Protein oxidation and degradation during cellular senescence of human BJ fibroblasts: part I--effects of proliferative senescence.
Oxidized and cross-linked proteins tend to accumulate in aging cells. Declining activity of proteolytic enzymes, particularly the proteasome, has been proposed as a possible explanation for this phenomenon, and direct inhibition of the proteasome by oxidized and cross-linked proteins has been demonstrated in vitro. We have further examined this hypothesis during both proliferative senescence (this paper) and postmitotic senescence (see the accompanying paper, ref 1 ) of human BJ fibroblasts. During proliferative senescence, we found a marked decline in all proteasome activities (trypsin-like activity, chymotrypsin-like activity, and peptidyl-glutamyl-hydrolyzing activity) and in lysosomal cathepsin activity. Despite the loss of proteasome activity, there was no concomitant change in cellular levels of actual proteasome protein (immunoassays) or in the steady-state levels of mRNAs for essential proteasome subunits. The decline in proteasome activities and lysosomal cathepsin activities was accompanied by dramatic increases in the accumulation of oxidized and cross-linked proteins. Furthermore, as proliferation stage increased, cells exhibited a decreasing ability to degrade the oxidatively damaged proteins generated by an acute, experimentally applied oxidative stress. Thus, oxidized and cross-linked proteins accumulated rapidly in cells of higher proliferation stages. Our data are consistent with the hypothesis that proteasome is progressively inhibited by small accumulations of oxidized and cross-linked proteins during proliferative senescence until late proliferation stages, when so much proteasome activity has been lost that oxidized proteins accumulate at ever-increasing rates. Lysosomes attempt to deal with the accumulating oxidized and cross-linked proteins, but declining lysosomal cathepsin activity apparently limits their effectiveness. This hypothesis, which may explain the progressive intracellular accumulation of oxidized and cross-linked proteins in aging, is further explored during postmitotic senescence in the accompanying paper (1).
Sitte
N
N
Clinics of Physical Medicine and Rehabilitation, Humboldt University Berlin, Germany.
Merker
K
K
Von Zglinicki
T
T
Grune
T
T
Davies
K J
KJ
D002455:Cell Division; D002460:Cell Line; D016922:Cellular Senescence / Q000502:physiology*; D003546:Cysteine Endopeptidases / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D009097:Multienzyme Complexes / Q000378:metabolism; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000502:physiology*; D010269:Paraquat / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex; D011506:Proteins / Q000378:metabolism*
D009097:Multienzyme Complexes; D011506:Proteins; D006861:Hydrogen Peroxide; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D010269:Paraquat