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Departments of 1 Surgery and 2 Molecular Genetics, Biochemistry and Microbiology, Howard Hughes Medical Institute, University of Cincinnati, 45267; and the Shriners Burns Institute, Cincinnati, Ohio 45529
Recent
studies suggest that sepsis stimulates ubiquitin-dependent protein
breakdown in skeletal muscle. In this proteolytic pathway,
ubiquitinated proteins are recognized, unfolded, and degraded by the
multicatalytic 26S protease complex. The 20S proteasome is the
catalytic core of the 26S protease complex. The role of the 20S
proteasome in the regulation of sepsis-induced muscle proteolysis is
not known. We tested the hypothesis that sepsis increases 20S
proteasome activity and the expression of mRNA for various subunits of
this complex. Proteolytic activity of isolated 20S proteasomes,
assessed as activity against fluorogenic peptide substrates, was
increased in extensor digitorum longus muscles from septic rats. The
proteolytic activity was inhibited by specific proteasome blockers.
Northern blot analysis revealed an approximately twofold increase in
the relative abundance of mRNA for the 20S
-subunits RC3 and RC9 and
the
-subunit RC7. However, Western blot analysis did not show any
difference in RC9 protein content between sham-operated and septic
rats. The increased activity and expression of the 20S proteasome in
muscles from septic rats lend further support for a role of the
ubiquitin-proteasome-pathway in the regulation of sepsis-induced muscle proteolysis.
subunits; ubiquitin; proteolysis
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