Nishimura, Y, Chunthorng-Orn, J, Lord, S, Musa, I, Dawson, P, Holm, L and Lai, YC (2022) Ubiquitin E3 ligase Atrogin-1 protein is regulated via the rapamycin-sensitive mTOR-S6K1 signaling pathway in C2C12 muscle cells. American Journal of Physiology: Cell Physiology, 323 (1). C215-C225. ISSN 0363-6143

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Text Ubiquitin E3 ligase Atrogin-1 protein is regulated via the rapamycin-sensitive mTOR-S6K1 signaling pathway in C2C12 muscle cells.pdf - Published Version Available under License Creative Commons Attribution. Download (2MB) | Preview

Abstract

Atrogin-1 and Muscle-specific RING finger protein 1 (MuRF1) are highly expressed in multiple conditions of skeletal muscle atrophy. The phosphoinositide 3-kinase (PI3K)/Akt/forkhead box (FoxO) signaling pathway is well known to regulate Atrogin-1 and MuRF1 gene expressions. However, Akt activation also activates the mechanistic target of rapamycin complex 1 (mTORC1), which induces skeletal muscle hypertrophy. Whether mTORC1-dependent signaling has a role in regulating Atrogin-1 and/or MuRF1 gene and protein expression is currently unclear. In this study, we showed that activation of insulin-mediated Akt signaling suppresses both Atrogin-1 and MuRF1 protein contents and that inhibition of Akt increases both Atrogin-1 and MuRF1 protein contents in C2C12 myotubes. Interestingly, inhibition of mTORC1 with a specific mTORC1 inhibitor, rapamycin, increased Atrogin-1, but not MuRF1, protein content. Furthermore, activation of AMP-activated protein kinase (AMPK), a negative regulator of the mTORC1 signaling pathway, also showed distinct time-dependent changes between Atrogin-1 and MuRF1 protein contents, suggesting differential regulatory mechanisms between Atrogin-1 and MuRF1 protein content. To further explore the downstream of mTORC1 signaling, we employed a specific S6K1 inhibitor, PF-4708671. We found that Atrogin-1 protein content was dose-dependently increased with PF-4708671 treatment, whereas MuRF1 protein content was decreased at 50 μM of PF-4708671 treatment. However, MuRF1 protein content was unexpectedly increased by PF-4708671 treatment for a longer period. Overall, our results indicate that Atrogin-1 and MuRF1 protein contents are regulated by different mechanisms, the downstream of Akt, and that Atrogin-1 protein content can be regulated by the rapamycin-sensitive mTOR-S6K1-dependent signaling pathway.

Item Type:	Article
Uncontrolled Keywords:	Muscle, Skeletal; Humans; Muscular Atrophy; Sirolimus; Ubiquitin-Protein Ligases; SKP Cullin F-Box Protein Ligases; Ubiquitins; Signal Transduction; Proto-Oncogene Proteins c-akt; Muscle Fibers, Skeletal; Phosphatidylinositol 3-Kinases; TOR Serine-Threonine Kinases; Tripartite Motif Proteins; Mechanistic Target of Rapamycin Complex 1; mTORC1; skeletal muscle; ubiquitin proteasome system; Humans; Mechanistic Target of Rapamycin Complex 1; Muscle Fibers, Skeletal; Muscle, Skeletal; Muscular Atrophy; Phosphatidylinositol 3-Kinases; Proto-Oncogene Proteins c-akt; SKP Cullin F-Box Protein Ligases; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases; Tripartite Motif Proteins; Ubiquitin-Protein Ligases; Ubiquitins; 0601 Biochemistry and Cell Biology; 0606 Physiology; 1116 Medical Physiology; Physiology
Subjects:	R Medicine > RC Internal medicine > RC1200 Sports Medicine
Divisions:	Sport & Exercise Sciences
Publisher:	American Physiological Society
SWORD Depositor:	A Symplectic
Date Deposited:	10 Feb 2023 12:35
Last Modified:	10 Feb 2023 12:45
DOI or ID number:	10.1152/ajpcell.00384.2021
URI:	https://researchonline.ljmu.ac.uk/id/eprint/18855

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