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A dominant negative RAS-specific guanine nucleotide exchange factor reverses neoplastic phenotype in K-ras
Abstract:
Ras proteins are small GTPases playing a pivotal role in cell proliferation and differentiation. Their activation state depends on the competing action of GTPase Activating Proteins (GAP) and Guanine nucleotide Exchange Factors (GEF). A tryptophan residue (Trp1056 in CDC25Mm-GEF), conserved in all ras-specific GEFs identified so far has been previously shown to be essential for GEF activity. Its substitution with glutamic acid results in a catalytically inactive mutant, which is able to efficiently displace wild-type GEF from p21ras and to originate a stable ras/GEF binary complex due to the reduced affinity of the nucleotide-free ras/GEF complex for the incoming nucleotide. We show here that this 'ras-sequestering property' can be utilized to attenuate ras signal transduction pathways in mouse fibroblasts transformed by oncogenic ras. In fact overexpression of the dominant negative GEFW1056E in stable transfected cells strongly reduces intracellular ras-GTP levels in k-ras transformed fibroblasts. Accordingly, the transfected fibroblasts revert to wild-type phenotype on the basis of morphology, cell cycle and anchorage independent growth. The reversion of the transformed phenotype is accompanied by DNA endoreduplication. The possible use of dominant negative ras-specific GEFs as a tool to down-regulate tumor growth is discussed.
Insights
A modified Guanine nucleotide Exchange Factor (GEF) protein can block Ras signaling by sequestering Ras proteins. This dominant-negative GEF mutant reverts Ras-transformed cells to a normal phenotype, suggesting a potential therapeutic strategy for tumors.
Area of Science:
- Molecular Biology
- Cell Signaling
- Oncology
Background:
- Ras proteins are key regulators of cell proliferation and differentiation, controlled by GTPase Activating Proteins (GAP) and Guanine nucleotide Exchange Factors (GEF).
- A conserved tryptophan residue (Trp1056) in ras-specific GEFs is critical for their activity.
- Mutating this residue to glutamic acid creates an inactive GEF (GEFW1056E) that binds Ras but prevents nucleotide exchange, forming a stable complex.
Purpose of the Study:
- To investigate the potential of a dominant-negative GEF mutant (GEFW1056E) to attenuate Ras signal transduction pathways.
- To assess the effect of GEFW1056E overexpression on oncogenic Ras-transformed mouse fibroblasts.
- To evaluate the therapeutic potential of dominant-negative Ras-specific GEFs in cancer treatment.
Main Methods:
- Overexpression of the dominant-negative GEFW1056E mutant in stable transfected mouse fibroblasts.
- Measurement of intracellular Ras-GTP levels.
- Assessment of cellular morphology, cell cycle progression, and anchorage-independent growth.
- Analysis of DNA endoreduplication.
Main Results:
- Overexpression of GEFW1056E significantly reduced intracellular Ras-GTP levels in k-ras transformed fibroblasts.
- Transfected fibroblasts exhibited reversion to a wild-type phenotype, including normalization of morphology, cell cycle, and anchorage-independent growth.
- The phenotypic reversion was associated with DNA endoreduplication.
Conclusions:
- The dominant-negative GEFW1056E mutant effectively inhibits Ras signaling by sequestering Ras proteins.
- This Ras-sequestering property can reverse the transformed phenotype of cancer cells.
- Dominant-negative Ras-specific GEFs represent a promising strategy for down-regulating tumor growth.