Received for publication September 14, 2006.
Revised November 13, 2006.
Accepted for publication November 28, 2006.

Novel G423S mutation of human 7 nicotinic receptor promotes agonist-induced desensitization by a protein kinase C-dependent mechanism

Abstract

The 7 nicotinic acetylcholine receptor subunit (CHRNA7) gene harbors a high degree of polymorphism. In this study, we found a novel variant (1267 G to A) in exon 10 of the CHRNA7 gene in a Japanese population. This variant results in glycine-to-serine substitution at position 423 (G423S) located in the large cytoplasmic loop of the protein. To clarify the possibility that the G423S mutation alters the pharmacological properties of 7 receptors, acetylcholine (ACh)-elicited current through 7-G423S mutant receptors expressed in Xenopus oocytes was measured using the two-electrode voltage-clamp technique. We found that the current elicited by ACh (1 mM, 5 s) through 7-G423S receptors, but not through 7 receptors, was significantly decreased by treatment with a protein kinase C activator, phorbol-12-myristate-13-acetate (PMA, 10-30 nM). In addition, PMA (10 nM) selectively promoted a progressive decrease in 7-G423S current induced by repetitive application of ACh pulses (1 mM, 0.1 s, 0.17-0.33 Hz) as compared with 7 current. PMA also enhanced the inactivation of 7-G423S mutant receptors induced by a prolonged application of choline (30 µM), without affecting 7 receptor responses. Western blot analysis showed that the treatment with PMA (30 nM) increased the serine phosphorylation level of the 7-G423S mutant receptors but not that of the wild-type receptors. These findings demonstrate that the G423S mutation promotes receptor desensitization by a protein kinase C-dependent mechanism. Thus, we provide the first evidence that a variant in the human CHRNA7 gene alters the function of 7 nicotinic receptors.

Key words: Nicotinic cholinergic, Func. analysis receptor/ion channel mutants