Hexavalent Chromium Cr(VI) Up-Regulates COX-2 Expression through an NFκB/c-Jun/AP-1–Dependent Pathway

Abstract

Background: Hexavalent chromium [Cr(VI)] is recognized as a human carcinogen via inhalation. However, the molecular mechanisms by which Cr(VI) causes cancers are not well understood.Objectives: We evaluated cyclooxygenase-2 (COX-2) expression and the signaling pathway leading to this induction due to Cr(VI) exposure in cultured cells.Methods: We used the luciferase reporter assay and Western blotting to determine COX-2 induction by Cr(VI). We used dominant negative mutant, genetic knockout, gene knockdown, and chromatin immunoprecipitation approaches to elucidate the signaling pathway leading to COX-2 induction.Results: We found that Cr(VI) exposure induced COX-2 expression in both normal human bronchial epithelial cells and mouse embryonic fibroblasts in a concentration- and time-dependent manner. Deletion of IKKβ [inhibitor of transcription factor NFκB (IκB) kinase β; an upstream kinase responsible for nuclear factor κB (NFκB) activation] or overexpression of TAM67 (a dominant-negative mutant of c-Jun) dramatically inhibited the COX-2 induction due to Cr(VI), suggesting that both NFκB and c-Jun/AP-1 pathways were required for Cr(VI)-induced COX-2 expression. Our results show that p65 and c-Jun are two major components involved in NFκB and AP-1 activation, respectively. Moreover, our studies suggest crosstalk between NFκB and c-Jun/AP-1 pathways in cellular response to Cr(VI) exposure for COX-2 induction.Conclusion: We demonstrate for the first time that Cr(VI) is able to induce COX-2 expression via an NFκB/c-Jun/AP-1–dependent pathway. Our results provide novel insight into the molecular mechanisms linking Cr(VI) exposure to lung inflammation and carcinogenesis.

Luteolin inhibits Cr(VI)-induced malignant cell transformation of human lung epithelial cells by targeting ROS mediated multiple cell signaling pathways

“…Previous studies have shown that AP-1, HIF-1α, Cox-2, and iNOS play an important role in carcinogenesis (Gao et al , 2002; Li et al , 2006; Farinati et al , 2010; Zuo et al , 2012). We investigated the effect of luteolin on Cr(VI)-induced transactivation of AP-1, HIF-1α, Cox-2, and iNOS using a luciferase reporter assay in BEAS-2B cells.…”

“…Cyclooxygenase-2 (COX-2) is a key enzyme in the conversion of arachidonic acid to prostanoids, and its activation is associated with inflammation and carcinogenesis (Hakozaki et al , 2014). Elevated COX-2 expression has been demonstrated in Cr(VI)-exposed cultured cells (Zuo et al , 2012; Son et al , 2013). Pro-inflammatory cytokines, including interleukin-1β (IL-1β), interleukin-6 (IL-6), interleukin-8 (IL-8) and tumor necrosis factor-alpha (TNF-α) are involved in several pathological processes (Bouraoui et al , 2008).…”

“…Altered activation of NF-κB has been reported in many tumors (Perkins, 1997). Exposure to Cr(VI) caused NF-κB activation in Jurkat cells (Shi et al , 1999) and human bronchial epithelial cells (Zuo et al , 2012). Hypoxia inducible factor 1 α (HIF-1α) plays a crucial role in coordinating the cellular response to oxygen stress conditions (Semenza, 2003; Vaupel, 2004).…”

Oxidative Stress: Noxious but Also Vital

“…Among other systems, ROS are recognized as activators of AP-1; however, the signaling transduction events involved are not totally understood. Chromium, cobalt, cadmium and vanadium are metals involved in the activation of AP-1 through signaling cascades involving the production of ROS and comprised of proteins and enzymes such as thioredoxin (Trx), redox factor-1 (Ref-1), ERK/MAPK, NADPH oxidase, I kappa B kinase (IKK), p38, JNK/c-jun [117,131,132].…”

Development of a cancer-based chronic inhalation reference value for hexavalent chromium based on a nonlinear-threshold carcinogenic assessment

“…For example, based on a review of relevant data (e.g., genetic characterization of CrVI-induced tumors, in vivo and in vitro genotoxicity/mutagenicity test results, epigenetic changes), Holmes et al (2008) proposed a mechanism for CrVI-induced lung carcinogenesis that involves genomic instability due to DNA double strand break-induced G2 arrest (as opposed to mutation in multistage carcinogenesis) ultimately resulting in neoplastic transformation and cancer. Other MOAs and mechanisms for CrVI-induced carcinogenicity have also been proposed (e.g., Zuo et al, 2012;Xie et al, 2008;Thompson et al, 2011), such as mutagenicity as the initiating step (McCarroll et al, 2009;USEPA, 2010) or cellular resistance to CrVI-induced death through dysregulated DNA repair and/or survival signaling and transcriptional repatterning (Nickens et al, 2010). As the earliest key events, what the proposed MOAs have in common is an assumption (inherent or explicitly stated) that CrVI has escaped extracellular reduction to enter cells of the target tissue, followed by the intracellular reduction of CrVI.…”