DYRK3 Encodes an Inhibitor of Erythroid Differentiation and Is Expressed at High Levels in Patients with Anemia

Background: Many patients (pts) with anemia due to impaired erythropoiesis fail to respond to currently available erythropoiesis-stimulating agents or do not wish to receive these agents due to safety concerns. For these pts, novel approaches are needed. DYRK3, an evolutionarily conserved member of an emerging family of serine-threonine kinases, is expressed at high levels in erythropoietic progenitors; murine models suggest that DYRK3 selectively inhibits red cell production during stress erythropoiesis. We sought to determine DYRK3 expression in pts with anemia, and whether in vitro inhibition of DYRK3 augments erythropoiesis. Methods: We performed quantitative RT-PCR for DYRK3 and 4 control genes using whole peripheral blood (WPB) from 14 healthy persons, 5 pts with anemia due to multiple myeloma (MM), and 3 pts with anemia of chronic disease (ACD); in addition, peripheral blood mononuclear cells (PBMCs) were assayed in the 3 ACD and 5 MM pts and bone marrow mononuclear cells (BMMCs) in the MM pts. Erythrocyte subpopulations (CD36+, CD71+, and dual CD36+/CD71+) were quantified by flow cytometry. CFU-E growth was measured from PBMCs and BMMCs in the presence of varying concentrations of GSK626616, an orally bioavailable first-generation DYRK3 kinase inhibitor. Results: Normalized expression of DYRK3 in WPB was 7.2 fold higher in MM pts (p=0.0001) and 3.4 fold higher in pts with ACD (p=0.026) compared to healthy controls. DYRK3 expression was proportional to the degree of anemia, and WPB and PBMC expression of DYRK3 in MM pts correlated well with BMMC expression. The level of DYRK3 expression was proportional to the population of marrow CD36+/CD71+ erythroid progenitors, and inversely proportional to the size of the more mature CD36−/CD71+ population, suggesting that high DYRK3 expression is associated with maturation arrest in humans at a stage of erythroid differentiation roughly corresponding to pre-Ter119pos/CD71high inhibition observed in murine models. Although incubation of pt-derived BMMC or PBMC with GSK626616 at concentrations up to 30 μM, either in the presence or absence of physiological concentrations of erythropoietin, did not augment in vitro CFU-E formation, CFU-E growth overall was poor in the pt samples studied. Conclusion: DYRK3 is expressed at high levels in pts with anemia due to neoplasia or inflammation, and elevated DYRK3 expression is associated with decreased numbers of CD36−/CD71+ red cells. Further studies of the effects of DYRK3 antagonists on human erythropoiesis in vitro are necessary, and clinical trials in anemic patients will be required to determine if DYRK3 antagonists can reverse DYRK3-associated inhibition.