Dexamethasone inhibits proliferation and stimulates ecto-5'-nucleotidase/CD73 activity in C6 rat glioma cell line

Malignant gliomas are the most common and devastating primary tumors of the adult central nervous system. Dexamethasone, a synthetic glucocorticoid, is commonly co-administered to control edema in the management of brain tumors during chemotherapy and radiotherapy. In the present study, the effect of dexamethasone on proliferation and ectonucleotidase activities in rat C6 glioma cell line was investigated. Dexamethasone concentrations ranging from 0.001 to 10 mu M induced a time- and concentration-dependent inhibition of C6 rat glioma cell proliferation after 24, 48 and 72-h treatment. The tetrazolium reduction assay (MTT) indicated a reduction of in cell viability (44 +/- 7.6%) after 48-h treatment with 1 mu M dexamethasone. Pretreatment with 10 mu M of RU38486, an antagonist of glucocorticoid receptors, abolished the effect of 1 mu M dexamethasone by 78 +/- 9.8% after 48 h of treatment, indicating that this action is mediated via the glucocorticoid receptor. Members of the E-NTP-Dase family and ecto-5'-nucleotidase/CD73 can modulate extracellular ATP degradation and adenosine formation, both of which have been described as proliferation factors. Treatment of C6 glioma cells for 48 h with 1 mu M dexamethasone increased in 38 +/- 8.09% the AMP hydrolysis and in 3.7-fold the ecto-5'-nucleotidase/CD73 expression, suggesting an increase in adenosine formation and, therefore, a possible modulatory role in the elicitation of cell death responses. In addition, pretreatment with 5 mu M GF 109203X, a protein kinase C (PKC) inhibitor, abolished the effect of dexamethasone on cell proliferation and on ecto-5'-NT activity, suggesting that dexamethasone could exert this action via PKC. The alterations in the catabolism of extracellular purines induced by dexamethasone treatment in glioma C6 cells could be related to its pharmacological effects.