Characterization of an Acetylcholine Receptor

Genes encoding neuronal nicotinic acetylcholine receptors exhibit restricted patterns of expression in the nervous system. We are interested in elucidating the molecular mechanisms responsible for establishing these patterns of expression. This paper presents the characterization of regulatory elements upstream of the neuronal nicotinic acetylcholine receptor a3 gene. We have identified a GC-rich multistart site promoter adjacent to the a3 coding region. Similar a3 start sites were identified in PC12 cells and sympathetic ganglion neurons, suggesting similar control mechanisms in the clonal line and peripheral neurons. The start site region lacks TATA-like sequences but does contain initiator-like sequences. We show, in transient transfection assays, that the POU domain transcription factor, SCIP/Tst-l, specifically activates a3 in a neural context. Other POU domain factors tested only weakly activated or repressed a3. Unexpectedly, we found that a3 basal activity and SCIPPTst-1 activation of a3 is not dependent on the SCIP/Tst-1 binding sites found upstream of the gene. In addition, mutations in the SCIPPTst-1 coding region that prevent the factor from binding to DNA with high affinity do not obliterate a3 activation. These results lead us to propose that a3 activation by SCIPPTst-1 is achieved via protein-protein interactions between SCIPPTst-1 and a specific complement of transcription factors that act directly on the promoter.