Differential [32P]-labeling of chemically induced stress proteins in S-phase mouse lymphoma cells

A portion of our research involves the investigation of biomarkers as preclinical indicators of toxic stress. Stemming from this effort, we report three unique proteins that phosphorylate and synthesize during the S-phase of lymphoma cells following chemical insult. Mouse lymphoma cell nuclei were physically sorted (using a fluorescence activated cell sorter) from partitions of the cell cycle and specific nuclear proteins in each partition were examined by gel microelectrophoresis. The changes in [32P]-incorporation by stress proteins (SPs) were examined in each of seven partitions following administration of sodium arsenite. Four SPs [80,000-84,000 relative molecular mass (Mr)], designated 'c','b','x', and 'y', underwent significant alterations in [32P]-labeling and each exhibited varying degrees of differential [32P]-incorporation in partition 3 of G1 phase, all five partitions of S-phase, and partition 1 of G2 phase of the cell cycle. Three other predominantly S-phase SPs (designated S1, S2 and S3) were phosphorylated after sodium arsenite treatment. Stress protein S1 was labeled exclusively in S-phase, while proteins S2 and S3 were labeled only in partition 3 of G1 and S-phase. Stress protein S1 possessed an identical isoelectric point, molecular mass, distribution of polypeptide fragments and immunochemical determinants as S-phase SPs found previously in mouse spleen (X') and mouse liver (LP-S). The identical biochemical characteristics of these three S-phase (SPs), found in diverse tissue types, suggest they are homologous.