Quantification of Ag-NOR proteins using Ag-NOR staining on western blots.
Ribosomal genes are associated with a set of silver-stained nucleolar proteins, the Ag-NOR proteins, whose amount is directly related to the duration of the cell cycle. Quantification of Ag-NOR proteins by image analysis is presently used to evaluate the rate of proliferation of cancer cells and nucleolar activity. Our objective was to establish a procedure to quantify independently each major Ag-NOR protein in cell extracts. Computerized densitometry established that the specific silver staining of Ag-NOR proteins (Ag-NOR staining) performed on Western blots makes it possible to quantify Ag-NOR proteins. Using purified Ag-NOR proteins, nucleolin, and protein B23, we observed that the intensity of Ag-NOR staining is proportional to the amount of protein. A linear relationship exists between the intensity of Ag-NOR staining and the amount of nucleolin, in the range of 0.2-1.6 micrograms. Using total nuclear extracts prepared from mammalian cells, the proportionality was maintained for total Ag-NOR-stained proteins or for a particular protein. We also determined the levels of nuclear proteins suitable for quantitative analysis. Individual Ag-NOR proteins can be quantified by computerized densitometry in nuclear extracts after Ag-NOR staining on Western blots. This procedure can be applied to establish the contribution of each Ag-NOR protein in general staining, estimate the variability of each Ag-NOR protein in normal and pathological conditions, and quantify each Ag-NOR protein contained per cell.
Roussel
P
P
Institut Jacques Monod, Paris, France.
Sirri
V
V
Hernandez-Verdun
D
D
D000818:Animals; D015153:Blotting, Western; D016466:CHO Cells; D002453:Cell Cycle; D006224:Cricetinae; D003720:Densitometry; D006367:HeLa Cells; D006801:Humans; D007091:Image Processing, Computer-Assisted; D009687:Nuclear Proteins / Q000032:analysis*; D009697:Nucleolus Organizer Region / Q000737:chemistry*; D012834:Silver
D009687:Nuclear Proteins; D012834:Silver