Cutting Edge: Phorbol Ester Induction of IFN-γ Receptors Leads to Enhanced DR α Gene Expression

We observed that IFN-γ-inducible expression of the DRα gene was enhanced when THP-1 cells are differentiated into macrophage-like cells by phorbol ester treatment. Here, we observed that class II MHC trans-activator and STAT1α mRNA, mediators of the signaling cascade from the IFN-γ receptor to the DRα induction, were markedly increased by IFN-γ stimulation in phorbol ester-activated THP-1 cells; however, both mRNAs were not increased by phorbol ester treatment alone. Then, we demonstrated that the mRNA and proteins of the IFN-γ receptor α- and β-chains were amplified by phorbol ester treatment in THP-1 cells. Consequently, these results indicate that the enhancement of DRα gene expression by IFN-γ treatment in phorbol ester-activated THP-1 cells is due to the phorbol ester-induced up-regulation of IFN-γ receptor α- and β-chains. As a result, the amplification of STAT1α and the increment of class II MHC trans-activator results in enhancement of DRα expression.