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High efficiency transient transfection of Cos-7 cells was previously used to establish the functional coupling between G alpha q/G alpha 11 and phospholipase C beta 1 (Wu, D., Lee, C-H., Rhee, S. G., and Simon, M. I. (1992) J. Biol. Chem. 267, 1811-1817). Here the same system was used to study the functional coupling between other guanine nucleotide-binding regulatory protein (G-protein) alpha subunits and phospholipases and to study which G alpha subunits mediate the activation of phospholipase C by the alpha 1-adrenergic receptor subtypes, alpha 1 A, alpha 1 B, and alpha 1 C. We found that G alpha 14 and G alpha 16 behaved like G alpha 11 or G alpha q, i.e. they could activate endogenous phospholipases in Cos-7 cells in the presence of AIFn. The synergistic increase in inositol phosphate release in Cos-7 cells after they were cotransfected with cDNAs encoding G alpha subunits and phospholipase C beta 1 indicates that both G alpha 16 and G alpha 14 can activate phospholipase C beta 1. The activation of phospholipase C beta 1 was restricted to members of the Gq subfamily of alpha subunits. They activated phospholipase C beta 1 but not phospholipase C gamma 1, gamma 2, or phospholipase C delta 3. The cotransfection of Cos-7 cells with cDNAs encoding three different alpha 1-adrenergic receptors and G alpha q or G alpha 11 leads to an increase in norepinephrine-dependent inositol phosphate release. This indicates that G alpha q or G alpha 11 can mediate the activation of phospholipase C by all three subtypes of alpha 1-adrenergic receptors. With the same assay system, G alpha 16 and G alpha 14 appear to be differentially involved in the activation of phospholipase C by the alpha 1-adrenergic receptors. The alpha 1 B subtype receptor gave a ligand-mediated synergistic response in the cells cotransfected with either G alpha 14 or G alpha 16. However, the alpha 1 C receptor responded in cells cotransfected with G alpha 14 but not G alpha 16, and the alpha 1 A receptor showed little synergistic response in cells transfected with either G alpha 14 or G alpha 16. The ability of the alpha 1 A and alpha 1 C receptors to activate phospholipase C through G alpha q and G alpha 11 was also demonstrated in a cell-free system.(ABSTRACT TRUNCATED AT 400 WORDS) |
