Notch Signaling in Acute Promyelocytic Leukemia

Acute promyelocytic leukemia (APL) is initiated by the PML-RARA fusion oncogene and has a characteristic expression profile that includes high levels of the Notch ligand JAG1. In this study, we used a series of bioinformatic, in vitro, and in vivo assays to assess the role of Notch signaling in human APL samples, and in a PML-RARA knockin mouse model of APL (Ctsg-PML-RARA). We identified a Notch expression signature in both human primary APL cells and in Kit+Lin−Sca1+ (KLS) cells from pre-leukemic Ctsg-PML-RARA mice. Both genetic and pharmacologic inhibition of Notch signaling abrogated the enhanced self-renewal seen in hematopoietic stem/progenitor cells (HSPCs) from pre-leukemic Ctsg-PML-RARA mice, but had no influence on cells from age-matched wildtype mice. In addition, 6 of 9 murine APL tumors tested displayed diminished growth in vitro when Notch signaling was inhibited pharmacologically. Finally, we found that genetic inhibition of Notch signaling with a dominant negative MAML protein reduced APL growth in vivo in a subset of tumors. These findings expand the role of Notch signaling in hematopoietic diseases, and further define the mechanistic events important for PML-RARA-mediated leukemogenesis.