BIVARIATE FLOW CYTOMETRIC ANALYSIS OF DNA CONTENT VERSUS IMMUNOPOSITIVITY FOR RIBONUCLEOTIDE REDUCTASE M1 SUBUNIT IN THE CELL-CYCLE

Ribonucleotide reductase (RR) is a cytoplasmatic enzyme catalyzing the reduction of all four ribonucleotides to their corresponding deoxyrib onucleotides. Its activity strongly correlates to the rate of DNA synt hesis. By using a specific monoclonal antibody against the large M1 su bunit of RR, we assessed the expression of M1-RR versus DNA content by dual-parameter flow cytometry. The aim of this paper was to compare t he variations in the immunopositivity for M1-RR during the cell cycle to the positivity for other cell cycle markers identifying either prol iferating cells (Ki-67 and PCNA) or quiescent cells (statin). To do th is, normal human embryonic fibroblasts in different growth conditions as well as several other mammalian cell lines (rat C6 glioma cells; mo use 3T3 fibroblasts and B16 melanoma cells; human epithelial EUE cells and mammary carcinoma MCF-7 cells) were used. The expression of M1-RR antigen was found to correlate positively with the expression of Ki-6 7 and PCNA, and negatively with the expression of statin. During early G(1) phase, M1-RR becomes detectable by specific antibodies relativel y later compared to PCNA and Ki-67; therefore, the lack of immunoposit ivity for M1-RR cannot be taken as an absolute indication of cell quie scence in G(0). (C) 1998 Wiley-Liss, Inc.