GRP-R AND NMB-R SIGNALLING

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Reconstitution studies using purified heterotrimeric GTP-binding proteins (G-proteins) in lipid vesicles indicate that the Gq sub-family of alpha subunits, in contrast to the Gs, Gi, and Go subfamilies, activate phospholipase C-1 after ligand receptor interaction, and are insensitive to pertussis toxin. We postulate that Gq, or structurally similar Galpha11, are important for bombesin receptor signal transduction. We have tested this hypothesis by observing the effects of Gq- and Galpha11- specific antisense molecules on bombesin-mediated responses in Xenopus oocytes expressing GRP-R or NMB-R. To rationally design antisense oligonucleotides, we have isolated and sequenced cDNA clones for Xenopus Gq and Galpha11. The Xenopus proteins are over 90% identical in amino acid sequence to their mammalian counterparts. These sequences were used to design the synthesis of antisense phosphothiorate oligonucleotides which were injected into Xenopus oocytes expressing either GRP-R or NMB-R to observe their effects on bombesin signalling. The antisense oligonucleotide specific for Gq inhibited NMB-R signalling, but did not effect GRP-R signalling. In contrast, the Galpha11 antisense oligonucleotide did not alter signalling from either GRP-R or NMB-R. These studies indicate that, although the signal transduction pathway for GRP-R and NMB-R is similar, the two receptors differ in their G-protein coupling properties. In addition, Gq and Galpha11 are not interchangeable for NMB-R coupling. We hypothesize that the pattern of expression of Gq family members may be used to modulate receptor responses in different cells.