KRIT1 helps cells to prevent oxidative stress.

KRIT1 is a gene responsible for Cerebral Cavernous Malformations (CCM), a major cerebrovascular disease characterized by abnormally enlarged and leaky capillaries that predispose to seizures, neurological deficits, and fatal intracerebral hemorrhage. We found that KRIT1 loss is associated with a significant increase in intracellular Reactive Oxygen Species (ROS) levels. Conversely, ROS levels in KRIT1-/- cells are significantly and dose-dependently reduced after restoration of KRIT1 expression. Moreover, we show that the modulation of intracellular ROS levels by KRIT1 loss/restoration is correlated with the modulation of the expression of the antioxidant protein SOD2 as well as of FoxO1, a master regulator of cell responses to oxidative stress and a modulator of SOD2 levels. Furthermore, we show that the KRIT1-dependent maintenance of low ROS levels facilitates the downregulation of cyclin D1 expression required for cell transition from proliferative growth to quiescence. Finally, we demonstrate that the enhanced ROS levels in KRIT1-/- cells are associated with an increased cell susceptibility to oxidative DNA damage and a marked induction of the DNA damage sensor gene Gadd45a. Taken together, our results point to a model where KRIT1 regulates the steady-state levels of intracellular ROS to prevent oxidative damage by controlling an antioxidant pathway involving FoxO1 and SOD2, thus providing an useful framework for understanding the molecular mechanisms of CCM pathogenesis.