Activity of the Nicotinic Acetylcholine Receptor α 5 and α 7 Subunit Promoters in Muscle Cells

The acetylcholine receptor α5 and α7 subunits are components of different nicotinic receptor subtypes expressed in the nervous system. However, they are also present in non-neuronal tissues. We have detected α5 and α7 transcripts in mouse C2C12 muscle cells. Moreover, on differentiation of myoblasts into myotubes, the amount of α7 transcripts increased significantly, whereas α5 remained unchanged. In order to explore how the expression of these neuronal genes is regulated in muscle, we have characterized their promoter activities. Deletion and mutagenesis analysis with transfected reporter genes showed that transcriptional activity was controlled by regulatory elements also operative in neuronal-like cells. Thus, the activity of the α5 subunit core promoter decreased to ∼50% on alteration of one, two, or three of the five Sp1 binding sites present in this region and was almost abolished when four or five sites were mutated simultaneously. In the case of the α7 subunit promoter, the upstream stimulatory factor and the early growth response gene transcription factor were involved in regulating its transcriptional activity. In addition, the α7 promoter was activated during the differentiation process, in a mechanism partially dependent on the mentioned factors.