Basic helix–loop–helix factors recruit nuclear factor I to enhance expression of the NaV 1.4 Na+ channel gene

Abstract

SummaryWe have previously shown that the basic helix-loop-helix (bHLH) transcription factors coordinate Na V 1.4 Na + channel gene expression in skeletal muscle, but the identity of the co-factors they direct is unknown. Using C2C12 muscle cells as a model system, we test the hypothesis that the bHLH factors counteract negative regulation exerted through a repressor E box (−90/−85) by recruiting positive-acting transcription factors to the nucleotides (−135/−57) surrounding the repressor E box. We used electrophoretic mobility shift assays to identify candidate factors that bound the repressor E box or these adjacent regions. Repressor E box-binding factors included the known transcription factor, ZEB/AREB6, and a novel repressor E box-binding factor designated REB. Mutations of the repressor E box that interfere with the binding of these factors prevented repression. The transcription factor, nuclear factor I (NFI), bound immediately upstream and downstream of the repressor E box. Mutation of the NFI binding sites diminished the ability of myogenin and MRF4 to counteract repression. Based on these observations we suggest that bHLH factors recruit NFI to enhance skeletal muscle Na + channel expression.

Early onset muscle weakness and disruption of muscle proteins in mouse models of spinal muscular atrophy

“…Na v 1.4, the predominant sodium channel isoform in adult skeletal muscle [ 31 ], must be expressed at the correct time point during development to fulfill its role. A delay in expression of the Na v 1.4 isoform can negatively impact muscle force production [ 32 ].…”

Loss of synaptic vesicles from neuromuscular junctions in aged MRF4-null mice

“…There was an increase in expression of the other three bHLH factors in the MRF4-null mice [19], perhaps compensating for the loss of MRF4 for most functions, although expression of the Na V 1.4 Na + channel is preferentially driven by MRF4 and thus very sensitive to the lack of this factor [23]. Like the MRF4-null mice, the MyoD-null mice initially appeared phenotypically normal, but recent ultrastructural analyses of these mice have revealed unexpected deficits in the structure of their NMJs [18].…”

Comparison of Genome-Wide Binding of MyoD in Normal Human Myogenic Cells and Rhabdomyosarcomas Identifies Regional and Local Suppression of Promyogenic Transcription Factors

“…5A). RUNX1 and JDP2, a potential component of AP-1 complexes, have previously been shown to be sufficient to drive myogenic differentiation in RD cells (9,21); NFIC has previously been shown to cooperate with bHLH proteins in myogenic cells (22); and MEF2 factors cooperate with MyoD at many muscle promoters. Our expression array analysis identified, and RT-PCR confirmed, that RD cells express fewer RUNX1, JDP2, NFIC, and MEF2C transcripts than primary myotubes (Fig.…”