Changes in Histone Code Regulation during the Initiation of Paraptosis-Like Death of HEp-2 Tumor Cells by Oxidized Disulfiram Derivatives

Disulfiram (DSF) and its oxidized derivatives (DSFoxy) are currently being investigated as potential anticancer agents. We previously found that DSFoxy initiate the paraptosis-like death of tumor cells, which is of potential interest for the treatment of tumors resistant to the initiation of apoptosis. Based on bioinformatics analysis of mass spectrometric data on protein ubiquitination, we formulated a conception about the important role of disruption of the retrograde transport of damaged proteins from the endoplasmic reticulum to the cytosol in the mechanism of initiation of paraptosis-like cell death. In the present work, it has been found that DSFoxy, in the process of initiating paraptosis-like death of human adenocarcinoma HEp-2 cells, also enhances the ubiquitination of histones and histone code enzymes. In particular, this applies to the ubiquitination of histone H2BC12, histone methyltransferases responsible for transcription and repair of damaged DNA, as well as acetylating and ubiquitin-conjugating proteins. Bioinformatics analysis of changes in ubiquitination of cell nuclear proteins using the STRING database revealed during this process an increase in the occurrence of ubiquitinated proteins (functional enrichment) of cell cycle regulation, cell response to DNA damage and DNA repair, the regulation of which also depends on the histone code. This directly indicates damage to the cell nucleus and is consistent with confocal microscopy data. These results indicate that paraptosis-like death initiated by DSFoxy is accompanied, along with impairment of retrograde transport and ER stress, also by a change in regulation of the histone code, which points to a pleiotropic mechanism of cell death induction.