Transcriptional regulation of IL-8 by iron chelator in human epithelial cells is independent from NF-κB but involves ERK1/2- and p38 kinase-dependent activation of AP-1

We have shown that the bacterial iron chelator, deferoxamine (DFO), triggers inflammatory signals including the production of CXC chemokine IL‐8, in human intestinal epithelial cells (IECs) by activating the ERK1/2 and p38 kinase pathways. In this study we investigated the mechanisms involved in IL‐8 generation by DFO, focusing on the transcription factors involved and the roles of both mitogen‐activated protein kinases (MAPKs) in the transcription factor activation. Treatment of human epithelial HT‐29 cells with DFO markedly up‐regulated the expression of the essential components of the transcription factor AP‐1 at a transcriptional level, while it minimally affected the expression of the NF‐κB subunits. DFO also induced AP‐1‐dependent transcriptional activity in HT‐29 cells, and this activity was further augmented by the wild‐type c‐Jun transfection. In contrast, the AP‐1 activity by DFO was markedly decreased by the dominant‐negative c‐Jun transfection. Electrophoretic mobility shift assays revealed that DFO increases the specific binding of AP‐1 but not of NF‐κB. Such AP‐1 binding and transcriptional activities were blocked by the inhibitors of the ERK1/2 and p38 kinase pathways, suggesting that both mitogen‐activated protein kinases (MAPKs) lie upstream of AP‐1. Besides its action on AP‐1, DFO also induced the specific binding of other transcription factors such as CREB and Egr‐1. In summary, our results indicate that iron chelator‐induced IL‐8 generation in IECs involves activation of ERK1/2 and p38 kinase and downstream activation of AP‐1. A possible link between iron status and two additional transcription factors, that is, CREB and Egr‐1, rather than NF‐κB, was also suggested. J. Cell. Biochem. 102: 1442–1457, 2007. © 2007 Wiley‐Liss, Inc.