Redox regulation of p53 during hypoxia

Abstract

The transcription factor p53 can induce growth arrest or death in cells. Tumor cells that develop mutations in p53 demonstrate a diminished apoptotic potential, which may contribute to growth and tumor metastasis. Cellular levels of p53 are stabilized during hypoxia. The present study tested the hypothesis that reactive oxygen species (ROS) released from mitochondria regulate the cytosolic redox state and are required for the stabilization of p53 protein levels in response to hypoxia. Our results indicate that hypoxia (1.5% O 2 ) increases mitochondrial ROS generation and increases p53 protein levels in human breast carcinoma MCF-7 cells and in normal human diploid ®broblast IMR-90 cells. MCF-7 cells depleted of their mitochondrial DNA (r8 cells) failed to stabilize p53 protein levels during hypoxia. The antioxidant Nacetylcysteine and the Cu/Zn superoxide dismutase inhibitor diethyldithiocarbamic acid abolished the hypoxia-induced increases in ROS and p53 levels. Rotenone, an inhibitor of mitochondrial complex I, and 4,4'-diisothiocyanato-stilbene-2,2'-disulfonate, a mitochondrial anion channel inhibitor, also abolished the increase in ROS signal and p53 levels during hypoxia. The p53-dependent gene p21 WAF1/CIP1 was also induced by hypoxia in both MCF-7 and IMR-90 cells without aecting the growth rate of either cell line. In contrast, both cell lines exhibited increases in p21 WAF1/CIP1 expression and growth arrest after gamma irradiation. Primary chick cardiac myocytes and murine embryonic ®broblasts also showed an increase in p53 protein levels in response to hypoxia without cell death or growth arrest. These results indicate that mitochondria regulate p53 protein levels during hypoxia through a redox-dependent mechanism involving ROS. Despite p53-induction, hypoxia alone does not cause either growth arrest or cell death.

Involvement of Bcl-2 family members, phosphatidylinositol 3'-kinase/AKT and mitochondrial p53 in curcumin (diferulolylmethane)-induced apoptosis in prostate cancer

“…These studies suggest that ROS are downstream mediators in p53-dependent apoptosis in transcription-dependent or transcriptionindependent pathways. When cells are exposed to oxidative stress, such as hypoxia or genomic damage, p53 is expressed at high levels by posttranslational modifications, including phosphorylation, acetylation, and glycosylation (64,65). These modifications occur rapidly and lead to the activation of p53, resulting in either G1 or G2-M cell cycle arrest or apoptosis.…”

“…Apoptosis triggered by p53 is dependent on an increase in ROS and the release of apoptotic factors from mitochondrial damage (63). When cells are exposed to stress stimuli, p53 is expressed at high levels by posttranslational modifications, including phosphorylation, acetylation, and glycosylation (64,65). We therefore measure the phosphorylation and acetylation of p53 by curcumin (Fig.…”

Pax2 expression occurs in renal medullary epithelial cells in vivo and in cell culture, is osmoregulated, and promotes osmotic tolerance

“…Another aspect is that oxygen tension is low in medullary rays, like it is in the medulla. Low oxygen tension can result in generation of reactive oxygen species (34,35), a possible alternative or additional signal for Pax2 expression. To elucidate how high NaCl levels increase Pax2 mRNA abundance, we measured Pax2 mRNA stability.…”

Mitochondrial complex III regulates hypoxic activation of HIF

“…[3][4][5] Cells exposed to hypoxia, or reduced oxygen levels, on the other hand, are able to maintain normal ATP synthesis and survive. 5,6 However, as cells replicate in a hypoxic environment, they reduce the oxygen supply even further and generate levels of local anoxia. Therefore, cells must respond quickly to decreasing oxygen levels before reaching an anoxic state ( Figure 1).…”