Activation of the ATP-ubiquitin-proteasome pathway in skeletal muscle of cachectic rats bearing a hepatoma.
Rats implanted with Yoshida ascites hepatoma (YAH) show a rapid and selective loss of muscle protein due mainly to a marked increase (63-95%) in the rate of protein degradation (compared with rates in muscles of pair-fed controls). To define which proteolytic pathways contribute to this increase, epitrochlearis muscles from YAH-bearing and control rats were incubated under conditions that modify different proteolytic systems. Overall proteolysis in either group of rats was not affected by removal of Ca2+ or by blocking the Ca(2+)-dependent proteolytic system. Inhibition of lysosomal function with methylamine reduced proteolysis (-12%) in muscles from YAH-bearing rats, but not in muscles of pair-fed rats. When ATP production was also inhibited, the remaining accelerated proteolysis in muscles of tumor-bearing rats fell to control levels. Muscles of YAH-bearing rats showed increased levels of ubiquitin-conjugated proteins and a 27-kDa proteasome subunit in Western blot analysis. Levels of mRNA encoding components of proteolytic systems were quantitated using Northern hybridization analysis. Although their total RNA content decreased 20-38%, pale muscles of YAH-bearing rats showed increased levels of ubiquitin mRNA (590-880%) and mRNA for multiple subunits of the proteasome (100-215%). Liver, kidney, heart, and brain showed no weight loss and no change in these mRNA species. Muscles of YAH-bearing rats also showed small increases (30-40%) in mRNA for cathepsins B and D, but not for calpain I or heat shock protein 70. Our findings suggest that accelerated muscle proteolysis and muscle wasting in tumor-bearing rats result primarily from activation of the ATP-dependent pathway involving ubiquitin and the proteasome.
Baracos
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VE
Department of Agricultural, Food, and Nutritional Science, University of Alberta, Edmonton, Canada.
DeVivo
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C
Hoyle
D H
DH
Goldberg
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D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001704:Biopolymers / Q000235:genetics; D015153:Blotting, Western; D002100:Cachexia / Q000378:metabolism; D006528:Carcinoma, Hepatocellular / Q000378:metabolism* / Q000473:pathology; D003546:Cysteine Endopeptidases / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D005260:Female; D008113:Liver Neoplasms / Q000378:metabolism* / Q000473:pathology; D009097:Multienzyme Complexes / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000473:pathology; D009929:Organ Size; D025821:Polyubiquitin; D011480:Protease Inhibitors / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex; D012313:RNA / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D014452:Ubiquitins / Q000145:classification / Q000235:genetics / Q000378:metabolism*
D001704:Biopolymers; D009097:Multienzyme Complexes; D011480:Protease Inhibitors; D012333:RNA, Messenger; D014452:Ubiquitins; D025821:Polyubiquitin; D012313:RNA; D000255:Adenosine Triphosphate; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex