Identification of a Neuregulin and Protein-Tyrosine Phosphatase Response Element in the Nicotinic Acetylcholine Receptor ε Subunit Gene: Regulatory Role of an Ets Transcription Factor

At the neuromuscular synapse, innervation induces endplate-specific expression of adult-type nicotinic acetylcholine receptors by selective expression of their subunit-encoding genes (α2β ε δ ) in endplate-associated myonuclei. These genes are specifically regulated by protein-tyrosine phosphatase (PTPase) activity. In addition, neuregulin/acetylcholine-receptor-inducing activity, a nerve-derived factor that stimulates nicotinic acetylcholine receptor synthesis, induces adult-type specific ε subunit gene expression via activation of a Ras/mitogen-activated protein kinase pathway. However, the DNA regulatory elements and the binding proteins that mediate PTPase and neuregulin-dependent gene expression remain unknown. Herein we report that PTPase, neuregulin, and Ras-dependent regulation of the ε subunit gene map to a 15-bp promoter sequence. Interestingly, this same 15-bp sequence appears to be necessary for low ε subunit gene expression in extrajunctional regions of the muscle fiber. Site-directed mutagenesis of a putative Ets binding site located within this 15-bp sequence, reduced PTPase, neuregulin, and Ras-dependent regulation. Overexpression of the rat muscle Ets-2 transcription factor resulted in a sequence-specific induction of ε subunit promoter activity. Further, a dominant negative mutant of Ets-2 abolished neuregulin-dependent induction of ε subunit gene expression. Thus, these results indicate a crucial role for the 15-bp element in determining synapse-specific and neuregulin-mediated motor neuron control of ε subunit gene expression and suggest the participation of Ets transcription factor(s) in this control.