A muscle‐specific MuRF1‐E2 network requires stabilization of MuRF1‐E2 complexes by telethonin, a newly identified substrate

Abstract

BackgroundMuscle wasting is observed in the course of many diseases and also during physiological conditions (disuse, ageing). Skeletal muscle mass is largely controlled by the ubiquitin‐proteasome system and thus by the ubiquitinating enzymes (E2s and E3s) that target substrates for subsequent degradation. MuRF1 is the only E3 ubiquitin ligase known to target contractile proteins (α‐actin, myosins) during catabolic situations. However, MuRF1 depends on E2 ubiquitin‐conjugating enzymes for ubiquitin chain formation on the substrates. MuRF1‐E2 couples are therefore putative targets for preventing muscle wasting.MethodsWe focused on 14 E2 enzymes that are either expressed in skeletal muscle or up‐regulated during atrophying conditions. In this work, we demonstrated that only highly sensitive and complementary interactomic approaches (surface plasmon resonance, yeast three‐hybrid, and split green fluorescent protein) allowed the identification of MuRF1 E2 partners.ResultsFive E2 enzymes physically interacted with MuRF1, namely, E2E1, E2G1, E2J1, E2J2, and E2L3. Moreover, we demonstrated that MuRF1‐E2E1 and MuRF1‐E2J1 interactions are facilitated by telethonin, a newly identified MuRF1 substrate. We next showed that the five identified E2s functionally interacted with MuRF1 since, in contrast to the non‐interacting E2D2, their co‐expression in HEK293T cells with MuRF1 led to increased telethonin degradation. Finally, we showed that telethonin governed the affinity between MuRF1 and E2E1 or E2J1.ConclusionsWe report here the first MuRF1‐E2s network, which may prove valuable for deciphering the precise mechanisms involved in the atrophying muscle programme and for proposing new therapeutical approaches.

Muscle wasting in patients with end‐stage renal disease or early‐stage lung cancer: common mechanisms at work

“…MuRF1 targets like α‐actin, myosin heavy chains, and telethonin) and a repression of protein synthesis and anabolic factors (i.e. MAFbx targets like eIF3f and MyoD) are necessary for maintaining long‐term muscle atrophy . In our study, we also found that two other E3 ligases were up‐regulated at the mRNA level, that is, human double minute (Hdm2) and F‐box protein 30/muscle Ub ligase of the SCF complex in atrophy‐1 (Fbxo30/MUSA1).…”

“…Indeed, none of the 20S and 19S RC subunits tested were up-regulated in both LC and HD patients at the mRNA levels, and only three of them were increased at the protein levels (Figure 1(C) and 1(D), Table 2, and Supporting Information, Table S1). E2 enzymes appeared also to be poor predictors of muscle atrophy in LC and HD patients (Figure 1(B) and Supporting Information, Table S1) in contrast with animal models in which UBE2B was considered as a bona fide atrogene and other E2s were often upregulated during catabolic situations (see Polge et al 41 for compiled data).…”

Small‐molecule‐mediated chemical knock‐down of MuRF1/MuRF2 and attenuation of diaphragm dysfunction in chronic heart failure

“…In accordance with this hypothesis and our previous report, a significant up‐regulated MuRF1 expression was evident in CHF, which was blunted by compound ID#704946. In line with the effect of compound ID#704946 on MuRF1 expression, also a trend towards a reduced expression of telethonin, a known substrate for MuRF1, was seen in CHF, which was also blunted in the compound‐treated group. To our surprise, we also detected a significant modulation of MuRF2 by compound ID#704946.…”

MicroRNAs in muscle wasting

“…These miRs are similar to mRNA when first transcribed as primary RNA and are subsequently processed by the endoribonuclease DROSHA associated with PASHA to a precursor miR, which is further processed by the endoribonuclease DICER1 to form mature miRs. 5 Two key players of muscle wasting are the E3 ubiquitin ligases MAFbx and MuRF-1, the latter being the only E3 ubiquitin ligase known to target contractile proteins in catabolic conditions 6 and which can be inhibited by small molecules. 2,3 While some miRs are expressed ubiquitously in most tissues and cell types, other miRs are highly and specifically enriched in certain tissues.…”