| Summary: | 碩士 === 臺北醫學大學 === 細胞及分子生物研究所 === 95 === The pro-inflammatory cytokine, tumor necrosis factor (TNF)-α, is linked to erythropoietic inhibition and may contribute to different forms of anemia. Activin A, a member of the transforming growth factor (TGF)-β superfamily, is an erythroid differentiation factor. In our previous study, we demonstrated that TNF-α up-regulated c-Jun expression through the NF-κB pathway to inhibit Activin A-mediated erythropoiesis with NF-κB inhibitor PDTC in chronic myeloid leukemia (CML)-derived K562 cells. In this study, we carry out the over-expression of different NF-κB family members, p50 and p65, by transient transfection or stable expression in K562 cells to further explore the role of NF-κB on TNF-α-induced c-Jun expression. Our data show that p65 activates c-Jun promoter; however, p50 represses c-Jun promoter. The c-Jun or NF-κB p65 activates c-Jun promoter through AP-1 binding site, suggesting NF-κB p65 act on AP-1 binding site through c-Jun which may lead to erythropoietic inhibition in TNF-α signaling. The JNK inhibitor SP600125 represses the TNF-α-activated c-Jun promoter, indicating that TNF-α?n also exerts its effect through JNK activation. Furthermore, p65-activated c-Jun promoter is partly inhibited by JNK inhibitor, suggesting TNF-α ?nregulates the c-Jun promoter through both NF-κB and JNK pathways. The results of RT-PCR show that activin A up-regulates the expression of erythroid genes (α-globin, ζ-globin, NF-E2p45 and GATA-1) and TNF-α?n down-regulates these genes. The over-expression of NF-E2 enhances Activin A-induced ζ-globin reporter activity, co-expression of c-Jun and NF-E2 can inhibit these effects. These results indicate that TNF-α up-regulates c-Jun through NF-κB pathway to antagonize the NF-E2 transcriptional activity by Activin A in erythroid differentiation. In the future work, whether NF-κB p65 binding to c-Jun on the AP-1 binding site of c-Jun promoter to enhance the c-Jun promoter activity will be investigated by ChIP assay.
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