Poly(ADP-ribose) polymerase activity in proliferating and quiescent murine mammary carcinoma cells

Previous studies have shown that the well-oxygenated but nutrient-deprived quiescent (QI) cells of the 67 murine mammary carcinoma line are significantly more sensitive to radiation-induced cell killing than the well-oxygenated proliferating (P) cells. These QI cells also sustain more initial strand breaks per radiation dose and repair them more slowly than do P cells. We now report that NAD+ levels and rates of poly(ADP-ribosylation) show a trend similar in that both these metabolic parameters are lower in QI cells by a factor of two or more. NAD+ levels were measured in acid extracts of intact monolayers using an enzymatic cycling assay, while poly(ADP-ribosylation) was followed through the incorporation of radioactive NAD+ into polymer by permeabilized cells. The major proteins labeled by [32P]NAD+ were the same in P and QI cells. However, qualitative differences exist among minor poly(ADP-ribosylated) proteins, with some bands labeled in P cells but not detectably labeled in QI cells. These studies suggest similarities between the physiological state of QI cells and that of mature resting lymphocytes.