Bleomycin-induced DNA damage and repair in human cells permeabilized with lysophosphatidylcholine.

We have examined bleomycin-induced DNA damage and repair in confluent human fibroblasts that were reversibly permeabilized to small molecules (e.g., deoxynucleotide triphosphates and trypan blue) by a short exposure to 80 micrograms/ml lysophosphatidylcholine. We found that this treatment dramatically increases the dose effectiveness of bleomycin in inducing DNA strand breaks and DNA repair synthesis in these cells. For example, when intact cells (not treated with lysophosphatidylcholine) were incubated with 100 micrograms/ml bleomycin, only about 5% of the cell population was observed to have undergone measurable DNA repair synthesis (by autoradiography). On the other hand, when these cells were reversibly permeabilized with lysophosphatidylcholine before treatment, we observed significant repair synthesis in greater than 80% of the cells using a bleomycin dose of only 5 micrograms/ml. Furthermore, sufficient levels of single- and double-strand breaks were introduced into nucleosome linker DNA of permeabilized cells to yield a nucleosomal repeat pattern in alkaline and neutral agarose gels. However, no change in the amount of DNA less than 23 kilobases was observed on these gels when intact cells were incubated with bleomycin.