Evidence for early induction of calmodulin gene expression in lymphocytes undergoing glucocorticoid-mediated apoptosis

Glucocorticoid treatment of certain lymphoma cell lines and thymocytes activates a self-destructive pathway of programmed cell death referred to as apoptosis. Calcium and calmodulin (CaM) may be important signals in the apoptotic cascade because an early event is a sustained elevation in cytosolic Ca²⁺ and CaM inhibitors interfere with the death pathway. In the present study, expression of the CaM gene was examined during glucocorticoid-induced apoptosis in WEHI7.2 lymphocytes. Steady state levels of CaM mRNA were increased up to 10-fold following a 4-6-h exposure of WEHI7.2 cells to 10^-6 M dexamethasone. This increase was mediated through the glucocorticoid receptor since the response was not observed in WEHI7.418, a variant line which does not express active glucocorticoid receptor. Induction of CaM mRNA was dose-dependent and highly specific for glucocorticoids, as other steroids were unable to elicit the response. A stringent cell specificity was also observed. Pretreatment of WEHI7.2 lymphocytes with cycloheximide did not interfere with dexamethasone-dependent increases in CaM mRNA levels, and studies with actinomycin D demonstrated that the stability of the transcript was not altered by hormone. Finally, a calmodulin inhibitor elicited a protective effect on WEHI7.2 cells following glucocorticoid exposure. These results indicate that CaM mRNA levels were hormonally controlled in WEHI7.2 lymphocytes and support the putative involvement of CaM in glucocorticoid-induced apoptosis.