Phosphorylation of p53 protein in A549 human pulmonary epithelial cells exposed to asbestos fibers.

Abstract

We examined effects of asbestos exposure on the phosphorylation of p53 protein in human pulmonary epithelial type II cells (A549), which express wild-type p53. In cells exposed to two different types of asbestos, chrysotile (approximately 1-6% iron content) and crocidolite (approximately 27% iron content) fibers, at the doses of 1, 5, and 10 microg/cm2 for 24 hr, the levels of p53 phosphorylated at Ser15 and p53 protein were correlated with the dose. On a per-weight basis, chrysotile was more potent in inducing Ser15 phosphorylation and accumulation of p53 protein than was crocidolite. After exposure to 10 micro g/cm2 chrysotile, the levels of p53 phosphorylated at Ser15 and of p53 protein increased after 18 hr. Among serines in p53 protein immunoprecipitated from A549 cells treated with chrysotile, only Ser15 was markedly phosphorylated. In contrast, no clear phosphorylation was observed at Ser6, Ser9, Ser20, Ser37, Ser46, or Ser392. Blocking of the extracellular signal-regulated protein kinase pathway with U0126 or inhibition of p38 activity with SB203580 did not suppress chrysotile-induced Ser15 phosphorylation. On the other hand, treatment with wortmannin, an inhibitor of DNA-activated protein kinase and ataxia-telangiectasia mutated, suppressed both chrysotile-induced Ser15 phosphorylation and accumulation of p53 protein. Treatment with either catalase or N-acetylcysteine failed to suppress chrysotile-induced Ser15 phosphorylation, suggesting that reactive oxygen species do not play a major role in the phosphorylation of p53 protein. The present results show that asbestos, particularly chrysotile, induces phosphorylation of p53 protein at Ser15 in A549 cells depending on a DNA damage-signaling pathway.

P53 Mediates Amosite Asbestos–Induced Alveolar Epithelial Cell Mitochondria-Regulated Apoptosis

“…Collectively, these data suggest a novel mechanism involving mitochondrial-derived ROS in mediating amosite asbestosinduced p53 expression and subsequent AEC apoptosis by the intrinsic pathway. In contrast to the findings presented here, Matsuoka and colleagues (33) showed that chrysotile asbestos increases p53 protein accumulation in A549 cells due to phosphorylation of serine 15 by phosphatidylinositol 3-kinase related kinase family member, such as ataxia-telangiectasia mutated kinase. Further, they found that this was not blocked by catalase, deferoxamine, or N-acetylcysteine, suggesting that p53 stabilization by Figure 6.…”

“…phosphorylation of serine 15 can occur by mechanisms that are independent of ROS production. Although ataxia-telangiectasia mutated kinase is implicated in mediating mitochondriaregulated apoptosis by radiation (34), the role of phosphorylation of serine 15 on p53 in mediating apoptosis was not examined in this study (33). A hypothetical model depicting the oxidantdependent and oxidant-independent mechanisms by which asbestos affects p53 expression and apoptosis is shown in Figure 8.…”

Tumor-suppressive p53 Signaling Empowers Metastatic Inhibitor KLF17-dependent Transcription to Overcome Tumorigenesis in Non-small Cell Lung Cancer

“…Therefore, we investigated the role of p53 on KLF17 regulation in A549 cells. A549 cell lines express tumor-suppressive p53 (TP53) (34,35). We depleted p53 expression in A549 cells using specific siRNA targeting p53.…”

Mitochondrial DNA Damage: Role of Ogg1 and Aconitase

“…Altered p53 expression has been implicated in the pathophysiology of pulmonary fibrosis, including that due to asbestos, as well as asbestos-associated malignancies, especially bronchogenic lung cancer (Nelson et al, 2001;Mishra et al, 1997;Burmeister et al, 2004;Plataki et al, 2005). Asbestos activates p53 and p21 expression in lung epithelial and mesothelial cells that result in cell cycle arrest (Levresse et al, 1997;Matsuoka et al, 2003;Kopnin et al, 2004). Furthermore, increased p53 levels are detected in lung cancers of patients with asbestosis (Nuorva et al, 1994) and p53 point mutations are present in the lung epithelium of smokers and asbestosexposed individuals (Husgafvel-Pursiainen et al, 1997).…”