The mERG1a channel modulates skeletal muscle MuRF1 , but not MAFbx , expression

ABSTRACT Introduction : We investigated the mechanism by which the MERG1a K + channel increases ubiquitin proteasome proteolysis (UPP). Methods : Hindlimb suspension and electro‐transfer of Merg1a cDNA into mouse gastrocnemius muscles induced atrophy. Results : Atrophic gastrocnemius muscles of hindlimb‐suspended mice express Merg1a , Murf1 , and Mafbx genes. Electrotransfer of Merg1a significantly decreases muscle fiber size (12.6%) and increases UPP E3 ligase Murf1 mRNA (2.1‐fold) and protein (23.7%), but does not affect Mafbx E3 ligase expression. Neither Merg1a ‐induced decreased fiber size nor Merg1a ‐induced increased Murf1 expression is curtailed significantly by coexpression of inactive HR ‐ Foxo3a , a gene encoding a transcription factor known to induce Mafbx expression. Conclusions : The MERG1a K + channel significantly increases expression of Murf1 , but not Mafbx . We explored this expression pattern by expressing inactive Foxo3a and showing that it is not involved in MERG1a‐mediated expression of Murf1 . These findings suggest that MERG1a may not modulate Murf1 expression through the AKT/FOXO pathway. Muscle Nerve 49 :378–388, 2014