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. 2007 Jul 15;110(2):735-42.
doi: 10.1182/blood-2006-12-060947. Epub 2007 Apr 26.

Inhibition of glycogen synthase kinase-3 activity leads to epigenetic silencing of nuclear factor kappaB target genes and induction of apoptosis in chronic lymphocytic leukemia B cells

Andrei V Ougolkov  1 , Nancy D Bone, Martin E Fernandez-Zapico, Neil E Kay, Daniel D Billadeau
Affiliations

Inhibition of glycogen synthase kinase-3 activity leads to epigenetic silencing of nuclear factor kappaB target genes and induction of apoptosis in chronic lymphocytic leukemia B cells

Andrei V Ougolkov et al. Blood. .

Abstract

Chronic lymphocytic leukemia (CLL) is commonly defined as a disease of failed apoptosis of B cells and remains an incurable disease. The mechanism of resistance to apoptosis in CLL is complex and influenced by numerous factors, including nuclear factor kappaB (NFkappaB)-mediated expression of antiapoptotic molecules. Recent evidence indicates that glycogen synthase kinase-3beta (GSK-3beta) positively regulates NFkappaB-mediated gene transcription and cell survival. Using malignant B cells collected from patients with CLL, we find that both GSK-3beta and NFkappaB accumulate in the nucleus of CLL B cells, and pharmacologic inhibition of GSK-3 results in decreased expression of two NFkappaB target genes Bcl-2 and XIAP and a subsequent increase in CLL B-cell apoptosis ex vivo. Furthermore, we observed that inhibition of GSK-3 leads to a decrease in NFkappaB-mediated gene transcription but does not affect the nuclear accumulation of NFkappaB in CLL B cells. Last, using chromatin immunoprecipitation, we show that GSK-3 inhibition abrogates NFkappaB binding to its target gene promoters (XIAP, Bcl-2), in part through epigenetic modification of histones. Our results establish that inhibition of GSK-3 abrogates NFkappaB binding to its target gene promoters through an epigenetic mechanism, enhances apoptosis in CLL B cells ex vivo and identifies GSK-3 as a potential therapeutic target in the treatment of CLL.

