Molecular mechanisms underlying the effects of the small molecule AMC-04 on apoptosis: Roles of the activating transcription factor 4-C/EBP homologous protein-death receptor 5 pathway

The unfolded protein response (UPR) is an emerging target pathway for Cancer treatment owing to its ability to induce cell death. In our previous analysis of UPR-modulating small molecules, we had reported that piperazine oxalate derivative compounds (AMC-01-04) are able to promote increased phosphorylation of eukaryotic translation initiation factor-2 alpha (eIF2α). In this study, we found that AMC-04 induces apoptotic cell death via the activation of UPR in human breast and liver Cancer cells. AMC-04 upregulated the expression of activating transcription factor-4 (ATF4)-C/EBP homologous protein (CHOP) and Death Receptor 5 (DR5) in Cancer cells, as revealed by microarray analysis, small-interference RNA assay, and western blotting. From a mechanistic perspective, cytotoxic UPR pathway activation by AMC-04 is mediated by Reactive Oxygen Species (ROS) and p38 mitogen-activated protein kinase (p38 MAPK) signaling. A chemical informatics approach predicted that AMC-04 modulates Histone Methyltransferase activity. Based on biochemical analysis, the activity of histone methyltransferases, including SUV39H1, SUV39H2, SETDB1, and EHMT1, was inhibited by AMC-04. Furthermore, chemical inhibition of the identified target proteins induced UPR activation and apoptotic cell death, suggesting that inhibition of histone methyltransferases is a promising strategy for Cancer therapy. Taken together, we showed that the small molecule AMC-04 modulates epigenetic Enzyme activity and mediates the link between cytotoxic UPR and histone modifications.

C/EBP homologous Protein; Death receptor-5; Histone methyl transferase; Human cancer cell; Reactive oxygen species; Unfolded protein response.