title: Endogenously expressed muscarinic receptors in HEK293 cells augment up-regulation of stably expressed α4β2 nicotinic receptors.
abstract: 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.
authors.affiliation: Department of Pharmacology and Physiology, Georgetown University School of Medicine, Washington, DC 20057, USA.
authors.forename: Gregory P
authors.initials: GP
authors.lastname: Hussmann
authors.forename: Robert P
authors.initials: RP
authors.lastname: Yasuda
authors.forename: Yingxian
authors.initials: Y
authors.lastname: Xiao
authors.forename: Barry B
authors.initials: BB
authors.lastname: Wolfe
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Kellar
mesh_terms: D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D057809:HEK293 Cells; D006801:Humans; D008954:Models, Biological; D009538:Nicotine / Q000494:pharmacology; D018722:Nicotinic Agonists / Q000494:pharmacology; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D011976:Receptors, Muscarinic / Q000096:biosynthesis* / Q000235:genetics; D011978:Receptors, Nicotinic / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D018722:Nicotinic Agonists; D012333:RNA, Messenger; D011976:Receptors, Muscarinic; D011978:Receptors, Nicotinic; C403531:nicotinic receptor alpha4beta2; D009538:Nicotine