Cytosolic ubiquitin and ubiquitylation rates in human peripheral blood mononuclear cells during sepsis.
The ubiquitin system plays a crucial role in the immune system, and ubiquitylation is regarded as one of the most common posttranslational modifications of proteins. However, its regulation in human peripheral blood mononuclear cells during sepsis is unknown. Thus, we investigated cytosolic levels of free and conjugated ubiquitin and the total ubiquitylation rate in cell free extracts from healthy donors (n = 10) and patients (n = 10) with sepsis. During sepsis, the total ubiquitin concentration was significantly reduced (P < 0.001), which was caused by a significant decrease in conjugated ubiquitin (7.4 +/- 1.9 ng vs. 11.75 +/- 1.4 ng conjugated ubiquitin/mug protein, P < 0.001), whereas free ubiquitin was unchanged. The proportion between free and conjugated ubiquitin showed a linear relationship in physiologic conditions (r, 0.76, P = 0.001) but not in sepsis (r, 0.27, P = 0.12). These changes were accompanied by a decreased total ubiquitin protein ligase activity (1.7 +/- 1.1 pkat/mg vs. 5.7 +/- 2.9 pkat/mg, P = 0.002). The tight regulation of the cytosolic ubiquitin pool appears to be significantly altered during sepsis. In addition to alterations in ubiquitin turnover, these findings suggest that reduced ubiquitylation rates also contribute to the decrease in endogenous conjugated ubiquitin. This indicates that a major pathway of posttranslational protein modification in all eukaryotes is profoundly altered in peripheral blood mononuclear cells from critically ill sepsis patients. This may contribute to the well-known impairment of host defense mechanisms in sepsis.
Ponelies
Norbert
N
Trauma Research Laboratory, Department of Trauma Surgery, University Hospital Mannheim, Ruprecht-Karls University, Heidelberg, 68167 Mannheim, Germany.
Hirsch
Thomas
T
Krehmeier
Ulrich
U
Denz
Christof
C
Patel
Mayur B
MB
Majetschak
Matthias
M
D001798:Blood Proteins / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D005260:Female; D006801:Humans; D007700:Kinetics; D007963:Leukocytes, Mononuclear / Q000166:cytology / Q000378:metabolism*; D008297:Male; D018805:Sepsis / Q000097:blood / Q000378:metabolism*; D025801:Ubiquitin / Q000097:blood / Q000378:metabolism*
D001798:Blood Proteins; D025801:Ubiquitin