Winter Peter S, Sarosiek Kristopher A, Lin Kevin H, Meggendorfer Manja, Schnittger Susanne, Letai Anthony, Wood Kris C
Department of Pharmacology and Cancer Biology, Duke University School of Medicine, Durham, NC 27710, USA.
Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA 02215, USA. Harvard Medical School, Boston, MA 02115, USA.
Sci Signal. 2014 Dec 23;7(357):ra122. doi: 10.1126/scisignal.2005301.
Myeloproliferative neoplasms (MPNs) frequently have an activating mutation in the gene encoding Janus kinase 2 (JAK2). Thus, targeting the pathway mediated by JAK and its downstream substrate, signal transducer and activator of transcription (STAT), may yield clinical benefit for patients with MPNs containing the JAK2(V617F) mutation. Although JAK inhibitor therapy reduces splenomegaly and improves systemic symptoms in patients, this treatment does not appreciably reduce the number of neoplastic cells. To identify potential mechanisms underlying this inherent resistance phenomenon, we performed pathway-centric, gain-of-function screens in JAK2(V617F) hematopoietic cells and found that the activation of the guanosine triphosphatase (GTPase) RAS or its effector pathways [mediated by the kinases AKT and ERK (extracellular signal-regulated kinase)] renders cells insensitive to JAK inhibition. Resistant MPN cells became sensitized to JAK inhibitors when also exposed to inhibitors of the AKT or ERK pathways. Mechanistically, in JAK2(V617F) cells, a JAK2-mediated inactivating phosphorylation of the proapoptotic protein BAD [B cell lymphoma 2 (BCL-2)-associated death promoter] promoted cell survival. In sensitive cells, exposure to a JAK inhibitor resulted in dephosphorylation of BAD, enabling BAD to bind and sequester the prosurvival protein BCL-XL (BCL-2-like 1), thereby triggering apoptosis. In resistant cells, RAS effector pathways maintained BAD phosphorylation in the presence of JAK inhibitors, yielding a specific dependence on BCL-XL for survival. In patients with MPNs, activating mutations in RAS co-occur with the JAK2(V617F) mutation in the malignant cells, suggesting that RAS effector pathways likely play an important role in clinically observed resistance.
骨髓增殖性肿瘤（MPNs）常常在编码Janus激酶2（JAK2）的基因中发生激活突变。因此，靶向由JAK及其下游底物信号转导和转录激活因子（STAT）介导的信号通路，可能会给携带JAK2（V617F）突变的MPN患者带来临床益处。尽管JAK抑制剂疗法可减轻患者的脾肿大并改善全身症状，但这种治疗并不能显著减少肿瘤细胞的数量。为了确定这种内在耐药现象的潜在机制，我们在JAK2（V617F）造血细胞中进行了以信号通路为中心的功能获得性筛选，发现鸟苷三磷酸酶（GTPase）RAS或其效应器通路[由激酶AKT和细胞外信号调节激酶（ERK）介导]的激活会使细胞对JAK抑制不敏感。当耐药的MPN细胞同时暴露于AKT或ERK通路的抑制剂时，它们会对JAK抑制剂变得敏感。从机制上讲，在JAK2（V617F）细胞中，促凋亡蛋白BAD[B细胞淋巴瘤2（BCL-2）相关死亡促进因子]的JAK2介导的失活磷酸化促进了细胞存活。在敏感细胞中，暴露于JAK抑制剂会导致BAD去磷酸化，使BAD能够结合并隔离促生存蛋白BCL-XL（BCL-2样蛋白1），从而触发细胞凋亡。在耐药细胞中，RAS效应器通路在存在JAK抑制剂的情况下维持BAD的磷酸化，导致细胞存活对BCL-XL产生特异性依赖。在MPN患者中，RAS的激活突变与恶性细胞中的JAK2（V617F）突变同时出现，这表明RAS效应器通路可能在临床上观察到的耐药中起重要作用。
