The International Prognostic Scoring System (IPSS) has been widely used to predict the prognosis of patients with myelodysplastic syndrome (MDS). However, IPSS does not always provide a sufficiently precise evaluation of patients to allow the appropriate choice of clinical interventions. Here, we analyzed the expression of Bmi-1, which is required to regulate the self-renewal in CD34+ cells from 51 patients with cases of MDS and acute myeloid leukemia preceded by MDS (MDS-AML). Higher positivity rate of Bmi-1 was preferentially seen in refractory anemia with excess blasts (RAEB), RAEB in transformation (RAEB-T), and MDS-AML compared with refractory anemia (RA) and RA with ringed sideroblasts (RARS). IPSS score was positively correlated with the percentage of Bmi-1 expression. Patients with RA and RARS with a higher percentage of Bmi-1+ cells showed disease progression to RAEB. Here, we propose Bmi-1 as a novel molecular marker to predict the progression and prognosis of MDS.

Subjects:
Brief Reports, Clinical Trials and Observations, Neoplasia
Topics:
biological markers, body mass index procedure, cd34 antigens, myelodysplastic syndrome, prostatic hypertrophy risk score, refractory anemia with excess blasts, refractory anemia with sideroblasts, disease progression, leukemia, myelocytic, acute, refractory anemias

Myelodysplastic syndrome (MDS) is a group of clonal hematopoietic disorders characterized by aberrant hematopoiesis and dysplasia.1,2  Because the disease entity includes quite heterogeneous pathogeneses, the clinical course and prognosis are highly variable. The International Prognostic Scoring System (IPSS) has achieved international acceptance to estimate prognosis in patients with MDS.3,4  However, IPSS score is not necessarily enough to evaluate the patient for the purpose of choosing intervention therapies. It would be helpful for the clinical treatment of patients with MDS to establish molecular markers that clearly reflect the disease progression.

Because the most critical event for the progression of MDS and prognosis of patients with MDS is susceptibility to acute leukemia, it is necessary to monitor the appearance and increase of leukemic stem cells (LSCs) in patients with MDS. Thus, we focused on molecular mechanisms supporting LSCs. Bmi1 is a member of the Polycomb group of transcriptional repressor genes, which may be expressed restrictedly in stem cells and progenitors.5,6  Some studies have demonstrated that Bmi-1 is required to regulate the adult self-renewing hematopoietic and LSCs.7-12  Others have shown that overexpression of the Bmi-1 gene could cause neoplastic proliferation of cells.13-16  A number of reports on Bmi-1 provide perspectives on the close association of its expression with the progression of hematopoietic malignancies.17-21 

In this study, we therefore examined the positivity of Bmi-1 expression in CD34+ cells from patients with MDS by flow cytometry to test whether Bmi-1 would be a novel biomarker that is well correlated with the disease progression and prognosis of the patients.

Cells

Four acute myeloid leukemia (AML) cell lines (KG1, HL60, HEL, and U937) were obtained from American Type Culture Collection (ATCC; Manassas, VA). Mono7 originated from MDS was available in our laboratory. Normal T cells were obtained from healthy donors and cultured in RPMI-1640 complete medium in the presence of interleukin-2 and/or PHA.

Patients

We studied bone marrow samples obtained from 50 patients with newly diagnosed MDS or MDS-AML (case 19 occurred in the same patient as case 27, which developed into refractory anemia with excess blasts [RAEB]). We used 10 bone marrow samples from healthy donors and from patients with renal anemia, iron deficiency anemia, and lymphoma without bone marrow involvement as controls. The patients with refractory anemia (RA) and RA with ringed sideroblasts (RARS) received supportive care such as blood-cell transfusion and low-intensity therapy, including granulocyte colony-stimulating factor (G-CSF), erythropoietin, and cyclosporine. The patients with RAEB, RAEB in transformation (RAEB-T), and MDS-AML received high-intensity therapy, including chemotherapy and bone marrow transplantation. Informed consent was obtained from these patients and donors. An independent pathologist confirmed the diagnosis.

