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Yeast alpha-mating factor receptor-linked G-protein signal transduction suppresses Ras-dependent activity
S J Arkinstall1, S G Papasavvas, M A Payton
1Department of Biological Chemistry, Glaxo Institute for Molecular Biology, Geneva, Switzerland.
Abstract:
Homologues of mammalian Ras conserved in Saccharomyces cerevisiae mediate glucose-stimulated cyclic AMP formation and we used this response to test for regulation of yeast Ras activity by the alpha-mating factor signal transduction pathway. alpha-Mating factor suppresses glucose-stimulated cyclic AMP formation by up to 57 +/- 12.6% (n = 5) and similar inhibition was observed in four different yeast strains (MATa cells). Moreover, this response is potent (IC50 = 0.14 +/- 0.19 microM (n = 4)), rapid (maximal within 1-2 min), and displays an absolute requirement for both the alpha-mating factor receptor (STE2) and associated G-protein beta-subunit (STE4). Inhibition appears independent of both phosphodiesterase activation and alpha-mating factor-stimulated cytoplasmic alkalinization. Also, basal cyclic AMP levels are unaffected by pheromone. This is the first demonstration that a cell-surface receptor linked to a heterotrimeric G-protein can suppress Ras-dependent activity and could provide important insight into mechanisms controlling p21ras in man. Inhibition of Ras-dependent cyclic AMP formation could also be a key event facilitating responses characteristic of yeast mating.
Insights
Alpha-mating factor in yeast suppresses glucose-stimulated cyclic AMP (cAMP) formation by inhibiting Ras activity. This pheromone signaling pathway provides insights into Ras regulation and yeast mating responses.
Area of Science:
- Molecular Biology
- Cell Signaling
- Yeast Genetics
Background:
- Ras proteins are crucial signaling molecules conserved across species, regulating processes like cyclic AMP (cAMP) formation.
- In yeast (Saccharomyces cerevisiae), Ras activity mediates glucose-stimulated cAMP production.
- The alpha-mating factor signal transduction pathway is involved in yeast sexual reproduction.
Purpose of the Study:
- To investigate whether the alpha-mating factor signal transduction pathway regulates yeast Ras activity.
- To elucidate the mechanism by which alpha-mating factor influences cAMP formation.
- To explore potential parallels between yeast and mammalian Ras regulation.
Main Methods:
- Utilized yeast strains (MATa cells) to measure glucose-stimulated cAMP levels.
- Administered alpha-mating factor and assessed its effect on cAMP formation.
- Investigated the role of the alpha-mating factor receptor (STE2) and G-protein beta-subunit (STE4) in the observed inhibition.
- Examined effects on phosphodiesterase activity and cytoplasmic alkalinization.
Main Results:
- Alpha-mating factor significantly suppressed glucose-stimulated cAMP formation by up to 57%.
- The inhibition was potent (IC50 = 0.14 microM), rapid (maximal within 1-2 min), and dependent on STE2 and STE4.
- Inhibition was independent of phosphodiesterase activation and cytoplasmic alkalinization, and basal cAMP levels remained unaffected.
Conclusions:
- This study demonstrates, for the first time, that a G-protein-linked cell-surface receptor can suppress Ras-dependent activity.
- The findings suggest a novel mechanism for regulating Ras activity via pheromone signaling in yeast.
- This Ras regulation pathway may be critical for facilitating yeast mating responses and offers insights into p21Ras control in mammals.