Cancer cachexia is regulated by selective targeting of skeletal muscle gene products
Swarnali Acharyya, … , Steven Swoap, Denis C. Guttridge
Swarnali Acharyya, … , Steven Swoap, Denis C. Guttridge
Published August 1, 2004
Citation Information: J Clin Invest. 2004;114(3):370-378. https://doi.org/10.1172/JCI20174.
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Article Oncology

Cancer cachexia is regulated by selective targeting of skeletal muscle gene products

Abstract

Cachexia is a syndrome characterized by wasting of skeletal muscle and contributes to nearly one-third of all cancer deaths. Cytokines and tumor factors mediate wasting by suppressing muscle gene products, but exactly which products are targeted by these cachectic factors is not well understood. Because of their functional relevance to muscle architecture, such targets are presumed to represent myofibrillar proteins, but whether these proteins are regulated in a general or a selective manner is also unclear. Here we demonstrate, using in vitro and in vivo models of muscle wasting, that cachectic factors are remarkably selective in targeting myosin heavy chain. In myotubes and mouse muscles, TNF-α plus IFN-γ strongly reduced myosin expression through an RNA-dependent mechanism. Likewise, colon-26 tumors in mice caused the selective reduction of this myofibrillar protein, and this reduction correlated with wasting. Under these conditions, however, loss of myosin was associated with the ubiquitin-dependent proteasome pathway, which suggests that mechanisms used to regulate the expression of muscle proteins may be cachectic factor specific. These results shed new light on cancer cachexia by revealing that wasting does not result from a general downregulation of muscle proteins but rather is highly selective as to which proteins are targeted during the wasting state.

Authors

Swarnali Acharyya, Katherine J. Ladner, Lori L. Nelsen, Jeffrey Damrauer, Peter J. Reiser, Steven Swoap, Denis C. Guttridge

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Figure 3

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TNF/IFN inhibits MyHC transcription through the concomitant reduction of...
TNF/IFN inhibits MyHC transcription through the concomitant reduction of MyoD. (A) C2C12 cells were transfected in triplicate with a MyHC IIb–luciferase reporter plasmid as described in Methods. The next day, cells were differentiated and at the indicated times were harvested for luciferase assays. (B) Myoblasts were transfected with MyHC IIb–luciferase and subsequently differentiated for 48 hours, at which time cells were left untreated or treated with TNF/IFN. At the indicated times, cells were harvested and luciferase levels determined. (C) Myotubes were either untreated or treated with TNF (5 ng/ml), IFN (50 U/ml), or TNF plus IFN for 48 hours. Northern blots probing for MyoD were performed (25), and GAPDH was used as a loading control. (D) Myoblasts were transfected under conditions similar to those described in B with a MyHC IIb–luciferase reporter along with empty vector or MyoD wild-type or mutant (mut) expression plasmids (50 ng each). Cells were differentiated for 48 hours and subsequently left untreated or treated with TNF and IFN for an additional 24 hours, at which time cell extracts were prepared and luciferase activities determined. (E) Myotubes were either untreated or treated with TNF and IFN in methionine/cysteine–free DM, then pulsed for 1 hour with [35S]-methionine/cysteine prior to collection of cells. Labeled MyHC was detected by immunoprecipitation. (F) Myotubes were pulsed with DM containing [35S]-methionine/cysteine, then chased with fresh DM with or without TNF/IFN. For histograms, the data are representative of experiments performed a minimum of three times, plotted as mean ± SD.