Regulated expression and functional role of the transcription factor CHOP (GADD153) in erythroid growth and differentiation

The hematopoietic growth factor erythropoietin (Epo) triggers changes in th e expression of genes that encode important regulators of erythroid cell gr owth and differentiation. We now report that Epo markedly upregulates chop (gadd153) expression and that this transcription factor plays a role in ery thropoiesis. Using a differential hybridization assay, we isolated a full-l ength cDNA of chop as an Epo upregulated gene in Rauscher murine erythroleu kemia cells. RNase protection assays demonstrated that Epo or dimethyl sulf oxide induction increased steady-state mRNA levels 10- to 20-fold after 24 to 48 hours. Western blot analysis confirmed a marked increase in CHOP prot ein. Among the other c/ebp family members, only c/ebp beta was also upregul ated during erythroid differentiation. Among normal hematopoietic cells exa mined, steady-state mRNA levels were highest in erythroid cells, with level s peaking during terminal differentiation. Transient overexpression of chop in Rauscher cells resulted in a significant increase in Epo- or dimethyl s ulfoxide (DMSO)-induced hemoglobinization, further linking chop upregulatio n to erythroid differentiation, Artificial downregulation of chop in normal murine bone marrow cells with antisense oligodeoxynucleotides inhibited co lony-forming unit-erythroid (CFU-E)-derived colony growth in a concentratio n-dependent manner. Burst-forming unit-erythroid (BFUE)-derived colony grow th was not affected. Using a Far Western type of analysis, we detected seve ral potential CHOP binding partners among the nuclear proteins of Rauscher cells. Importantly, the number and relative abundance of these proteins cha nged with differentiation. The results strongly suggest that CHOP plays a r ole in erythropoiesis, possibly through interactions with both C/EBP and no n-C/EBP family members. (C) 1999 by The American Society of Hematology.