Increases in nuclear p65 activation in dystrophic skeletal muscle are secondary to increases in the cellular expression of p65 and are not solely produced by increases in IκB-α kinase activity

Dystrophin-deficient muscle exhibits substantial increases in nuclear NF-kappa B activation. To examine potential mechanisms for this enhanced activation, the present study employs conventional Western blot techniques to provide the first determination of the relative expression of NF-kappa B signaling molecules in adult nondystrophic and dystrophic (mdx) skeletal muscle. The results indicate that dystrophic muscle is characterized by increases in the whole cell expression Of I kappa B-alpha, p65, p50, RelB, p100, p52, IKK, and TRAF-3. The proportion of phosphorylated I kappa B-alpha, p65, NIK, and IKK beta, and the level of cytosolic I kappa B-alpha, were also increased in the mdx diaphragm. Proteasomal inhibition using MG-132 increased the proportion of phosphorylated I kappa B-alpha in nondystrophic diaphragm, but did not significantly increase this proportion in the mdx diaphragm. This result Suggests that phosphorylated I kappa B-alpha accumulates in dystrophic cytosol because the rate of I kappa B-alpha degradation is lower than the effective rate of I kappa B-alpha synthesis and phosphorylation. Dystrophic increases in SUMO-1 (Small ubiquitin modifier-1) protein and in Akt activation were also observed. The results indicate that increases in nuclear p65 activation in dystrophic muscle are not produced solely by increases in the activity Of I kappa B-alpha kinase (IKK), but are due primarily to increases in the expression of p65 and other NF-kappa B signaling components. (c) 2009 Elsevier B.V. All rights reserved.