SPI1 and acute promyelocytic leukemia: We also defined the action of RARAα1, RARα2 and PML-RAR shRNAs on 3 transcription factors controlling APL blast granulocytic maturation, i.e. PU.1 [27, 28], cEBPβ [29, 30] and STAT1α [31] (Figure 3C).