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Specific biochemical inactivation of oncogenic Ras proteins by nucleoside diphosphate kinase
Michael A Fischbach1, Jeffrey Settleman
1Massachusetts General Hospital Cancer Center and Harvard Medical School, Charlestown, Massachusetts 02129, USA.
Abstract:
Activating mutations of Ras have been implicated in approximately 30% of human cancers. In every case, the biochemical consequence of such mutations is to disrupt the GTPase activity of Ras and to render Ras resistant to the actions of GTPase activating proteins. Consequently, oncogenic Ras mutants are "locked" in a GTP-bound active state. We detected a potent activity in Escherichia coli extract that can efficiently convert mutationally activated GTP-bound Ras to the inactive GDP-bound form. Purification of the protein responsible for this activity led to the identification of the enzyme nucleoside diphosphate kinase (Ndk). The human orthologue of Ndk is the NM23 metastasis suppressor, which we found to exhibit a similar activity. Purified Ndk effectively inactivates several of the oncogenic forms of Ras that are seen frequently in human cancers, including RasD12, the most commonly detected Ras mutation. Significantly, Ndk does not detectably affect wild-type Ras or an activated form of the Ras-related Rho GTPase. These results demonstrate that it is possible, through biochemical means, to specifically inactivate oncogenic Ras as a potential therapeutic approach to tumors that harbor Ras mutations. Moreover, the results suggest that the loss of NM23 expression that is commonly observed during tumor progression could lead to increased potency of oncogenic Ras proteins.
Insights
Scientists discovered nucleoside diphosphate kinase (Ndk) can inactivate oncogenic Ras proteins, offering a potential therapy for cancers with Ras mutations. This enzyme specifically targets mutated Ras, not normal versions.
Area of Science:
- Biochemistry
- Molecular Biology
- Oncology
Background:
- Activating Ras mutations are found in ~30% of human cancers, leading to a constitutively active GTP-bound state.
- Oncogenic Ras mutants resist inactivation by GTPase activating proteins, remaining in a persistent active conformation.
Purpose of the Study:
- To identify biochemical factors capable of inactivating oncogenic Ras.
- To explore the therapeutic potential of targeting Ras GTPase activity in cancer.
Main Methods:
- Purification and identification of proteins from Escherichia coli extract with Ras inactivation activity.
- Biochemical assays to test the activity of purified enzymes on various Ras mutants and related GTPases.
Main Results:
- Nucleoside diphosphate kinase (Ndk) from E. coli was identified as an enzyme that converts GTP-bound oncogenic Ras to its inactive GDP-bound form.
- The human orthologue, NM23 metastasis suppressor, also demonstrated this inactivating activity.
- Ndk specifically inactivated common oncogenic Ras forms (e.g., RasD12) without affecting wild-type Ras or Rho GTPase.
Conclusions:
- Biochemical inactivation of oncogenic Ras is feasible, presenting a potential therapeutic strategy for Ras-mutated cancers.
- The findings suggest that reduced NM23 expression during tumor progression may enhance oncogenic Ras activity.