Tumor Necrosis Factor-like Weak Inducer of Apoptosis Inhibits Skeletal Myogenesis through Sustained Activation of Nuclear Factor-κB and Degradation of MyoD Protein

In this study we have investigated the effect and the mechanisms by which tumor necrosis factor-like weak inducer of apoptosis (TWEAK) modulates myogenic differentiation. Treatment of C2C12 myoblasts with TWEAK inhibited their differentiation evident by a decrease in the expression of creatine kinase, myosin heavy chain-fast twitch, myogenin, and the formation of multinucleated myotubes. TWEAK also inhibited the differentiation of mouse primary myoblasts. Conversely, the proliferation of C2C12 myoblasts and the expression of a cell-cycle regulator cyclin D1 were increased in response to TWEAK treatment. Inhibition of cellular proliferation using hydroxyurea only partially reversed the inhibitory effect of TWEAK on myogenic differentiation. Treatment of C2C12 myoblasts with TWEAK resulted in the activation of nuclear factor-κB (NF-κB), the (IkappaB) IκB kinase (IKK) complex, and the phosphorylation and degradation of IκBα protein. Inhibition of NF-κB activity by overexpression of a dominant negative mutant of IκBα (IκBαΔN) significantly increased the myogenic differentiation in TWEAK-treated C2C12 cultures. Furthermore, overexpression of a dominant negative mutant of IKKβ (IKKβK44A) but not IKKα (IKKαK44M) reversed the inhibitory effect of TWEAK on myogenesis. TWEAK inhibited the expression of myogenic regulatory factors MyoD and myogenin and also induced the degradation of MyoD protein. Finally, inhibition of NF-κB activation through overexpression of IKKβK44A prevented the degradation of MyoD protein. Overall, our data suggest that TWEAK inhibits myogenesis through the activation of NF-κB signaling pathway and degradation of MyoD protein.