ANKRD1 modulates inflammatory responses in C2C12 myoblasts through feedback inhibition of NF-κB signaling activity

Transcription factors of the nuclear factor-kappa B (NF-kappa B) family play a pivotal role in inflammation, immunity and cell survival responses. Recent studies revealed that NF-kappa B also regulates the processes of muscle atrophy. NF-kappa B activity is regulated by various factors, including ankyrin repeat domain 2 (AnkrD2), which belongs to the muscle ankyrin repeat protein family. Another member of this family, AnkrD1 is also a transcriptional effector. The expression levels of AnkrD1 are highly upregulated in denervated skeletal muscle, suggesting an involvement of AnkrD1 in NF-kappa B mediated cellular responses to paralysis. However, the molecular mechanism underlying the interactive role of AnkrD1 in NF-kappa B mediated cellular responses is not well understood. In the current study, we examined the effect of AnkrD1 on NF-kappa B activity and determined the interactions between AnkrD1 expression and NF-kappa B signaling induced by TNF alpha in differentiating C2C12 myoblasts. TNF alpha upregulated AnkrD1 mRNA and protein levels. AnkrD1-siRNA significantly increased TNF alpha-induced transcriptional activation of NF-kappa B, whereas overexpression of AnkrD1 inhibited TNF alpha-induced NF-kappa B activity. Co-immunoprecipitation studies demonstrated that AnkrD1 was able to bind p50 subunit of NF-kappa B and vice versa. Finally, CHIP assays revealed that AnkrD1 bound chromatin at a NF-kappa B binding site in the AnrkD2 promoter and required NF-kappa B to do so. These results provide evidence of signaling integration between AnkrD1 and NF-kappa B pathways, and suggest a novel anti-inflammatory role of AnkrD1 through feedback inhibition of NF-kappa B transcriptional activity by which AnkrD1 modulates the balance between physiological and pathological inflammatory responses in skeletal muscle. Published by Elsevier Inc.