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Biological activity of human N-ras and K-ras genes containing the Asn17 dominant negative mutation
1Oncology and Immunology Research Department, Lederle Laboratories, Pearl River, NY 10965, USA.
Abstract:
Substitution of asparagine for serine at position 17 of human H-ras results in an impaired GTP-binding activity, causing the mutant Ras protein to be locked in a constitutively inactive GDP-bound state. Expression of this mutant in NIH 3T3 cells inhibits cell proliferation by blocking endogenous ras function. Plasmids that encode the analogous dominant negative mutation at position 17 in human N- and K-ras were constructed. These mutant ras genes, driven by a heavy metal-inducible sheep metallothionein promoter, were introduced by transfection into a variety of animal cell lines. All three mutant ras genes displayed an inhibitory phenotype when expressed in NIH 3T3 cells. This inhibition could be overcome by cotransfection with either activated H-ras or v-raf. These data indicate that the three human Ras proteins probably act through the same signal transduction pathway in NIH 3T3 cells and suggest that these mutations may confer similar phenotypes to other GTP/GDP-binding proteins.
Insights
A specific mutation in human Ras proteins (Ras GTPase) impairs their function, locking them in an inactive state. This dominant-negative effect inhibits cell growth, suggesting a common signaling pathway for Ras family members.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- Ras proteins are key regulators of cell signaling pathways.
- Mutations in Ras genes are common in human cancers.
- Understanding Ras function is crucial for cancer research.
Purpose of the Study:
- To investigate the functional consequences of a dominant-negative mutation in human H-ras, N-ras, and K-ras.
- To determine if these mutant Ras proteins inhibit cell proliferation.
- To explore the signal transduction pathway utilized by Ras proteins.
Main Methods:
- Constructing plasmids encoding dominant-negative mutations at position 17 of human H-ras, N-ras, and K-ras.
- Utilizing a heavy metal-inducible sheep metallothionein promoter for gene expression.
- Transfecting these plasmids into various animal cell lines, including NIH 3T3 cells.
- Assessing the effect of mutant Ras expression on cell proliferation and signaling.
Main Results:
- Substitution of serine with asparagine at position 17 of human H-ras resulted in impaired GTP-binding activity, leading to a constitutively inactive GDP-bound state.
- Expression of the mutant H-ras in NIH 3T3 cells inhibited cell proliferation by blocking endogenous Ras function.
- Analogous dominant-negative mutations in N-ras and K-ras also displayed an inhibitory phenotype in NIH 3T3 cells.
- The inhibitory effects of the mutant Ras genes could be overcome by co-expression with activated H-ras or v-raf.
Conclusions:
- The three human Ras proteins (H-ras, N-ras, K-ras) likely converge on the same signal transduction pathway in NIH 3T3 cells.
- These dominant-negative mutations may confer similar inhibitory phenotypes to other GTP/GDP-binding proteins.
- The findings provide insights into Ras-mediated signaling and potential therapeutic strategies for Ras-driven cancers.