Immunoblot analysis and flow cytometric assessment

Immunoblot analysis using anti–Bmi-1 monoclonal antibody (Upstate Cell Signaling Solutions, Lake Placid, NY) was performed. The immunoblot results demonstrated that Bmi-1 was highly expressed in 5 AML cell lines. For flow cytometric analysis, cells were stained with anti-CD34 antibody-PE (BD Biosciences, San Jose, CA). After fixation with 3% paraformaldehyde in PBS supplemented with 5% bovine serum albumin, the cells were incubated with anti–Bmi-1 monoclonal antibody. They were incubated with goat anti–mouse IgG antibody-FITC (BD Biosciences). We confirmed that the Bmi-1 expression of all cell lines was detected by flow cytometric analysis.

Statistical analysis

The correlation between the positivity of Bmi-1 expression of CD34+ cells and IPSS was evaluated by the Spearman correlation coefficient. We used the Fisher protected least significant difference (Fisher PLSD) to evaluate differences in Bmi-1 expression ratio of CD34+ cells according to French-American-British (FAB) classification. We then used the Cox proportional hazards model to evaluate the correlation of prognosis with the percentage of Bmi-1 expression. P values less than .05 were considered statistically significant. These studies were approved by the Hiroshima University institutional review board for these studies.

Bmi-1 protein is related to cell proliferation

Bmi-1 is known to play a role for sustaining self-renewing cell activity by repressing the INK4A locus encoding p16INK4A and p19ARF, which are capable of inducing growth arrest, cellular senescence, and apoptosis.22-24  In this context, to determine whether cells expressing Bmi-1 proliferate, a BrdU-labeling assay was performed. Normal proliferating T cells, which incorporated BrdU, were predominantly stained with anti–Bmi-1 antibody. Furthermore, Bmi-1 positivity was also higher in CD34+ cells mobilized with G-CSF than for controls (data not shown). Thus, it appears that Bmi-1 protein not only sustains self-renewing stem cells, but it also plays an important role in providing cells the potential for proliferation.

Bmi-1 expression in CD34+ cells is high in RAEB, RAEB-T, and MDS-AML, and is correlated with IPSS score

Because CD34+ cells, in which LSCs are supposed to be enriched, have an important role in leukemogenesis, by applying flow cytometric analysis, we examined the percentage of Bmi-1 expression in CD34+ bone marrow cells from 51 patients with cases of MDS and MDS-AML, whose profiles are summarized in Table 1. Representative results of flow cytometric patterns are shown in Figure 1A. Higher positivity rate of Bmi-1 was preferentially seen in RAEB, RAEB-T, and MDS-AML compared with RA and RARS. The percentages of Bmi-1+ cells in CD34+ cells in RA and RARS were almost the same as that in controls (Figure 1B). Interestingly, the positivity of Bmi-1 expression at diagnosis was significantly higher in the patients with progression to RAEB (cases 6, 10, 11, 18, and 19) (28.29% ± 20.30%) compared with those without progression (4.03% ± 3.53%) (P < .001). Especially, even though the patient with case 19, whose percentage of Bmi-1+ cells was as high as 63.44% at diagnosis, had IPSS score of 1.0, the disease developed into RAEB in 3 months. However, the patient with case 32 with RAEB-T, had IPSS score of 2.0 and Bmi-1 positivity of about 7.58%, and has remained alive for more than 18 months after diagnosis without chemotherapy. Individuals with cases 20 to 31 with RAEB have died, except for the patient with case 25, who received successful allogeneic bone marrow transplantation, and the patient with case 20, who has been observed for just 7 months. Furthermore, Bmi-1 positivity in CD34+ cells was positively correlated with IPSS score (Figure 1C) (P < .001). Within a given IPSS group, cases of RA and RARS that progressed to RAEB showed the highest percentage of Bmi-1. Bmi-1 positivity in CD34+ cells independently seemed to predict the risk of mortality (hazard ratio, 1.025; P < .001). We then analyzed whether Bmi-1 is expressed more strongly in the stem-cell subpopulations among CD34+ cells, which are supposed to be heterogeneous. However, there was no significant difference in the positivity of Bmi-1 expression between hematopoietic stem cells (CD34+CD38- cells)25  and progenitors (CD34+CD38+ cells) in MDS and MDS-AML. Further phenotypic analyses did not reveal any correlation of Bmi-1 positivity in CD34+ cells in MDS and MDS-AML with other maturation markers, including CD13, CD33, or CD7 (data not shown). These results suggest that increased Bmi-1 expression could reflect qualitative difference of CD34+ cells. Although heterogeneity in study population of patients with MDS has prevented us from predicting the disease progression and prognosis, it might be possible to stratify patients to estimate them according to Bmi-1 expression in CD34+ cells. The detection and follow-up of this marker might also tell us when to initiate chemotherapy and/or stem-cell transplantation. Because our study suggested that Bmi-1 expression is useful for a molecular marker to predict progression and prognosis of MDS, the prospective study with a large group of patients is required to further evaluate Bmi-1 as a molecular maker for MDS.

