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Abstract
Background:
Notch is a gene family encoding receptors to transduce intercellular signals involved in cell-fate determination. Although several lines of evidence indicate that abnormal Notch signaling may contribute to neoplastic transformation, little is known regarding the role of Notch in the pathogenesis of leukemia.
Methods:
To explore the functional significance of Notch1 in acute myeloid leukemia (AML), the expression of Notch1 and its association with survivin and p27Kip1 expression was examined in 50 patients with de novo AML.
Results:
Notch1 transcripts were expressed in 40 (80%) cases with a variable degree of expression, and the fraction of AML cells in the G0/G1 phase was higher in Notch1-positive cases than in Notch1-negative cases. Survivin was shown to be present in 38 (76.0%) cases, and Notch1 expression highly correlated with survivin mRNA expression (r=0.7170, P＜0.001). p27Kip1 was present in 40 (80.0%) cases of AML and p27Kip1 expression was significantly associated with Notch1 expression (r=0.8770, P＜0.001). Except for one case, the simultaneous expression of survivin and p27Kip1 was not seen in all cases that were negative for Notch1 expression. There were no differences in clinical outcomes according to Notch1 expression.
Conclusion:
Notch1 expression was a frequent event and has functional significance in the alteration of the cell cycle in AML cells. Notch1 expression was also significantly associated with survivin and p27kip1 expression in AML cells. To evaluate the clinical significanceand functional role of Notch1 expression in the aberrant regulation of survivin and p27Kip1 expression in de novo AML, a further study with a larger number of patients is necessary.
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Fig. 1
RT-PCR analysis of Notch1, survivin, and p27Kip1 expression in representative AML samples. RT-PCR was performed with specific primers described in Materials and Methods. PCR products derived from 1μg of total RNA were applied to each lane. Lane 1, 100-bp molecular weight marker. Cases expressing Notch1 transcript (lanes 2∼3) demonstrate both of survivin and p27Kip1 transcripts. Survivin and p27Kip1 transcripts are not expressed in two cases that do not express Notch1 transcript (lanes 4∼5).
Fig. 2
Expression of Notch1 by AML cells. Fluorescence histograms of permeabilized AML cells show no shift in the fluorescent intensity after staining with Notch1 antibody in a representative case, indicating absence of Notch1 (A), and a homogenous shift in the fluorescent intensity curve in another case, indicating a high expression of Notch1 (B). The y-axis represents cell number, and the x-axis represents log fluorescence intensity. The solid line indicates staining with mouse anti-human Notch1 monoclonal antibody, and the dashed line represents staining with an isotype-matched control antibody of irrelevant specificity.
Fig. 3
Kaplan-Meier survival curves for AML patients according to the Notch1 expression. The dotted line represents AML cases that expressed Notch1, and the solid line represents AML cases that did not express Notch1. Squares and triangles represent censored patients. The difference between the curves is not statistically significant (P=.83 for overall survival by log-rank analysis).
Table 1.
Characteristics of AML patients according to Not-ch1 expression
Notch1 expression in AML cells was evaluated by RT-PCR analysis. Notch1 (−), cases did not express Notch1 transcript; Notch1 (+), cases expressed Notch1 transcript. Abbreviations: AML, acute myeloid leukemia; WBC, white blood cell; NS, not significant. Favorable cytogenetics include t(8;21), and inv (16). Intermediate cytogenetics include normal 46XX or 46XY. Unfavorable cytogenetics include 5-, 7-, 5q-, 7q- or of exaggerated hyperdiploidy, trisomy 8, t(6;9), trisomy 11, & multiple chromosomal abnormalities. ∗Data represent the mean value±standard deviations.
Table 2.
Cell-cycle distribution according to Notch1 expression
| G0/G1 phase | S phase | G2/M phase | |
|---|---|---|---|
| Notch1 (+) (n=40) | 86.1±5.4 | 7.3±2.1 | 6.4±2.9 |
| Notch1 (−) (n=10) | 74.2±5.9 | 15.6±3.7 | 10.2±4.5 |
| P value | ＜0.05 | ＜0.05 | ＜0.05 |
Table 3.
Expression of survivin, or p27Kip1 according to Notch1 expression
Numerical data represent the number of cases showing the respective pattern of expression. Survivin & p27Kip1 positive, cases coexpressing survivin and p27Kip1 mRNA; Survivin & p27Kip1 negative, cases lacking both of survivin and p27Kip1 mRNA. Correlation coefficiency between Notch1 and survivin expression, Notch1 and p27Kip1 expression, Notch1 and coex-pression of survivin/p27Kip1 was calculated using the Spearman's test.
Table 4.
Clinical outcomes according to Notch1, survivin, or p27 mRNA expression
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