Our assay relies on accumulation of UbG76V GFP using the rap idly reversible proteasome inhibitor MG132. MG132 is then removed and the decay of the pre accumulated these UbG76V GFP signal is monitored Inhibitors,Modulators,Libraries in the presence of the protein synthesis inhibitor cycloheximide. To evaluate spe cificity, we monitor degradation of an ODD luciferase chimera. p97 is not required for ODD luciferase degradation, and hence p97 inhibitors stabilize UbG76V GFP but not ODD luciferase. By this criter ion, DBeQ was identified Inhibitors,Modulators,Libraries as a selective p97 inhibitor and is the first selective inhibitor of an AAA ATPase activity. Structure activity relationships analysis of DBeQ iden tified the more potent derviatives ML240 and ML241.
Inhibitors,Modulators,Libraries Whereas all three compounds stabilize UbG76V GFP, cause accumulation of ubiquitin conjugates, and inhibit degradation of an ERAD substrate, DBeQ and ML240 also cause accumulation of LC3 II and induce rapid cell death, whereas ML241 does not. The basis for this different be havior remains unclear. NMS859 and NMS873, arose from a high throughput screen for p97 ATPase inhibitors followed by a structure activity relationships analysis. Of par ticular interest is NMS873, which is a reversible, allosteric inhibitor Inhibitors,Modulators,Libraries of p97 ATPase. It is the most potent p97 ATPase inhibitor reported to date, with an IC50 of approximately 30 nM. Similar to DBeQ, NMS873 impinges on both the UPS and autophagy, and is cytotoxic across a broad range of cancer cell lines. Interestingly, unlike proteasome inhib itors, it is not more cytotoxic to MM cells than to other cancer cells.
Inhibitors,Modulators,Libraries Its relative cytotoxicity in non transformed cells was not reported. p97 inhibitors sellectchem and the proteasome recovery pathway When the proteasome is inhibited, cells respond by upreg ulating the transcription of genes that encode proteasome subunits. This regulation depends on the transcription factor Nrf1 NFE2L1. We and others have investigated the mechanism by which Nrf1 is acti vated. Nrf1 is initially synthesized as a type II transmembrane protein of the ER, such that a very small segment of the amino terminus faces the cytosol, and the bulk of the protein is in the ER lumen. However, this spe cies is a very short lived intermediate, and the carboxy terminal domain of Nrf1 is quickly retrotranslocated to the cytosolic face of the ER in a manner that depends upon p97. Under normal circumstances, retrotransloca tion of Nrf1 is coupled to its degradation by the prote asome, so that active Nrf1 does not accumulate. However, if the proteasome is inhibited, the retrotranslocated Nrf1 is cleaved after Trp103 to release a carboxy terminal frag ment, p110, which travels to the nucleus and activates gene expression.