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Effects of the ras-related rap2 protein on cellular proliferation
B Jimenez1, V Pizon, I Lerosey
1INSERM U-248 Faculté de Médecine Lariboisière-St. Louis, Paris, France.
Abstract:
Ras oncogenes encode 21-kDa (p21s) GTP binding proteins that are capable of transforming immortalized cells in culture. The ras-related rap1A/Krev-1/smgp21A protein, that exhibits a similar structural organization and contains the same effector domain as ras proteins, antagonizes ras-transformation. In order to investigate whether the closely related (61% identical) rap2 protein had similar capacities, the corresponding cDNA was inserted into constitutive as well as inducible mammalian expression vectors. Neither the wild-type, nor an "activated" mutant carrying a glycine-to-valine substitution at position 12, had any transforming activity. Several independent lines of evidence demonstrate that the rap2 protein exhibits neither growth-promoting nor growth-inhibitory effects, and that its over-expression does not interfere with ras-induced transformation. Thus, in spite of their great similarities, the rap1A/Krev-1/smgp21A and rap2 proteins have distinct physiological properties.
Insights
The rap2 protein, despite structural similarities to Ras proteins, does not transform cells. Overexpression of rap2 has no effect on cell growth or Ras-induced transformation, indicating distinct physiological roles.
Area of Science:
- Molecular biology
- Cell biology
- Oncogenes
Background:
- Ras oncogenes encode GTP-binding proteins (p21s) that transform cells.
- Ras-related rap1A/Krev-1/smgp21A protein antagonizes Ras-transformation.
- Rap1A shares structural and effector domain similarities with Ras proteins.
Purpose of the Study:
- To investigate if the closely related rap2 protein shares similar capacities with rap1A.
- To determine the transforming activity and cellular effects of rap2 protein expression.
Main Methods:
- Insertion of rap2 cDNA into mammalian expression vectors (constitutive and inducible).
- Expression of wild-type and activated (G12V mutant) rap2 proteins in mammalian cells.
- Assessment of transforming activity, cell growth effects, and interference with Ras-induced transformation.
Main Results:
- Neither wild-type nor activated rap2 mutant exhibited transforming activity.
- Rap2 protein overexpression did not affect cell growth (neither promoting nor inhibiting).
- Rap2 overexpression did not interfere with Ras-induced transformation.
Conclusions:
- Rap2 protein possesses distinct physiological properties compared to rap1A/Krev-1/smgp21A.
- Despite high sequence identity, rap2 and rap1A do not share the same biological functions regarding cell transformation.