CELL-CYCLE REGULATION OF MEMBRANE GLUCOCORTICOID RECEPTOR IN CCRF-CEMHUMAN ALL CELLS - CORRELATION TO APOPTOSIS

The human leukemic cell line (CCRF-CEM) and a subline enriched for the plasma membrane-resident glucocorticoid receptor (mGR) were studied f or the influence of the cell cycle on the expression and function of m GR. Three synchronization procedures (double thymidine, colcemid, and combined thymidine-colcemid blocks) were used. Fluorescent microscopy and flow cytometry simultaneously assessed antibody-tagged mGR and DNA . In addition, mGR was quantitated and characterized by immunoprecipit ation and immuno-blotting. Apoptosis was assayed by DNA fragmentation (TUNEL assay) and by cell survival (trypan blue exclusion). All synchr onization procedures demonstrated that progression from DNA replicatio n (S) to the second growth phase and mitosis (G(2)/M) leads to cells h aving the highest levels of mGR expression and being highly glucocorti coid sensitive in the apoptosis assays: 32 and 80% sensitivity of wild type and mGR-enriched cells, respectively, compared with 12 and 30% s ensitivity in asynchronous cells. Therefore, mGR expression appears to be cell cycle regulated, with its highest expression at late S-G(2)/M , when the cells are most sensitive to the lymphocytolytic effects of glucocorticoids.