of Stat3α by inhibition of calpain (CAPN), a family of proteolytic enzymes. CAPN reduces Stat3α and enhances Stat3β by specifically cleaving Stat3α protein and also SFRS5, a splice regulator for alternative splicing for Stat3α. Inhibition of Rip1-Rip3 kinase signaling results in depletion of Stat3α and an increase of Stat3β. Our study suggested that, as with co-inhibition of Stat3 and NF-κB, co-inhibition of Rip1-Rip3 signaling and NF-κB also compromises self-renewal of LSCs and sensitizes AML to standard chemotherapy. We want to test our novel combination treatment regimen in primary human AML cells using xenograft models. We also intend to elucidate the molecular mechanisms by which Stat3 and NF-κB regulate self-renewal and drug-resistance in LSCs as well as the molecular mechanism by which Rip3 signaling regulates CAPN-dependent Stat3 isoform switch. The expected results of this study will allow us to determine whether combinations of currently known inhibitors of Rip1/Rip3 and NF-kB signaling could improve treatment for MLL-r and NPM1c+ AML when combined with standard chemotherapy. The mechanistic studies will provide detailed information allowing us to more effectively target the Rip3-CAPN-Stat3 pathway to treat AML.