Bisindolylmaleimides (Bis) were originally described as
protein kinase C inhibitors. Several studies have shown that Bis potentiate
tumor necrosis factor (
TNF) receptor family-mediated apoptosis in lymphoid and dendritic cells, but the inhibition of
protein kinase C cannot account for these effects (Zhou, T., Song, L., Yang, P., Wang, Z., Lui, D., and Jope, R. S. (1999)
Nat. Med. 5, 42-48). We investigated the effect of four Bis derivatives (I, II, VIII, and IX) in human prostatic
carcinoma cell lines and found that
Bis IX was the most potent inducer of apoptosis under simultaneous treatment with
TNF-alpha, agonistic
anti-Fas monoclonal antibody, and
TNF-related apoptosis-inducing ligand (TRAIL).
Bis IX synergistically induced
caspase activity in combination with apoptosis-inducing
ligands and converted the phenotype of cell lines from apoptosis-resistant to -sensitive.
Bis IX induced p53 accumulation in LNCaP (lymph node
carcinoma of prostate), which expresses wild-type p53 that was not accompanied by the induction of p53-responsive genes, p21/WAF1, and Mdm2. Moreover, the induction of p21/WAF1 and Mdm2 by
doxorubicin was abrogated by simultaneous treatment with
Bis IX. These effects apparently result from general inhibition of transcription by
Bis IX. We have shown by Northern blot analysis that the transcription activity of the
hygromycin gene after transient transfection of pcDNA3.1-Hygro plasmid in 293 and HeLa cells was inhibited by
Bis IX in a dose-dependent manner. Moreover,
DNA binding activity of
Bis IX was prevented by
actinomycin D, suggesting that
actinomycin D and
Bis IX have similar mechanisms of interaction with
DNA. In addition, we found that
actinomycin D and
Bis IX induced
caspase activity to the same extent during TRAIL-mediated apoptosis. In summary, these results suggest that
Bis IX potentiates
TNF receptor family-mediated cell death in part as an inhibitor of transcription.