ChemicalProteomic Profiling of the HistaminylationProteome in Cancer Cells Unveils Uncharted Epigenetic Marks on CoreHistones

Abstract Histamine is a key signaling molecule in pathophysiology that can exhibit significant regulatory roles in diverse health and disease states. Besides the well-studied noncovalent interactions between histamine and its receptors, protein histaminylation is a recently discovered mechanism of action through which histamine regulates cellular signaling pathways in a covalent modification manner. Histaminylation is an emerging protein post-translational modification (PTM), where an isopeptide bond is formed between the histamine primary amine and the γ-carboxyl group of glutamine through a transamidation reaction catalyzed by transglutaminase 2 (TGM2). However, due to the lack of efficient pan-specific antibodies targeting histaminylated glutamine, the histaminylation proteome in cells remains poorly explored. Here, we report the design and development of a novel Nτ-propargylated histamine (Nτ-PH) probe as well as its successful application in chemical proteomic profiling of the histaminylation proteome in cancer cells. Notably, new TGM2-catalyzed epigenetic marks on core histones, e.g., H2AX-Q84 and Q104 histaminylation, have been identified from cancer cells and verified. Lastly, the crosstalk between H2AX histaminylation and γH2AX formation was discovered in this study, suggesting that TGM2-mediated histaminylation plays a critical role in DNA damage responses.