Nicotinic acetylcholine receptor alpha 7 regulates cAMP signal within lipid rafts.
Neuronal nicotinic acetylcholine receptors (nAChRs) are made of multiple subunits with diversified functions. The nAChR alpha 7-subunit has a property of high Ca2+ permeability and may have specific functions and localization within the plasma membrane as a signal transduction molecule. In PC-12 cells, fractionation by sucrose gradient centrifugation revealed that nAChR alpha 7 existed in low-density, cholesterol-enriched plasma membrane microdomains known as lipid rafts where flotillin also exists. In contrast, nAChR alpha 5- and beta2-subunits were located in high-density fractions, out of the lipid rafts. Type 6 adenylyl cyclase (AC6), a calcium-inhibitable isoform, was also found in lipid rafts and was coimmunoprecipitated with nAChR alpha 7. Cholesterol depletion from plasma membranes with methyl-beta-cyclodextrin redistributed nAChR alpha 7 and AC6 diffusely within plasma membranes. Nicotine stimulation reduced forskolin-stimulated AC activity by 35%, and this inhibition was negated by either treatment with alpha-bungarotoxin, a specific antagonist of nAChR alpha 7, or cholesterol depletion from plasma membranes. The effect of cholesterol depletion was negated by the addition of cholesterol. These data suggest that nAChR alpha 7 has a specific membrane localization relative to other nAChR subunits and that lipid rafts are necessary to localize nAChR alpha 7 with AC within plasma membranes. In addition, nAChR alpha 7 may regulate the AC activity via Ca2+ within lipid rafts.
Department of Physiology and Medicine, Yokohama City University School of Medicine, Yokohama, Japan.
Jin
J
Oshikawa
Yoshiyuki
Y
Toya
Takayuki
T
Fujita
Masato
M
Egawa
Junichi
J
Kawabe
Satoshi
S
Umemura
Yoshihiro
Y
Ishikawa
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002784:Cholesterol / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism*; D021962:Membrane Microdomains / Q000378:metabolism*; D009538:Nicotine / Q000494:pharmacology; D018722:Nicotinic Agonists / Q000494:pharmacology; D016716:PC12 Cells; D051381:Rats; D011978:Receptors, Nicotinic / Q000378:metabolism*; D064569:alpha7 Nicotinic Acetylcholine Receptor
C579165:Chrna7 protein, rat; D018722:Nicotinic Agonists; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor; D009538:Nicotine; D002784:Cholesterol; D000242:Cyclic AMP; D000262:Adenylyl Cyclases