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. 2014 Feb 13;6(3):528-40.
doi: 10.1016/j.celrep.2014.01.007. Epub 2014 Jan 30.

ZFX Controls Propagation and Prevents Differentiation of Acute T-lymphoblastic and Myeloid Leukemia

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Free PMC article

ZFX Controls Propagation and Prevents Differentiation of Acute T-lymphoblastic and Myeloid Leukemia

Stuart P Weisberg et al. Cell Rep. .
Free PMC article

Abstract

Tumor-propagating cells in acute leukemia maintain a stem/progenitor-like immature phenotype and proliferative capacity. Acute myeloid leukemia (AML) and acute T-lymphoblastic leukemia (T-ALL) originate from different lineages through distinct oncogenic events such as MLL fusions and Notch signaling, respectively. We found that Zfx, a transcription factor that controls hematopoietic stem cell self-renewal, controls the initiation and maintenance of AML caused by MLL-AF9 fusion and of T-ALL caused by Notch1 activation. In both leukemia types, Zfx prevents differentiation and activates gene sets characteristic of immature cells of the respective lineages. In addition, endogenous Zfx contributes to gene induction and transformation by Myc overexpression in myeloid progenitors. Key Zfx target genes include the mitochondrial enzymes Ptpmt1 and Idh2, whose overexpression partially rescues the propagation of Zfx-deficient AML. These results show that distinct leukemia types maintain their undifferentiated phenotype and self-renewal by exploiting a common stem-cell-related genetic regulator.

