Transcriptional regulation of Hsp70 is involved in ROS controls by p400.
(A) U2OS cells were transfected using the indicated siRNA and Hsp70 or FANCA expression vector (1.5 µg). Total amount of DNA in the transfection was kept constant using the corresponding empty vector. 48 h later, cells were collected and ROS levels were measured by flow cytometry and calculated relative to 1 for cells transfected by the control siRNA and empty vector. The mean and SD from three independent experiments are shown. The two stars (**) indicate a p value below 10−5 (Student t-test). B) U2OS cells were transfected using the indicated siRNA and 48 h following transfection, cells were collected and ROS levels were measured by flow cytometry. The mean and SD from 3 independent experiments are shown (after standardisation relative to 1 for cells transfected with the control siRNA). (C) Our model of cell proliferation control by p400: p400 prevents oxidative stress through transcriptional regulation of specific promoters. Oxidative stress in turn induces persistent DNA damage. These persistent DNA damages favour an additional oxidative stress increase (“positive feedback loop”) and induce the activation of the DNA damage response pathways, resulting in a potent inhibition of cell proliferation (through senescence, cell cycle arrest or apoptosis induction depending on the cell type). The dash line represents a putative role of p400 in DNA repair (demonstrated in other species), which may contribute to the persistence of DNA damage.