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Abstract:
Members of the ras multigene family have been found in virtually all eukaryotes, from yeast to mammals. ras is required for normal cell growth in the yeast Saccharomyces cerevisiae and in at least some mammalian cells. These genes induce tumorigenic transformation of established NIH 3T3 cells by increased expression of a normal ras gene, certain point mutations or amino acid deletion. In tumours, point mutation appears to be the most common mechanism of activation. The ras proteins are found at the plasma membrane, bind guanine nucleotides GDP and GTP and possess a GTPase activity. At least some ras proteins that have been activated by single amino acid substitutions possess a GTPase activity that is lower than that of the normal version. These results are consistent with the hypothesis that ras protein stimulates its putative target(s) when GTP is bound to it, as is true for the G regulatory proteins or elongation factor Tu. In Saccharomyces cerevisiae, ras has been shown to stimulate adenylate cyclase. However, there does not appear to be a direct interaction between ras and adenylate cyclase in mammalian cells.
Insights
Ras genes are crucial for cell growth in eukaryotes. Activated ras proteins, often via point mutations in tumors, regulate cellular processes by binding GTP, though their interaction with adenylate cyclase varies between species.
Area of Science:
- Molecular Biology
- Cell Biology
- Genetics
Background:
- Ras genes are highly conserved across eukaryotes, playing essential roles in cell growth.
- Ras proteins are plasma membrane-bound GTPases involved in cell signaling.
- Tumorigenesis is frequently associated with ras gene activation, commonly through point mutations.
Purpose of the Study:
- To investigate the role of ras genes in normal cell growth.
- To understand the mechanisms of ras gene activation in tumorigenesis.
- To elucidate the function and regulation of ras proteins, including their GTPase activity and interactions.
Main Methods:
- Analysis of ras gene family members across eukaryotes.
- Studying ras gene function in yeast (Saccharomyces cerevisiae) and mammalian cells.
- Investigating ras protein localization, nucleotide binding, and GTPase activity.
- Examining the effects of ras gene mutations on NIH 3T3 cell transformation.
Main Results:
- Ras is essential for normal cell growth in yeast and mammalian cells.
- Increased ras expression or specific mutations induce tumorigenic transformation.
- Point mutation is the predominant mechanism for ras activation in tumors.
- Activated ras proteins often exhibit reduced GTPase activity compared to normal versions.
- Ras stimulates adenylate cyclase in yeast, but direct interaction is not evident in mammals.
Conclusions:
- Ras proteins function as GTP-binding proteins regulating cellular processes.
- Aberrant ras activation, particularly through point mutations, drives tumorigenesis.
- The GTP-bound state of ras is likely the active form, analogous to G proteins.
- Ras signaling pathways, including interactions with adenylate cyclase, show species-specific differences.