Human APOBEC3 proteins play pivotal roles in intracellular defense against viral infection by catalyzing deamination of cytidine residues, leading to base substitutions in viral DNA. Activation-induced cytidine deaminase (AID), another member of the APOBEC family, is capable of editing immunoglobulin (Ig) and non-Ig genes, and aberrant expression of AID leads to tumorigenesis. However, it remains unclear whether APOBEC3 (A3) proteins affect stability of human genome. Here we demonstrate that both A3A and A3B can induce base substitutions into human genome as AID can. A3B is highly expressed in several lymphoma cells and somatic mutations occur in some oncogenes of the cells highly expressing A3B. Furthermore, transfection of A3B gene into lymphoma cells induces base substitutions in cMYC gene. These data suggest that aberrant expression of A3B can evoke genomic instability by inducing base substitutions into human genome, which might lead to tumorigenesis in human cells.

Acute myeloid leukemia (AML) pathogenesis often involves a mutation in the NPM1 nucleolar chaperone, but the bases for its transforming properties and overall association with favorable therapeutic responses remain incompletely understood. Here we demonstrate that an oncogenic mutant form of NPM1 (NPM1c) impairs mitochondrial function. NPM1c also hampers formation of PML nuclear bodies (NBs), which are regulators of mitochondrial fitness and key senescence effectors. Actinomycin D (ActD), an antibiotic with unambiguous clinical efficacy in relapsed/refractory NPM1c-AMLs, targets these primed mitochondria, releasing mtDNA, activating cGAS signaling and boosting ROS production. The latter restore PML NB formation to drive TP53 activation and senescence of NPM1c-AML cells. In several models, dual targeting of mitochondria by venetoclax and ActD synergized to clear AML and prolong survival through targeting of PML. Our studies reveal an unexpected role for mitochondria downstream of NPM1c and implicate a mitochondrial/ROS/PML/TP53 senescence pathway as an effector of ActD-based therapies. SIGNIFICANCEActinomycin D induces complete remissions in NPM1-mutant AMLs. We found that NPM1c affects mitochondrial biogenesis and PML bodies (NBs).Actinomycin D targets mitochondria, yielding ROS which enforce PML NB-biogenesis and restore senescence. Dual targeting of mitochondria with actinomycin D and venetoclax sharply potentiates their anti-AML activities in vivo.Research.

The case histories of 124 children irradiated for brain tumors were reviewed to determine survival rate and functional prognosis, with special reference to somatic growth. Five-year survival rates (29% of 97 patients with gliomas and 70% of 27 patients with non-gliomatous tumors) were approximately the same as in our adult series, despite the differences in histology and predilection. Although 70% of 42 long-term survivors had active, useful lives, stunted growth was observed in 15 of them. More attention should be directed to the growth of children irradiated for brain tumors.