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Insulin-like growth factor-I augments erythropoietin-induced proliferation through enhanced tyrosine phosphorylation of STAT5.

Okajima Y., Matsumura I., Nishiura T., Hashimoto K., Yoshida H., Ishikawa J., Wakao H., Yoshimura A., Kanakura Y., Tomiyama Y., Matsuzawa Y.

Insulin-like growth factor (IGF-I) is known to synergistically stimulate the proliferation of hematopoietic cells in combination with other hematopoietic growth factors. However, the precise mechanism underlying the cooperative effects of IGF-I is unknown. In a human interleukin-3 or erythropoietin (EPO)-dependent cell line, F-36P, IGF-I alone failed to stimulate DNA synthesis but did augment the EPO-dependent DNA synthesis of F-36P cells. The treatment of F-36P cells with a combination of EPO and IGF-I (EPO/IGF-I) was found to enhance EPO-induced tyrosine phosphorylation of STAT5, whereas IGF-I alone did not. Furthermore, c-CIS mRNA expression, one of the target molecules of STAT5, was more effectively induced by EPO/IGF-I than by EPO alone. To examine the mechanisms of the EPO- and EPO/IGF-I-induced proliferation of F-36P cells, we expressed dominant negative (dn) mutants of STAT5 and Ras in an inducible system. The EPO-induced DNA synthesis and the cooperative effect of EPO/IGF-I were significantly inhibited by the inducible expression of dn-STAT5 or dn-Ras. In addition, the inducible expression of dn-Ras abolished the IGF-I-enhanced tyrosine phosphorylation of STAT5. These results suggest that IGF-I may augment EPO-induced proliferation by enhancing tyrosine phosphorylation of STAT5 and raise the possibility that Ras may be involved in the augmentation of STAT5 tyrosyl phosphorylation.

J. Biol. Chem. 273:22877-22883(1998) [PubMed] [Europe PMC]

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