Bleomycin induces apoptosis in human alveolar macrophages in vitro;
inhibition of heat shock protein 72 induction is an early indicator
of cell injury.
Hamilton, Raymond F., Jr, Li Li, Tyrone B. Felder, and Andrij Holian.
Division of Pulmonary and Critical Care Medicine, Departments of
Internal Medicine and Pharmacology, Toxicology Program, University of
Texas Medical School, Houston, Texas 77030
APStracts 2:0092L, 1995.
Bleomycin (BLM) is an effective antineoplastic drug, however
cumulative dosage is often associated with inflammation that can
progress to pulmonary fibrosis. The mechanisms by which this occurs
is not understood, but it has been proposed to involve the alveolar
macrophage (AM). I this study, we examined the in vitro effects of
BLM on human AM cytotoxicity and the role of heat shock proteins (HSP
or stress proteins) in this process. While BLM did not cause marked
necrosis, it caused significant DNA fragmentation detected by in situ
DNA labelling and confirmed by BLM-induced DNA ladder formation,
after 24 hours. The DNA fragmentation was significantly blocked by 10
and 50 [mu]M ZnCl2, suggesting that BLM was inducing apoptosis. BLM
did not alter intracellular bcl-2 or GSH levels. However, BLM
significantly (50%) blocked HSP72 expression by 4 hours during a mild
heat stress (39.8 C). This inhibition occurs without affecting mRNA
levels (in situ hybridization) for HSP72 or overall protein synthesis
(35S-methionine incorporation), suggesting that BLM is blocking the
stress response relatively specifically and post-transcriptionally.
In summary, these results suggest that BLM causes apoptosis in human
AM in vitro that is preceded by the inhibition of HSP72 induction
that appears to be by a post-transcriptional mechanism.
Received 1 February 1995; accepted in final form 19 April 1995.
APS Manuscript Number L32-5.
Article publication pending Am. J. Physiol. (Lung Cell. Mol.
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 May 1995.