Pml nuclear body disruption cooperates in APL pathogenesis and impairs DNA damage repair pathways in mice

A hallmark of acute promyelocytic leukemia (APL) is altered nuclear architecture, with disruption of promyelocytic leukemia (PML) nuclear bodies (NBs) mediated by the PML-retinoic acid receptor alpha (RAR alpha) oncoprotein. To address whether this phenomenon plays a role in disease pathogenesis, we generated a knock-in mouse model with NB disruption mediated by 2 point mutations (C62A/C65A) in the Pml RING domain. Although no leukemias developed in Pml(C62A/C65A) mice, these transgenic mice also expressing RAR alpha linked to a dimerization domain (p50-RAR alpha model) exhibited a doubling in the rate of leukemia, with a reduced latency period. Additionally, we found that response to targeted therapy with alltrans retinoic acid in vivo was dependent on NB integrity. PML-RAR alpha is recognized to be insufficient for development of APL, requiring acquisition of cooperating mutations. We therefore investigated whether NB disruption might bemutagenic. Compared with wild-type cells, primary Pml(C62A/C65A) cells exhibited increased sister-chromatid exchange and chromosome abnormalities. Moreover, functional assays showed impaired homologous recombination (HR) and nonhomologous end-joining (NHEJ) repair pathways, with defective localization of Brca1 and Rad51 to sites of DNA damage. These data directly demonstrate that Pml NBs are critical for DNA damage responses, and suggest that Pml NB disruption is a central contributor to APL pathogenesis.