Interestingly, transfection of WT PHOX2B significantly decreased the luciferase activity of U3 as compared with control (Figure 6 C), indicating that WT PHOX2B acts as a repressor via the U3 enhancer.
Both del5 and del8 PHOX2B mutants showed a significant increase in luciferase activity, even as compared with mock-transfected controls, indicating that mutant PHOX2B acts as a transactivator via U3.