Histone hypoacetylation is involved in 1,10-phenanthroline-Cu2+-induced human hepatoma cell apoptosis.

The 1,10-orthophenanthroline (OP)-Cu(2+) combination, one generally used reactive oxygen species (ROS) generation system, is known to induce cell apoptosis, but the mechanism of ROS generation in this process remains unclear. Here we found that in the presence of 5 microM Cu(2+), OP inhibited histone acetyltransferase (HAT) activity, resulting in decreased acetylation in both histone H3 and H4. This inhibition of histone acetylation and HAT activity was significantly attenuated by preventing or scavenging ROS generation with the Cu(2+) chelator of bathocuproine disulfonate, or the antioxidants of N-acetyl-cysteine and mannitol, respectively, indicating the involvement of ROS generation in OP-Cu(2+) -induced histone hypoacetylation. At the same time, this ROS generation is found to be involved in OP-Cu(2+) -induced apoptosis in human hepatoma Hep3B cells. The important role of histone hypoacetylation in the induction of apoptosis was also proven by the marked diminution of apoptosis by 100 nM trichostatin A, a specific inhibitor of histone deacetylase, or the overexpression of p300, an HAT protein. Collectively, these observations suggest that histone hypoacetylation represents one unrevealed mechanism involved in the in vivo function of OP-Cu(2+) -generated ROS, at least in their induction of cell apoptosis.