MASL1 induces erythroid differentiation in human erythropoietin-dependent CD34+ cells through the Raf/MEK/ERK pathway

Abstract

Human erythropoiesis is a dynamic and complex multistep process involving differentiation of early erythroid progenitors into enucleated RBCs. The mechanisms underlying erythropoiesis still remain incompletely understood. We previously demonstrated that erythropoietin-stimulated clone-1, which is selectively expressed in normal human erythroid-lineage cells, shares 99.5% identity with malignant fibrous histiocytoma-amplified sequences with leucine-rich tandem repeats 1 (MASL1). In this study, we hypothesized that the MASL1 gene plays a role in erythroid differentiation, and used a human erythroid cell culture systemto explore this concept. MASL1 mRNA and protein expression levels were significantly increased during the erythroid differentiation of CD34+ cells following erythropoietin (EPO) treatment. Conversely, MASL1 knockdown reduced erythroid differentiation in EPO-treated CD34+ cells. In addition, MASL1 knockdown interrupted the Raf/MEK/ERK signaling pathway in CD34+ cells. MASL1 mutant-transfected CD34+ cells also showed decreased erythroid differentiation. Furthermore, inhibition of the SH3 domain of Son of Sevenless, which is an upstream adapter protein in EPO-induced erythroid differentiation, also reduced MASL1 expression and phosphorylation of Raf/MEK/ERK kinases that consequently reduced erythroid differentiation of EPO-induced CD341 cells. Importantly,we also demonstrated that MASL1 interacts physicallywith Raf1. Taken together, our data provide novel insights into MASL1 regulation of erythropoiesis through the Raf/MEK/ERK pathway.