Voltage-sensitive sodium channels play critical roles in the establishment and maintenance of cell excitability. Two isoforms of mammalian striated skele tal muscle and heart muscle sodium channels (SkM1, and SkM2/H1, hereafter SkM2) show strict temporal and anatomical regulation, providing a model for tissue-specific gene expression. Understanding the regulation of these channels may provide avenues of treatment for human diseases involving abnormal excitability. In this study, we use the identification of positive and negative cis-acting sequences upstream from the SkM2 core promoter (Sheng et al., DNA & Cell Biology 13: 9-23, 1994) to examine the role played by the myogenic bHLH proteins MyoD, Myf 5, Mrf 4, Myogenin, and MEF-2c. Expressed similarly as SkM2 temporally, we tested whether this system would follow the common paradigm of gene-specific regulatory DNA sequences interacting with general and cell-type specific positive and negative-acting transcription factors. This was studied by transient transfection into 3T3 fibroblasts (which do not normally express SkM2) of each myogenic factor with four varying lengths of the SkM2 core promoter (terminating downstream at +124 bp) containing upstream sequences initiating upstream at -129 bp, -357 bp, -2.1 kb, and -3kb driving the CAT reporter gene. Significantly, addition of myogenic factors did not affect reporter gene expression, indicating that myogenic factors are not individually capable of inducing SkM2 gene transcription, suggesting that either cooperative interaction between bHLH proteins and/or an entirely new factor may be necessary for SkM2 expression.
|Original language||English (US)|
|State||Published - Dec 1 1997|
ASJC Scopus subject areas
- Molecular Biology