UC San Diego

Histone modifications play significant roles in many cellular processes, including cell cycle control, cancer, senescence, X-inactivation, cell fate decisions, and stem cell differentiation.[44] H3 lysine 27 trimethylation is a repressive histone modification regulated by methyltransferase enzyme EZH2 and demethylases KDM6.Previous research shows that staurosporine resulted in the cleavage of caspase-3, decrease of cell viability and decrease of histone H3 lysine 27 trimethylation (H3K27me3)[1]. However, this process has not been visualized in living cells and the mechanism of caspase-3 substrate proteins that lead to the H3K27me3 decline have not been fully specified yet. In this paper, we monitored the dynamics of H3K27me3 and caspase-3 in HeLa cells via engineered caspase-3 NES FRET biosensor and H3k27me3 FRET biosensor. Imaging results intuitively revealed the dynamic decrease of H3K27me3 as a consequence of caspase-3 activation, which is consistent with previous findings. Caspase-6 and lamin A were the downstream proteins of caspase-3 involved in this process and by inhibiting caspase-6, the un-cleaved lamin A accelerated the decline of H3K27me3 during apoptosis. We hypothesize that caspase-3 activation induces the downregulation of EZH2 and the upregulation of KDM6, which ultimately leads to the diminish of H3K27 tri-methylation. Furthermore, the lack of lamin A disrupts the heterochromatin-lamina interaction, leading to the reduced accessibility of H3K27me3 by KDM6 and therefore a decreased

rate of demethylation.