Hypoxia inhibits JAK2V617F activation via suppression of SHP-2 function in myeloproliferative neoplasm cells

Effect of hypoxia on HIF-1α and NOS3 expressions in CD34+ cells of JAK2V617F-positive myeloproliferative neoplasms

PURPOSE

Myeloproliferative neoplasms (MPN) are a heterogeneous group of hematopoietic stem-cell diseases with excessive proliferation of one or more blood cell lines. In this study, we evaluated the effect of different oxygen concentrations on HIF-1α and NOS3 gene expression to determine the effect of the bone marrow microenvironment on JAK2V617F positive Philadelphia chromosome negative (Ph-) MPNs.

PATIENTS AND METHODS

Peripheral blood mononuclear cells (MNC) of 12 patients with Ph- MPN were collected. The presence of JAK2V617F allele status was determined with allele-specific nested PCR analysis. MPN CD34+ and CD34depleted populations were isolated from MNC by magnetic beads. Separate cell cultures of CD34+/depleted populations were managed at different oxygen concentrations including anoxia (∼0%), hypoxia (∼3%), and normoxia (∼20%) conditions for 24 ​h. HIF-1α and NOS3 gene expression changes were examined in each population related to JAK2V617F status with real time RT-PCR.

RESULT

It was revealed that relative HIF-1α and NOS3 expressions were significantly increased in response to decreased oxygen concentration in all samples. Relative HIF-1α and NOS3 expressions were found to be higher especially in CD34+ and CD34depleted populations carrying JAK2V617F mutations compared to MPN patients carrying wild-type JAK2.

CONCLUSION

JAK2V617F might have specific role in HIF-1α and NOS3 regulations with respect to low oxygen concentrations in Ph- MPN. Further evaluations might reveal the effect of JAK2V617F on Ph- MPN pathogenesis in bone marrow microenvironment.

Bone marrow niche dysregulation in myeloproliferative neoplasms

The bone marrow niche is a complex and dynamic structure composed of a multitude of cell types which functionally create an interactive network facilitating hematopoietic stem cell development and maintenance. Its specific role in the pathogenesis, response to therapy, and transformation of myeloproliferative neoplasms has only recently been explored. Niche functionality is likely affected not only by the genomic background of the myeloproliferative neoplasm-associated mutated hematopoietic stem cells, but also by disease-associated 'chronic inflammation', and subsequent adaptive and innate immune responses. 'Cross-talk' between mutated hematopoietic stem cells and multiple niche components may contribute to propagating disease progression and mediating drug resistance. In this timely article, we will review current knowledge surrounding the deregulated bone marrow niche in myeloproliferative neoplasms and suggest how this may be targeted, either directly or indirectly, potentially influencing therapeutic choices both now and in the future.

Hypoxia-inducible factor 1 (HIF-1) is a new therapeutic target in JAK2V617F-positive myeloproliferative neoplasms

Classical Philadelphia chromosome-negative myeloproliferative neoplasms (MPN) are a heterogeneous group of hematopoietic malignancies including polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). The JAK2V617F mutation plays a central role in these disorders and can be found in 90% of PV and ~50-60% of ET and PMF. Hypoxia-inducible factor 1 (HIF-1) is a master transcriptional regulator of the response to decreased oxygen levels. We demonstrate the impact of pharmacological inhibition and shRNA-mediated knockdown (KD) of HIF-1α in JAK2V617F-positive cells. Inhibition of HIF-1 binding to hypoxia response elements (HREs) with echinomycin, verified by ChIP, impaired growth and survival by inducing apoptosis and cell cycle arrest in Jak2V617F-positive 32D cells, but not Jak2WT controls. Echinomycin selectively abrogated clonogenic growth of JAK2V617F cells and decreased growth, survival, and colony formation of bone marrow and peripheral blood mononuclear cells and iPS cell-derived progenitor cells from JAK2V617F-positive patients, while cells from healthy donors were unaffected. We identified HIF-1 target genes involved in the Warburg effect as a possible underlying mechanism, with increased expression of Pdk1, Glut1, and others. That was underlined by transcriptome analysis of primary patient samples. Collectively, our data show that HIF-1 is a new potential therapeutic target in JAK2V617F-positive MPN.

SHP-2 Activating Mutation Promotes Malignant Biological Behaviors of Glioma Cells

Background

This study investigated the mechanism underlying the activating mutation of SHP-2 in promoting malignant biological behaviors of glioma cells.

Material/Methods

The SHP-2 empty plasmid pcDNA3.1 and SHP-2 activating mutation plasmid pcDNA3.1 SHP-2 ^D61G mutant eukaryotic expression vectors were designed; stable SHP-2-expressing cells transfected with pcDNA3.1 SHP-2 ^D61G mutant were set as the mutation group; cells transfected with pcDNA3.1 were set as the empty vector group; and cells without transfection were set as the control group. The cell reproductive capacity in each group was measured by MTT method. The invasion ability of cells in vitro was detected by Transwell chamber assay, the cell apoptosis in each group was detected by Annexin-V/PE dual-staining method, and the clone formation ability of cells in vitro was detected by Tablet clone-forming assay. The activation of ERK1/2, ARK, and p38MAPK signal pathways in each group was determined by Western blot.

Results

After transfection, the expression of SHP-2 protein in the mutant group was significantly higher than that in the control group and empty vector group. The proliferation ability of transfected cells, the apoptosis rate, the invasion ability, and the expression levels of phosphorylated ERK1/2, AKT, and p38 in the mutation group was significantly higher than in the empty vector group and the control group (P<0.05). Moreover, the cell clone formation ability of the mutation group was obviously enhanced (P<0.05).

Conclusions

The activating mutation of SHP-2 can lead to malignant changes in biological behaviors of glioma cells, and the specific mechanism may be related to the activation of ERK1/2, AKT, and p38 signal pathway. SHP-2 protein may become a new target for anti-malignant transformation of glioma.

Metformin inhibits JAK2V617F activity in MPN cells by activating AMPK and PP2A complexes containing the B56α subunit

Metformin suppresses the growth of a variety of malignant hematologic cells. It is widely accepted that metformin inhibits the growth of malignant cells primarily by suppressing the mTOR pathway or regulating autophagy. In contrast, we found another possible mechanism that inhibits the growth of malignant cells, suppression of the activity of the oncogenic kinase JAK2V617F. We identified at least two distinct mechanisms involved in metformin-induced JAK2V617F inhibition. First, metformin increases reactive oxygen species levels in these cells, leading to the inhibition of SHP-2, a positive regulator of JAK2V617F. These effects of metformin require AMPK. Second, metformin activates protein tyrosine phosphatase PP2A, a negative regulator of JAK2V617F. Furthermore, we determined that among the numerous PP2A subfamily members, the PP2A complex containing the B56α subunit is responsible for the inhibition of JAK2V617F. In contrast, the B56α-containing PP2A complex functions as a positive regulator of JAK2V617F by inhibiting AMPK. Finally, we determined that metformin enhances the antileukemic action of ruxolitinib in HEL and SET-2 cells. Our present observations suggest that the combination of metformin with ruxolitinib might be a new therapeutic option for treating JAK2V617F-induced myeloproliferative neoplasms. In addition, activators specific for PP2A complexes containing the B56α subunit may be useful for the treatment of JAK2V617F-induced myeloproliferative neoplasms.