Table 1.

Characteristics of patients with MDS and MDS-AML

Case
FAB
Sex
Age (y)
Outcome
Follow-up (mo)
Blasts (%)
Karyotype
IPSS
Risk
Bmi-1 (%)
1   RA   M   62   Alive   8   1.0   Normal   0   Low   1.53  
2   RA   F   60   Alive   8   3.5   Normal   0   Low   4.80  
3   RA   F   56   Alive   8   0.5   Normal   0   Low   0.45  
4   RA   F   38   Alive   7   1.5   Normal   0   Low   7.58  
5   RA   F   63   Alive   8   3.5   Normal   0   Low   8.88  
6   RA*  M   75   Alive   21   1.5   Normal   0   Low   23.00  
7   RA   F   66   Alive   22   2.0   46, XX, add(5)(q13)   0.5   Int-1   8.39  
8   RA   F   56   Alive   19   1.0   Normal   0.5   Int-1   7.50  
9   RA   M   51   Alive   48   2.0   Normal   0.5   Int-1   1.36  
10   RA*  M   61   Dead   10   2.5   46, XY, add(13)(q14)   0.5   Int-1   25.84  
11   RA*  F   80   Alive   8   1.0   Normal   0.5   Int-1   16.04  
12   RA   M   63   Alive   27   0.5   46, XY, +1, der(1;7)(q10;p10)   1   Int-1   8.33  
13   RA   M   81   Dead   12   3.5   47, XY, +8   1   Int-1   0.70  
14   RA   M   75   Alive   5   2.5   47, XY, +14   1   Int-1   0.31  
15   RARS   F   47   Alive   22   1.5   Normal   0   Low   5.18  
16   RARS   F   67   Alive   108   1.5   Normal   0.5   Int-1   0.10  
17   RARS   M   96   Alive   4   2.5   Normal   0.5   Int-1   1.24  
18   RARS*  F   75   Alive   22   3.5   Normal   0.5   Int-1   13.15  
19   RARS*  M   72   Dead   10   2.0   46, XY, del(5)(q15q33), del(11)(q21)   1   Int-1   63.44  
20   RAEB   M   78   Alive   7   8.5   Normal   1   Int-1   48.12  
21   RAEB   M   80   Dead   7   5.0   Complex   1.5   Int-2   59.25  
22   RAEB   M   73   Dead   4   7.5   Complex   2   Int-2   60.80  
23   RAEB   M   66   Dead   2   7.5   Complex   2   Int-2   62.86  
24   RAEB   F   66   Dead   6   8.5   Complex   2   Int-2   78.51  
25   RAEB   F   49   Alive   28   18.5   Normal   2   Int-2   61.88  
26   RAEB   M   81   Dead   24   13.0   Normal   2   Int-2   53.00  
27   RAEB   M   72   Dead   6   18.5   Complex   2.5   High   69.06  
28   RAEB   M   69   Dead   2   11.0   Complex   3   High   60.28  
29   RAEB   F   93   Dead   6   14.0   Complex   3   High   36.60  
30   RAEB   M   63   Dead   2   11.0   46, XY, –7   3   High   31.52  
31   RAEB   M   55   Dead   1   11.5   Complex   3   High   40.34  
32   RAEB-T   M   78   Alive   18   20.5   Normal   2   Int-2   7.58  
33   RAEB-T   M   70   Dead   10   23.0   46, XY, add(21)(q22)   2.5   High   73.96  
34   RAEB-T   M   81   Dead   2   29.5   45, X, –Y, t(8;21)(q22;q22)   3   High   71.94  
35   RAEB-T   M   74   Dead   1   20.0   Complex   3   High   83.80  
36   RAEB-T   M   74   Dead   11   21.0   45, XY, add(3)(q13.2), –7   3.5   High   88.81  
37   RAEB-T   M   74   Dead   5   25.0   Complex   3.5   High   73.98  
38   RAEB-T   F   81   Dead   5   20.5   Complex   3.5   High   63.96  
39   RAEB-T   M   71   Dead   8   20.5   Complex   3.5   High   99.59  
40   MDS-AML   M   79   Dead   18   35.0   Normal   NA   NA   74.31  
41   MDS-AML   F   65   Dead   13   47.0   45, XX, add(5)(q22), add(7)(p11.2), –22   NA   NA   99.99  
42   MDS-AML   F   76   Dead   17   34.0   Complex   NA   NA   86.11  
43   MDS-AML   M   68   Dead   4   39.0   Complex   NA   NA   97.04  
44   MDS-AML   F   70   Dead   5   61.0   46, XY, add(8)(q22), –21, +mar   NA   NA   90.44  
45   MDS-AML   M   77   Dead   17   74.5   47XY, +8   NA   NA   82.52  
46   MDS-AML   M   81   Dead   6   35.0   Complex   NA   NA   99.00  
47   MDS-AML   M   75   Dead   4   45.0   Complex   NA   NA   82.13  
48   MDS-AML   F   60   Dead   20   30.5   46, XX, del(6)(q?)   NA   NA   100.00  
49   MDS-AML   M   64   Dead   5   83.0   46, XY   NA   NA   76.17  
50   MDS-AML   M   59   Dead   1   85.5   Complex   NA   NA   93.84  
51
 		 MDS-AML
 		 M
 		 65
 		 Dead
 		 3
 		 49.0
 		 Complex
 		 NA
 		 NA
 		 82.55
 
