Amount variability of total and individual Ag-NOR proteins in cells stimulated to proliferate.
Ribosomal genes are associated with a subset of acidic proteins called Ag-NOR proteins. The amount of nucleolar Ag-NOR proteins varies, depending on nucleolar activity and/or cell proliferation. To understand the linkage between the amount of Ag-NOR proteins, ribosome biogenesis, and cell proliferation, we investigated the variability of Ag-NOR proteins in rRNA-stimulated cells maintained in G1 and in rRNA-stimulated cells entering the mitotic cycle. Rat hepatocytes were stimulated with cortisol for rRNA synthesis (1, 4, and 8 hr) and the cell cycle was induced by hepatectomy in regenerating hepatocytes (3-21 hr). In non-stimulated hepatocytes, nucleolin and protein B23 were the two major Ag-NOR proteins, corresponding to 70% of total Ag-NOR staining. In hepatocytes stimulated for rRNA synthesis in G1, the amount of Ag-NOR proteins was only slightly increased, whereas in cycle-stimulated cells it was increased 3.04-fold. This is the consequence of a differential increase of the major Ag-NOR proteins that appears earlier and is proportionally more important for nucleolin (3.5-fold) than for protein B23 (twofold) and also for the increase of several minor Ag-NOR proteins. We conclude that, in dividing cells, the mean value of the Ag-NOR proteins measured reflects the percentage of cells in the different phases. This could explain why the amount of Ag-NOR proteins can be used as a marker of cell proliferation.
Sirri
V
V
Institut Jacques Monod, Paris, France.
Roussel
P
P
Trerè
D
D
Derenzini
M
M
Hernandez-Verdun
D
D
D000818:Animals; D034961:Antigens, Nuclear; D015153:Blotting, Western; D002453:Cell Cycle; D002455:Cell Division; D016193:G1 Phase; D006498:Hepatectomy; D006854:Hydrocortisone / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D008115:Liver Regeneration; D009687:Nuclear Proteins / Q000032:analysis / Q000378:metabolism*; D009697:Nucleolus Organizer Region / Q000502:physiology* / Q000648:ultrastructure; D010750:Phosphoproteins / Q000032:analysis / Q000378:metabolism; D016601:RNA-Binding Proteins; D051381:Rats; D017208:Rats, Wistar; D012016:Reference Values; D012270:Ribosomes / Q000502:physiology / Q000648:ultrastructure; D013997:Time Factors; D000097796:Nucleolin
D034961:Antigens, Nuclear; D006854:Hydrocortisone; D009687:Nuclear Proteins; D010750:Phosphoproteins; D016601:RNA-Binding Proteins; D000097796:Nucleolin; C051963:nucleolar organizer region associated proteins