Abstract
Histone H3 is a nucleosome scaffold protein that is involved in a variety of intracellular processes. Aberrant modification of H3 is important in carcinogenesis. In contrast, free histones in cells can act as stimuli to trigger cellular immune responses and cell death. In this study, we linked cell-penetrating peptide HIV Tat to a histone H3 fragment to achieve intracellular delivery in tumor cells. We found that Tat-conjugated histone polypeptides localized to nuclei of lung and breast cancer cells and caused cell death. A trans-configured Tat sequence displayed dramatically improved peptide half-life and cytotoxicity. Mechanistic studies demonstrated that treatment with the peptides significantly elevated mitogen-activated protein kinase (MAPK) signaling, reactive oxygen species (ROS) production, as well as levels of stress-inducible transcription factor ATF3 (activating transcription factor 3) and AP-1 (activating protein-1). Cytotoxicity of the peptide was significantly reduced by inhibition of AP-1 activity and ROS production. These results suggest the potential of Tat-conjugated H3 peptides as antitumor agents to induce cell death via increased cellular stress response by activating p38-MAPK signaling and intracellular ROS production.