Inhibitors of histone deacetylases alter kinetochore assembly by disrupting pericentromeric heterochromatin.

The kinetochore, a multi-protein complex assembled on centromeric chromatin in mitosis, is essential for sister chromosome segregation. We show here that inhibition of histone deacetylation blocks mitotic progression at prometaphase in two human tumor cell lines by interfering with kinetochore assembly. Decreased amounts of hBUB1, CENP-F and the motor protein CENP-E were present on kinetochores of treated cells. These kinetochores failed to nucleate and inefficiently captured microtubules, resulting in activation of the mitotic checkpoint. Addition of histone deacetylase inhibitors prior to the end of S-phase resulted in decreased HP1-beta on pericentromeric heterochromatin in S-phase and G(2), decreased pericentromeric targeting of Aurora B kinase, resulting in decreased premitotic phosphorylation of pericentromeric histone H3(S10) in G(2), followed by assembly of deficient kinetochores in M-phase. HP1-beta, Aurora B and the affected kinetochore proteins all were present at normal levels in treated cells; thus, effects of the inhibitors on mitotic progression do not seem to reflect changes in gene expression. In vitro kinase activity of Aurora B isolated from treated cells was unaffected. We propose that the increased presence in pericentromeric heterochromatin of histone H3 acetylated at K9 is responsible for the mitotic defects resulting from inhibition of histone deacetylation.