Ectopic expression of CCAAT/enhancer binding protein beta (C/EBP beta) in long-term bone marrow cultures induces granulopoiesis and alters stromal cell function

CCAAT/enhancer binding proteins (C/EBP) have been demonstrated to impact di rectly the development of multiple hematopoietic lineages. However, the rol e of C/EBP beta in the differentiation of various hematopoietic lineages ha s not been thoroughly examined. We used primary bone marrow cultures to ass ess directly the ability of C/EBP beta to influence myelopoiesis. Retrovira l expression vectors were used to express C/EBP beta ectopically in murine primary long-term bone marrow cultures. The differentiation potential of th ese cells was determined using hematopoietic colony assays and differential staining of cells within the cultures. Bone marrow cultures that overexpre ssed C/EBP beta had fewer myeloid progenitors and a significant increase in the number of granulocytes. The ability of C/EBP beta to alter hematopoies is in vitro was dependent on the presence of the transcriptional activation domain because LIP, which lacks this functional domain, did not decrease t he ability of bone marrow cultures to support myeloid progenitors. These da ta also show that C/EBP beta influences hematopoiesis by altering stromal c ell function rather than the intrinsic developmental potential of myeloid p rogenitor cells.