Endogenously Expressed Muscarinic Receptors in HEK293 Cells Augment Up-regulation of Stably Expressed α4β2 Nicotinic Receptors

• Published in: The Journal of biological chemistry 2011-11, Vol.286 (46), p.39726-39737
• Main Authors: Hussmann, Gregory P., Yasuda, Robert P., Xiao, Yingxian, Wolfe, Barry B., Kellar, Kenneth J.
• Format: Article
• Language: English
• Subjects: Carbachol; Drug Action; G Protein-coupled Receptors (GPCR); Gene Expression Regulation - drug effects; Gene Expression Regulation - physiology; HEK293 Cells; Humans; Models, Biological; Muscarinic Acetylcholine Receptors; Neurobiology; Neurochemistry; Nicotine; Nicotine - pharmacology; Nicotinic Acetylcholine Receptors; Nicotinic Agonists - pharmacology; Receptors, Muscarinic - biosynthesis; Receptors, Muscarinic - genetics; Receptors, Nicotinic - biosynthesis; Receptors, Nicotinic - genetics; RNA, Messenger - biosynthesis; RNA, Messenger - genetics; Up-regulation
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M111.289546

Nicotine-induced up-regulation of neuronal nicotinic receptors (nAChRs) has been known and studied for more than 25 years. Other nAChR ligands can also up-regulate nAChRs, but it is not known if these ligands induce up-regulation by mechanisms similar to that of nicotine. In this study, we compared up-regulation by three different nicotinic agonists and a competitive antagonist of several different nAChR subtypes expressed in HEK293 cells. Nicotine markedly increased α4β2 nAChR binding site density and β2 subunit protein. Carbachol, a known nAChR and muscarinic receptor agonist, up-regulated both α4β2 nAChR binding sites and subunit protein 2-fold more than did nicotine. This increased up-regulation was shown pharmacologically to involve endogenously expressed muscarinic receptors, and stimulation of these muscarinic receptors also correlated with a 2-fold increase in α4 and β2 mRNA. Muscarinic receptor activation in these cells appears to affect CMV promoter activity only minimally (∼1.2 fold), suggesting that the increase in α4 and β2 nAChR mRNA may not be dependent on enhanced transcription. Instead, other mechanisms may contribute to the increase in mRNA and a consequent increase in receptor subunits and binding site density. These studies demonstrate the possibility of augmenting nAChR expression in a cell model through mechanisms and targets other than the nAChR receptor itself. Background: Nicotinic ligands up-regulate neuronal nicotinic receptors in vitro and in vivo. Results: Carbachol or oxotremorine plus nicotine up-regulate α4β2 nicotinic receptors more than nicotine alone. Conclusion: Muscarinic receptor activity augments nicotinic receptor up-regulation by increasing α4 and β2 subunit mRNA and protein. Significance: This study reveals a novel target for modulating neuronal nicotinic receptor expression.