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.

Glucocorticoid hormones induce apoptosis in lymphoid cells. This process requires de novo RNA/protein synthesis. Here we report the identification and cloning of a novel dexamethasone-induced gene designated dig2. Using Affymetrix oligonucleotide microarray analysis of ϳ10,000 genes and expressed sequence tags, we found that the expression of dig2 mRNA is significantly induced not only in the murine T cell lymphoma lines S49.A2 and WEHI7.2 but also in normal mouse thymocytes following dexamethasone treatment. This result was confirmed by Northern blot analysis. The induction of dig2 mRNA by dexamethasone appears to be mediated through the glucocorticoid receptor as it is blocked in the presence of RU486, a glucocorticoid receptor antagonist. Furthermore, we demonstrated that dig2 is a novel stress response gene, as its mRNA is induced in response to a variety of cellular stressors including thapsigargin, tunicamycin, and heat shock. In addition, the levels of dig2 mRNA were up-regulated after treatment with the apoptosis-inducing chemotherapeutic drug etoposide. Though the function of dig2 is unknown, dig2 appears to have a pro-survival function, as overexpression of dig2 reduces the sensitivity of WEHI7.2 cells to dexamethasone-induced apoptosis.Glucocorticosteriod hormones are potent inhibitors of T cell proliferation and inducers of thymocyte death (1, 2). Hence, glucocorticoids are frequently used as immunosuppressives to treat a broad range of autoimmune and inflammatory disorders and prevent graft rejection following bone marrow or organ transplantation. Also, glucocorticoids are effective agents for treatment of lymphomas and lymphoid leukemias, including acute lymphoblastic leukemia and chronic lymphocytic leukemia (3-5).Glucocorticoids suppress lymphocyte proliferation and survival by two fundamental processes. First, glucocorticoids arrest proliferating lymphocytes in the G 1 phase of the cell cycle (6). Second, glucocorticoids induce apoptosis in immature lymphocytes (7). The negative effects of glucocorticoids on lymphocyte proliferation and survival are mediated through the glucocorticoid receptor, a ligand-activated transcription factor that induces or represses transcription of individual genes and gene networks (8). The transactivation activity of the glucocorticoid receptor appears essential for glucocorticoid-induced cell death, although glucocorticoid-induced "death genes" have not yet been identified (reviewed in Ref.2).Recent developments in DNA microarray technology permit a large number of cellular transcripts to be analyzed in parallel fashion (9). Using this technology, we have analyzed gene expression profiles of dexamethasone (Dex) 1 -treated lymphocytes to identify genes that are potentially involved in mediating or regulating glucocorticoid-induced apoptosis. For this purpose, we have utilized three separate but related Dex-sensitive model systems, i.e. the S49.A2 murine T cell lymphoma line, the WEHI7.2 murine T cell lymphoma line, and primary murine thymocytes. Although there were ...

Recent work has established important roles for basophils in regulating immune responses. To exert their biological functions, basophils need to be expanded to critical numbers. However, the mechanisms underlying basophil expansion remain unclear. In this study, we established that IL-3 played an important role in the rapid and specific expansion of basophils. We found that the IL-3 complex (IL-3 plus anti-IL-3 Ab) greatly facilitated the differentiation of GMPs into basophil lineage-restricted progenitors (BaPs) but not into eosinophil lineage-restricted progenitors or mast cells in the bone marrow. We also found that the IL-3 complex treatment resulted in ∼4-fold increase in the number of basophil/mast cell progenitors (BMCPs) in the spleen. IL-3-driven basophil expansion depended on STAT5 signaling. We showed that GMPs but not common myeloid progenitors expressed low levels of IL-3 receptor. IL-3 receptor expression was dramatically up-regulated in BaPs but not eosinophil lineage-restricted progenitors. Approximately 38% of BMCPs expressed the IL-3Rα-chain. The up-regulated IL-3 receptor expression was not affected by IL-3 or STAT5. Our findings demonstrate that IL-3 induced specific expansion of basophils by directing GMPs to differentiate into BaPs in the bone marrow and by increasing the number of BMCPs in the spleen.