Microarray Analysis Uncovers the Induction of the Proapoptotic BH3-only Protein Bim in Multiple Models of Glucocorticoid-induced Apoptosis

Abstract

Despite being one of the earliest recognized and most clinically relevant forms of apoptosis, little is known about the transcriptional events that mediate glucocorticoid-induced apoptosis. Therefore, we used oligonucleotide microarrays to identify the pattern of dexamethasone-induced changes in gene expression in two well characterized models of glucocorticoid-induced apoptosis, the murine lymphoma cell lines S49.A2 and WEHI7.2. Dexamethasone treatment induced a diverse set of gene changes that evolved over a 24-h period preceding the onset of cell death. These include previously reported changes in the expression of genes regulating prosurvival signals mediated by c-Myc and NFB. Unexpectedly, we discovered that glucocorticoid treatment increases expression of the gene encoding Bim, a BH3-only member of the Bcl-2 family that is capable of directly activating the apoptotic cascade. Induction of Bim was confirmed by immunoblotting not only in S49.A2 and WEHI7.2 cells but also in the human leukemia cell line CEM-C7 and in primary murine thymocytes. All three prototypical isoforms of Bim (Bim EL , Bim L , and Bim S ) were induced by dexamethasone. Because elevated expression of Bim initiates the execution phase of cell death, this report that Bim is induced by dexamethasone provides novel insight into the mechanism through which glucocorticoid-mediated changes in gene expression induce apoptosis in lymphoid cells.

TRAIL and thymocyte apoptosis: not so deadly?

“…[11][12][13] It is well established that antigen-, glucocorticoid-, UV and g-irradation-induced apoptosis in thymocytes proceeds predominantly via the activation of proapoptotic members of the Bcl-2 family associated with changes in the Thymocytes from age-and sexmatched wild-type or TRAIL-deficient Balb/c mice were isolated and exposed to various doses of plate-bound anti-CD3 (0-3 mg/ml) plus soluble anti-CD28 (10 mg/ml), the glucocorticoid dexamethasone (Dex, 0-40 nM), UV-irradiation (0-40 000 mJ/cm 2 ), g-irradiation (135 rad), or anti-Fas antibody (Jo-2, 0-1000 ng/ml plus 0.1 mM cycloheximide). Apoptosis in CD4 þ CD8 þ thymocytes was assessed 18 h later by Annexin V staining and flow cytometry.…”

Glucocorticoid receptor heterozygosity combined with lack of receptor auto-induction causes glucocorticoid resistance in Jurkat acute lymphoblastic leukemia cells

“…5,6 Upon ligand binding, the activated GR translocates into the nucleus, where it acts as a sequence-specific transcription factor to induce or repress the expression of a large number of target genes. [7][8][9][10] Alternatively, the GR can influence gene expression without directly interacting with DNA through proteinprotein interaction with a number of transcription factors and co-factors. 11 The subsequent alterations in gene expression are considered responsible for GC induction of cell death and cell cycle arrest, another important antileukemic GC effect.…”

Apoptosis inhibition by Bcl-2 gives way to autophagy in glucocorticoid-treated lymphocytes

“…The anti-apoptotic protein Bcl-2 is virtually absent in WEHI7.2 cells; hence, these cells readily undergo apoptosis following exposure to the glucocorticoid hormone dexamethasone (Dex) and represent a good experimental system for investigating glucocorticoid-induced apoptosis. 2 Moreover, Tome et al, 21 have shown that glucocorticoid treatment inhibits glucose uptake and represses glycolysis in WEHI7.2 cells, reflecting similar metabolic alterations observed in primary thymocytes. 8,9 As reported here, we discovered that Dex induces autophagy in WEHI7.2 cells, based on multiple complementary detection methods.…”

“…Glucocorticoid-induced apoptosis is mediated through the glucocorticoid receptor, a ligand regulated transcription factor, and involves induction of a variety of genes that contribute to cell death, including the gene encoding the pro-apoptotic protein Bim. 2,3 In addition to apoptosis-related genes, gene expression profiling has uncovered glucocorticoid regulation of genes involved in cellular metabolism, including genes that regulate glucose homeostasis and respond to ER stress. 2,[4][5][6][7] This is not surprising since it has been known for over forty years that glucocorticoids inhibit glucose uptake and glycolysis in thymocytes.…”

“…2,3 In addition to apoptosis-related genes, gene expression profiling has uncovered glucocorticoid regulation of genes involved in cellular metabolism, including genes that regulate glucose homeostasis and respond to ER stress. 2,[4][5][6][7] This is not surprising since it has been known for over forty years that glucocorticoids inhibit glucose uptake and glycolysis in thymocytes. 8,9 These welldocumented effects on lymphocyte metabolism suggested to us that glucocorticoids might induce macroautophagy (hereafter referred to as autophagy), as well as apoptosis.…”