Modulated Expression of BCL-xL and GATA-1 Genes Is a Common Feature in Myeloproliferative Disorders (MPD) Both in JAK2-V617F Positive and Negative Patients

JAK2-V617F mutation has been identified in more than 90% of patients with Polycythemia Vera (PV) and in 50 to 60% of patients with Essential Thrombocythemia (ET) or Primary Myelofibrosis (PMF). The mutation has reinforced the original idea that ET, PV, and PMF have a common background; however, some key questions remain open:

1. why, in JAK2-V617F patients, only a proportion of progenitors is bearing the mutation and the other is wild type (wt);

2. why patients with the same mutation have a different disease;

3. what have in common patients JAK2-V617F positive (mutated) and wt with the same disease.

We observed that a new synthetic peptide (072RB) able to bind Bcl-xL molecule, exerting an apoptotic effect, inhibited the in vitro cord blood (CB) mononuclear cells (MNC) growth. Moreover, this effect correlated with a high expression level of Bcl-xL messenger (RQ-PCR). Since Bcl-xL was involved in erythropoiesis, we extended the expression studies to bone marrow (BM) MNC from16 PV (13/16 mutated),15 ET (9/15 mutated) and peripheral blood (PB) MNC from 18 PMF (9/18 mutated). JAK2 mutational status was assigned by allele-specific-PCR (AS-PCR). MNC from PV-BM and PMF-PB showed a Bcl-xL level of expression significantly higher than in MNC from healthy donors (NBM and NPB) both in mutated and in wt patients (PV: p=0.01 and p=0.004; PMF: p=0.005 and p=0.05 respectively). In ET, the expression level of Bcl-xL tended to be elevated compared to controls but did not reach the statistical significance. Since other factors can modulate Bcl-xL expression independently from the constitutive activation of JAK2/STATs pathway induced by JAK2-mutated, we analysed GATA-1 gene, a transcription factor that binds the Bcl-xL promoter and that is involved in erythropoiesis and megakariocytopoiesis. We observed that GATA-1 was highly expressed in PV-BM and PMF-PB MNC both in mutated and in wt patients (PV: p=0.01 and p=0.05; PMF: p=0.001 and p=0.03). In ET-BM MNC, GATA-1 followed the Bcl-xL pattern of expression. The highest messengers levels were observed PMF-PB MNC and CB MNC that, after in vitro 072RB peptide treatments, showed a 25%–50% of cells growth inhibition with respect to untreated controls. The protein expression was confirmed by cytofluorimetric analyses. Our finding may indeed be compatible with reduced apoptosis both in mutated and wt patients. Thus, the elevated expression levels of Bcl-xL and GATA-1 genes may represent a common feature in MPD, independent from the presence of the JAK2-V617F mutation and supports the hypothesis of a “phenotypic continuum” in MPD. It is noteworthy that in patients bearing the mutation, a variable proportion of hematopoietic progenitors in PV, ET and PMF have been documented to be wt. In this context, our findings may explain why wt hematopoiesis is not overtaken by the mutated counterpart. These results could open a new insight in the field of MPD molecular characterization and may lead to new therapeutic approaches.