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Figures

Figure 1
Figure 1
GSK-3β accumulates in the nucleus of CLL B cells. (A) Equivalent amounts (50 μg) of nuclear and cytosolic proteins isolated from the indicated sample from patients with CLL and from normal human B cells were separated by SDS-PAGE, immunoblotted, and probed with antibodies to the indicated proteins. P = patient. Cu/Zn super oxide dismutase (Cu/Zn SOD) and ORC2 are used as markers for the purity of the cytoplasmic and nuclear proteins, respectively. (B) Nuclear/cytosolic fractions were prepared from the indicated samples from patients with CLL, and protein expression was analyzed as described in panel A. (C) Immunofluorescence staining of GSK-3β (probed with TRITC-labeled anti-mouse secondary antibody, red fluorescence) in CLL B cells (top) and normal human B cells (bottom). Nuclei were counterstained with Hoechst 33342 (blue fluorescence).
Figure 2
Figure 2
Pharmacologic inhibition of GSK-3 induces apoptosis in CLL cells. (A) Malignant B cells from 3 patients with CLL were treated with 25 μmol/L concentrations of the 3 distinct GSK-3 inhibitors AR-A014418 (AR), SB216763 (SB), TDZD8 (TD), or diluent (DMSO); 24 hours after treatment, the cell pellet was collected and protein was obtained. Cell lysates were separated by SDS-PAGE, transferred to PVDF membrane, and immunoblotted with the indicated antibodies. (B) MEC1 CLL cells were treated with DMSO or AR-A014418 at indicated concentrations for 24 hours and protein expression was analyzed as described in (A). ARA10 = 10 μmol/L AR-A014418; ARA25 = 25 μmol/L AR-A014418. (C) MEC1 cells were treated for 24 hours with DMSO or AR-A014418 at indicated concentrations, then assayed for apoptosis using Annexin-V-FITC staining as determined by flow cytometry. Columns, mean; bars, standard deviation (SD). (D) Malignant B cells from 10 patients with CLL were treated for 48 hours with diluent (DMSO) or AR-A014418 at indicated concentrations, then assayed for apoptosis using Annexin-V-FITC staining as determined by flow cytometry (mean ± SD; n = 10). Columns, mean; bars, SD.
Figure 3
Figure 3
Pharmacologic inhibition of GSK-3 decreases NFκB-mediated survival of CLL cells. Malignant B cells from 11 patients with CLL were treated with diluent (DMSO) or 25 μmol/L AR-A014418; at the indicated time after treatment, the cell pellet was collected and protein was obtained. Cell lysates were separated by SDS-PAGE, transferred to PVDF membrane, and immunoblotted with the indicated antibodies. Western blot band intensities were quantified by using the Image J software (National Institutes of Health). The quantitative analysis of Bcl-2 protein levels (normalized to β-actin levels in each case) in DMSO versus AR-A014418–treated CLL B cells obtained from 11 patients with CLL are presented in the lower panel. ARA indicates AR-A014418; P, patient.
Figure 4
Figure 4
Inhibition of GSK-3 decreased NFκB-mediated expression of antiapoptotic molecules in CLL cells. (A) CLL B cells from patients with CLL were treated with diluent (DMSO) or 25 μmol/L AR-A014418; 12 hours after treatment, the cell pellet was collected and RNA was obtained. RT-PCR analysis was performed as described in “Materials and methods.” P = patient; B2M = β-2-microglobulin. (B) MEC1 cells were treated with diluent (DMSO), 25 μmol/L AR-A014418 (ARA), 50 μmol/L Z-VAD-FMK (ZVAD), or AR-A014418 + Z-VAD-FMK; the cell pellet was collected and RNA (12 hours after treatment) and protein (24 hours after treatment) were obtained. Cell lysates were separated by SDS-PAGE, transferred to PVDF membrane, and immunoblotted with the indicated antibodies (left panel). RT-PCR analysis was performed as described in “Materials and methods.” (C) CLL B cells from a patient with CLL were treated with diluent (DMSO) or 25 μmol/L AR-A014418 (ARA), 50 μmol/L Z-VAD-FMK (ZVAD), or AR-A014418 + Z-VAD-FMK; the cell pellet was collected and RNA (12 hours after treatment) and protein (24 hours after treatment) were obtained. mRNA and protein expression analysis was performed as described in panel B.
Figure 5
Figure 5
Inhibition of GSK-3 affects the binding of NFκB p65 to its target gene promoters in CLL cells. (A) MEC1 cells were treated with 25 μmol/L AR-A014418 for 0, 12, and 24 hours, as indicated. Nuclear/cytosolic fractions were prepared, and 50 μg of nuclear and cytosolic proteins were separated by SDS-PAGE, transferred to PVDF membrane, and immunoblotted as indicated. (B-C) Binding of NFκB p65 to the promoters of its target genes XIAP and Bcl-2 was assayed with the use of chromatin immunoprecipitation (ChIP) in MEC1 CLL cells treated with 25 μmol/L AR-A014418 (ARA), 50 μmol/L Z-VAD-FMK, or AR-A014418 + Z-VAD-FMK for 12 hours. (D) Immunoprecipitated chromatin was analyzed by PCR for the binding of NFκB p65 to the promoters of its target genes XIAP and Bcl-2 in malignant B cells from 5 patients with CLL treated with 25 μmol/L AR-A014418 (ARA) for 12 hours.
Figure 6
Figure 6
Inhibition of GSK-3 affects histone modification in CLL cells. (A-B) Twelve hours after treatment, genomic chromatin fragments from DMSO or 25 μmol/L AR-A014418 (ARA)-treated MEC1 cells (panel A) and malignant B cells from 5 patients with CLL (panel B) were immunoprecipitated with dimethyl-H3-K9, trimethyl-H3-K27, and dimethyl-H4-K20 antibodies. Immunoprecipitated chromatin was analyzed by PCR for the methylation of H3-K9, H3-K27, and H4-K20 at the XIAP and Bcl-2 promoters. PCR analysis on input chromatin (first 2 lanes) confirmed that equal chromatin amounts were used for ChIP. (C) Binding of NFκB p65 to the promoters of its target genes XIAP, and Bcl-2 was assayed in malignant B cells from a CLL patient treated with 25 μmol/L AR-A014418 (ARA) or 50 μmol/L Z-VAD-FMK (ZVAD) or AR-A014418 + Z-VAD-FMK for 12 hours by ChIP. Immunoprecipitated chromatin was also analyzed for the methylation of H3-K9, H3-K27, and H4-K20 at the XIAP and Bcl-2 promoters as described in (panels A and B).
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