Characterization of biologically active, platelet-derived growth factor-like molecules produced by murine erythroid cells in vitro and in vivo.

Platelet-derived growth factor (PDGF) is an important serum regulator of erythropoiesis in vitro. We have now obtained evidence suggesting that PDGF-like molecules may also modulate erythropoiesis in vivo. Western blot analysis of cytoplasmic extracts from Rauscher murine erythroleukemia cells and phenylhydrazine-treated mouse splenic erythroid cells revealed the presence of several PDGF-like proteins. The presence of PDGF-like proteins in the cytoplasm of these two erythroid cell types was confirmed by immunohistochemical staining. Using a serum-free biologic assay, PDGF-like biological activity was found in cell lysates and conditioned medium of both Rauscher cells and phenylhydrazine-treated mouse erythroid cells. Subcellular localization experiments revealed the biological activity to be concentrated in the cytosolic fraction. Using a series of antibodies to hematopoietic growth factors we demonstrated that PDGF-like biological activity was specifically immunoprecipitated by both monoclonal and polyclonal anti-human PDGF antibodies but not by antibodies to burst-promoting activity, granulocyte-macrophage colony-stimulating factor, IL-3, or erythropoietin. Taken together, the data are consistent with the hypothesis that PDGF-like molecules play a role in the regulation of mammalian erythropoiesis in vivo.