A NOVEL, MYELOID TRANSCRIPTION FACTOR, C EBP-EPSILON, IS UP-REGULATEDDURING GRANULOCYTIC, BUT NOT MONOCYTIC, DIFFERENTIATION/

Human C/EBP epsilon is a newly cloned CCAAT/enhancer-binding transcrip tion factor. Initial studies indicated it may be an important regulato r of human myelopoiesis. To elucidate the range of expression of C/EBP epsilon, we used reverse transcription-polymerase chain reaction (RT- PCR) analysis and examined its expression in 28 hematopoietic and 14 n onhematopoietic cell lines, 16 fresh myeloid leukemia samples, and nor mal human hematopoietic stem cells and their mature progeny. Prominent expression of C/EBP epsilon mRNA occurred in the tate myeloblastic an d promyelocytic cell lines (NB4, HL60, GFD8), the myelomonoblastic cel l lines (U937 and THP-1), the early myeloblast cell lines (ML1, KCL22, MDS92), and the T-cell lymphoblastic leukemia cell lines CEM and HSB- 2. For the acute promyelocytic leukemia cell line NB4, C/EBP epsilon w as the only C/EBP family member that was easily detected by RT-PCR. No C/EBP epsilon mRNA was found in erythroid, megakaryocyte, basophil, B lymphoid, or nonhematopoietic cell lines. Most acute myeloid leukemia samples (11 of 12) from patients expressed C/EBP epsilon. Northern bl ot and RT-PCR analyses showed that C/EBP epsilon mRNA decreased when t he HL60 and KG-I myeloblast cell lines were induced to differentiate t oward macrophages. Similarly, Western blot analysis showed that expres sion of C/EBP epsilon protein was either unchanged or decreased slight ly as the promyelocytic cell line NB4 differentiated down the macropha ge-like pathway after treatment with a potent vitamin DB analog (KH106 0). In contrast, C/EBP epsilon protein levels increased dramatically a s NB4 cells were induced to differentiate down the granulocytic pathwa y after exposure to g-cis retinoic acid. Furthermore, very early, norm al hematopoietic stem cells (CD34(+)/CD38(-)), purified from humans ha d very weak expression of C/EBP epsilon mRNA, but levels increased as these cells differentiated towards granulocytes. Likewise, purified gr anulocytes appeared to express higher levels of C/EBP epsilon mRNA tha n purified macrophages. Addition of phosphothiolated antisense, but no t sense oligonucleotides to C/EBP epsilon, decreased clonal growth of HL-60 and NB4 cells by about 50% compared with control cultures. Taken together, our results indicate that expression of C/EBP epsilon is re stricted to hematopoietic tissues, especially myeloid cells as they di fferentiate towards granulocytes and inhibition of its expression in H L-60 and NB4 myeloblasts and promyelocytes decreased their proliferati ve capacity. Therefore, this transcriptional factor may play an import ant role in the process of normal myeloid development. (C) 1997 by The American Society of Hematology.