COMPARISON OF THE CELL-CYCLE-REGULATED SYNTHESIS AND PHOSPHORYLATION OF STRESS PROTEINS, ACTIN ISOFORMS AND A NOVEL ACTIN-LIKE PROTEIN FOLLOWING DRUG ADMINISTRATION IN CULTURED RAT LYMPHOCYTES

Administration of phytohemagglutinin initiated cycling of rat lymphocy tes in vitro, and following treatment with this drug and other drugs i n combination, lymphocytes were pulse labeled with [H-3] leucine or [P -32] phosphate. The nuclei were isolated from lymphocytes and collecte d from partitions of the cell cycle, and the proteins analyzed from fl uorographs following gel electrophoresis for protein biomarkers after drug exposure. Stress proteins (sps) were dependent on a specific drug or drugs in combination (i.e., interleukin-2, bleomycin) for their sy nthesis that occurred only during the G(1)-phase of the cell cycle. An ''actin-like'' protein (A(4)) With electrophoretic mobilities similar to the actin complex, was synthesized in S and G(2) phases and phosph orylated in all phases of the cell cycle only following the administra tion of drugs in combination. A(4) exhibited a binding affinity for sp 24 that was cell cycle regulated (i.e., A(4) from S phase did not bin d with sp 24, but A(4) from G(2) phase did bind with the sp. Protein A (4) appeared similar in some structural aspects to the nonmuscular act in isoform family but differed in epitope, suggesting a unique relatio nship and represented a stable protein, perhaps a product from the mut ation of an actin gene. The dependence of certain sps and protein A(4) for their induction by drugs in combination may serve as biomarkers o f chemical interaction and toxicity.