MicroRNA-101 Is Down-Regulated In PV and ET Granulocytes and Its Decrease Is Associated with Over-Expression of Histone Methyltransferase In EZH2 In MPN Patients

Abstract 1989

Polycythemia vera (PV), essential thrombocythemia (ET) and idiopathic myelofibrosis (MF) are hematological malignancies due to clonal proliferation arising from a multilineage stem cell and have been classified as myeloproliferative neoplasms (MPNs). A somatic point JAK2 V617F mutation occurs in the majority (>95%) of PV patients and about 50–60% of ET and MF patients. The nonspecificity of this mutation, presence of JAK2V617F-negative PV patients, and evidence of both JAK2V617F-negative and positive PV clones demonstrate that the JAK2V617F mutation is not the initial or sole somatic event in the pathogenesis of PV. However, JAK2V617F plays an important role in the dysregulation of hematopoiesis in MPNs.

MicroRNAs (miRs) have been shown to be important regulators of hematopoiesis. We searched for miRs that directly regulate JAK2 expression by in silico analysis. Two of these miRs, namely miR101-1 and miR101-2, had JAK2 as a putative target. Interestingly, miR101-2 is located on chromosome 9p adjacent to the JAK2 locus. miR101 also negatively regulates the enhancer of zeste homolog 2 (EZH2), a member of the polycomb group of proteins involved in controlling and maintaining stem cell pluripotency and cell proliferation. Loss of miR101 in the cancer genome leads to overexpression of EZH2, contributing to cancer progression.

We analyzed the expression of miR101 in 35 PV, 15 ET and 3 MF patients and 20 normal controls by quantitative RT-PCR and found it was decreased in PV, ET and MF patients compared to normal controls (PV; P<0.03 and ET; P<0.01). We next investigated whether miR101 expression inversely correlates with EZH2 mRNA levels in MPN patients, as had been previously reported in human tumors. We examined the expression level of EZH2 for the same cohort of PV, ET and MF patients by quantitative RT-PCR and found a significant increase of EZH2 expression compared with normal controls (PV; P<0.02 and ET; P<0.05).

Analysis of the molecular bases of these observations is in progress. We will test the hypothesis that the dysregulation of these miRs further increases the expression of EZH2 and contributes to the severity and pathophysiology of the MPNs.