Phorbol esters potentiate the induction of class I HLA expression by interferon α

We have studied the effect of phorbol esters on the induction of class I histocompatibility antigen (HLA) expression by interferons (IFNs) in the T-cell line MOLT-4 and in the MOLT-4 mutant YHHH. Addition of IFN-α to phorbol 12,13-dibutyrate-pretreated MOLT-4 cells causes a > 20-fold increase in the expression of class I HLA, as compared to a 4- to 7-fold IFN-α-induced increase in control cells. Pretreatment with phorbol 12,13-dibutyrate does not alter the class I HLA response to IFN-γ or the responses of other IFN-induced genes. This effect of phorbol 12,13-dibutyrate reproduces in MOLT-4 cells and phenotype of the mutant YHHH, which also displays a selective enhanced class I HLA response to IFN-α. Pretreatment of YHHH with phorbol 12,13-dibutyrate does not affect any of the responses induced by IFN. These findings suggest the existence of a phorbol ester-sensitive factor, inducible in MOLT-4 and constitutively expressed or modified in YHHH, which operates in te pathway of induction of class I HLA by IFN-α but not in the pathway used by IFN-γ.