Increased erythropoiesis of β-thalassaemia/Hb E proerythroblasts is mediated by high basal levels of ERK1/2 activation

P>beta-thalassaemia is one of the most common inherited anaemias, arising from a partial or complete loss of beta-globin chain synthesis. In severe cases, marked bone marrow erythroid hyperplasia, believed to result from erythropoietin (EPO)-mediated feedback from the anaemic condition is common, however, as yet, no study has investigated EPO-mediated signal transduction in thalassaemic erythroid cells. Using proerythroblasts generated from peripheral blood circulating CD34(+) haematopoietic progenitor cells, the activation of the mitogen-activated protein kinase/extracellular signal-regulated kinases (MAPK/ERKs) pathway was examined under conditions of steady state growth, cytokine deprivation and post-EPO stimulation. Levels of cellular cyclic adenosine monophosphate (cAMP) and Ca2+ were determined as was the degree of erythroid expansion. A significantly higher basal level of phosphorylation of ERK1/2 was observed in beta-thalassaemia/Hb E proerythroblasts as compared to normal controls, which was coupled with significantly higher levels of both cAMP and Ca2+. Modulation of either cAMP or Ca2+ or direct inhibition of MAPK/ERK kinase (MEK) reduced basal levels of ERK1/2 phosphorylation, as well as significantly reducing the level of erythroid expansion. These results suggest that, in contrast to current models, hyper proliferation of beta-thalassaemia/Hb E proerythroblasts is an intrinsic process driven by higher basal levels of ERK1/2 phosphorylation resulting from deregulation of levels of cAMP and Ca2+.