INDUCTION OF CASPASE-3 PROTEASE ACTIVITY AND APOPTOSIS BY BUTYRATE AND TRICHOSTATIN-A (INHIBITORS OF HISTONE DEACETYLASE) - DEPENDENCE ON PROTEIN-SYNTHESIS AND SYNERGY WITH A MITOCHIONDRIAL CYTOCHROME C-DEPENDENT PATHWAY

The induction of apoptosis of tumor cells by the colonic fermentation product butyrate is thought to be an important mechanism in protection against colorectal cancer. Because a major action of butyrate is to i nhibit histone deacetylase (leading to chromatin relaxation and altere d gene expression), butyrate mag induce apoptosis by derepression of s pecific cell death genes. Here we show that butyrate and trichostatin A (a more selective inhibitor of histone deacetylase) induce the same program of apoptosis in Jurkat lymphoid and LIM 1215 colorectal cancer cell lines that is strictly dependent on new protein synthesis (withi n 10 h) and that leads to the conversion of the proenzyme form of casp ase-3 to the catalytically active effector protease (within 16 h) and apoptotic death (within 24 h). Cells primed with a low concentration o f butyrate that itself did not induce activation of caspase-3 or apopt osis were, nevertheless, rendered highly susceptible to induction of a poptosis by staurosporine (an agent that has recently been shown to ac t by causing mitochondrial release of cytochrome c). Synergy between b utyrate and staurosporine was due to the presence of a factor in the c ytosol of butyrate-primed cells which enhanced over 7-fold the activat ion of caspase-3 induced by the addition of cytochrome c and dATP to i solated cytosol. We propose that changes at the level of chromatin str ucture, induced by a physiological substance butyrate, lead to the exp ression of a protein that facilitates the pathway by which mitochondri a activate caspase-3 and trigger apoptotic death of lymphoid and color ectal cancer cells.