Tumor necrosis factor alpha-mediated inhibition of erythropoiesis involves GATA-1/GATA-2 balance impairment and PU.1 over-expression

Many physiological perturbations can cause anemia. In cancer patients, activation of the immune system leads to the production of proinflammatory cytokines including tumor necrosis factor alpha (TNF alpha), that have been shown to inhibit red-cell production via poorly understood mechanisms. Treatment of anemia by human recombinant erythropoietin (EPO) is strongly suspected to induce tumor growth. This study focuses on the mechanisms involved in TNF alpha-mediated inhibition of erythropoiesis. CD34(+) hematopoietic stem/progenitor cells (HSPCs) were isolated from human cord blood. Erythropoiesis was achieved in vitro by stimulating cells with EPO. We show that TNFa clearly affected erythroid development, as assessed by May-Grunwald/Giemsa staining, flow cytometry analysis and fluorescent microscopy. The amount of hemoglobin-producing cells as well as the expression of GATA-1 target erythro-specific genes (EPO receptor, glycophorin A and globins) was found decreased after TNF alpha treatment of HSPC. In correlation, TNF alpha induced the expression of the transcription factors GATA-2 and PU.1, described as inhibitors of erythropoiesis. In this regard, TNFa promoted the formation of the GATA-1/PU.1 complex that has been reported to block the transcriptional activity of GATA-1. Our results clearly demonstrate that TNFa prevents EPO-mediated erythropoiesis of HSPC as an early event, by directly affecting erythroid cell development. (C) 2011 Elsevier Inc. All rights reserved.