Ubiquitin pools, ubiquitin mRNA levels, and ubiquitin-mediated proteolysis in aging human fibroblasts.
Senescent cells have less free ubiquitin and more ubiquitin-protein conjugates than do young cells. The ubiquitin-protein conjugates are heterogeneous in size but contain prominent bands at 106, 55, and 22 kDa. The age-related increase in ubiquitin-protein conjugates applies primarily to the 55-kDa band, while the 106-kDa and 22-kDa conjugates change little with age. Ubiquitin mRNA levels do not change with age, and the ability of cells to degrade two proteins that are good substrates for ubiquitin-mediated proteolysis is unaltered by aging. These results indicate that an increase in ubiquitin-protein conjugates does not necessarily reflect alterations in ubiquitin-mediated proteolysis. Furthermore, an overactive pathway of ubiquitin-mediated proteolysis does not appear to contribute to the proliferative arrest in senescent cells.
Pan
J X
JX
Department of Physiology, Tufts University School of Medicine, Boston, Massachusetts 02111.
Short
S R
SR
Goff
S A
SA
Dice
J F
JF
D000199:Actins / Q000096:biosynthesis / Q000235:genetics; D015152:Blotting, Northern; D015153:Blotting, Western; D002460:Cell Line; D016922:Cellular Senescence / Q000502:physiology*; D005347:Fibroblasts / Q000737:chemistry / Q000378:metabolism; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000096:biosynthesis / Q000235:genetics; D006207:Half-Life; D006801:Humans; D006868:Hydrolysis; D007074:Immunoglobulin G / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis*; D011863:Radioimmunoassay; D014452:Ubiquitins / Q000032:analysis / Q000235:genetics / Q000502:physiology*
D000199:Actins; D007074:Immunoglobulin G; D011506:Proteins; D012333:RNA, Messenger; D014452:Ubiquitins; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases