USP19-deubiquitinating enzyme regulates levels of major myofibrillar proteins in L6 muscle cells

Abstract

The ubiquitin-proteasome system plays an important role in the degradation of myofibrillar proteins that occurs in muscle wasting. Many studies have demonstrated the importance of enzymes mediating conjugation of ubiquitin. However, little is known about the role of deubiquitinating enzymes. We previously showed that the USP19-deubiquitinating enzyme is induced in atrophying skeletal muscle (Combaret L, Adegoke OA, Bedard N, Baracos V, Attaix D, Wing SS. Am J Physiol Endocrinol Metab 288: E693-E700, 2005). To further explore the role of USP19, we used small interfering RNA (siRNA) in L6 muscle cells. Lowering USP19 by 70-90% in myotubes resulted in a 20% decrease in the rate of proteolysis and an 18% decrease in the rate of protein synthesis, with no net change in protein content. Despite the decrease in overall synthesis, there were approximately 1.5-fold increases in protein levels of myosin heavy chain (MHC), actin, and troponin T and a approximately 2.5-fold increase in tropomyosin. USP19 depletion also increased MHC and tropomyosin mRNA levels, suggesting that this effect is due to increased transcription. Consistent with this, USP19 depletion increased myogenin protein and mRNA levels approximately twofold. Lowering myogenin using siRNA prevented the increase in MHC and tropomyosin upon USP19 depletion, indicating that myogenin mediated the increase in myofibrillar proteins. Dexamethasone treatment lowered MHC and increased USP19. Depletion of USP19 reversed the dexamethasone suppression of MHC. These studies demonstrate that USP19 modulates transcription of major myofibrillar proteins and indicate that the ubiquitin system not only mediates the increased protein breakdown but is also involved in the decreased protein synthesis in atrophying skeletal muscle.

The ubiquitin proteasome system in atrophying skeletal muscle: roles and regulation

“…Moreover, as mentioned earlier, USP19 downregulates myogenin, which plays an important role in myogenesis (106). Loss of Trim72 function promotes myogenesis (55) through its ability to modulate fusion and myogenin expression.…”

“…Silencing its expression in cultured myotubes promotes the transcription of myofibrillar proteins. This effect is due to increased levels of the myogenic transcription factor myogenin, but how USP19 modulates myogenin remains unknown (106). At a posttranscriptional level, atrogin-1/MafBx/ Fbxo32 has been observed to target the initiation factor eIF3-f to proteasomal degradation in cultured muscle cells (54).…”

Proteolysis in illness-associated skeletal muscle atrophy: from pathways to networks

“…Silencing of USP19 in L6 muscle cells results in increased expression of myofibrillar proteins 56 . The finding that this is dependent on increased expression of myogenin implies that USP19 acts on signaling pathways that regulate myogenin and thereby a transcriptional program regulating myofibrillar protein genes.…”

17β-Estradiol Represses Myogenic Differentiation by Increasing Ubiquitin-specific Peptidase 19 through Estrogen Receptor α

“…Recently, the expression of ubiquitin-specific peptidase 19 (USP19), which is a member of USP family proteins, was found to be elevated in skeletal muscle during catabolic states (15). Depletion of USP19 increases not only the levels of myofibrillar proteins such as MHC, troponin T, and tropomyosin, but also the level of a muscle-specific transcription factor myogenin in L6 muscle cells (16). In the present paper, we report that E2 inhibits myogenic differentiation of mouse C2C12 myoblasts and mouse satellite cells and increases the expression of USP19 in skeletal muscle in vitro and in vivo.…”