p53 content in relation to cell growth and proliferation in murine L1210 leukemia and normal lymphocytes

The protein p53 has been reported to be associated with cell transformation and/or proliferation. Using p53 monoclonal antibodies we estimated by flow cytometry the relative content of this protein in individual L1210 leukemic cells from exponentially growing and plateau-phase cultures and compared it with that in normal thymocytes of parental DBA/2 mice and in mitogen-stimulation and nonstimulated human lymphocytes. Simultaneous differential staining of p53 vs DNA and p53 vs RNA, followed by bivariate analysis, made it possible to estimate p53 with respect to cell position in the cell cycle and correlate it with RNA (predominantly rRNA) content. The data show that in exponentially growing L1210 cells p53 is being progressively accumulated during the G1, S and G2 phases and that the content of p53 and RNA are highly correlated. In plateau L1210 cultures most cells are arrested in G1, some cells, however, still continue to progress through S and G2. In these cultures the p53 content of all cells, regardless of the phase of the cell cycle, is diminished and the decrease in p53 is more pronounced than that of RNA or total protein content. The normal thymocytes as well as the stimulated lymphocytes show bimodal distribution with respect to p53 expression, compatible with the assumption that the cycling cells have increased expression of this protein related to the G0 cells. Some cycling cells, however, have minimal p53. The quantitative p53 immunofluorescence data were confirmed by the immunoprecipitation and gel electrophoresis. The results suggest that expression of p53 in leukemic and normal cells is more correlated with cell growth than with entrance to the cell cycle or progression through particular phases of the cycle.