Case
FAB
Sex
Age (y)
Outcome
Follow-up (mo)
Blasts (%)
Karyotype
IPSS
Risk
Bmi-1 (%)
1   RA   M   62   Alive   8   1.0   Normal   0   Low   1.53  
2   RA   F   60   Alive   8   3.5   Normal   0   Low   4.80  
3   RA   F   56   Alive   8   0.5   Normal   0   Low   0.45  
4   RA   F   38   Alive   7   1.5   Normal   0   Low   7.58  
5   RA   F   63   Alive   8   3.5   Normal   0   Low   8.88  
6   RA*  M   75   Alive   21   1.5   Normal   0   Low   23.00  
7   RA   F   66   Alive   22   2.0   46, XX, add(5)(q13)   0.5   Int-1   8.39  
8   RA   F   56   Alive   19   1.0   Normal   0.5   Int-1   7.50  
9   RA   M   51   Alive   48   2.0   Normal   0.5   Int-1   1.36  
10   RA*  M   61   Dead   10   2.5   46, XY, add(13)(q14)   0.5   Int-1   25.84  
11   RA*  F   80   Alive   8   1.0   Normal   0.5   Int-1   16.04  
12   RA   M   63   Alive   27   0.5   46, XY, +1, der(1;7)(q10;p10)   1   Int-1   8.33  
13   RA   M   81   Dead   12   3.5   47, XY, +8   1   Int-1   0.70  
14   RA   M   75   Alive   5   2.5   47, XY, +14   1   Int-1   0.31  
15   RARS   F   47   Alive   22   1.5   Normal   0   Low   5.18  
16   RARS   F   67   Alive   108   1.5   Normal   0.5   Int-1   0.10  
17   RARS   M   96   Alive   4   2.5   Normal   0.5   Int-1   1.24  
18   RARS*  F   75   Alive   22   3.5   Normal   0.5   Int-1   13.15  
19   RARS*  M   72   Dead   10   2.0   46, XY, del(5)(q15q33), del(11)(q21)   1   Int-1   63.44  
20   RAEB   M   78   Alive   7   8.5   Normal   1   Int-1   48.12  
21   RAEB   M   80   Dead   7   5.0   Complex   1.5   Int-2   59.25  
22   RAEB   M   73   Dead   4   7.5   Complex   2   Int-2   60.80  
23   RAEB   M   66   Dead   2   7.5   Complex   2   Int-2   62.86  
24   RAEB   F   66   Dead   6   8.5   Complex   2   Int-2   78.51  
25   RAEB   F   49   Alive   28   18.5   Normal   2   Int-2   61.88  
26   RAEB   M   81   Dead   24   13.0   Normal   2   Int-2   53.00  
27   RAEB   M   72   Dead   6   18.5   Complex   2.5   High   69.06  
28   RAEB   M   69   Dead   2   11.0   Complex   3   High   60.28  
29   RAEB   F   93   Dead   6   14.0   Complex   3   High   36.60  
30   RAEB   M   63   Dead   2   11.0   46, XY, –7   3   High   31.52  
31   RAEB   M   55   Dead   1   11.5   Complex   3   High   40.34  
32   RAEB-T   M   78   Alive   18   20.5   Normal   2   Int-2   7.58  
33   RAEB-T   M   70   Dead   10   23.0   46, XY, add(21)(q22)   2.5   High   73.96  
34   RAEB-T   M   81   Dead   2   29.5   45, X, –Y, t(8;21)(q22;q22)   3   High   71.94  
35   RAEB-T   M   74   Dead   1   20.0   Complex   3   High   83.80  
36   RAEB-T   M   74   Dead   11   21.0   45, XY, add(3)(q13.2), –7   3.5   High   88.81  
37   RAEB-T   M   74   Dead   5   25.0   Complex   3.5   High   73.98  
38   RAEB-T   F   81   Dead   5   20.5   Complex   3.5   High   63.96  
39   RAEB-T   M   71   Dead   8   20.5   Complex   3.5   High   99.59  
40   MDS-AML   M   79   Dead   18   35.0   Normal   NA   NA   74.31  
41   MDS-AML   F   65   Dead   13   47.0   45, XX, add(5)(q22), add(7)(p11.2), –22   NA   NA   99.99  
42   MDS-AML   F   76   Dead   17   34.0   Complex   NA   NA   86.11  
43   MDS-AML   M   68   Dead   4   39.0   Complex   NA   NA   97.04  
44   MDS-AML   F   70   Dead   5   61.0   46, XY, add(8)(q22), –21, +mar   NA   NA   90.44  
45   MDS-AML   M   77   Dead   17   74.5   47XY, +8   NA   NA   82.52  
46   MDS-AML   M   81   Dead   6   35.0   Complex   NA   NA   99.00  
47   MDS-AML   M   75   Dead   4   45.0   Complex   NA   NA   82.13  
48   MDS-AML   F   60   Dead   20   30.5   46, XX, del(6)(q?)   NA   NA   100.00  
49   MDS-AML   M   64   Dead   5   83.0   46, XY   NA   NA   76.17  
50   MDS-AML   M   59   Dead   1   85.5   Complex   NA   NA   93.84  
51
 		 MDS-AML
 		 M
 		 65
 		 Dead
 		 3
 		 49.0
 		 Complex
 		 NA
 		 NA
 		 82.55
 

