Correlation of membrane glucocorticoid receptor levels with glucocorticoid-induced apoptotic competence using mutant leukemic and lymphoma cells lines

We have studied the presence and functional implications of membrane glucocorticoid receptor (mGR) in several wild type (WT) and mutant mouse lymphoid cell lines (nuclear transfer decrease, NT^-; nuclear transfer increase, NTⁱ; and receptorless, R^-). Direct fluorescent antibody staining revealed large aggregates of mGR-specific fluorescing antigens in the plasma membrane of the WT and mGR-enriched (mGR⁺⁺) S-49 cells. While R^- cells totally lacked mGR, this receptor level was low in NT^- and NTⁱ groups. FACS analysis corroborated these results, showing a ∼4-10-fold difference between the highest mGR levels (mGR⁺⁺) and the R^- and NTⁱ cells. Membrane extracts were analyzed for mGR by immunoblotting. Multiple receptor forms, ranging in M_r from 94,000 to > 200,000, were observed in the WT cells, while only smaller peptides (85,000-94,000) were found in NT^- cells. No detectable immunoreactive bands were identified in either membrane or cytosol immunoprecipitates of NTⁱ and R^- cell groups. Within 48 h post dexamethasone exposure > 98% of WT and mGR⁺⁺ S-49 cells underwent apoptosis, compared to 0-30% in the mutant cells, albeit the total receptor number is two to three times higher in NTⁱ compared to WT. These results suggest a better correlation between the quantity and quality of mGRs (rather than total cellular GRs) and the ability of glucocorticoids (GCs) to lyse lymphoid cells.