Protein methyltransferases orchestrate epigenetic pathways through diverse posttranslational methylation. The reaction is carried out by protein lysine methyltransferases (PKMTs) through transferring the methyl group of SAM (S-adenosyl-L- methionine) to specific lysine(s) of substrates. The errors in the process have been implicated in many cancers. Accumulated evidence indicated that epigenetic diversity requires PKMTs to methylate histones and nonhistone proteins. However, few tools are available to unambiguously profile the nonhistone targets of designated PKMTs, particularly in context of proliferating cancer cells. In addition, few PKMT inhibitors are available to disrupt PKMT functions. Such situations significantly hinder our capability to develop cancer-therapeutic strategies with the PKMTs as novel targets. Our long-term goal is to elucidate and manipulate the biological functions of PKMT for cancer diagnosis and treatment. The objective of this proposal is to develop novel technologies and apply them to identify protein targets and small-molecule inhibitors of a cancer-relevant PKMT. Knowing the targets of the PKMT will be a key step toward fully understanding the epigenetic functions of the PKMT. More importantly, the inhibitors of the PKMT can be examined for their cancer-therapeutic effects. To profile the targets of the PKMT, we envision that the enzyme can be engineered to utilize SAM analogue cofactors and thus label its targets with distinct chemical groups. The distinct modifications will then be recognized by respective reporters. Meanwhile, a novel high-throughput screening approach will be implemented to identify the inhibitors of the PKMT. The impact of our target-profiling and inhibitor-identifying methods is further strengthened by their general applicability to other PKMTs.
This proposal is expected to advance the understanding of how disrupting protein methylation affects cancer cell proliferation, and manipulate the process pharmacologically for cancer therapy. In a broad manner, the target-profiling technology proposed here will allow the comparison of the methylation profiles in normal versus cancerous cells or in non-aggressive versus aggressive cancers. This proposal further establishes the feasibility to identify methyltransferase inhibitors as potential cancer-therapeutic reagents.
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