PDLIM7 is a novel target of the ubiquitin ligase Nedd4-1 in skeletal muscle

Skeletal muscle atrophy remains a complication occurring both as a natural response to muscle disuse and as a pathophysiological response to illness such as diabetes mellitus and nerve injury, such as traumatic muscle denervation. The ubiquitin-proteasome system (UPS) is the predominant proteolytic machinery responsible for atrophy of skeletal muscle, and Nedd4-1 (neural precursor cell-expressed developmentally down-regulated 4-1) is one of a series of E3 ubiquitin ligases identified to mediate inactivity-induced muscle wasting. Targets of Nedd4-1 mediated ubiquitination in skeletal muscle remain poorly understood. In the present study, we identified PDLIM7 (PDZ and LIM domain 7, Enigma), a member of the PDZ-LIM family of proteins, as a novel target of Nedd4-1 in skeletal muscle. The PDZ-LIM family of proteins is known to regulate muscle development and function. We show that Nedd4-1 expression in muscle atrophied by denervation is co-incident with a decrease in PDLIM7 and that PDLIM7 protein levels are stabilized in denervated muscle of Nedd4-1 skeletal muscle-specific knockout mice (SMS-KO). Exogenous PDLIM7 and Nedd4-1 transfected into human embryonic kidney (HEK)293 cells co-immunoprecipitate through binding between the PY motif of PDLIM7 and the second and third WW domains of Nedd4-1 and endogenous PDLIM7 and Nedd4-1 interact in the cytoplasm of differentiated C2C12 myotubes, leading to PDLIM7 ubiquitination. These results identify PDLIM7 as a bona fide skeletal muscle substrate of Nedd4-1 and suggest that this interaction may underlie the progression of skeletal muscle atrophy. This offers a novel therapeutic target that could be potentially used to attenuate muscle atrophy.