C/EBPδ Modulates Cell Growth, Differentiation and Apoptosis of Myeloid Leukemia, Prostate and Breast Cancer Cells.

C/EBPδ belongs to the family of highly conserved CCAAT/enhancer binding protein (C/EBP) transcription factors. Members of this family play a critical role in the regulation of mitotic growth arrest and differentiation in numerous cell types. To examine the consequences of C/EPBδ expression, we transfected C/EPBδ into CML myeloid leukemia (KCL22, K562), prostate (LNCaP, PC3, DU145), and breast (MCF-7, T47D, MDA-MB-231) cancer cell lines. C/EBPδ expression resulted in a proliferative arrest and an increase in apoptosis of the myeloid leukemia cells, as well as the prostate cells LNCaP and PC3, and the breast cells MCF-7 and T47D. In contrast, DU145 prostate and MDA-MB-231 breast cancer cells were not inhibited by C/EBPδ, indicating that the biologically properties of C/EBPδ depend upon its cellular context. We further studied the molecular mechanisms underlying the affect of C/EPBδ expression in CML leukemic cells. Myeloid differentiation of KCL22 and K562 blast cells as shown by morphologic changes and induction of secondary specific granule genes, occurred within 4 days of inducing expression of C/EBPδ. Furthermore, expression of C/EBPδ was associated with downregulation of c-Myc and cyclin E, and upregulation of the forkhead transcription factor FoxO1a (FKHR) and the cyclin-dependent kinase inhibitor p27Kip1. In addition, microarray analysis showed that C/EBPδ mRNA is upregulated during granulocytic differentiation of normal CD34+ bone marrow cells, suggesting that C/EBPδ is involved in lineage-specific differentiation. Taken together, these results show that expression of C/EBPδ in BCR-ABL-positive CML cells in blast crisis, is sufficient for neutrophil differentiation and suggest that ectopic induction of C/EBPδ in the blastic phase of CML, as well as in certain cases of prostate and breast cancers, may hold promising therapeutic potential.