Protein kinase A regulates nicotinic cholinergic receptors and subunit messenger ribonucleic acids in PC 12 cells

To delineate mechanisms regulating the expression of neuronal nicotinic cholinergic receptors (nAcChRs), we studied the cAMP-dependent second messenger system. PC 12 cells were grown in (Bu)2cAMP (0.001-1.0 mM) or vehicle for 7 days, and specific [3H] nicotine binding was measured. (Bu)2cAMP (0.1 mM) increased specific binding 2- and 4-fold at 3 and 7 days, respectively, whereas 1.0 mM enhanced binding 4-fold at both time intervals. Cells grown in 8-bromo-cAMP (1.0 mM) showed a 2-fold increase in [3H]nicotine binding at 3 days. Forskolin (10-100 microM), in combination with isobutyl-methylxanthine (1.0 mM), enhanced [3H]nicotine binding 2- to 3-fold at 7 days; forskolin or isobutyl-methylxanthine alone had no effect. Specific [3H] nicotine binding to PC 12 cell mutants (A126.1B2 and A123.7), deficient in cAMP-responsive protein kinase A types I and II, were unaffected by (Bu)2cAMP. Northern gel analysis of nAcChR subunit messenger RNAs showed that the alpha-3, alpha-5, and beta-4 subunits were significantly decreased by (Bu)2cAMP at 4 h. However, (Bu)2cAMP caused an increase in the beta-2 messenger RNA transcript at 4 h, which returned to baseline by 24 h. These studies indicate that the cAMP-protein kinase A system regulates expression of nAcChR by PC 12 cells. These studies also suggest that enhancement of [3H]nicotine binding by activated protein kinase A may not involve synthesis of new receptor subunit proteins.