CaM Kinase II-dependent Suppression of Nicotinic Acetylcholine Receptor δ-Subunit Promoter Activity

Nerve-induced muscle activity suppresses nicotinic acetylcholine receptor (nAChR) gene expression by increasing intracellular calcium levels. This suppression is mediated by nAChR promoter sequences harboring at least 1 E-box (CANNTG) that bind myogenic helix-loop-helix transcription factors. How muscle depolarization or increased calcium mediates changes in nAChR promoter activity is not well understood. In chick muscle, protein kinase C (PKC) activation is necessary for activity-dependent nAChR gene suppression. Similar effects of PKC activation have not been found in mammalian skeletal muscle. Therefore, we used rat primary muscle cultures to screen for other calcium-regulated enzymatic activities that may mediate the effects of muscle activity and calcium on nAChR promoter activity. We report here that calcium/calmodulin-dependent protein kinase II (CaM kinase II) can specifically suppress nAChR promoter activity in mammalian muscle. This regulation was mediated by a single E-box sequence residing in the previously characterized nAChR delta-subunit genes 47-base pair activity-dependent enhancer. In vitro protein/DNA interaction studies suggest that CaM kinase II inhibits binding of the myogenic factor, myogenin, to the delta-promoter 47-base pair activity-dependent enhancer. CaM kinase activity is increased in active muscle and inhibition of this enzymatic activity results in increased nAChR delta-promoter activity. Therefore, CaM kinase II may represent a previously unappreciated activity that participates in coupling muscle depolarization to nAChR gene expression.