Targeting ISG15 and USP18

Division Of Basic Sciences - Nci

Investigators

Linked publications, trials & patents

Abstract

USP18 is the only ISG15-specific protease identified to date although several DUBs have been reported to be cross-reactivity with ISG15 in vitro, such as USP2, USP14 and USP21. We are screening combinatorial peptide libraries and using computational modeling to develop ISG15-based probes that can distinguish closely related ISG15-reactive DUBs. ISG15 probes are generated by solid-phase peptide synthesis and native chemical ligation and conjugated with fluorescent- and affinity tags to profile USP18 and other deISGylase activity in various cell types and physiologic states. This will not only allow us to elucidate the molecular and structural basis of specificity and kinetics, and cellular context of USP18 activity but also provide useful reagents for inhibitor screening. We are also developing selective small molecule inhibitors of USP18. We have developed and optimized a biochemical assay that is suitable for high-throughput screening to identify catalytic inhibitors of USP18. We are currently screening NCI's vast natural product library that encompasses structurally and functionally diverse chemical entities. Simultaneously, we are computationally screening virtual libraries of small molecules and performing small molecule microarray screens to identify druglike molecules that bind to USP18. Hit molecules will be validated in functional assays that probe protein ISGylation and IFN pathways. Once validated, probes will be used to define USP18's role in cancer development and its therapeutic potential.