Etoposide and cisplatin induced apoptosis in activated RAW 264.7 macrophages is attenuated by cAMP-induced gene expression.

Previous observations suggest expression of cyclooxygenase-2 to convey macrophage protection towards apoptotic cell death. We reasoned prostaglandin formation and in turn a cAMP increase as the underlying protective principle. Here we report that exposure of macrophages to lipopolysaccharide/interferon-gamma or lipophilic cAMP analogs such as dibutyryl-cAMP or 8-bromo-cAMP for 15 h attenuated DNA fragmentation and accumulation of the tumor suppressor p53 in response to the chemotherapeutic agents cisplatin and etoposide, compared to cells that received chemotherapeutic agents only. In contrast, a 1 h lasting preexposure period revealed no protection. The demand for a long incubation period with cAMP-derivates implied cAMP-mediated gene activation as the underlying principle. Therefore, we treated cells with oligonucleotides containing a cAMP-response element (CRE) binding site. Using this decoy-approach we scavaged activated cAMP response element binding protein prior to its promoter activating ability. Incubating macrophages with decoy, but not with control oligonucleotides, reduced cAMP evoked protection and simultaneously restored p53 accumulation in response to chemotherapeutic agents. Our studies demonstrate that cAMP-initiated gene activation regulates the sensitivity towards DNA damaging agents via inhibition of a p53 dependent pathway.