Abstract
To study behavior of activated Gαs in living cells, green fluorescent protein (GFP) was inserted within the internal amino acid sequence of Gαs to generate a Gαs-GFP fusion protein. The fusion protein maintained a bright green fluorescence and was identified by immunoblotting with antibodies against Gαs or GFP. The cellular distribution of Gαs-GFP was similar to that of endogenous Gαs. Gαs-GFP was tightly coupled to the β adrenergic receptor to activate the Gαs effector, adenylyl cyclase. Activation of Gαs-GFP by cholera toxin caused a gradual displacement of the fusion protein from the plasma membrane throughout the cytoplasm in living cells. Unlike the slow release of Gαs-GFP from the membrane induced by cholera toxin, the β-adrenergic agonist isoproterenol caused a rapid partial release of the fusion protein into the cytoplasm. At 1 min after treatment with isoproterenol, the extent of Gαs-GFP release from plasma membrane sites was maximal; however, insertion of Gαs-GFP at other membrane sites occurred during the same time period. Translocation of Gαs-GFP fusion protein induced by isoproterenol suggested that the internalization of Gαs might play a role in signal transduction by interacting with effector molecules and cytoskeletal elements at multiple cellular sites.
- The American Society for Pharmacology and Experimental Therapeutics
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