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To investigate the interaction of stimulatory GTP binding protein (G(s)) pathways with others, we overexpressed wild type α subunit of G(s) (G(s) α), constitutively activated R201E G(s) α, and dominant negative G226A G(s) α in COS-1 cells by transfection with DEAE-dextran, respectively, The expression of various G proteins in the transfected cells was analyzed after 72 h by quantitative Western blots, and cAMP production by stimulation with isoproterenol and forskolin was quantitated using cAMP binding proteins, The expression of Gs α increased about 5-fold in the transfected cells, with concomitant increase in the small forms. However, there was no significant alteration the in the level of the α subunit of inhibitory G protein (G(i)) and G(q), and the β subunits of G proteins. The cAMP level without stimulation increased in the cells transfected with G(s) α regardless to the type of mutation, Treatment with either isoproterenol or forskolin resulted in comparable increase of the cAMP level in all the transfected cells, though the ratio to its respective basal level was smaller in the G(s) α-transfected cells, From this experiment, we found that the expression of the other G proteins and the signaling pathway producing cAMP did not change significantly by transiently expressing wild type, constitutively activated type, and dominant negative type of G(s) α. Analysis of the effects of long-term expression of Gs α would contribute to better understanding on how the G(s) α signaling system interacts with other signaling pathways and how it adapts to the changed environments.
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