In acute promyelocytic leukemia, the promyelocytic leukemia-retinoic acid receptor-α fusion protein suppresses the function of PU.1, a key transcription factor that is required for ImP expression (Figure 2), and all-trans retinoic acid, which degrades the fusion protein, was shown to restore ImP expression and is seen as a promising therapeutic option of the patients (74). This evidence concerns the gene SPI1 and acute promyelocytic leukemia.