Activation of JAK2/STAT5 Pathway Reduces Expression Level of DNMT3a in MPN Cell Line

Introduction: Myeloproliferative neoplasms (MPN) are clonal hematopoietic stem cell (HSC) disorders characterized by overproduction of mature blood cells and increased risk of transformation to acute myeloid leukemia (AML), and JAK2V167F is the most frequent MPN driving mutation detected in >95% of PV and 50-60% ET and PMF. DNMT3A is a de novo DNA methyltransferase that catalyzes the addition of methyl groups into active chromatin in CpG-rich regions leading to gene inactivation. Dnmt3a^-/- HSC have enhanced self-renewal and a block in differentiation in vivo. Previous study showed that JAK2V617F and Dnmt3a loss cooperate to induce myelofibrosis through activated enhancer-driven inflammation, while whether JAK2V617F regulates DNMT3a still remains unclear. AZ960 is a potent and selective ATP competitive inhibitor of the JAK2 kinase, and previous studies reported that AZ960 possessed the activity selectively against JAK2. LY2784544 has been identified as a selective inhibitor of JAK2V617F and has undergone clinical trials for the treatment of several myeloproliferative disorders.

Methods: Empty vector (control) and mutant JAK2V617F were transduced into BaF3 cells using a lentivirus system. JAK2V617F-expressing BaF3 cells grow IL-3 independent and were selected by fluorescence-activated cell sorting (FACS) for GFP expression. The protein expression levels of p-STAT5 and DNMT3a were detected by western blotting. JAK2V617F-expressing and control BaF3 cells were incubated with gradient concentration of LY2784544 or AZ960 to inhibit JAK2/STAT5 pathway.

Results: The expression levels of p-STAT5 were obviously up-regulated in the JAK2V617F-expressing BaF3 cells, and DNMT3a was down-regulated. After 1-hour incubation in the serial diluted LY2784544, p-STAT5 were reduced in JAK2V617F-expressing BaF3 cells, with expression of DNMT3a elevated. To further confirm the correlation between JAK2/STAT5 pathway and expression of DNMT3a, another JAK2 inhibitor AZ960 was tested similar to LY2784544. With p-STAT5 expression suppressed, protein level of DNMT3a showed significantly promotion.

Conclusion: We observed that JAK2V167F mutation suppresses protein expression levels of DNMT3a in MPN cell lines. JAK2 inhibition by AZ960 and LY2784544 significantly improved expression levels of DNMT3a. The activation of JAK2/STAT5 pathway reduces expression level of DNMT3a in MPN cell line, and the specific mechanism still needs to be explored.

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