Tumor necrosis factor-alpha exerts interleukin-6-dependent and -independent effects on cultured skeletal muscle cells.
In vivo studies have shown that cancer-associated skeletal muscle wasting (cachexia) is mediated by two cytokines, tumor necrosis factor-alpha (TNF) and interleukin-6 (IL-6). It has been unclear from these studies whether TNF exerts direct effects on skeletal muscle and/or whether these effects are mediated via IL-6. Previous studies from our laboratory have shown that TNF induces IL-6 mRNA expression in cultured skeletal muscle cells. To further investigate the relationship between TNF and IL-6, the effects of TNF and IL-6 on protein and DNA dynamics in murine C2C12 skeletal myotube cultures were determined. At 1000 U/ml, TNF induced 30% increases in protein and DNA content. The effects of TNF on protein accumulation were inhibited by aphidicolin, an inhibitor of DNA synthesis. IL-6 mimicked the effects of TNF on C2C12 cultures, inducing a 32% increase in protein accumulation and a 71% increase in the rate of protein synthesis. IL-6 also decreased expression of mRNA for several proteolytic system components, including ubiquitin 2.4 kb (51%) and 1.2 kb (63%), cathepsin B (39%) and m-calpain (47%), indicating that IL-6 acts on both protein synthesis and degradation. Incubation of murine C2C12 myotube cultures with TNF (1000 U/ml) in the presence of a polyclonal mouse anti-IL-6 antibody resulted in an abolishment of the effects of TNF on protein synthesis, but did not inhibit TNF-induced stimulation of DNA synthesis. These findings indicate that the effects of TNF on muscle protein synthesis are mediated by IL-6, but that TNF exerts IL-6-independent effects on proliferation of murine skeletal myoblasts.
Alvarez
Belen
B
Cancer Research Group, Departament de Bioquímica i Biologia Molecular, Universitat de Barcelona, Spain.
Quinn
LeBris S
LS
Busquets
Sijlvia
S
Quiles
Maria T
MT
Lopez-Soriano
Francisco J
FJ
Argiles
Josep M
JM
D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D015850:Interleukin-6 / Q000096:biosynthesis / Q000378:metabolism* / Q000494:pharmacology; D051379:Mice; D009124:Muscle Proteins / Q000096:biosynthesis / Q000235:genetics; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D015850:Interleukin-6; D009124:Muscle Proteins; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha