RNA interference (RNAi) is a eukaryotic gene-silencing system. Although the biochemistry of RNAi is relatively well defined, how this pathway is regulated remains incompletely understood. To identify genes involved in regulating the RNAi pathway, we screened for genetic mutations in Drosophila that alter the efficiency of RNAi. We identified the Drosophila homolog of the mammalian CR6-interacting factor 1 (CRIF1), also known as growth arrest and DNA-damage-inducible 45-gamma interacting protein (Gadd45GIP1), as a potential new regulator of the RNAi pathway. Loss-of-function mutants of Drosophila CRIF1 (dCRIF) are deficient in RNAi-mediated target gene knock-down, in the biogenesis of small interfering RNA (siRNA) molecules, and in antiviral immunity. Moreover, we show that dCRIF may function by interacting with, and stabilizing, the RNase III enzyme Dicer-2. Our results suggest that dCRIF may play an important role in regulating the RNAi pathway.

Leukemia stem cells (LSCs) are thought to drive the genesis of acute myeloid leukemia (AML) as well as relapse following chemotherapy. Because of their unique biology, developing effective methods to eradicate LSCs has been a significant challenge. In the present study, we demonstrate that intrinsic overexpression of the mitochondrial dynamics regulator FIS1 mediates mitophagy activity that is essential for primitive AML cells. Depletion of FIS1 attenuates mitophagy and leads to inactivation of GSK3, myeloid differentiation, cell cycle arrest, and a profound loss of LSC self-renewal potential. Further, we report that the central metabolic stress regulator AMPK is also intrinsically activated in LSC populations and is upstream of FIS1. Inhibition of AMPK signaling recapitulates the biological effect of FIS1 loss. These data suggest a model in which LSCs co-opt AMPK/FIS1-mediated mitophagy as a means to maintain stem cell properties that may be otherwise compromised by the stresses induced by oncogenic transformation.