Bmi-1 (%) denotes the positivity of Bmi-1 in CD34+ cells; Complex denotes more than 3 chromosomal abnormalities. Case 19 occurs in the same individual as case 27, which developed into RAEB.

NA indicates not applicable.

*

Progression to RAEB from RA or RARS

View Large
Figure 1.
Figure 1. Expression of Bmi-1 in CD34+ cells from MDS and MDS-AML. (A) Representative expression of Bmi-1 in bone marrow mononuclear cells from patients with RA, RAEB, and MDS-AML by flow cytometry is shown. The positivity of Bmi-1 in CD34+ cells was highest in the patient with case 44 with MDS-AML and also high in the patient with case 23 with RAEB. It was lowest in the patient with case 7 with RA. (B) The percentage of Bmi-1 expression in CD34+ cells according to MDS subtype is as follows: RA, 8.19% ± 8.20%; RARS, 16.62% ± 26.67%; RAEB, 55.27% ± 13.79%; RAEB-T, 70.45% ± 27.74%; MDS-AML, 88.68% ± 9.29%; and controls, 4.02% ± 3.89%. Data are expressed as percentage of mean ± SD of results obtained. *Progression to RAEB from RA or RARS. (C) Bmi-1 expression ratio in CD34+ cells was correlated with IPSS score in patients with MDS. The R value = 0.809 and P < .001 obtained indicates a good correlation between the 2 parameters (Bmi-1 [%] and IPSS score) considered. *Progression to RAEB from RA or RARS.
View largeDownload PPT

Expression of Bmi-1 in CD34+ cells from MDS and MDS-AML. (A) Representative expression of Bmi-1 in bone marrow mononuclear cells from patients with RA, RAEB, and MDS-AML by flow cytometry is shown. The positivity of Bmi-1 in CD34+ cells was highest in the patient with case 44 with MDS-AML and also high in the patient with case 23 with RAEB. It was lowest in the patient with case 7 with RA. (B) The percentage of Bmi-1 expression in CD34+ cells according to MDS subtype is as follows: RA, 8.19% ± 8.20%; RARS, 16.62% ± 26.67%; RAEB, 55.27% ± 13.79%; RAEB-T, 70.45% ± 27.74%; MDS-AML, 88.68% ± 9.29%; and controls, 4.02% ± 3.89%. Data are expressed as percentage of mean ± SD of results obtained. *Progression to RAEB from RA or RARS. (C) Bmi-1 expression ratio in CD34+ cells was correlated with IPSS score in patients with MDS. The R value = 0.809 and P < .001 obtained indicates a good correlation between the 2 parameters (Bmi-1 [%] and IPSS score) considered. *Progression to RAEB from RA or RARS.

