Replication stress in activated human NK cells induces sensitivity to apoptosis

Natural killer cells are innate immune effectors that kill virally infected or malignant cells. Natural killer cell deficiency (NKD) occurs when NK cell development or function are impaired, and individuals with NKD are susceptible to severe and recurrent viral infections. Several gene deficiencies result in NKD, including variants in MCM4, GINS1, MCM10 and GINS4, which are components of the CDC45-MCM-GINS (CMG) helicase. The CMG helicase unwinds DNA during replication and is expressed in any actively proliferating cell. NK cells are more strongly impacted by mutational deficiencies in helicase proteins than other lymphocytes, though the mechanisms underlying this susceptibility are not completely understood. NK cells from individuals with NKD as a result of helicase deficiency have increased DNA damage, cell cycle arrest, and replication stress. Here, we induced replication stress in activated mature NK cells or T cells by chemical methods, using aphidicolin, and through shRNA knockdown of MCM10 in an NK cell line. We found that the CD56 bright subset of NK cells accumulates more DNA damage and replication stress during activation than CD56 dim NK cells or activated T cells. Aphidicolin treatment increases apoptosis of CD56 bright NK cells through increased pan-caspase expression and decreases perforin expression in surviving cells. This effect is modeled by shRNA mediated knockdown of MCM10, thus linking decreased helicase protein expression to replication stress and impaired NK cell function. These findings show that sensitivity to replication stress affects human NK cell survival and function and can contribute to NK cell deficiency.