A soluble form of human Delta-like-1 inhibits differentiation of hematopoietic progenitor cells

Two Notch ligand families, Delta and Serrate/Jagged, have been identified i n vertebrates. Members of the Jagged family have been shown to affect in vi tro hematopoiesis. To determine whether members of the Delta family might p lay a similar role in hematopoiesis, we examined the expression of mouse De lta like-1 (mDII1), mDII1 protein was detected in whole marrow and in a mar row stromal cell line MS-5. At the RNA level, both mDII1 and Notch1 were se en in marrow precursor, differentiated hematopoietic, marrow stromal, and M S-5 cells. We isolated a cDNA encoding the human homologue of mDII1, design ated human Delta-like-1 (hDII1). A soluble form of hDII1, hDII1(NDSL), cont aining the DSL domain and the N-terminal sequences, was expressed and purif ied from bacteria as a glutathione S-transferase (GST) fusion protein. We o bserved that hDII1(NDSL) delayed the acquisition of differentiation markers by murine hematopoietic progenitor cells (Lin(-)) cultured in vitro with c ytokines. In addition, it promoted greater expansion (more than 3 times) of the primitive hematopoietic precursor cell population, measured in high-pr oliferative potential colony assay and day 12 colony-forming unit spleen (C FU-S) assay, than GST controls. We also observed that the percentage of apo ptotic cells decreased and that the number of cells in the S-phase of the c ell cycle increased in the cultures of Lin- cells with hDII1NDSL The effect s of hDII1NDSL were blocked by antibody against the mouse counterpart of hD II1(NDSL), mDII1(NDSL). These observations demonstrate that hDII1 plays a r ole in mediating cell fate decisions during hematopoiesis. (C) 2000 by The American Society of Hematology.