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Identification of distinct cytoplasmic targets for ras/R-ras and rho regulatory proteins
M D Garrett1, A J Self, C van Oers
1Institute of Cancer Research, Chester Beatty Laboratories, London, Great Britain.
Abstract:
The protein products of the mammalian ras genes, p21ras, are regulatory guanine nucleotide binding proteins that are involved in the control of cell proliferation, though the exact biochemical processes regulated are unknown. Recently a cytoplasmic protein has been identified that interacts with and increases the GTPase activity of p21ras. It has been shown that this GTPase-activating protein, or GAP, interacts with the effector domain of ras, leading us and others to propose that GAP may be the target for regulation by p21ras. It has become apparent that ras is part of a much larger family of proteins, and at least 15 ras-related genes have now been identified in the mammalian genome. Each encodes a small (about 21 kDa) guanine nucleotide binding protein, but the functions of none of these regulatory molecules are known. We report here that mammalian cytoplasmic extracts contain GAP-like activity toward the products of two other ras-related genes, R-ras and rho. It appears that p23R-ras interacts with the same 125-kDa GAP protein as p21ras whereas p21rho interacts with a distinct 29-kDa protein, rho GAP.
Insights
Mammalian cytoplasmic extracts contain GTPase-activating protein (GAP)-like activity. This activity targets ras-related proteins, including R-ras and rho, suggesting broader GAP involvement in cell signaling.
Area of Science:
- Molecular Biology
- Cell Signaling
- Protein Biochemistry
Background:
- Ras proteins (p21ras) are key regulators of cell proliferation.
- GTPase-activating protein (GAP) enhances p21ras GTPase activity.
- Ras proteins belong to a large gene family with largely unknown functions.
Purpose of the Study:
- To investigate GAP-like activity in mammalian cytoplasmic extracts.
- To determine if GAP activity extends to other ras-related proteins like R-ras and rho.
- To identify the specific GAP proteins interacting with R-ras and rho.
Main Methods:
- Assaying GTPase-activating protein (GAP) activity in mammalian cytoplasmic extracts.
- Utilizing ras-related proteins (R-ras, rho) as substrates.
- Identifying interacting proteins via molecular weight analysis.
Main Results:
- Mammalian cytoplasmic extracts exhibit GAP-like activity towards R-ras and rho.
- p23R-ras interacts with the known 125-kDa GAP protein.
- p21rho interacts with a distinct 29-kDa protein, rho GAP.
Conclusions:
- GAP-mediated regulation extends beyond p21ras to other ras-related proteins.
- Specific GAPs exist for different ras family members, indicating diverse signaling pathways.
- Identification of rho GAP provides a molecular target for rho protein function studies.