Project description:It has been shown previously that glucocorticoids exert a dual mechanism of action, entailing cytotoxic, mitogenic as well as cell proliferative and anti-apoptotic responses, in a dose-dependent manner on CCRF-CEM cells at 72 h. Early gene expression response implies a dose-dependent dual mechanism of action of prednisolone too, something reflected on cell state upon 72 h of treatment. In this work, a generic, computational microarray data analysis framework is proposed, in order to examine the hypothesis whether CCRF-CEM cells exhibit an intrinsic or acquired mechanism of resistance and to investigate the molecular imprint of this, upon prednisolone treatment. The experimental design enables the examination of both the dose (0 nM, 10 nM, 22 uΜ, 700 uΜ) effect of glucocorticoid exposure and the dynamics (early and late, namely 4 h, 72 h) of the molecular response of the cells at the transcriptomic layer. In this work we demonstrated that CCRF-CEM cells may attain a mixed mechanism of response to glucocorticoids, however, there is clear evidence predicating towards an intrinsic mechanism of resistance. More specifically, at 4 h prednisolone appeared not to perform its expected function by down-regulating apoptotic genes, which is re-enforced by mechanisms, which down-regulate other sets of apoptotic genes. Also, low and high prednisolone concentrations up-regulates metabolic and signal-transduction related genes in both time points, thus grounding for a cell proliferation machinery. In addition, regulation of NF-κB-related genes implies an inherent mechanism of resistance through the established link of NF-κB inflammatory role and GC-induced resistance. The analysis framework applied here allows derivation of regulatory mechanisms activated by prednisolone through identification of early responding sets of genes. On the other hand, study of the prolonged exposure to glucocorticoids (72 h exposure) highlights the effect of homeostatic feedback mechanisms of the treated cells. Overall, it appears that CCRF-CEM cells in this study exhibit a diversified, combined pattern of intrinsic and acquired resistance to prednisolone, yet with a tendency towards inherent resistant characteristics, through activation of different molecular courses of action.

Project description:Background: Glucocorticoids are important pharmaceutical agents in the treatment of acute lymphoblastic leukemia in children. Resistance or sensitivity to glucocorticoids is considered to be of crucial importance for disease prognosis. Prednisolone is a first-line chemotherapeutic agent in the treatment of acute lymphoblastic leukemia. Here, the effects of prednisolone on the resistant CCRF-CEM leukemic cell line were studied. Methods: Prednisolone’s cytotoxic and cell cycle effects were studied with flow cytometry. NF-κB translocation was studied with Western Blotting and differential gene expression was studied with cDNA microarrays. Results: Prednisolone exerted a delayed biphasic effect, necrotic at low doses and apoptotic at higher doses. At low doses, prednisolone exerted a pre-dominant mitogenic effect despite its induction on total cell death, while at higher doses, prednisolone’s mitogenic and cell death effects were counterbalanced. NF-κB was constitutively present in the nucleus. Early gene microarray analysis revealed 40 differentially expressed genes upon 4 hours of prednisolone’s exposure. Notable differences in gene regulation were observed between the lowest and the highest glucocorticoid doses. Prednisolone activated genes related to apoptosis/tumor suppression, cell cycle progression, metabolism and intra-/ extra-cellular signaling pathways. Conclusions: The mitogenic/biphasic effects of prednisolone are of clinical importance in the case of resistant leukemic cells. This approach might lead to the identification of gene candidates for future molecular drug targets in combination therapy with glucocorticoids, along with early markers for glucocorticoid resistance. Elucidation of the mechanisms of GC action may lead to identification of gene targets responsible for GC resistance. Key tools in this process are high-throughput technologies such as microarray-based gene expression analysis. For this purpose, the parental CCRF-CEM cell line was chosen as the system of study for the effects of prednisolone treatment. This is a T-cell leukemia cell line characterized by a mutation (L753F) on one GR gene allele that impairs ligand binding (Thompson and Johnson 2003). It is known that both the DNA and ligand binding domains of the GR are required in order to repress NF-κB transactivation (Wissink, van Heerde et al. 1997). Interestingly, concerning the question whether this mutation would affect GC resistance, it has been reported previously that both the GC-resistant as well as the GC-sensitive CCRF-CEM subclones express heterogeneous populations of the GR (GRwt/GRL753F) (Palmer and Harmon 1991; Powers, Hillmann et al. 1993). The CCRF-CEM cell line has been reported to be resistant to GCs, presumably due to the accumulation of more resistant variants after long periods of prolonged culture (Norman and Thompson 1977). It is possible that these cells are clonally inhomogeneous, as possibly the cells obtained in vivo by patients. Moreover, the large number of the CCRF-CEM subclone studies in the literature makes it difficult to choose an appropriate resistant cell model. In addition, the utilization of an in vitro system for this study offered reproducibility, an opportunity to closely examine intracellular signals and avoid interference from other in vivo-participating systems. Thus, the cell line used for this study was considered to be useful in studying GC action and resistance in leukemic cells. The aim of this work was to determine the cytotoxic, cell cycle phase distribution and early cancer-specific gene expression effects of prednisolone in CCRF-CEM cells, as an in vitro model of ALL resistance to glucocorticoids. The early gene expression profile allowed identification of genes initiating pivotal, early onset regulatory mechanisms activated by GC and excluded ensuing feedback responses and further downstream signals. Samples tested were in the form of a loop-design i.e. control vs. 10nM prednisolone (designated 0vs1) , 10nM prednisolone vs.700uM prednisolone (designated 1vs3) and control vs. 700uM prednisolone (designated 0vs3), the sum of the logarithms of the first two should equal the third. In other words if Rj,i is the ratio of the ith gene in the jth experiment then R0vs1,i+R1vs3,i=R0vs3,i. We tested this using a statistical test. We have applied an intensity-dependent z-score where the sum of the ratios was compared to the ratio of the third experiment. If the difference was significant genes, in a standard deviation threshold of ±1.5 in relative units, were rejected from further analysis (Kerr and Churchill 2001; Kerr and Churchill 2001; Altman and Hua 2006; Kerr and Churchill 2007).

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Expression data changes induced by 3D conditions in T-ALL cells [CCRF-CEM cells]

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