γ-IFN May Act As a Positive Regulator to Hematogenesis Through PI3K/Akt and JAK2/STAT5 Pathways

Abstract 4785

It is known to us all that γ-IFN is a growth inhibitory to hematogenesis and plays a critical role in the pathophysiology of aplastic anemia(AA). However, γ-IFN actually is a bilateral regulatory factor. In certain experimental situations, it can facilitate the proliferation and growth of hematopoitic stem cells. Interferon regulatory factor-1 (IRF-1) and IRF-2 are the key regulators of IFN system and IRF-1 has been shown to participate in development of CD8+ T cells, Th1 differentiation, and NK cell development. Thus, IRF-1 may has crucial functions against hematopoietic stem and/or progenitors cells. To investigate the function of IRF-1and the molecular mechanism of proliferative effect of γ-IFN, IRF-1-siRNA was designed to knocked out IRF-1 gene in 32D cells, mouse multipotent progenitor cells, and the apoptosis was assayed by flow cytometry 48 hr after incubation with γ-IFN in three different concentrations. It showed that after IRF-1 gene was knocked out, γ-IFN reversed its action on hematogenesis and apoptosis,it potentiated the proliferation and growth of 32D cells. Interestingly, at this situations, the inhibitory effect of γ-IFN on Akt activation was abolished completely and reversed to enhanced Akt phosphorylation significantly. The expression of pStat5 also changed when γ-IFN only exert proliferative effect.Nevertheless,The negative effect of γ-IFN on Erk1/2 activation was not blocked after IRF-1 gene was knocked out. Taken together, γ-IFN can enhance or antagonize cell proliferation depending on the function of IRF-1 and may act as a positive regulator to hematogenesis through PI3K/Akt and JAK2/STAT5 signaling pathways. Our findings may contribute to understanding the decreased number of stem cells characteristic of aplastic anemia and will provide novel therapeutic strategies for this disease.