Figures

Figure 1
Figure 1. Zfx contributes to the development of Notch-driven T-ALL
Mice carrying T cell-specific Cre transgene (CD4-Cre) and Cre-inducible activated Notch1 (Eef1a1-NotchIC) with (NotchIC Zfx) or without (NotchIC) the conditional Zfxfl allele were analyzed. (A) Recombination kinetics of the Eef1a1-NotchIC allele during T cell development. The indicated thymocyte subsets from pre-leukemic 4-wk old animals were sorted and analyzed by genomic PCR. (B) Representative staining profiles of T cells in the peripheral blood; the abnormal DP population associated with T-ALL is highlighted. (C) The cellularity of the thymus and spleen from moribund mice (mean ± SEM of 5–6 animals). (D) The survival of experimental animals and of the indicated control mice (Eef1a1-NotchIC only; CD4-Cre only; CD4-Cre+ Zfxfl without Eef1a1-NotchIC) (n =12–30). See also Fig. S1.
Figure 2
Figure 2. Zfx contributes to the propagation of pre-established T-ALL
(A) Schematic of experimental approach to test the role of Zfx in pre-established NotchIC dependent T-ALL. (B) The survival of mice transplanted with T-ALL cells followed by inducible Zfx deletion. Independent primary R26-CreER+ T-ALL lines carrying wild-type (ZfxWT) or conditional (Zfxfl) Zfx allele (7 of each genotype) were transplanted into recipient mice, which were treated 2 days later with either Tmx or vehicle. Arrowhead indicates the only recipient of R26-CreER+ Zfxfl cells that died from Zfx-deficient leukemia. (C) The propagation of secondary T-ALL after delayed Zfx deletion. Three primary R26-CreER+ Zfxfl/y T-ALL lines were transplanted into recipient mice, which were treated 6 days later with either Tmx or vehicle. Shown is the fraction of GFP+ T-ALL cells in the peripheral blood at the indicated time points after Tmx treatment. (D–E) The phenotype of T-ALL cells after Zfx deletion. Secondary recipients of T-ALL cells described in panel C were sacrificed at 7 or 14 days after vehicle/Tmx treatment, and their BM were analyzed by flow cytometry. Panel D shows the CD4/CD8 expression profile of gated GFP+ T-ALL 14 days after treatment with vehicle (Zfx fl) or Tmx (Zfx Δ). Panel E shows the staining level of indicated markers or forward scatter (FSC) of gated GFP+ T-ALL after the treatment with vehicle on day 14 or with Tmx on day 7 (for CD25) or 14. See also Fig. S2.
Figure 3
Figure 3. Zfx contributes to the initiation and propagation of MA9-induced AML
(A) Schematic of experiment to test the transformation of Zfx-deficient myeloid progenitors by the MLL-AF9 (MA9) retrovirus. (B) Clonal outgrowth of Zfxwt/y and ZfxΔ/y common myeloid progenitors (CMP) and granulocyte-monocyte progenitors (GMP) transduced with MA9. Shown are colony yields at the indicated passages (P) in semi-solid medium (mean S.E.M. of 3–5 independent parallel cultures). **P<0.01. (C) Schematic of experimental approach to test the role of Zfx in pre-established AML in vivo. (D) The effect of Zfx deletion on leukemia initiation by primary MA9-induced AML. Independent primary R26-CreER+ AML lines carrying wild-type (ZfxWT) or conditional (Zfxfl) Zfx allele (7–8 of each genotype) were incubated with 4-OHT or vehicle for 3 days and transplanted into secondary recipients. Shown is the Kaplan-Meier survival plot of recipient mice; arrowheads indicate recipients of R26-CreER+ Zfxfl cells that died from Zfx-deficient leukemia. (E) The effect of Zfx deletion in vivo on the progression of MA9-induced AML. Untreated primary R26-CreER+ AML lines carrying ZfxWT or Zfxfl alleles were transplanted into secondary recipients, which were treated with Tmx 10 days later. The results are shown as in panel (D). (F) The effect of Zfx deletion on leukemia initiation by Hoxa9/Meis1-induced AML. The experiment was performed and is presented as in panel (D), except that AML was induced by Hoxa9/Meis1 instead of MA9 retrovirus. The results are shown as in panel (D). See also Fig. S3.
Figure 4
Figure 4. Zfx controls the clonogenic growth and immature phenotype of murine MA9 AML
(A) Schematic of experimental approach to test the role of Zfx in the growth and phenotype of pre-established AML. (B–C) The effect of Zfx loss on MA9 AML cells grown in cytokine-supplemented culture. Primary R26-CreER+ AML lines carrying wild-type (ZfxWT) or conditional (Zfxfl) Zfx allele were incubated with 4-OHT or vehicle for 4 days (passage 1, P1) and passaged in semi-solid medium. Shown are representative microphotographs of colonies at P1 (panel B) and colony yields at P3 (mean ± SEM of 6 independent cultures). **P<0.01. (D–G) The effect of Zfx loss on MA9 AML cells co-cultured with BM stromal cells. Primary AML lines described above were cultured with 4-OHT or vehicle in cytokine-supplemented liquid culture and plated on stromal cells without cytokines. (D) Representative staining profiles of OHT-treated cells after 4 days of stromal co-culture (E) The fraction of cells with progenitor phenotype (c-Kit+ CD14) after 7 days of stromal co-culture (mean ± SEM of 6 independent cultures). **P<0.01. (F) Mean fluorescence intensity of myeloid differentiation markers during stromal co-culture (mean ± SEM of 7–8 independent cultures). *P<0.05, **P<0.01. (G) The growth potential of Zfx-deficient AML cells after stromal co-culture. Cell fractions of the indicated phenotype were sorted from OHT-treated R26-CreER+ Zfxfl AML cells grown in stromal co-culture, and replated into cytokine-supplemented liquid culture (mean ± SEM of 3 independent cultures). **P<0.01. See also Fig. S4.
