Objective: Glucocorticoid (GC) has occupied a central role in the treatment of acute lymphoblastic leukemia due to its ability to induce apoptosis in neoplastic lymphoid cells. Glucocorticoid resistance is present among 20% initial acute lymphoblastic leukemia, even 80% refractory acute lymphoblastic leukemia. Glucocorticoid resistance has been an important determinant of clinical outcome. Glucocorticoid depends on glucocorticoid receptor (GR) to induce apoptosis. Glucocorticoid receptor, a number of nuclear hormone receptor superfamily, is mediated by many signal transduction systems. The mitogen-activated protein kinases (MAPK) superfamily of serine/threonine kinases has emerged as an important component of cellular signal transduction. Four MAP kinase families, ERK, p38 MAP kinase, JNK, and ERK5, have been well characterized. p38 MAPK usually plays a role in regulating apoptosis, cell cycle arrest and cytokines production, et al. In steroid resistance patients, IL-2 combined with IL-4 can decrease glucocorticoid receptor ligand-binding affinity via p38MAPK. In human alveolar epithelial A549 cells, dexamethasone could inhibit the activation of p38MAPK. It is unclear that the effect of p38MAPK on glucocorticoid receptor function induced by dexamethasone in CEM cells. This study aimed to investigate effect of p38 mitogen-activated protein kinase on glucocorticoid receptor function induced by dexamethasone in CEM cells.
Methods: Cell viability was determined by trypan blue dye exclusion. Apoptosis was evaluated by morphology and flow cytometry. Glucocorticoid receptor protein and p-p38MAPK protein were analyzed by Western Blot.
Results: When treatment with SB203580 and dexamethasone for 24 h to 72 h, the survival percentage was increased from 62.3%, 35.5% and 11.6% to 82.8%, 54.7% and 48.1%, respectively (P < 0.01). Co-treatment with SB203580 and dexamethasone resulted in the decrease of apoptotic percentage from 26.2% to 7.1% for 36 h (P < 0.01). p38 MAPK activation was apparent at 15 min, peaked at 1 h after dexamethasone treatment, and was sustained for 6 h. The phosphorylation was still observed at 48 h. Treatment with dexamethasone at 5 micromol/L for 12, 24, 36 and 48 h resulted in increase of GR(alpha) protein to 117%, 121%, 122% and 125% respectively. Unbinding to dexamethasone, GR(alpha) is in the cytoplasm. Nuclear-to-cytoplasmic ratio of GR(alpha) is 0.27. Treatment with dexamethasone at the same concentration and time resulted in the nuclear-to-cytoplasmic ratio increase to 0.48, 0.59, 0.95, 2.16 and 4.08 respectively. Combined treatment with SB203580 and dexamethasone resulted in the nuclear-to-cytoplasmic ratio decrease from 4.08 to 0.43 for 48 h (P < 0.05). The total GR(alpha) protein was unaffected.
Conclusions: Expression of GR(alpha) protein is upregulated and translocated into nucleus. p38MAPK enhances GR(alpha) protein translocation into nucleus.