OVEREXPRESSION OF THE ZINC-FINGER PROTEIN MZF1 INHIBITS HEMATOPOIETICDEVELOPMENT FROM EMBRYONIC STEM-CELLS - CORRELATION WITH NEGATIVE REGULATION OF CD34 AND C-MYB PROMOTER ACTIVITY

Zinc finger genes encode proteins that act as transcription factors. T he myeloid zinc finger 1 (MZF1) gene encodes a zinc finger protein wit h two DNA-binding domains that recognize two distinct consensus sequen ces, is preferentially expressed in hematopoietic cells, and may be in volved in the transcriptional regulation of hematopoiesis-specific gen es. Reverse transcription-PCR analysis of human peripheral blood CD34( +) cells cultured under lineage-restricted conditions demonstrated MZF 1 expression during both myeloid and erythroid differentiation. Sequen ce analysis of the 5'-flanking region of the CD34 and c-myb genes, whi ch are a marker of and a transcriptional factor required for hematopoi etic proliferation and differentiation, respectively, revealed closely spaced MZF1 consensus binding sites found by electrophoretic mobility shift assays to interact,vith recombinant MZF1 protein. Transient or constitutive MZF1 expression in different cell types resulted in speci fic inhibition of chloramphenicol acetyltransferase activity driven by the CD34 or C-myb 5'-flanking region. To determine whether transcript ional modulation by MZF1 activity plays a role in hematopoietic differ entiation, constructs containing the MZF1 cDNA under the control of di fferent promoters were transfected into murine embryonic stem cells wh ich, under defined in vitro culture conditions, generate colonies of m ultiple hematopoietic lineages. Constitutive MZF1 expression interfere d with the ability of embryonic stem cells to undergo hematopoietic co mmitment and erythromyeloid colony formation and prevented the induced expression of CD34 and c-myb mRNAs during differentiation of these ce lls. These data indicate that MZF1 plays a critical role in hematopoie sis by modulating the expression of genes involved in this process.