AMLi Is Expressed in Skeletal Muscle and Is Regulated by Innervation

Although most skeletal muscle genes are expressed at similar levels in electrically active, innervated muscle and in electrically inactive, denervated muscle, a small number of genes, including those encoding the acetylcholine receptor, N-CAM, and myogenin, are expressed at significantly higher levels in denervated than in innervated muscle. The mechanisms that mediate electrical activity-dependent gene regulation are not understood, but these mechanisms are likely to be responsible, at least in part, for the changes in muscle structure and function that accompany a decrease in myofiber electrical activity. To understand how muscle activity regulates muscle structure and function, we used a subtractive-hybridization and cloning strategy to identify and isolate genes that are expressed preferentially in innervated or denervated muscle. One of the genes which we found to be regulated by electrical activity is the recently discovered acute myeloid leukemia 1 (AMLI) gene. Disruption and translocation of the human "MLI gene are responsible for a form of acute myeloid leukemia. AML1 is a DNA-binding protein, but its normal function is not known and its expression and regulation in skeletal muscle were not previously appreciated. Because of its potential role as a transcriptional mediator of electrical activity, we characterized expression of the AMLI gene in innervated, denervated, and developing skeletal muscle. We show that AMLI is expressed at low levels in innervated skeletal muscle and at 50to 100-fold-higher levels in denervated muscle. FourAML1 transcripts are expressed in denervated muscle, and the abundance of each transcript increases after denervation. We transfected C2 muscle cells with an expression vector encoding AML1, tagged with an epitope from hemagglutinin, and we show that AMLI is a nuclear protein in muscle. AML1 dimerizes with core-binding factor P (CBF 0), and we show that CBF I8 is expressed at high levels in both innervated and denervated skeletal muscle. PEBP2ot, which is structurally related to AML1 and which also dimerizes with CBF 1, is expressed at low levels in skeletal muscle and is up-regulated only weakly by denervation. These results are consistent with the idea that AML1 may have a role in regulating gene expression in skeletal muscle.