Transcriptional regulation of dual‐specificity phosphatase 4 (Dusp4) by muscle‐specific RING finger 1 (MuRF1) (LB822)

Abstract

Skeletal muscle wasting is a consequence of numerous physiological conditions, including denervation, corticosteroid treatment, and aging. The E3 ubiquitin ligase, MuRF1, is induced under most atrophy conditions and is believed to play a key role in protein degradation in atrophying muscle. However, the preliminary data described in this study provides new evidence that MuRF1 may also act as a transcriptional modulator of atrophy‐induced gene activity, including the regulation of Dusp4 expression. In order to characterize the transcriptional regulation of Dusp4, reporter gene constructs containing fragments of the proximal promoter region of this gene were developed, transfected into C2C12 cells with or without a MuRF1 expression plasmid and analyzed for differences in reporter gene activity.The Dusp4 reporters showed repressed activity in cells ectopically expressing MuRF1 compared to cells that did not overexpress MuRF1. Furthermore, ectopic expression of the myogenic regulatory factors (MRFs), MyoD1 and myogenin, also caused repression of the Dusp4 reporter constructs, while co‐overexpression of MuRF1 with MyoD1 or Myogenin resulted in additional cooperative repression of reporter gene activity. To further characterize the role of MuRF1 in the repression of Dusp4 expression, a MuRF1 RING domain mutant was created. The MuRf1 RING mutant was overexpressed in combination with MyoD1 or Myogenin and Dusp4 reporter gene activity was assessed. The MuRF1 RING mutant failed to cooperate with the MRFs to repress the Dusp4 reporter gene, suggesting that ubiquitin ligase activity is required for MuRF1 transcriptional regulatory effects. These data offer evidence that MuRF1 may act as a transcriptional modulator of atrophy‐induced gene expression.