BLEOMYCIN INDUCES APOPTOSIS IN HUMAN ALVEOLAR MACROPHAGES

Bleomycin (BLM) is an effective antineoplastic drug; however, cumulati ve dosage is often associated with inflammation that can progress to p ulmonary fibrosis. The mechanisms by which this occurs are not underst ood, but they have been proposed to involve the alveolar macrophage (A M). In this study, we examined the in vitro effects of BLM on human AM cytotoxicity and the role of heat shock proteins (HSP or stress prote ins) in this process. Although BLM did not cause marked necrosis, it c aused significant DNA fragmentation detected by in situ DNA labeling a nd confirmed by BLM-induced DNA ladder formation after 24 h. The DNA f ragmentation was significantly blocked by 10 and 50 mu M ZnCl2, sugges ting that BLM was inducing apoptosis. BLM did not alter intracellular protooncogene bcl-2 or glutathione levels. However, BLM significantly (50%) blocked HSP-72 expression by 4 h during a mild heat stress (39.8 degrees C). This inhibition occurs without affecting mRNA levels (in situ hybridization) for HSP-72 or overall protein synthesis ([S-35]met hionine incorporation), suggesting that BLM is blocking the stress res ponse relatively specifically and post-transcriptionally. In summary, these results suggest that BLM causes apoptosis in human AM in vitro t hat is preceded by the inhibition of HSP-72 induction that appears to be caused by a posttranscriptional mechanism.