p53-dependent generation of reactive oxygen species mediates apoptosis by luteolin Free

LB-146

p53, a tumor suppressor, plays a key role in several biological processes and is found to be functionally inactivated in a great majority of human cancers. It is, therefore, important to develop strategies or develop novel compounds that exert differential growth regulation dependent on p53. By comparing the responses of several pair of isogenic cell lines either expressing or lacking p53 and using siRNA methodology we find that a natural dietary flavanoid, luteolin exhibits such differential effects. Treatment with luteolin stabilizes and activates p53 as indicated by increase in the level and its phosphorylation and transactivation of its target genes, such as p21 and Mdm2. While investigating the mechanism of p53 induction/activation we find that luteolin treatment leads to DNA damage as assayed by incorporation of 8-oxoG moieties. Furthermore, luteolin treatment induces apoptosis in cells expressing wild-type p53 but not in those lacking p53. The p53-dependent apoptosis is associated with activation of caspase-3 and cleaved PARP. Furthermore, luteolin treatment leads to the generation of reactive oxygen species (ROS). Interestingly, the ROS formation was observed much more in cells expressing p53 compared to the ones lacking p53, thereby suggesting the generation of ROS in a p53-dependent manner. In order to further investigate if ROS was responsible for apoptosis, cells expressing p53 were pretreated with N-acetyl cysteine (NAC) followed by luteolin treatment. NAC treatment rendered a remarkable protection against luteolin-induced apoptosis. Taken together our results suggest that luteolin may potentiate DNA damage associated with p53-dependent ROS generation that, in turn regulates apoptosis in cancer cell lines.