Abstract
Neurofibromatosis type 1 (NF1) is characterized by a high incidence of benign and malignant tumors attributed to loss of function of Nf1, which encodes neurofibromin, a tumor suppressor with Ras-GAP activity. Neurofibromin deficiency typically causes chronic activation of Ras, considered the major contributor to manifestation of NF1. Resistance to radio- and chemotherapy are typical of NF1-associated tumors, but the underlying mechanism is unknown. Here, we investigated interrelationships between neurofibromin expression, Ras activity, and sensitivity to apoptosis. Neurofibromin-deficient mouse embryonic fibroblasts (MEFs) and human NF1 tumor cells were more resistant than neurofibromin-expressing cells to apoptosis. Moreover, Nf1−/−, Nf1+/−, and Nf1+/+ MEFs exhibited gene-dosage-related resistance to apoptosis. Resistance of the Nf1-deficient cells was mediated by two survival pathways: a Ras-dependent pathway, and a Ras-independent pathway promoted by the lack of an NF1-GRD-independent proapoptotic action of neurofibromin. Therefore, besides its Ras-dependent growth inhibition, neurofibromin can exert tumor suppression via a proapoptotic effect.
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Abbreviations
- Ac-DEVD-7AMC:
-
Ac-Asp-Glu-Val-Asp-7-amino-4-methylcoumarin Ac-DEVD-7AMC
- ERK:
-
extracellular signal-regulated kinase
- DMEM:
-
Dulbecco's-modified Eagle's medium
- DN:
-
dominant negative
- FTS:
-
farnesylthiosalicylic acid
- GAP:
-
GTPase activating protein
- GFP:
-
green fluorescent protein
- GRD:
-
GAP-related domain
- IBMX:
-
3-isobutyl-1-methylxanthine
- MEF:
-
mouse embryonic fibroblast
- MPNST:
-
malignant peripheral nerve sheath tumor
- MTT:
-
3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide
- NF1:
-
neurofibromatosis type 1
- PI3-kinase:
-
phosphatidylinositol-3-kinase
- RBD:
-
Ras-binding domain
- SEAP:
-
secreted alkaline phosphatase
- TBS:
-
Tris-buffered saline
- UV:
-
ultra-violet
- XIAP:
-
X-linked inhibitor of apoptosis
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Acknowledgements
We are grateful to Ms Shirley Smith for excellent editorial assistance. We thank Dr. N Ratner for providing us with the C57BL/6J mice with a targeted Nf1 gene allele. This work was supported by DOD Grant NF 030009 (YK and RS), the Israel Ministry of Health (YK and RS), and the Recanati Foundation for Research in Medicine (YK and RS). Yoel Kloog is the incumbent of the Jack H Skirball Chair in Applied Neurobiology.
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Shapira, S., Barkan, B., Fridman, E. et al. The tumor suppressor neurofibromin confers sensitivity to apoptosis by Ras-dependent and Ras-independent pathways. Cell Death Differ 14, 895–906 (2007). https://doi.org/10.1038/sj.cdd.4402057
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DOI: https://doi.org/10.1038/sj.cdd.4402057
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