Synapse-specific and neuregulin-induced transcription require an Ets site that binds GABPα/GABPβ

Abstract

Localization of acetylcholine receptors (AChRs) to neuromuscular synapses is mediated by multiple pathways. Agrin, which is the signal for one pathway, stimulates a redistribution of previously unlocalized AChRs to synaptic sites. The signal for a second pathway is not known, but this signal stimulates selective transcription of AChR genes in myofiber nuclei located near the synaptic site. Neuregulin (NRG) is a good candidate for the extracellular signal that induces synapse-specific gene expression, since NRG is concentrated at synaptic sites and activates AChR gene expression in cultured muscle cells. Previous studies have demonstrated that 181 bp of 5' flanking DNA from the AChR delta-subunit gene are sufficient to confer synapse-specific transcription in transgenic mice and NRG responsiveness in cultured muscle cells, but the critical sequences within this cis-acting regulatory region have not been identified. We transfected AChR delta-subunit-hGH gene fusions into a muscle cell line, and we show that a potential binding site for Ets proteins is required for NRG-induced gene expression. Furthermore, we produced transgenic mice carrying AChR delta-subunit-hGH gene fusions with a mutation in this NRG-response element (NRE), and we show that this NRE is necessary for synapse-specific transcription in mice. The NRE binds proteins in myotube nuclear extracts, and nucleotides that are important for NRG responsiveness are likewise critical for formation of the protein-DNA complex. This complex contains GABPalpha, an Ets protein, and GABPbeta, a protein that lacks an Ets domain but dimerizes with GABPalpha, because formation of the protein-DNA complex is inhibited by antibodies to either GABPalpha or GABPbeta. These results demonstrate that synapse-specific and NRG-induced gene expression require an Ets-binding site and suggest that GABPalpha/GABPbeta mediates the transcriptional response of the AChR delta-subunit gene to synaptic signals, including NRG.

Regulation of the Intermediate Filament Protein Nestin at Rodent Neuromuscular Junctions by Innervation and Activity

“…Such selective transcription would explain the synaptic localization of the nestin protein. One of the transcriptional control elements believed to lead to local expression at the synapse is the so-called N-box that binds an Ets transcription factor (Fromm and Burden, 1998). Interestingly, disruption of mRNAs selectively transcribed at the nmj by expression in muscle fibers of a dominant-negative Ets is found to alter junctional morphology and synaptic folding (de Kerchove D'Exaerde et al, 2002).…”

The Unliganded Glucocorticoid Receptor Positively Regulates the Tumor Suppressor GeneBRCA1through GABP Beta

“…Human GABP exists as a heterodimer consisting of an ets helix-loop-helix DNA-binding domain (DBD) subunit (GABPa) and a Notch-ankyrin repeat subunit (GABPb) which contains the activation domain as well as a domain required for the formation of tetrameric complexes (12). GABP has been implicated in the regulation of genes in response to cell growth, activation of respiration-related genes (13), as a downstream mediator of ErbB3 and ErbB4 signaling (14), and recently in connecting mitochondrial metabolism and breast differentiation (15). The interaction of the a-and b-subunits with each other and with other transcription factors defines the ability of GABP to regulate the expression of its target genes.…”

Characterization of a Muscle-specific Enhancer in Human MuSK Promoter Reveals the Essential Role of Myogenin in Controlling Activity-dependent Gene Regulation

“…MuSK expression is tightly controlled by a combination of muscle activity that suppresses extrajunctional expression (3,4) and nerve-derived factors such as agrin and neuregulin that promotes synapse-specific expression (5). Neuregulin mediates its action via Erb receptor tyrosine kinases (6) that stimulate a Ras/mitogen-activated protein (MAP) kinase signal transduction cascade (7,8), resulting in activation of GABP ␣␤ transcription factors in endplate-associated myonuclei (9,10). These transcription factors bind to N-box sequences within the MuSK promoter, resulting in its activation (5).…”