Meeting Abstract

P2.181  Saturday, Jan. 5  Transcriptional Regulation of Muscle Atrophy F-box (MAFbx) by Muscle RING Finger 1 (MuRF1) OLSON, TB*; WADDELL, DS; University of North Florida; University of North Florida d.s.waddell@unf.edu

Skeletal muscle wasting is a consequence of numerous physiological conditions, including denervation, corticosteroid treatment, immobilization, and aging. Muscle RING Finger 1 (MuRF1) is an E3 ubiquitin ligase that is induced under nearly all atrophy conditions and is believed to play a key role in muscle wasting or atrophy. However, the preliminary data described in this study provides evidence that MuRF1 may act as a transcriptional regulator of a second E3 ubiquitin ligase called MAFbx. The MAFbx gene, also induced under virtually all atrophy conditions, is believed to play an equally important role in modulating skeletal muscle wasting. To characterize the transcriptional regulation of MAFbx, a reporter construct containing a fragment of the proximal promoter region of the MAFbx gene was constructed, co-transfected into C2C12 mouse muscle cells with or without a MuRF1 expression plasmid and reporter gene activity was then measured over four days. The MAFbx reporter showed a significant increase in activity in cells ectopically expressing MuRF1 compared to cells that did not overexpress MuRF1. To further characterize the function of MuRF1 in regulating MAFbx expression, two MuRF1 mutants were created in which either the carboxyl-terminal domain was deleted or the RING finger domain was inactivated. These constructs were co-transfected with the MAFbx reporter construct into C2C12 cells, and reporter gene activity was measured over four days. The MAFbx promoter again showed a significant increase in activation when co-transfected with MuRF1, however the activating effect on the reporter was attenuated in cells that were co-transfected with either of the MuRF1 mutant constructs. This data offers evidence of a potential new function for MuRF1 as a transcriptional modulator of atrophy-regulated genes.