Previous studies from our laboratory have suggested a central role for reactive oxygen species (ROS) in the pathogenesis of occupational lung diseases. Environmental and occupational exposure to vanadium is common and is linked to an increased incidence of lung cancer. We hypothesized that the carcinogenicity of vanadium may be associated with its ROS-generating potential leading to activation of the transcription factor activator protein-1 (AP-1). In the present study, we investigated the activation of AP-1 with vanadate using mouse epidermal cells (JB6 p+) stably transfected with AP-1 luciferase reporter plasmid. This resulted in a dose dependent transactivation of AP-1, which was inhibited by SOD and catalase. Sodium formate, a specific OH scavenger, did not inhibit vanadate-induced AP-1 activation, whereas NADPH enhanced AP-1 activation. An antioxidant, N-acetyl-cysteine, decreased the activation, further showing that vanadate induced AP-1 activation is involved in redox reactions. Calphostin C, a specific inhibitor of protein kinase C (PKC), inhibited the activation of AP-1, demonstrating that PKC is involved in the cell signal cascades leading to vanadate-induced AP-1 activation. Electron spin resonance (ESR) measurements showed that JB6 p+ cells are able to reduce vanadate to vanadium (IV) in the presence of NADPH. Molecular oxygen was consumed during the vanadate reduction process to generate 028. SOD inhibited the ESR spin adduct signal, further demonstrating the generation of 028 in the cellular reduction of vanadate. These results provide support for a model in which vanadium, like other classes of tumor promoters (e.g., phorbol esters), transactivates AP-1-dependent gene expression. In the case of vanadium, the AP-1 transactivation is dependent on the generation of 02 and H202 but not OH.
Analytical-processes; Analytical-methods; Animal-studies; Animals; Laboratory-animals; Vanadium-compounds; Carcinogens; Carcinogenicity; Carcinogenesis; Toxins; Toxic-effects; Cancer; Antioxidants; Exposure-assessment; Statistical-analysis; Metal-oxides; Metal-compounds; Respiratory-system-disorders; Pulmonary-system-disorders