GATA1 Is Over-Expressed in Essential Thrombocytemia

GATA1, founding member of the GATA transcription factor family, is essential for cell maturation and differentiation within the erythroid and megakaryocyte (MK) lineages. Disruption of DNA- or protein-binding capacity of GATA1 causes severe hematopoietic dysfunction and plays a role in blood disorders such as thrombocytopenia, anemia or leukemia. GATA1 expression seems to be related to the MK commitment both in mice and in humans; indeed, similarly to the murine myeloid M1 cell line, in which the enforced expression of GATA1 induces the c-Mpl appearance and MK differentiation, transduction of human hematopoietic stem cells with a GATA1 highly expressing vector results in self-renewal block and in the exclusive generation of Meg-E lineages. More recently, a role for GATA1 also in myeloproliferative disorders (MPDs) was indicated by the “GATA1-low” mouse model which develop a disease closely resembling the human idiopathic myelofibrosis. Interestingly, patients affected by myelofibrosis was also shown to express decreased GATA1 levels by immunostaining of BM sections. In this study, we investigated by Real Time PCR the levels of GATA1 in a myeloproliferative disorders such as essential thrombocytemia (ET) tipically characterized by a neoplastic megakaryocitic proliferation. We have studied BM samples of 40 newly diagnosed patients (M:F ratio 1:1 - median age 53 years, range 18–84) affected by ET, as for the PVSG group criteria. These patients were selected from a cohort of 65 ET patients considering a similar erythroid/myeloid ratio at the FACS analysis to reduce a possible bias for the RT-PCR results due to the erythroid compartment interference. The median platelets count of the selected patients was 670,000/mL (range 493,000–1,400,000/mL), myelofibrotic index 0/1, and 18 out of 40 patients (45%) showed mild splenomegaly both at the physical examination and US scan (median spleen vol 550 ml - range 430–1400 mL). No chromosomal abnormalities were detected by cytogenetic analysis. JAK2 sequencing in 21/40 patients indicated that 9/21 patients (43%) were positive for the JAK2 V617F genomic mutation. At the end of observation time (median 18 mo.) no patients had evidence or signs of thrombotic or hemorrhagic complications. BM cells from six healthy donors were used as normal controls in the study. The relative GATA1 quantification was calculated in according to the DCt method with GAPDH as internal control. The results showed a significant increase of GATA1 expression in BM cells from ET patients (median DCt + 6,11 ; range −0,41/+18,11) compared to the controls (median DCt + 0,172 ; range −4,03/+1,7) (p < 0,003). Interestingly, the GATA1 overexpression is not a mere consequence of the proliferation and activation of MKs, indeed samples from three patients affected by idiopathic thrombocytopenic purpura, whose BM smears had the typical secondary megakaryocytic hyperplasia, showed GATA1 levels much lower than the ET patients (median DCt − 0,6 ; range − 3,21/−0,9). No significant difference in GATA1 level was found between patients harbouring a JAK mutation (median DCt +5,86 ; range 0,85/16,12) and those with wild type alleles (median DCt +4,75 ; range −0,41/10,21). In conclusion, our results suggest that GATA1 overexpression could be a trigger for MK neoplastic commitment and proliferation and, consequently, seems to have a central role for ET pathogenesis both in JAK2 mutated and in JAK2 WT patients.