Stimulation of increases in intracellular calcium and prostaglandin E ₂ generation in Chinese hamster ovary cells expressing receptor-Gα₁₆ fusion proteins

We examined whether fusion proteins of G protein-coupled receptors with the α subunit of G₁₆ (Gα₁₆) could activate downstream signals. We expressed fusion proteins of G_i-coupled receptors, i.e. CX₃C chemokine receptor 1 (CX₃CR1) and M₂ receptor, in Chinese hamster ovary cells. An agonist for CX ₃CR1 induced greater increases in intracellular Ca²⁺ and prostaglandin E₂ generation in cells expressing CX ₃CR1-Gα₁₆ fusion protein than in cells expressing CX₃CR1 alone or both CX₃CR1 and Gα₁₆ separately. Similarly, agonist-induced prostaglandin E₂ generation was greater in cells expressing M₂-Gα₁₆ fusion protein than ones expressing M₂ alone or both M₂ and Gα₁₆ separately. In cells expressing fusion proteins with Gα₁₆ of G_q-coupled receptors, i.e. urotensin II receptor and M₁ receptor, the relevant agonists induced similar increases in intracellular Ca²⁺ and prostaglandin E₂ generation as in ones expressing the receptor alone. In cells expressing urotensin II receptor-Gα₁₆ fusion protein, prostaglandin E ₂ generation exhibited a lower EC₅₀ value than the intracellular Ca²⁺ increase. These results indicate that agonist-stimulated receptor-Gα₁₆ fusion proteins are coupled to downstream signaling pathways, and suggest that receptor-Gα₁₆ fusion proteins may be useful for screening for ligands of orphan G protein-coupled receptors and G_i-coupled receptors.