The MuRF1-E2 network: search for inhibitors impeding muscle atrophy

The ubiquitin proteasome system (UPS) is a major player of skeletal muscle wasting, a common characteristic of many diseases (cancer, sepsis, heart failure, kidney diseases, etc.) that negatively impacts treatment and life prognosis. MuRF1 is so far the only E3 ligase known for targeting several sarcomeric proteins (-actin, MYHC, Troponin I, telethonin) [1]. However, like most E3s, MuRF1 does not possess any intrinsic catalytic activity and belongs to the presence of an E2 enzyme for targeting its substrates and targeting MuRF1-E2 interactions is a potential strategy for fighting against muscle atrophy. We previously identified the E2s interacting with MuRF1 [1, 2] and we hypothesize that each MuRF1-E2 couple is dedicated to specific roles of MuRF1 in various metabolic pathways (i.e. UPS-dependent muscle atrophy, energy sensing, modulation of transcription factors levels, etc.). We now know that among the MuRF1-E2 network, 3 E2s are potentially involved in the targeting of contractile proteins, i.e. E2J1, E2J2 and E2L3. We addressed the role of E2J1, E2J2 and E2L3 in cultured C2C12 myotubes and in the gastrocnemius muscle from mice. We used dexamethasone (Dex) treatment, which induces a catabolic situation, and we either overexpressed or knocked down each of the studied E2. We found that E2L3 knockdown induced an hypertrophy of muscle fibers, while E2J1 knockdown aggravated muscle atrophy (experiments on E2J2 are currently in progress). In parallel, we have set-up a split-GFP-based strategy that can be used as a readout for cell-based (HEK293) High Throughput Screening and have tested its applicability to a collection of 9000 small compounds