Glutamine starvation of monocytes inhibits the ubiquitin-proteasome proteolytic pathway.
Peripheral blood monocytes utilize free glutamine (Gln) in addition to glucose as an important energy substrate. Although this demand increases upon activation, monocytes are commonly confronted with decreased plasma Gln during critical illness and thus suffer from Gln-starvation. Here we investigate the influence of Gln-starvation on protein stability and its effects on the monocyte proteome. Gln-starvation caused a reduction of protein degradation which was accompanied by an accumulation of ubiquitin-protein conjugates and a reduction of intracellular ATP. Similar effects were observed under ATP-reducing conditions and in the presence of a proteasome inhibitor. Using two-dimensional gel electrophoresis we identified the IL-1beta precursor protein (pIL-1beta) as the, by far, most induced protein in endotoxin-treated monocytes. The degradation of the short-lived pIL-1beta was strongly reduced during Gln-starvation, while the degradation of the long-lived, constitutively expressed beta-actin was less affected. This indicates that although Gln-starvation reduces protein breakdown on the overall proteasome level, it leads to differential changes in the stability of specific proteins. This selective effect is likely to contribute to the immunocompromised state of monocytes commonly observed during critical illness.
Zellner
Maria
M
Surgical Research Laboratories, University of Vienna, AKH (8G9.05), Waehringer-Guertel 18-20, A-1090 Vienna, Austria.
Gerner
Christopher
C
Munk Eliasen
Maja
M
Wurm
Susanne
S
Pollheimer
Jürgen
J
Spittler
Andreas
A
Brostjan
Christine
C
Roth
Erich
E
Oehler
Rudolf
R
D000199:Actins / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D005973:Glutamine / Q000378:metabolism*; D006801:Humans; D007375:Interleukin-1 / Q000378:metabolism; D008070:Lipopolysaccharides / Q000378:metabolism / Q000494:pharmacology; D008715:Methionine / Q000378:metabolism; D009000:Monocytes / Q000187:drug effects / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D014176:Protein Biosynthesis; D011506:Proteins / Q000378:metabolism*; D013997:Time Factors; D020298:U937 Cells; D014452:Ubiquitins / Q000378:metabolism*
D000199:Actins; D007375:Interleukin-1; D008070:Lipopolysaccharides; D009097:Multienzyme Complexes; D011506:Proteins; D014452:Ubiquitins; D005973:Glutamine; D000255:Adenosine Triphosphate; D008715:Methionine; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex