Insulin-Like Growth Factor II Is an Autocrine Growth Factor To Prevent Apoptosis as Well as To Enhance Proliferation and Maturation of Erythroid Progenitor Cells.

To reveal the novel function of erythroid progenitor cells in fetal erythropoiesis, the gene expression pattern in umbilical cord blood (CB)-derived CD36⁺ erythroid progenitor cells (EPCs) was analyzed using cDNA microarray containing 240 cytokine and growth factor related genes. Among the genes analyzed, insulin-like growth factor II (IGF-II) gene showed a 124-fold higher level of expression in CB-EPCs, compared with that seen in phytohemagglutinin (PHA)-stimulated adult peripheral blood mononuclear cells (PBMCs) (table1). Real-time PCR revealed that the IGF-II mRNA levels in CB-EPCs were higher than those seen in lymphocytes or monocytes separated from CB or PBMCs. When CB-EPCs were cultured with erythropoietin (EPO) in serum-free medium, the number of erythroid colonies was decreased in the presence of IGF-II-neutralizing antibody. To further assess the role of IGF-II in erythropoiesis, we purified erythroid colony-forming cells (ECFCs) from human umbilical cord blood by magnetic selection and liquid culture with IL-3, stem cell factor and EPO. The expression levels of IGF-II, type 1 or 2 IGF receptor in the mature ECFCs were higher than those in the immature ECFCs. Addition of IGF-II-neutralizing antibody decreased the number of ECFCs in liquid culture with EPO. The anti-proliferative effect of IGF-II-neutralizing antibody was evident in both dimethylthiazole tetrazolium bromide (MTT) and bromodeoxyuridine (BrdU) incorporation assays. When apoptosis of cells was examined using Annexin V, the addition of IGF-II-neutralizing antibody increased apoptosis, thereby indicating the anti-apoptotic effects of IGF-II secreted from erythroid cells. Furthermore, ECFCs failed to undergo normal erythroid maturation in the presence of IGF-II-neutralizing antibody, as assessed by flow cytometric and morphologic analyses. These findings indicate that IGF-II, which is produced by erythroid progenitor cells themselves, has crucial roles in controlling erythropoiesis by modulating apoptosis, proliferation and maturation via an autocrine mechanism.