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Apoptosis induced by the myelodysplastic syndrome-associated NPM-MLF1 chimeric protein
N Yoneda-Kato1, S Fukuhara, J Kato
1First Department of Internal Medicine, Kansai Medical University, Moriguchi, Osaka, Japan.
Abstract:
The NPM-MLF1 chimeric protein is produced by the t(3;5)(q25.1;q34) chromosomal translocation, which is associated with myelodysplastic syndrome (MDS) prior to progression into acute myeloid leukemia (AML). Here we report that K562 human leukemia cells ectopically expressing NPM-MLF1, but not those with wild-type MLF1, were gradually eliminated from the culture by undergoing apoptosis. NIH3T3 mouse fibroblasts engineered to overexpress NPM-MLF1 grew normally but serum deprivation triggered apoptotic cell death with slower kinetics than did other well-known apoptotic inducers such as c-Myc or E2F-1. Quantitative analysis of apoptotic induction confirmed that, neither NPM nor MLF1, but the NPM-MLF1 fusion protein was able to induce apoptosis. Analyses using a variety of deletion mutants of NPM-MLF1 revealed that induction of apoptosis required the N-terminal domain of MLF1 and the NPM domain containing nuclear localization signal and that removal of the NPM dimerization domain markedly impaired the ability to induce apoptosis. Co-expression of Bcl-2 rescued NIH3T3 fibroblasts from NPM-MLF1-mediated cell death without affecting the expression level or the subcellular localization of NPM-MLF1 and enabled cells to progress into S phase in low serum. These findings provide an NPM-MLF1-mediated novel mechanism of apoptotic induction and imply that NPM-MLFI in collaboration with anti-apoptotic oncoproteins may play an important role in multi-step progression from MDS to AML.
Insights
The NPM-MLF1 fusion protein induces apoptosis, a programmed cell death, in leukemia cells. This discovery sheds light on the progression of myelodysplastic syndrome to acute myeloid leukemia.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- The NPM-MLF1 chimeric protein arises from a specific chromosomal translocation (t(3;5)(q25.1;q34)).
- This translocation is linked to myelodysplastic syndrome (MDS) and its progression to acute myeloid leukemia (AML).
Purpose of the Study:
- To investigate the functional role of the NPM-MLF1 fusion protein in cellular apoptosis.
- To elucidate the mechanism by which NPM-MLF1 induces programmed cell death.
Main Methods:
- Ectopic expression of NPM-MLF1 in K562 human leukemia cells and NIH3T3 mouse fibroblasts.
- Analysis of apoptotic cell death using various deletion mutants of NPM-MLF1.
- Assessment of the role of anti-apoptotic proteins like Bcl-2 in NPM-MLF1-mediated cell death.
Main Results:
- Ectopic expression of NPM-MLF1 induced apoptosis in K562 cells, unlike wild-type MLF1.
- NPM-MLF1 triggered apoptotic cell death in NIH3T3 fibroblasts upon serum deprivation.
- Apoptosis induction required specific domains of both NPM and MLF1 within the fusion protein.
- Bcl-2 co-expression rescued cells from NPM-MLF1-induced apoptosis.
Conclusions:
- The NPM-MLF1 fusion protein is a novel inducer of apoptosis.
- Specific domains of NPM and MLF1 are critical for NPM-MLF1's apoptotic function.
- NPM-MLF1 may contribute to the multi-step progression of MDS to AML, potentially in conjunction with anti-apoptotic factors.