Cutting edge: phorbol ester induction of IFN-gamma receptors leads to enhanced DR alpha gene expression.

We observed that IFN-gamma-inducible expression of the DR alpha 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 STAT1 alpha mRNA, mediators of the signaling cascade from the IFN-gamma receptor to the DR alpha induction, were markedly increased by IFN-gamma 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-gamma receptor alpha- and beta-chains were amplified by phorbol ester treatment in THP-1 cells. Consequently, these results indicate that the enhancement of DR alpha gene expression by IFN-gamma treatment in phorbol ester-activated THP-1 cells is due to the phorbol ester-induced up-regulation of IFN-gamma receptor alpha- and beta-chains. As a result, the amplification of STAT1 alpha and the increment of class II MHC trans-activator results in enhancement of DR alpha expression.