Transcriptional regulation of the human alpha5 nicotinic receptor subunit gene in neuronal and non-neuronal tissues

The human alpha5 nicotinic receptor subunit gene appears to be expressed in several structures of the nervous system, but also in a number of non-neuronal tissues, with maximal expressions occurring in the entire gastrointestinal tract, thymus and testis. To understand whether specific transcriptional mechanisms are involved in the tissue-specific expression of the alpha5 subunit in neuronal and non-neuronal cells, we isolated the 5'-regulatory region of the human gene and characterized its functional properties. We demonstrate that specific DNA elements, with positive or negative activities depending on the cell type, are responsible for the diversified expression of the alpha5 subunit in different tissues. We therefore conclude that the expression of the alpha5 subunit relies on a highly complex promoter that uses distinct regulatory elements to comply with the different functional and developmental requirements of the various tissues and organs.