Figure 1.
Figure 1. Expression of Bmi-1 in CD34+ cells from MDS and MDS-AML. (A) Representative expression of Bmi-1 in bone marrow mononuclear cells from patients with RA, RAEB, and MDS-AML by flow cytometry is shown. The positivity of Bmi-1 in CD34+ cells was highest in the patient with case 44 with MDS-AML and also high in the patient with case 23 with RAEB. It was lowest in the patient with case 7 with RA. (B) The percentage of Bmi-1 expression in CD34+ cells according to MDS subtype is as follows: RA, 8.19% ± 8.20%; RARS, 16.62% ± 26.67%; RAEB, 55.27% ± 13.79%; RAEB-T, 70.45% ± 27.74%; MDS-AML, 88.68% ± 9.29%; and controls, 4.02% ± 3.89%. Data are expressed as percentage of mean ± SD of results obtained. *Progression to RAEB from RA or RARS. (C) Bmi-1 expression ratio in CD34+ cells was correlated with IPSS score in patients with MDS. The R value = 0.809 and P < .001 obtained indicates a good correlation between the 2 parameters (Bmi-1 [%] and IPSS score) considered. *Progression to RAEB from RA or RARS.
View largeDownload PPT

Expression of Bmi-1 in CD34+ cells from MDS and MDS-AML. (A) Representative expression of Bmi-1 in bone marrow mononuclear cells from patients with RA, RAEB, and MDS-AML by flow cytometry is shown. The positivity of Bmi-1 in CD34+ cells was highest in the patient with case 44 with MDS-AML and also high in the patient with case 23 with RAEB. It was lowest in the patient with case 7 with RA. (B) The percentage of Bmi-1 expression in CD34+ cells according to MDS subtype is as follows: RA, 8.19% ± 8.20%; RARS, 16.62% ± 26.67%; RAEB, 55.27% ± 13.79%; RAEB-T, 70.45% ± 27.74%; MDS-AML, 88.68% ± 9.29%; and controls, 4.02% ± 3.89%. Data are expressed as percentage of mean ± SD of results obtained. *Progression to RAEB from RA or RARS. (C) Bmi-1 expression ratio in CD34+ cells was correlated with IPSS score in patients with MDS. The R value = 0.809 and P < .001 obtained indicates a good correlation between the 2 parameters (Bmi-1 [%] and IPSS score) considered. *Progression to RAEB from RA or RARS.

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Prepublished online as Blood First Edition Paper, September 20, 2005; DOI 10.1182/blood-2005-06-2393.

The publication costs of this article were defrayed in part by page charge payment. Therefore, and solely to indicate this fact, this article is hereby marked “advertisement” in accordance with 18 U.S.C. section 1734.

We thank M. Kuroda and R. Matsumoto for their technical support. We also thank Dr H Harada for his help in collecting patient samples.

