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

Abstract

Administration of phytohemagglutinin initiated cycling of rat lymphocytes in vitro, and following treatment with this drug and other drugs in combination, lymphocytes were pulse labeled with [ 3H] leucine or [ 32P] phosphate. The nuclei were isolated from lymphocytes and collected from partitions of the cell cycle, and the proteins analyzed from fluorographs 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 synthesis 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 phosphorylated in all phases of the cell cycle only following the administration 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 bind 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 actin isoform family but differed in epitope, suggesting a unique relationship and represented a stable protein, perhaps a product from the mutation of an actin gene. The dependence of certain sps and protein A 4 for their induction by drugs in combination may serve as biomarkers of chemical interaction and toxicity.