Phosphorylation of chromosomal proteins from mammary cell lines

Phosphorylation of histone and none-histone chromosomal proteins in two clonal mouse mammary cell lines having low (V-14) and high (T-19) tumorigenicity was investigated. Logarithmic phase cells were incubated in medium containing 125 muCi/ml[32P]-orthophosphate. Cell nuclei were isolated, chromosomal proteins (histones and non-histones) extracted and their amino acid composition, protein/DNA mass ratios, 32P-uptake and gel electrophoretic patterns examined. Significant differences in the histone and NHC-protein phosphorylation of these two cell lines were found. Comparison of radioactivity profiles of electrophoretically separated T-19 and V-14 NHC-proteins showed that 60% of the T-19 bands in the mol. wt range of 160,000 to 15,000 daltons had increased [32P]-orthophosphate uptake. Differences in histone radiolabelling between V-14 and T-19 were confined to the H1, H3 and H4 classes. [32P]-ATP-pool measurements of V-14 and T-19 at 30, 60 and 120 min of incubation were similar, hence the difference in 32P-uptake was not due to ATP-pool fluctuations. Results of studies on growth rate, growth potential and the possibility that comparisons were made between cells at different stages of the growth cycle indicated that these variables did not account for the higher phosphorylation of T-19 chromosomal proteins. The increased [32P]-phosphate uptake into T-19 cell protein was correlated with an elevated content of NHC and histone proteins and pointed towards a correlation between the degree of phosphorylation and the high tumorigenicity of this cell line.