We previously reported an interorgan system in which stress-related
hormones (
corticosterone and
noradrenaline),
interleukin-6, and
glutathione (GSH) coordinately regulate metastatic growth of highly aggressive B16-F10
melanoma cells.
Corticosterone, at levels measured in
tumor-bearing mice, also induces apoptotic cell death in metastatic cells with low GSH content. In the present study we explored the potential role of
glucocorticoids in the regulation of metastatic cell death/survival during the early stages of organ invasion.
Glucocorticoid receptor (GCR) knockdown decreased the expression and activity of γ-
glutamylcysteine synthetase (γ-GCS), the rate-limiting step in GSH synthesis, in metastatic cells in vivo independent of the
tumor location (liver, lung, or subcutaneous). The decrease in γ-GCS activity was associated with lower intracellular GSH levels. Nrf2- and p53-dependent down-regulation of γ-GCS was associated with a decrease in the activities of
superoxide dismutase 1 and 2,
catalase,
glutathione peroxidase, and
glutathione reductase, but not of the O2--generating
NADPH oxidase. The GCR knockdown-induced decrease in
antioxidant protection caused a drastic decrease in the survival of metastatic cells during their interaction with endothelial cells, both in vitro and in vivo; only 10% of
cancer cells attached to the endothelium survived compared to 90% survival observed in the controls. This very low rate of metastatic cell survival was partially increased (up to 52%) in vivo by inoculating B16-F10 cells preloaded with GSH
ester, which enters the cell and delivers free GSH. Taken together, our results indicate that
glucocorticoid signaling influences the survival of metastatic cells during their interaction with the vascular endothelium.