NSAID-Induced Apoptosis in Rous Sarcoma Virus-Transformed Chicken Embryo Fibroblasts is Dependent on v-src and c-myc and is Inhibited by bcl-2

Mounting epidemiological and experimental evidence implicates nonsteroidal antiinflammatory drugs as anti-tumorigenic agents. Our previous work showed that nonsteroidal antiinflammatory drug treatment of src-transformed chicken embryo fibroblasts caused apoptosis -- a mechanism by which these drugs might exert their anti-tumorigenic effect. The present studies employ a sensitive technique for detecting single- and double-stranded DNA cleavage (the comet assay) to quantitate apoptosis. By this method pp60^v-src, which antagonizes apoptosis in many cell systems, was found to induce apoptosis in 11–23% of serum-starved fibroblasts. However, treatment with diclofenac following pp60^v-src activation produced a much stronger response beginning within 6 hours of treatment that resulted in 100% lethality. During cell death, cyclooxygenase-2 but not cyclooxygenase-1 mRNA was found to be uniformly increased by all apoptotic drugs tested.

Examination of the expression of apoptosis-associated genes showed that c-rel and p53 (found in normal or v-src-transformed chicken embryo fibroblasts at moderate levels), and bcl-2 (present at an extremely low level) were largely unchanged by treatment with eight different nonsteroidal antiinflammatory drugs. However, over-expression of human bcl-2 inhibited diclofenac-mediated apoptosis by 90%, demonstrating directly that bcl-2 expression can regulate nonsteroidal antiinflammatory drug induction of cell death.

The proto-oncogene c-myc is known to cause apoptosis in chicken embryo fibroblasts when artificially overexpressed in cells deprived of trophic factors. We found that nonsteroidal antiinflammatory drug treatment following pp60^v-src activation persistently induced myc protein and mRNA by more than 20-fold above that evoked by pp60^v-src activation alone. Moreover, transfection of antisense c-myc oligonucleotides reduced drug-induced myc expression by 80% and caused a concomitant 50% reduction in cell death. These findings suggest that nonsteroidal antiinflammatory drug-induced apoptosis proceeds through a src/myc dependent pathway which is negatively regulated by bcl-2.