Molecular changes associated with induction of cell death in a human T-cell leukaemia line: Putative nucleases identified as histones

Following treatment of the human T-cell leukaemia line, CEM-C7, with the glucocorticoid, dexamethasone, a rapid decrease in viability occurred after 40 h which coincided with fragmentation of DNA in these cells. A similar pattern of DNA fragmentation was observed when these cells were γ-irradiated or treated with cycloheximide. Distinct morphological changes occurred after treatment, indicating a form of cell death, regulated from within, termed apoptosis. A set of nuclear proteins ranging in size from 10–18 kDa appeared by 40 h following treatment with dexamethasone. Treatment of cells with γ-irradiation or cycloheximide also produced the same protein pattern. This set of proteins, and a doublet approximately 55 kDa in size, had apparent nuclease activity which was not observed in untreated cells. However, protein microsequencing of these bands in the 10–18 kDa region revealed that they were histone proteins. These results cast doubt on a recent report which provided evidence that these proteins were induced nucleases.