RESUMO
Objective:To investigate the mechanism for the synergistic effect of interferon regulatory factor 4 (IRF4) and microphthalmia-associated transcription factor (MITF) on tyrosinase (TYR)promoter.Methods:The synergistic transcriptional effect,subcellular localization,and protein-protein interaction for IRF4 and MITF were observed by luciferase assay,immunofluorescence,GST-pull down,and co-immunoprecipitation,respectively.Results:IRF4 and MITF proteins were co-expressed in the cell nucleus.IRF4 augmented the transcriptional function of MITF (but not the mutant MITF) to activate the expression of the TYR promoter,but with no effect on other MITF-specific target promoters.IRF4 alone did not affect TYR promoter significantly.No direct interaction between the two proteins was noted.Conclusion:IRF4 and MITF exert a specifically synergistic effect on activation of TYR promoter through IRF4-mediated upregulation of transcriptional function of MITF.This synergistic effect is mainly regulated by MITF;DNA might be involved in the interaction between the two proteins.