Chromium(VI) Inhibits the Transcriptional Activity of Nuclear Factor-κB by Decreasing the Interaction of p65 with cAMP-responsive Element-binding Protein-binding Protein

Abstract

Chromium(VI) promotes pulmonary fibrosis and is a human carcinogen. Cr(VI) affects expression of various genes, including catalase, heme oxygenase, 5-aminolevulinate synthase, and urokinase plasminogen activator receptor (1-3). These chromium-mediated changes in gene expression are attributed to the generation of reactive chromium and oxygen species, DNA damage, or alterations in mRNA stability. This study examined whether Cr(VI) has additional effects on gene expression at the level of transcription factor activation or transcriptional competence. This type of epigenetic interference with the transcriptional machinery would have profound effects by shifting the patterns of genes expressed without causing molecular damage.Nuclear factor-B (NF-B) 1 is a mammalian transcription activator protein involved in regulating expression of immune and inflammatory response genes. It occurs in both homo-and heterodimeric forms. The most common transcriptionally competent form is composed of a p50 DNA-binding subunit attached to a p65 transactivation subunit. In nonstimulated cells, NF-B is localized in the cytoplasm bound to its inhibitor, IB, and to the catalytic subunit of protein kinase A (PKAc) (4). Upon cellular activation by cytokines, viral infection, lipopolysaccharide, and reactive oxygen species, IB is phosphorylated and degraded. This degradation unmasks the ATP-binding site on PKAc, resulting in activation and NF-B p65 phosphorylation (4). Furthermore, loss of IB exposes the NF-B nuclear localization sequence, allowing NF-B to translocate to the nucleus and to bind to its consensus sequence within the promoter region of genes.Studies have shown that, in addition to DNA binding, the interaction of p65 with CREB-binding protein (CBP) is essential for NF-B-enhanced transcriptional activity (5, 6). CBP is a coactivator molecule that links enhancer-bound transcription factors (transcription factor IIB and TATA-binding protein) to the basal transcriptional machinery. Interaction of CBP with p65 occurs at two sites. PKAc-induced phosphorylation of p65 on serine 276 mediates the phosphorylation-dependent interaction of p65 with the KIX region of CBP (amino acids 452-661). Alternatively, the C-terminal portion of p65 interacts with CBP in a phosphorylation-independent manner (5). In addition to p65, CBP interacts with various other transcription factors, including CREB, c-Jun, c-Fos, p53, glucocorticoid receptor, and retinoid X receptor (7-11). Thus, differences in the interaction of p65 with CBP may occur as a result of decreases in p65 phosphorylation or competition between transcription factors for limiting quantities of CBP.In this study, the complex multistep pathway for NF-B-dependent gene expression was chosen to examine how nontoxic concentrations of Cr(VI) produce epigenetic effects on cell phenotype. The effects of Cr(VI) on both basal and TNF-␣-stimulated gene expression were investigated in A549 human lung carcinoma cells. Cr(VI) inhibited both basal and stimulated expression of an NF-B-driven luciferase repo...

Signaling from toxic metals to NF-kappaB and beyond: not just a matter of reactive oxygen species.

“…Several studies from different groups indicate that, at a noncytotoxic concentration, arsenic trioxide [As(III)] (32), chromium(VI) [Cr(VI)] (28), and vanadium(V) [V(V)] (28) are capable of activating NF-κB as monitored by either gel shift assay, reflecting the activation and nuclear translocation of NF-κB, or NF-κB-dependent reporter gene assay, an indicator of NF-κB activity. In contrast, it has been reported that Cr(VI), As(III), and other metals inhibit NF-κB activation through interfering with IKK NF-κB DNA binding, or the interactions with nuclear cofactor, cAMP-responsive element-binding protein (CREB)-binding protein (30,31). How can metals mediate both activation and inhibition of NF-κB?…”

“…The final concentration of Cr(VI) is critical for this metal to induce or inhibit NF-κB. The inhibitory effect of Cr(VI) at higher concentrations (>50 mM) on NF-κB may be due to the cytotoxic effect on the cells or interference with the DNA binding activity of NF-κB (31). We recently demonstrated that Cr(VI) activated NF-κB at 5-10 µM in human bronchial epithelial cells cultured at a relatively higher cell density, possibly through activating IKK.…”

“…To date, the results are not straightforward. Both activation and inhibition of NF-κB by metals have been reported (29)(30)(31). Several studies from different groups indicate that, at a noncytotoxic concentration, arsenic trioxide [As(III)] (32), chromium(VI) [Cr(VI)] (28), and vanadium(V) [V(V)] (28) are capable of activating NF-κB as monitored by either gel shift assay, reflecting the activation and nuclear translocation of NF-κB, or NF-κB-dependent reporter gene assay, an indicator of NF-κB activity.…”

Plasmid profile and curing analysis of Pseudomonas aeruginosa as metal resistant

“…Similarly chromium (VI) is the toxic form of chromium released during many industrial processes, including electroplating, leather tanning and pigment manufacture (Prasenjit and Sumathi, 2005). Chromium (VI) is extremely toxic, mutagenic (Cheng and Dixon, 1998), carcinogenic (Shumilla et al, 1999) and terartogenic (Asmatullah et al, 1998) which effects on biological systems. The role of microorganisms in bioremediation is important because of their ability to degrade hazardous compounds into harmless ones.…”

Oxidative Stress, hogg1 Expression and NF‐κB Activity in Cells Exposed to Low Level Chromium

“…, whereas other researchers have reported that NF-κB activation is inhibited by Cr (VI) 17,18) . It has been reported in several studies that Cr (VI) induces the generation of 8-OH-dG.…”