Figure 5
Figure 5. Characterization of gene expression program controlled by Zfx in T-ALL and AML
(A) Schematic of the approach to define Zfx-controlled gene expression programs in leukemia, using the overlap between Zfx-regulated gene sets and genomic Zfx binding regions (as determined by microarrays and ChIP-seq, respectively). (B) The identification of direct Zfx target genes in T-ALL and AML. Shown is the percentage of Zfx-regulated genes in murine T-ALL and AML that had significant Zfx binding regions within 1 Kb of the TSS in murine ESCs and/or the respective human leukemia cell line. (C) The expression of leukemia-derived Zfx target gene sets in normal Zfx-deficient stem cells. Shown are expression levels (as heat maps) in control vs Zfx-deficient HSCs and ESCs (Galan-Caridad et al., 2007) of direct Zfx target genes defined in T-ALL and AML. Arrowheads highlight Zfx target genes Ptpmt1 (black) and Idh2 (grey). (D) The expression of leukemia-derived Zfx target genes during normal development of the respective lineages. Genes that were decreased or increased by Zfx loss in T-ALL were analyzed for their expression in normal DN versus DP thymocytes; genes that were decreased or increased by Zfx loss in AML were analyzed for their expression in normal HSCs and myeloid progenitors versus mature myeloid cells. Shown is the output of gene set enrichment analysis (GSEA), with the enrichment score graphs on top. See also Fig. S5 and Tables S1–S5.
Figure 6
Figure 6. Zfx contributes to Myc-induced progenitor transformation
(A) Schematic of experiment to test the role of Zfx in the transformation of myeloid progenitors by Myc. (B) Effect of Zfx deletion on clonogenic growth of Myc-transformed myeloid progenitors. Myeloid progenitors from mice with Tmx-induced Zfx deletion (ZfxΔ/y) or from control Tmx-treated mice (Zfxwt/y) were transduced with Myc-GFP or GFP only retroviruses, and GFP+ progenitors were sorted and propagated in semi-solid medium. Shown are the colony yields over serial passages (mean ± SEM of 6 independent cultures) ** P<0.01. (C) Response to Myc overexpression in Zfx-deficient progenitors. Wild-type or Zfxdeficient myeloid progenitors transduced with Myc/GFP or GFP only as above were cultured for 4 days and analyzed by microarray (3 independent cultures for each sample). Average differential expression in Myc-expressing versus GFP-expressing cells of each Zfx genotype (Myc response) was calculated for each probe. Shown is the pairwise comparison of Myc responses in wild-type versus Zfx-deficient cells, with the probes showing differential responses in blue. The probes whose levels were increased by Myc in wild-type cells are circled in red. See also Fig. S6 and Tables S6–S7.
Figure 7
Figure 7. Zfx activates the expression of Ptpmt1 and Idh2 in leukemia cells
(A) The overlap between conserved direct targets of Zfx activation in T-ALL and AML. (B) The expression of Idh2 and Ptpmt1 in murine leukemia cells after Zfx deletion. The deletion was induced by Tmx (or vehicle as a control) in the R26-CreER+ conditional (Zfxfl/y) or control (Zfxwt/y) leukemia cells. NotchIC-transformed T-ALL cells were sorted from secondary recipients 5 days after Tmx treatment; MA9-transformed primary AML were incubated with 4-OHT for 3 days. Shown are relative expression levels as determined by qRT-PCR (mean ± SEM of 5 independent lines for T-ALL and 7–8 independent lines for AML). **P<0.01. (C) The expression of Idh2 and Ptpmt1 in Zfx-deficient progenitors during transformation by Myc. Shown are relative transcript levels determined by qRT-PCR in ZfxΔ/y or Zfxwt/y progenitors 4 days after transduction by Myc-GFP or GFP only (mean ± SEM of 6 independent cultures) * P<0.05, ** P<0.01. (D) Effect of Zfx deletion on the glycolysis rate of murine AML cells grown in liquid culture with cytokines. MA9-transformed R26-CreER+ Zfxfl/y AML line was transduced with retroviral vectors expressing Idh2 or GFP alone. The cells were incubated with 4-OHT to induce Zfx deletion, propagated for 4 days in liquid culture and analyzed for the steady-state glucose consumption and lactate excretion rates (mean ± SEM of triplicate cultures). *P<0.05, **P<0.01. (E–F) Effect of Zfx deletion on the expression and function of Ptpmt1. MA9-transformed R26-CreER+ Zfxfl/y AML line was incubated with 4-OHT for 5 days to induce Zfx deletion, and analyzed 4 days later by Western blotting for Ptpmt1 (panel D) and by thin layer chromatography for 32P-labeled mitochondrial lipids (panel E). The position of PGP was confirmed by parallel analysis of pure 14C-labeled PGP. (G) Effect of Idh2 and Ptpmt1 overexpression on the growth of Zfx-deficient AML. MA9-transformed R26-CreER+ Zfxfl/y AML line was transduced with retroviral vectors expressing Idh2, Ptpmt1 or GFP alone. The cells were incubated with 4-OHT to induce Zfx deletion, and the resulting ZfxΔ/y cells were transferred into secondary recipients. Each recipient received one cell line resulting from an independent transduction with the respective vector. Shown are Kaplan-Meier survival plots of the recipient groups; the difference between Idh2 or Ptpmt1-expressing and control GFP-expressing ZfxΔ/y AML is significant (P<0.01). The results represent a summary of 3 independent experiments involving 1–3 lines of each genotype. See also Fig. S7.

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