1
Heaney ML, Golde DW. Myelodysplasia.
N Engl J Med
.
1999
;
340
;
1649
-1660.
2
Lowenthal RM, Marsden KA. Myelodysplastic syndromes.
Int J Hematol
.
1997
;
65
:
319
-338.
3
Maes B, Meeus P, Michaux L, et al. Application of the International Prognostic Scoring System for myelodysplastic syndromes.
Ann Oncol
.
1999
;
10
:
825
-829.
4
Sanz GF, Sanz MA, Greenberg PL. Prognostic factors and scoring systems in myelodysplastic syndromes.
Haematologica
.
1998
;
83
:
358
-368.
5
Jacobs JJ, van Lohuizen M. Polycomb repression: from cellular memory to cellular proliferation and cancer.
Biochim Biophys Acta
.
2002
;
1602
:
151
-161.
6
Orlando V. Polycomb, epigenomes, and control of cell identity.
Cell
.
2003
;
112
:
599
-606.
7
Park IK, Qian D, Kie M, et al. Bmi-1 is required for maintenance of adult self-renewing haematopoietic stem cells.
Nature
.
2003
;
423
:
302
-305.
8
Dick JE. Stem cells: self-renewal writ in blood.
Nature
.
2003
;
423
:
231
-233.
9
Ohta H, Sawada A, Kim JY, et al. Polycomb group gene rae28 is required for sustaining activity of hematopoietic stem cells.
J Exp Med
.
2002
;
195
:
759
-770.
10
Lessard J, Sauvageau G. Bmi-1 determines the proliferative capacity of normal and leukaemic stem cells.
Nature
.
2003
;
423
:
231
-233.
11
van der Lugt NM, Domen J, Linders K, et al. Posterior transformation, neurological abnormalities, and severe hematopoietic defects in mice with a targeted deletion of the bmi-1 proto-oncogene.
Genes Dev
.
1994
;
8
:
757
-769.
12
Iwama A, Oguro H, Negishi M, et al. Enhanced self-renewal of hematopoietic stem cells mediated by the polycomb gene product Bmi-1.
Immunity
.
2004
;
21
:
843
-851.
13
Dimri GP, Martinez JL, Jacobs JJ, et al. The Bmi-1 oncogene induces telomerase activity and immortalizes human mammary epithelial cells.
Cancer Res
.
2002
;
62
:
4736
-4745.
14
Leung C, Lingbeek M, Shakhova O, et al. Bmi1 is essential for cerebellar development and is overexpressed in human medulloblastomas.
Nature
.
2004
;
428
:
337
-341.
15
Raaphorst FM, Meijer CJ, Fieret E, et al. Poorly differentiated breast carcinoma is associated with increased expression of the human polycomb group EZH2 gene.
Neoplasia
.
2003
;
5
:
481
-488.
16
Vonlanthen S, Heighway J, Altermatt HJ, et al. The bmi-1 oncoprotein is differentially expressed in non-small cell lung cancer and correlates with INK4A-ARF locus expression.
Br J Cancer
.
2001
;
84
:
1372
-1376.
17
Bea S, Tort F, Pinyol M, et al. BMI-1 gene amplification and overexpression in hematological malignancies occur mainly in mantle cell lymphomas.
Cancer Res
.
2001
;
15
:
2409
-2412.
18
Dukers DF, van Galen JC, Giroth C, et al. Unique polycomb gene expression pattern in Hodgkin's lymphoma and Hodgkin's lymphoma-derived cell lines.
Am J Pathol
.
2004
;
164
:
873
-881.
19
van Kemenade FJ, Raaphorst FM, Blokzijl T, et al. Coexpression of BMI-1 and EZH2 polycomb-group proteins is associated with cycling cells and degree of malignancy in B-cell non-Hodgkin lymphoma.
Blood
.
2001
;
97
:
3896
-3901.
20
Zhang P, Iwasaki-Arai J, Iwasaki H, et al. Enhancement of hematopoietic stem cell repopulating capacity and self-renewal in the absence of the transcription factor C/EBP alpha.
Immunity
.
2004
;
21
:
853
-863.
21
Takihara Y, Hara J. Polycomb-group genes and hematopoiesis.
Int J Hematol
.
2000
;
72
:
165
-172.
22
Jacobs JJ, Kieboom K, Marino S, DePinho RA, van Lohuizen M. The oncogene and Polycomb-group gene bmi-1 regulates cell proliferation and senescence through the ink4a locus.
Nature
.
1999
;
397
:
164
-168.
23
Smith KS, Chanda SK, Lingbeek M, et al. Bmi-1 regulation of INK4A-ARF is a downstream requirement for transformation of hematopoietic progenitors by E2a-Pbx1.
Mol Cell
.
2003
;
12
:
393
-400.
24
Quelle DE, Zindy F, Ashmun RA, Sherr CJ. Alternative reading frames of the INK4a tumor suppressor gene encode two unrelated proteins capable of inducing cell cycle arrest.
Cell
.
1995
;
83
:
993
-1000.
25
Miller JS, McCullar V, Punzel M, Lemischka IR, Moore KA. Single adult human CD34(+)/Lin-/CD38(-) progenitors give rise to natural killer cells, B-lineage cells, dendritic cells, and myeloid cells.
Blood
.
1999
;
93
:
96
-106.
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2006
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