ABSTRACT
Metals such as cadmium and arsenic are ubiquitous toxicants that cause a variety of adverse health effects. Heat shock proteins (HSPs) response to metal-induced stress and protect cells from further damage. However, the intracellular signalling pathways responsible for activation of HSPs expression are not fully understood. Here, we demonstrate that protein phosphatase 2A (PP2A) regulates expression of HSP70 and HSP27 via dephosphorylation of an AMP-activated protein kinase α subunit (AMPKα) at Thr172. Dephosphorylated AMPKα phosphorylates heat shock factor 1 (HSF1) at Ser303, leading to significant transcriptional suppression of HSP70 and HSP27 in CdCl2- or NaAsO2-treated cells. Suppression of PP2A regulatory B56δ subunit resulted in the sustained phosphorylation of AMPKα upon CdCl2 treatment, subsequent reduction in expression of HSP70 and HSP27, and thereby dramatic reduction of reactive oxygen species (ROS) clearance. We further revealed that PP2A B56δ physically interacted with AMPKα, providing evidence that PP2A B56δ-AMPKα-HSF1 signalling pathway participated in regulating the inducible expression of HSPs and ROS clearance. Taken together, we identified a novel PP2A-dependent signalling pathway involved in regulation of HSPs expression in response to metal stress.
Subject(s)
AMP-Activated Protein Kinases/metabolism , DNA-Binding Proteins/metabolism , Heat-Shock Proteins/metabolism , Metals/toxicity , Protein Phosphatase 2/metabolism , Reactive Oxygen Species/metabolism , Signal Transduction/drug effects , Transcription Factors/metabolism , Arsenic/toxicity , Cadmium/toxicity , Cell Line , Gene Expression Regulation/drug effects , HEK293 Cells , HSP27 Heat-Shock Proteins/genetics , HSP27 Heat-Shock Proteins/metabolism , HSP70 Heat-Shock Proteins/genetics , HSP70 Heat-Shock Proteins/metabolism , HSP72 Heat-Shock Proteins/genetics , HSP72 Heat-Shock Proteins/metabolism , Heat Shock Transcription Factors , Heat-Shock Proteins/genetics , Humans , Phosphorylation/drug effects , Protein Binding , Transcriptional ActivationABSTRACT
BACKGROUND: Aberrant methylation of promoter DNA and transcriptional repression of specific tumor suppressor genes play an important role in carcinogenesis. Recently, many studies have investigated the association between cigarette smoking and p16(INK4α) gene hypermethylation in lung cancer, but could not reach a unanimous conclusion. METHODS AND FINDINGS: Nineteen cross-sectional studies on the association between cigarette smoking and p16(INK4α) methylation in surgically resected tumor tissues from non-small cell lung carcinoma (NSCLC) patients were identified in PubMed database until June 2011. For each study, a 2×2 cross-table was extracted. In total, 2,037 smoker and 765 nonsmoker patients were pooled with a fixed-effects model weighting for the inverse of the variance. Overall, the frequency of p16(INK4α) hypermethylation was higher in NSCLC patients with smoking habits than that in non-smoking patients (ORâ=â2.25, 95% CIâ=â1.81-2.80). The positive association between cigarette smoking and p16(INK4α) hypermethylation was similar in adenocarcinoma and squamous-cell carcinoma. In the stratified analyses, the association was stronger in Asian patients and in the studies with larger sample sizes. CONCLUSION: Cigarette smoking is positively correlated to p16(INK4α) gene hypermethylation in NSCLC patients.
