Activity-Based Imaging Probes of the Proteasome

Abstract

Over the years, the proteasome has been extensively investigated due to its crucial roles in many important signaling pathways and its implications in diseases. Two proteasome inhibitors—bortezomib and carfilzomib—have received FDA approval for the treatment of multiple myeloma, thereby validating the proteasome as a chemotherapeutic target. As a result, further research efforts have been focused on dissecting the complex biology of the proteasome to gain the insight required for developing next-generation proteasome inhibitors. It is clear that chemical probes have made significant contributions to these efforts, mostly by functioning as inhibitors that selectively block the catalytic activity of proteasomes. Analogues of these inhibitors are now providing additional tools for visualization of catalytically active proteasome subunits, several of which allow real-time monitoring of proteasome activity in living cells as well as in in vivo settings. These imaging probes will provide powerful tools for assessing the efficacy of proteasome inhibitors in clinical settings. In this review, we will focus on the recent efforts towards developing imaging probes of proteasomes, including the latest developments in immunoproteasome-selective imaging probes.

Androgen receptor polyglutamine expansion drives age-dependent quality control defects and muscle dysfunction

“…To test the functional status of the proteasome, we employed the activity-based probe Me 4 BodipyFL-Ahx 3 Leu 3 VS. This fluorescent probe binds the active site of catalytic proteasome subunits, allowing detection of changes in constitutive proteasome subunits as well as induction of the immunoproteasome (38,39). We initially confirmed that signal in this assay is inhibited by MG132, a small molecule that similarly binds catalytic sites to inhibit proteasome activity and thereby competes for binding by the activity-based probe (Supplemental Figure 6).…”

Monitoring Target Engagement of Deubiquitylating Enzymes Using Activity Probes: Past, Present, and Future

“…Probably one of the most promising avenues for developing cell-and tissue-permeable selective ubiquitin ABPs for DUBs will rely on the modifi cation of selective small molecule inhibitors of DUBs . Similar approaches have already achieved some preliminary success for other enzymes of the UPS such as E1 enzymes [ 95 ] and proteasome probes [ 96 ]. The limiting step in developing such probes for DUBs is currently a lack of potent, specifi c and selective DUB inhibitors available, however, the community is successfully designing novel generations of selective DUB inhibitors.…”

Activity‐Based Protein Profiling: Recent Advances in Probe Development and Applications

“…Therefore, many of the best examples of ABPs have been designed to target hydrolases, such as fluorophosphonate probes (1) for serine hydrolases [10] and epoxide and AOMK probes for cysteine proteases (2, 3), [11] which have a reactive nucleophilic residue in the active site and possess a distinct catalytic mechanism. [12] Other such directed ABPs includes probes targeting cathepsins, legumains, [13] caspases, [14] protein arginine methyltransferases (4), [15] proteasomal proteases (5), [16] kinases (6), [17] tyrosine phosphatase, [18] serine/threonine phosphatase, [19] and glycosidases. [20] It may be expected that the design of ABPs for enzyme classes with known covalent inhibitors is, at least in concept, straightforward.…”