Gery Sigal, Tanosaki Sakae, Hofmann Wolf-K, Koppel Ahrin, Koeffler H Phillip
Cedars-Sinai Medical Center, Division of Hematology/Oncology, UCLA School of Medicine, Los Angeles, CA 90048, USA.
Oncogene. 2005 Feb 24;24(9):1589-97. doi: 10.1038/sj.onc.1208393.
CCAAT/enhancer-binding proteins (C/EBPs) are a family of highly conserved transcription factors that have important roles in normal myelopoiesis as well as associated with myeloid disorders. The chronic myelogenous leukemia (CML) cell lines, KCL22 and K562, express exceptionally low levels of endogenous C/EBPs and provide a good model to test the effects of C/EBPs on myeloid differentiation. To explore the possibility that C/EBPdelta can promote differentiation in BCR-ABL-positive cells, we generated stable KCL22 and K562 clones that expressed an inducible C/EBPdelta gene. C/EBPdelta expression resulted in G0/G1 proliferative arrest and a moderate increase in apoptosis of the KCL22 and the K562 cells. Within 4 days of inducing expression of C/EBPdelta, myeloid differentiation of the CML blast cells occurred as shown by morphologic changes and induction of secondary granule-specific genes. We also showed that during granulocytic differentiation of KCL22 cells, the C/EBPdelta protein was detected in immunocomplexes with both Rb and E2F1. Furthermore, expression of C/EBPdelta was associated with downregulation of c-Myc and cyclin E and upregulation of the cyclin-dependent kinase inhibitor p27(Kip1) in both the KCL22 and K562 cell lines. These results show that expression of C/EBPdelta in BCR-ABL-positive leukemic cells in blast crisis is sufficient for neutrophil differentiation and point to the therapeutic potential of ectopic induction of C/EBPdelta in the acute phase of CML.
CCAAT/增强子结合蛋白（C/EBPs）是一类高度保守的转录因子，在正常骨髓生成中发挥重要作用，并且与髓系疾病相关。慢性粒细胞白血病（CML）细胞系KCL22和K562内源性C/EBPs表达水平极低，为测试C/EBPs对髓系分化的影响提供了良好模型。为探究C/EBPδ能否促进BCR-ABL阳性细胞分化，我们构建了表达可诱导C/EBPδ基因的稳定KCL22和K562克隆。C/EBPδ表达导致KCL22和K562细胞出现G0/G1期增殖停滞，凋亡适度增加。诱导C/EBPδ表达4天内，CML原始细胞发生髓系分化，表现为形态学改变及二级颗粒特异性基因的诱导。我们还发现，在KCL22细胞的粒细胞分化过程中，C/EBPδ蛋白在与Rb和E2F1形成的免疫复合物中被检测到。此外，在KCL22和K562细胞系中，C/EBPδ的表达与c-Myc和细胞周期蛋白E的下调以及细胞周期蛋白依赖性激酶抑制剂p27（Kip1）的上调相关。这些结果表明，在急变期BCR-ABL阳性白血病细胞中表达C/EBPδ足以诱导中性粒细胞分化，并提示在CML急性期异位诱导C/EBPδ具有治疗潜力。
