Immunological detection of DNA-protein complexes induced by chromate

A select group of non-histone proteins becomes complexed to DNA after Chinese hamster ovary (CHO) cells are treated with potassium chromate. The most abundant complexed protein has a mol. wt of approximately 45 kd and is thought to be actin. An antiserum to the chromate-induced DNA-protein complexes (DPCs) was prepared to facilitate the study of these complexes. Rather than detecting the predominant silver-stained proteins of DPCs described in an earlier study, this antiserum reacts primarily with an acidic 95-kd protein (p95) that does not silver stain. The antiserum can be used routinely to assay for the induction of p95-DNA complexes produced by chromate and perhaps by other carcinogens. Immunofluorescent staining of CHO cells and immunoblotting of cell fractions show the reactive antigens are within the cell nucleus. Blotting experiments with the antiserum indicate the chromate-induced p95-DNA complex dissociates in the presence of 2-mercaptoethanol, suggesting similarity to the DPCs formed by carcinogenic platinum compounds. A reduced species of chromium (probably Cr3+) may form DPCs by binding to the nitrogen, oxygen or sulfur atoms of proteins and DNA. These results illustrate the usefulness of immunological detection methods to study specific DNA-protein interactions induced by carcinogens. The possible relevance of DPCs in the carcinogenic process is discussed.