Nickel Compounds Render Anti-apoptotic Effect to Human Bronchial Epithelial Beas-2B Cells by Induction of Cyclooxygenase-2 through an IKKβ/p65-dependent and IKKα- and p50-independent Pathway

Jin Ding,J. Andrés Meléndez,Dongyun Zhang,Xinhai Zhang,Caifang Xue,Lun Song,Max Costa,Chuanshu Huang,Jingxia Li,Weiming Ouyang

doi:10.1074/jbc.m604798200

Abstract

The carcinogenicity of nickel compounds has been well documented both in vitro and in vivo; however, the molecular mechanisms by which nickel compounds cause cancers are far from understood. Because suppression of apoptosis is thought to contribute to carcinogenesis, we investigated the mechanisms implicated in nickel-induced anti-apoptotic effect in human bronchial epithelial (Beas-2B) cells. We found that exposure of Beas-2B cells to nickel compounds resulted in increased cyclooxygenase-2 (COX-2) expression and that small interfering RNA (siCOX-2) knockdown of COX-2 expression resulted in increased cell sensitivity to nickel-triggered cell apoptosis, demonstrating that COX-2 induction has an anti-apoptotic effect on Beas-2B cells. Overexpression of IKKbeta-KM, a kinase inactive mutant of IKKbeta, blocked NF-kappaB activation and COX-2 induction by nickel compounds, indicating that activated NF-kappaB may be a mediator for COX-2 induction. To further explore the contribution of the NF-kappaB pathway in COX-2 induction and in protection from nickel exposure, mouse embryonic fibroblasts deficient in IKKbeta, IKKalpha, p65, and p50 were analyzed. Loss of IKKbeta impaired COX-2 induction by nickel exposure, whereas knockout of IKKalpha had a marginal effect. Moreover, the NF-kappaB p65, and not the p50 subunit, was critical for nickel-induced COX-2 expression. In addition, a deficiency of IKKbeta or p65 rendered cells more sensitive to nickel-induced apoptosis as compared with those in wild type cells. Finally, it was shown that reactive oxygen species H(2)O(2) were involved in both NF-kappaB activation and COX-2 expression. Collectively, our results demonstrate that COX-2 induction by nickel compounds occurs via an IKKbeta/p65 NF-kappaB-dependent but IKKalpha- and p50-independent pathway and plays a crucial role in antagonizing nickel-induced cell apoptosis in Beas-2B cells.

Highlights

Aerosols of nickel salts can be generated in electroplating and electrolysis areas of nickel refineries [1]
Epidemiological studies have demonstrated that exposure to nickel is associated with increased risk of human lung cancer, the mechanism involved in the carcinogenic effects of nickel compounds remains obscure
We found that COX-2 protein expression was significantly induced in both human Beas-2B cells and mouse embryonic fibroblasts (MEFs) upon nickel treatment

Summary

Introduction

Aerosols of nickel salts can be generated in electroplating and electrolysis areas of nickel refineries [1]. Epidemiological studies have associated occupational exposure to nickel compounds to elevated incidences of human cancer such as lung and nasal cancers [4]. The mechanisms implicated in the carcinogenic effect of nickel compounds are not well understood, it is accepted that the carcinogenic effects of nickel occur through alterations in cancer development-related gene expression [6]. It has been reported that nickel compounds can promote the generation of reactive oxygen species (ROS), which can regulate the expression of specific genes related to tumor development [7]. In the current study we utilized human bronchial epithelial Beas-2B cells to define whether nickel compounds are able to promote survival by inducing COX-2 expression and to define the signals regulating nickel-induced COX-2 expression

Methods

Results

Conclusion