HEMATOPOIESIS Induction of C/EBP activity alters gene expression and differentiation of human

The CCAAT/enhancer binding protein al-pha (C/EBP) belongs to a family of tran-scription factors that are involved in the differentiation process of numerous tis-sues, including the liver and hematopoi-etic cells. C/EBP/ mice show a block in hematopoietic differentiation, with an accumulation of myeloblasts and an ab-sence of mature granulocytes, whereas expression of C/EBP in leukemia cell lines leads to granulocytic differentiation. Recently, dominant-negative mutations in the C/EBP gene and down-regulation of C/EBP by AML1-ETO, an AML associ-ated fusion protein, have been identified in acute myelogenous leukemia (AML). To better understand the role of C/EBP in the lineage commitment and differentia-tion of hematopoietic progenitors, we transduced primary human CD34 cells with a retroviral construct that expresses the C/EBP cDNA fused in-frame with the estrogen receptor ligand-binding domain. Induction of C/EBP function in primary human CD34 cells, by the addition of -estradiol, leads to granulocytic differen-tiation and inhibits erythrocyte differentia-tion. Using Affymetrix (Santa Clara, CA) oligonucleotide arrays we have identified C/EBP target genes in primary human hematopoietic cells, including granulo-cyte-specific genes that are involved in hematopoietic differentiation and inhibi-tor of differentiation 1 (Id1), a transcrip-tional repressor known to interfere with erythrocyte differentiation. Given the known differences in murine and human promoter regulatory sequences, this in-ducible system allows the identification of transcription factor target genes in a physiologic, human hematopoietic pro-genitor cell background. (Blood. 2003