Muscle-specific E3 ubiquitin ligases are involved in muscle atrophy of cancer cachexia: an in vitro and in vivo study.

Muscle atrophy F-Box (MAFbx)/atrogin-1 and muscle ring-finger-1 (MuRF-1) have been identified as two muscle-specific E3 ubiquitin ligases that are highly expressed in skeletal muscle during muscle atrophy. However, the role of muscle-specific E3 ubiquitin ligases during the process of muscle atrophy of cancer cachexia remains largely unknown. In the present study, we analyzed the expression of atrogin-1 and MuRF-1 in the skeletal muscle of patients with malignant and benign disease. The possible mechanisms were studied both in a colon 26-induced cancer cachexia mouse model and in tumor necrosis factor-alpha (TNF-alpha) induced atrophy C2C12 cells. Our results demonstrated that atrogin-1 and MuRF-1 tended to be increased in the skeletal muscle of patients with malignant disease even before weight loss. Non-tumor body weights and gastrocnemius weights were significantly decreased while expression levels of ubiquitin proteasome pathway associated genes (atrogin-1, MuRF-1, ubiquitin and E2-14K) were upregulated in cancer cachexia mice. Significant myotube atrophy with atrogin-1 overexpression was observed in the C2C12 cells treated with TNF-alpha. Meanwhile, knockdown of atrogin-1 by small interfering RNA (siRNA) protected C2C12 cells from the adverse effect of TNF-alpha. In conclusion, muscle-specific E3 ubiquitin ligases were upregulated during cancer cachexia, and atrogin-1 may be a potential molecular target for treating muscle atrophy induced by cancer cachexia.