| Acute phase response involves the activation by many different transcription factors, such as STATs, NF-κB, and AP-1 which are activated by proinflammatory cytokines. Although IFNα has been used clinically to treat viral hepatitis and certain cancers, it has not been considered as an inflammatory cytokine. IFN rapidly activates latent cytoplasmic transcription factors, such as STATs and NF-κB which are known as important transcription factors in acute phase response. This research was designed to examine if IFNα acts as an acute phase cytokine by activating transcription factors involved in the regulation of acute phase response genes.; We found that IFNα activates STAT1, STAT3 and NF-κB not only in human hepatoma cell lines but also in rat primary hepatocytes. Moreover, IFNα induces AP-1 DNA binding activity not only in human hepatoma cell lines but also in a variety of other cell lines. Several different type I IFNs activate AP-1 activity in human hepatoma cell lines. Also, the induction of AP-1 activity by IFNα-stimulation was inhibited by the tyrosine kinase inhibitor staurosporine, but not by the PI-3 kinase inhibitors wortmannin or Ly294002. It suggests that IFN-induced AP-1 apparently does not involve PI-3 kinase activation.; To explore the effect of IFN in regulating the expression of an acute phase response gene, a series of luciferase reporter constructs of the human c-fos gene were made which encompassed −450 by to +12 of the 5′ promoter region. This region contains several cis elements such as SIE, SRE, AP-1, CRE and TATA box. Transient transfection assays of human c-fos promoter show that the full-length c-fos promoter has a dramatic increase in luciferase activity upon PMA stimulation. Pretreatment with IFNα prior to the PMA addition dramatically repressed the PMA-inducibility of this construct. Deletion of the SIE markedly decreased the PMA-inducibility of the c-fos promoter construct. However, this deletion construct was sensitive to inhibition by IFN.; In conclusion, these studies have provided evidences suggesting that IFNα should be reconsidered as an inflammatory cytokine and this is a reasonable area for future investigation. |
