Radiation-induced association of beta-glucuronidase with purified nuclei from irradiated MOLT-4 and HeLa cells

Beta-glucuronidase, a lysosomal marker enzyme, associates with purified nuclei from HeLa and MOLT-4 cell lines in a radiation dose-dependent manner, up to 300 cGy in MOLT-4 cells, and 1000 cGy in HeLa cells. In MOLT-4 cells (200-cGy exposure), there is a significant increase in beta-glucuronidase activity detected in the nuclear fraction 24 h postirradiation with a maximum association occurring at 72 h. In HeLa cells (1000-cGy exposure), a significant association is first detected 24 h postirradiation with a maximum association at 48 h. The association is not the result of nonspecific contamination occurring during nuclei purification since nuclei from irradiated cells show no greater levels of plasma membrane marker and mitochondrial marker than controls. The nature of the association remains unclear, but activity is not removed by detergents used in the nuclei isolation procedure, and incubation of the nuclei with EDTA reverses the association only modestly. Exposure of nuclei from irradiated cells to anisotonic buffers also results in only a small decrease in beta-glucuronidase activity associated with the nuclei. These observations suggest that lysosomal hydrolases become intimately associated with the nuclei of irradiated cells.