UBE2C promotes myoblast differentiation and skeletal muscle regeneration through the Akt signaling pathway

Abstract

Ubiquitin-conjugation enzyme E2C (UBE2C) is a crucial component of the ubiquitin-proteasome system that is involved in numerous cancers. In this study, we find that UBE2C expression is significantly increased in mouse embryos, a critical stage during skeletal muscle development. We further investigate the function of UBE2C in myogenesis. Knockdown of UBE2C inhibits C2C12 cell differentiation and decreases the expressions of MyoG and MyHC, while overexpression of UBE2C promotes C2C12 cell differentiation. Additionally, knockdown of UBE2C, specifically in the tibialis anterior muscle (TA), severely impedes muscle regeneration in vivo. Mechanistically, we show that UBE2C knockdown reduces the level of phosphorylated protein kinase B (p-Akt) and promotes the degradation of Akt. These findings suggest that UBE2C plays a critical role in myoblast differentiation and muscle regeneration and that UBE2C regulates myogenesis through the Akt signaling pathway.

1. Introduction

Skeletal muscle is a highly complex and heterogeneous tissue that has a broad range of functions. Among these processes, myogenesis and skeletal muscle regeneration are two processes involved in muscle generation, including myoblast proliferation, differentiation, and fusion [1,2]. These coordinated events depend on highly complex molecular regulatory networks [3]. The myogenic regulatory factors (MRFs), including myogenic differentiation 1 (MyoD), myogenic factor 5 (Myf5), myogenin (MyoG), and myogenic regulator factor 4 (MRF4), play well-defined roles in muscle development and regeneration [4,5]. In addition, numerous key genes that participate in muscle development have been described in recent years [6–9]. Moreover, signaling pathways are the key link in the regulatory network of muscle differentiation [10,11]. The PI3K/Akt/mTOR pathway was confirmed to be a critical regulator of skeletal muscle differentiation and growth [12,13]. Akt contributes to muscle hypertrophy and myofiber growth in adult muscle without activating the proliferation of muscle satellite cells [14] and stimulates myogenesis by promoting the expressions of MyoD [15] and MyoG [16].

Ubiquitination is an important type of posttranslational modification of proteins that requires ubiquitin-activating enzyme (E1), ubiquitin-conjugating enzyme (E2), and ubiquitin-ligase enzymes (E3), and through three-step sequential actions, it transfers the activated ubiquitin from the E2 to the substrate [17,18]. The ubiquitin-conjugating enzyme E2C is a ubiquitin-binding enzyme that accepts ubiquitin from E1 and transfers it to a substrate associated with E3. Previous studies confirmed that UBE2C plays an important role in various malignancies [19,20] and affects cancers through the PI3K/Akt/mTOR signaling pathways [21–23]. However, little is known about the function and molecular mechanisms of UBE2C in skeletal muscle.

In the present study, our findings indicated that knockdown of UBE2C impedes myoblast differentiation and muscle regeneration. Specifically, inhibiting UBE2C in C2C12 cells results in reduced level of phosphorylated Akt (p-Akt) and accelerated Akt degradation. These observations provide compelling evidence for the critical involvement of UBE2C in the regulatory mechanisms underlying myogenesis by regulating the Akt signaling pathway.