Nuclear matrix antigens in azo dye-induced primary rat hepatomas

Polyvalent antisera, monoclonal antibodies, and immunotransfer methodology have been used to identify and characterize a group of chromosomal protein antigens which appear during azo dye hepatocarcinogenesis. Experiments were designed to probe for the location and placement of antigens in chromatin according to solubility and possible DNA-binding properties. The majority of nuclear antigens were associated with high-speed DNA-containing pellets after ultracentrifugation of chromatin solubilized with denaturing buffers containing 6 M guanidine-HCl:2% sodium dodecyl sulfate, or 2 M NaCl:5 M urea. The addition of 2-mercaptoethanol or dithiothreitol to guanidine-HCl or sodium dodecyl sulfate solutions resulted in solubilization of nearly all antigens from the DNA pellets, suggesting the presence of complexes (protein:protein and/or DNA:protein) cross-linked with sulfhydryl linkages. Preparation of nuclear matrix from the primary hepatomas under several kinds of conditions indicated these antigens to be components of the residual nuclear matrix, envelope, and/or associated structures. Two-dimensional gel analysis showed most antigens to exist in a range of isoelectric forms, suggesting posttranslational modifications. Studies with monoclonal antibodies prepared to these proteins revealed extensive antigenic homology among the members comprising these fractions. Our results document antigenic differences in the nuclear matrix proteins of primary tumors and their normal tissue counterparts.