Activation of caspase-3 is an initial step triggering accelerated muscle proteolysis in catabolic conditions
Jie Du, … , S. Russ Price, William E. Mitch
Jie Du, … , S. Russ Price, William E. Mitch
Published January 1, 2004
Citation Information: J Clin Invest. 2004;113(1):115-123. https://doi.org/10.1172/JCI18330.
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Article

Activation of caspase-3 is an initial step triggering accelerated muscle proteolysis in catabolic conditions

Abstract

With trauma, sepsis, cancer, or uremia, animals or patients experience accelerated degradation of muscle protein in the ATP-ubiquitin-proteasome (Ub-P’some) system. The initial step in myofibrillar proteolysis is unknown because this proteolytic system does not break down actomyosin complexes or myofibrils, even though it degrades monomeric actin or myosin. Since cytokines or insulin resistance are common in catabolic states and will activate caspases, we examined whether caspase-3 would break down actomyosin. We found that recombinant caspase-3 cleaves actomyosin, producing a characteristic, approximately 14-kDa actin fragment and other proteins that are degraded by the Ub-P’some. In fact, limited actomyosin cleavage by caspase-3 yields a 125% increase in protein degradation by the Ub-P’some system. Serum deprivation of L6 muscle cells stimulates actin cleavage and proteolysis; insulin blocks these responses by a mechanism requiring PI3K. Cleaved actin fragments are present in muscles of rats with muscle atrophy from diabetes or chronic uremia. Accumulation of actin fragments and the rate of proteolysis in muscle stimulated by diabetes are suppressed by a caspase-3 inhibitor. Thus, in catabolic conditions, an initial step resulting in loss of muscle protein is activation of caspase-3, yielding proteins that are degraded by the Ub-P’some system. Therapeutic strategies could be designed to prevent these events.

Authors

Jie Du, Xiaonan Wang, Christiane Miereles, James L. Bailey, Richard Debigare, Bin Zheng, S. Russ Price, William E. Mitch

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Actin fragment degradation requires ATP, proteasome activity, and caspas...
Actin fragment degradation requires ATP, proteasome activity, and caspase-3. (a) L6 cells were incubated with staurosporine to activate caspase-3 as in Figure 2. Cell lysates were incubated on ice or at 37°C for 3 hours as indicated. We then tested for production of the 14-kDa actin fragment. When we added 2 mM ATP, the accumulation of the fragment was largely eliminated, and this outcome was blocked by adding MG132 (10 μM). (b) Lysates from control or staurosporine-treated cells were incubated for 3 hours at 37°C with Ac-DEVD-CHO (DEVD) (5 μM), and Western blot analysis revealed that caspase-3 was responsible for the appearance of the 14-kDa actin fragment.