Trypsin-induced Changes in Cell Shape and Chromatin Structure Result in Radiosensitization of Monolayer Chinese Hamster V79 Cells

Summary

Trypsin is the enzyme commonly used to prepare single cell suspensions from monolayer and spheroid cultures, both to determine survival and to assay DNA damage. Trypsin induces rounding, dissociation and radiosensitization of anchorage-dependent cells. Radiosensitivity and chromatin structure were compared between trypsin-treated (0·05%) round V79 cells from monolayers and spheroids vs. untreated spread monolayer cells in situ. The fluorescent halo technique was used to measure the changes in DNA supercoiling in nucleoids isolated from control and irradiated round and spread cells. Maximal halo diameters, the amount of initial and residual radiation-induced DNA damage (estimated from nucleoid halo diameter changes), and the radiosensitivity were higher in round cells than in spread monolayer V79 cells. The effects on cellular radiosensitivity and maximal halo diameter of other agents which also round and dissociate cells, e.g. 0·25% trypsin, pronase E and a non-enzymatic cell-dissociation solution, were similar to those of 0·05% trypsin. In LY-S cells, which are anchorage-independent, DNA loop size, the initial amount of DNA damage and radiosensitivity were not affected by trypsin. We suggest that the higher radiosensitivity of anchorage-dependent cells under immediate trypsinization and plating conditions, compared to cells with postirradiation in situ repair incubation, is due to correlated changes in cell shape and chromatin structure.