Introduction. Glucocorticoids are a commonly used adjuvant treatment for breast cancer, alleviating side effects of chemotherapy. However, glucocorticoids also alter tumour cell behaviour. We have previously identified a drug class effect of glucocorticoids in inhibiting serum-induced migration in the breast tumour cell line, MDA-MB-231, in a 2-dimensional scrape wound healing assay and a 3-dimensional modified Boyden chamber assay.
Aim. To characterise the mechanism of glucocorticoid inhibition of breast tumour cell migration.
Methods. Scrape wound healing assays were performed on MDA-MB-231 cells incubated with fetal calf serum (FCS), following pre-treatment with glucocorticoids, the glucocorticoid receptor antagonist, RU486 or protein synthesis inhibitor, cycloheximide. Time-lapse microscopy images of the wound were taken every 30min for 16 hours. MDA-MB-231 cells were transiently transfected with a Glucocorticoid Response Element (GRE)-SEAP reporter construct to examine the effect of glucocorticoids on GRE activity, as a measure of transactivation.
Results. The transactivation antagonist RU486 completely prevents glucocorticoid inhibition of FCS-induced MDA-MB-231 cell migration in the scrape wound healing assay. Transactivation-selective glucocorticoid RU24782 and non-steroidal glucocorticoid receptor agonist GSK9027 also inhibited FCS-induced tumour cell migration. The protein synthesis inhibitor, cycloheximide, reduced the extent to which dexamethasone inhibited FCS-induced migration by 57 ± 10%, (n=3, P<0.05). Dexamethasone induced GRE activity at migration-inhibiting concentrations; these responses were blocked by RU486 (n=3, P<0.05). GSK9027 and RU24782 showed increased GRE activity at concentrations that inhibit FCS-induced migration of MDA-MB-231 cells.
Discussion. Inhibition of migration is prevented by the transactivation antagonist, RU486, and by the protein synthesis inhibitor, cycloheximide. The inhibitory effects are also associated with an increase in GRE activity. These results suggest the inhibitory effects of glucocorticoids on tumour cell migration are mediated through altered transcription of genes containing GREs.