Comparative studies of the erythroid-potentiating effects of biosynthetic human insulin-like growth factors-I and -II.

The erythroid-potentiating effects of biosynthetic human insulin-like growth factor-I (IGF-I) and IGF-II were evaluated and compared in serum-free cultures of human marrow erythroid progenitors. IGF-I and IGF-II enhanced the in vitro growth of relatively mature (CFU-E) and primitive (BFU-E) erythroid progenitors at similar dose-dependent magnitudes. Significant elevations in erythroid colony counts were detected at 0.2-0.6 ng/mL of both peptides, with a maximal increase in CFU-E and BFU-E numbers detected at 2-6 ng/mL. Similar enhancement of erythroid progenitor cell growth by both peptides was also detected in cultures of marrow cells that had been depleted of accessory cells or in cultures of highly enriched hemopoietic progenitors. IGF-I and IGF-II enhanced erythroid progenitor cell growth at both limiting and saturating concentrations of recombinant human erythropoietin or granulocyte-macrophage colony-stimulating factor, but did not alter the sensitivity of CFU-E and BFU-E to their respective hemopoietic regulators. The erythroid-potentiating effects of IGF-I and IGF-II were completely abrogated by monoclonal antibodies directed against IGF-I membrane receptors. IGF-I and IGF-II thus appear to exert their effects on human marrow erythroid progenitors via a direct mechanism involving the type I IGF receptor.