Increased Expression of the PRV-1 Gene in Thalassemia Reflects the Rate of the Underlying Erythropoietic Activity.

Over the last years, PRV-1 expression has been considered to be closely connected with polycythemia vera (PV). However, the precise function of the PRV-1 protein has never been clarified while the search for the pathogenetic mechanism of PV has shifted to the association between the PRV-1 gene and the JAK2 V617F mutation rather than the activity of PRV-1 alone. Our present knowledge regarding the PRV-1 protein is summarized in that it is a GPI-anchored membrane protein and that its amount in the surface of the mononuclear cells of PV patients is almost normal in contrast to its high mRNA expression. The PRV-1 gene is also overexpressed in some ET and IMF cases, but not in CML, AML and secondary erythrocytosis and thrombocytosis. Whilst studying PRV-1 expression in PV patients, we noticed elevated expression of this gene in a number of controls. Further analysis revealed that these controls were not hematologically normal but instead were beta thalassaemia carriers. We therefore went onto to study PRV-1 expression in 20 beta-thalassemia carriers, 20 patients with thalassemia intermedia (hence, intensive ineffective erythtopoiesis), 20 with sickle cell thalassemia (not transfused; hence, moderately intensive ineffective erythropoiesis), 14 heavily transfused patients with thalassemia major (hence, suppressed erythropoiesis) and 34 normal controls. Expression of PRV-1 was determined by RQ-PCR assay using the ABI PRISM 7000SDS. The values obtained were normalized using the ABL gene as endogenous control with the deltadeltaCt method. Furthermore, we examined two more parameters which are considered to reflect the extent of total erythropoiesis, i.e. the serum levels of (a) Erythropoetin (EPO) and (b) Transferrin Receptors, using standard ELISA based assays. Results in TABLE I display an unequivocally elevated expression of the PRV-1 transcripts in all groups of patients with thalassemia, in apparent relation with the intensity of ineffective erythropoiesis occurring in each individual case. The latter statement is supported by the observation that the increase of PRV-1 expression in the mononuclear cells of patients with various types of thalassemia occurs in close relation to their EPO and sTFR levels. We conclude that elevated PRV-1 expression is not confined to the myeloproliferative disorders, but is also seen in genetic disorders with ineffective hematopoiesis. This finding brings up a number of challenging hypotheses regarding the significance of the PRV-1 protein, especially when considering that the high expression of this gene is detected in the mononuclear WBC of the patients and not in their erythroid cells, and opens the way for several additional experiments.