Stathmin 1 inhibition amplifies ruxolitinib-induced apoptosis in JAK2V617F cells

The JAK/STAT pathway is constitutively activated in myeloproliferative neoplasms and can be inhibited by ruxolitinib, a selective JAK1/2 inhibitor. The JAK2^V617F mutation leads to constitutive STAT3 phosphorylation and potentially leads to inhibition of Stathmin 1 activity via STAT3. In support of this hypothesis, we found that, in HEL JAK2^V617F cells, ruxolitinib treatment decreased STAT3 and Stathmin 1 association, induced Stathmin 1 activation and microtubule instability. Silencing of Stathmin 1 significantly reduced cell proliferation and clonal growth, and increased apoptosis induced by ruxolitinib. Stathmin 1 silencing also prevented ruxolitinib-induced microtubule instability. To phenocopy the effect of Stathmin 1 inhibition, cells were treated with paclitaxel, a microtubule-stabilizing drug, in association or not with ruxolitinib; combined treatment significantly increased apoptosis, when compared to monotherapy. Notably, Stathmin 1 mRNA levels were highly expressed in CD34⁺ cells from primary myelofibrosis patients. We then proposed that an undesired effect of ruxolitinib treatment may constitute Stathmin 1 activation and microtubule instability in JAK2^V617F cells. Induction of microtubule stability, through Stathmin 1 silencing or paclitaxel treatment, combined with ruxolitinib could be an effective strategy for promoting apoptosis in JAK2^V617F cells.     

The V617F JAK2 mutation and the myeloproliferative disorders

The discovery this year of a single mutation in the Janus Kinase (JAK)-2 gene in a high percentage of cases of polycythaemia vera (PV), essential thrombocythaemia (ET) and myelofibrosis suggests that it maybe the underlying molecular mechanism for these disorders. Different approaches from the inhibition of the tyrosine kinase JAK2, widespread search for mutations in tyrosine kinases, and investigation of the short arm of chromosome 9 where JAK2 is located all led to the discovery of the V617F JAK2 mutation. Substitution of a valine for a phenylalanine destabilizes the JH2 domain of JAK2 causes loss of the auto-inhibitory activity of this domain and explains some of the biological phenomena observed in patients with myeloproliferative disorders (MPD). The V617F JAK2 mutation can be detected by PCR-direct sequencing using DNA from the granulocyte lineage or with increased sensitivity by the amplification refractory mutation system using DNA from unfractionated blood. Pyrosequencing assays can be used to quantitate allele ratios to accurately define homozygote and heterozygote status. This single mutation is widespread having been detected in related MPD and other haematological malignancies. This leads to a number of further questions about the role of this single mutation in the clinical pattern of disease.     

JAK2(V617F) and leukemic transformation in myelofibrosis with myeloid metaplasia

Amongst 42 consecutive patients with leukemic transformation (LT) from myelofibrosis with myeloid metaplasia (MMM) 72% carried the JAK2(V617F) mutation. The mutation was observed at expected frequencies in all subtypes of MMM and acute myeloid leukemia. Although the patients with the mutation were younger and had a shorter interval to LT there was no difference in survival. Additionally, both the lack of mutation status progression in serial analysis (available in nine patients) and the low frequency of patients with high mutated allele burden suggest that LT arising from MMM is probably not dependent on changes in JAK2(V617F) mutation status.     

JAK2基因突变与骨髓增生性疾病的关系

 骨髓增生性疾病（MPD）中真性红细胞增多症（PV）、特发性血小板增多症（ET）、特发性骨髓纤维化（IMF）发现蛋白酪氨酸激酶（JAK2）基因上有一个碱基突变JAK2 V617F,突变明显与PV、ET和IMF的发生有关,这一发现可能成为诊断这类综合征的一种方式,也为寻找新的药物治疗MPD提供了明确的作用目标,同时还为研究细胞生长紊乱和细胞功能紊乱提供新的研究思路。     

JAK2 V617F mutation is uncommon in non-Hodgkin lymphomas

Recently, the JAK2 V617F mutation has been reported in high proportions of chronic myeloproliferative disorders, including polycythemia vera. To see whether the JAK2 V617F is important in the pathogenesis of lymphoid malignancies, this study analysed the occurrence of the JAK2 V617F mutation in 117 non-Hodgkin lymphomas (NHLs) by a single strand conformation polymorphism assay. However, there was no JAK2 V617F mutation in the NHLs and the data suggest that the JAK2 V617F mutation may not play a role in the development of NHL.     

Usefulness of JAK2V617F mutation in distinguishing idiopathic erythrocytosis from polycythemia vera

Idiopathic erythrocytosis (IE) is a primary erythrocytosis not fulfilling the criteria for polycythemia vera (PV) diagnosis. In order to verify the relationship between IE and PV, we screened JAK2V617F mutation in a consecutive series of 11 IE and, for comparison, in 15 PV. JAK2V617F mutation was screened by both cDNA sequencing and mutation specific PCR in both peripheral blood and bone marrow samples. All 11 IE tested negative for JAK2V617F mutation, which, conversely, occurred in 11/15 (73.3%) PV. Our results demonstrate that JAK2V617F is absent in IE and may represent a useful molecular marker for distinguishing IE from PV.     

干扰素α对JAK2V617阳性的骨髓增殖性疾病的影响

目的 探讨干扰素α(IFN-α)在治疗JAK2V617F突变阳性的骨髓增殖性疾病中的作用机制.方法 应用荧光定量PCR检测IFN-α治疗前后不同时间骨髓液JAK2V617F和PRV-1 mRNA表达水平;体外半固体集落培养检测自发性红系集落形成(EEC),流式细胞术检测体外IFN-α促凋亡作用.结果 10例JAK2V617F阳性真性红细胞增多症(PV),5例特发性血小板增多症(ET),2例特发性骨髓纤维化(MF)患者在应用干扰素α治疗前骨髓液JAK2V617F mRNA平均拷贝数量为(4.35±0.98)×107,治疗1年后降低为(1.56±0.67)×103,并与PRV-1 mRNA降低呈时间依赖性负相关.同时可见IFN-α也有抑制EEC形成和促进骨髓单个粒细胞凋亡作用.结论 IFN-α可以降低JAK2V617F阳性克隆比例、PRV-1的表达以及EEC的形成.JAK2V617F mRNA可作为患者骨髓液中治疗效果的分子生物学标记.