Oxidative stress and thioredoxin-interacting protein promote intravasation of melanoma cells.

Although intravasation may be a critical rate-limiting step in the metastatic cascade, the role of oxidative stress in intravasation is unknown. We tested the hypothesis that reactive oxygen species (ROS), regulated by thioredoxin interacting protein (Txnip) through the action of thioredoxin (Trx), influence human SK-MEL-28 melanoma cell reverse (basolateral-to-apical) transendothelial migration (TEM) in vitro as a model for intravasation. Reverse transendothelial migration was dose-dependently induced by hydrogen peroxide 2.4-fold for 0.1 microM (P < 0.01) and 3.9-fold for 1 microM (P < 0.001) vs. control, and this effect was blocked by the antioxidant N-acetylcysteine. Overexpression of Txnip by infecting melanoma cells with adenovirus increased TEM 3-fold vs. control (P < 0.001), and this increase was blocked by N-acetylcysteine, indicating a redox-sensitive mechanism. Conversely, thioredoxin overexpression blocked hydrogen peroxide-induced TEM. Exposure to ultraviolet-A radiation increased ROS 1.8-fold (P < 0.01), and this was accompanied by a 45% reduction (P < 0.05) in thioredoxin activity and an 11.4-fold (P < 0.001) increase in Txnip gene expression. These data suggest that TEM of melanoma cells during intravasation is in part mediated by ROS-sensitive cellular signaling cascades, may be controlled by Txnip and its interaction with thioredoxin that in turn modulates cellular levels of oxidative stress, and may be initiated by ultraviolet-A induction of this cascade.