Erythroid differentiation in vitro is blocked by cyclopamine, an inhibitorof hedgehog signaling

Adult hematopoietic differentiation is a developmental process that employs many of the same molecular mechanisms as embryogenesis. To explore the pos sibility that hedgehog signaling is involved in the control of hematopoieti c differentiation, we screened a panel of human leukemia cell lines for the expression of Patched1 and Smoothened, the receptor and coreceptor for hed gehog ligands, Expression was found in multiple cell lines, and Patched1 ex pression was detected in normal marrow, Induction of myeloid differentiatio n in cell lines downregulated expression of both genes. When normal marrow mononuclear cells were grown in semisolid medium in the presence of 10 muM cyclopamine, development of colonies of,granulocytic/monocytic lineage was unaffected in terms of both number and morphology. The number of erythroid colonies, however, was significantly reduced (P < 0.01). Furthermore, hemog lobinization was substantially delayed relative to controls in those erythr oid colonies that did form. Incubation of hematopoietic progenitors with Sh h-N and GM-CSF resulted in increased granulocyte/monocyte colonies (P < 0.0 1); the increase was blocked by cyclopamine. Incubation of hematopoietic pr ogenitors with Shh-N and stem cell factor resulted in larger erythroid colo nies. These results suggest that elements of the hedgehog signaling pathway are involved in the control of hematopoietic differentiation. (C) 2000 Aca demic Press.