Uncoupling of apoptosis and Jun/AP-1 activity in human promonocytic cells treated with DNA-damaging and stress-inducing agents

Abstract

Earlier studies have indicated that Jun/AP-1 activity is associated with, and probably required for apoptosis induction by DNA-damaging and stress-inducing agents in human myeloid cells. To investigate this possibility, we examined the capacity of continuous treatments with etoposide (10 μM) and camptothecin (0.4 μM), and pulse treatments with X-rays (20 Gy), heat (2 h at 42.5°C) and cadmium chloride (2 h at 200 μM) followed by recovery, to provoke apoptosis and to simulate c-jun and c-fos expression and AP-1 binding in U-937 human promonocytic cells. All these treatments generated apoptosis with similar efficacy (50-60% apoptotic cells at 6 h of treatment or recovery). However, the capacity to increase c-jun and c-fos mRNA levels and to stimulate AP-1 binding was very different, ranging from more than a twelve-fold increase in the case of cadmium, to almost no increase in the case of heat-shock and etoposide. When the cells were pre-conditioned with a soft heat shock (1 h at 42°C) the cadmium-provoked apoptosis was greatly inhibited, but the stimulation of AP-1 binding was not affected. The administration of cAMP-increasing agents also reduced the etoposide- and cadmium-provoked apoptosis. However, cAMP greatly stimulated c-jun and c-fos expression and AP-1 binding when applied together with etoposide (which itself was ineffective), and potentiated the cadmium-induced AP-1 binding. Conversely, retinoic acid abrogated the cadmium-provoked stimulation of AP-1 binding and transactivation capacity, and greatly inhibited the stimulation of binding caused by camptothecin and X-rays. However, retinoic acid did not inhibit the induction of apoptosis by these agents. These results indicate that Jun/AP-1 activity is not necessarily coupled with apoptosis, nor required for apoptosis induction by DNA-damaging and stress-inducing agents in human promonocytic cells.