Opposing Roles Of The 19s Regulatory And 20s Core Proteasomal Subunits In Controlling Sensitivity To Proteasome Inhibitors

Targeted therapies for cancer are often hindered by the variable genetic makeup within and between tumors. This hurdle makes the identification of therapeutic targets challenging. Genetic susceptibilities found within networks encoded in the genome of a cancer cell can provide such therapeutic opportunities. Essential cellular networks overseeing homeostasis are often rewired in tumors, providing a landscape where synthetic lethal pairs may exist. A prominent example is the susceptibility of multiple myeloma (MM) cells to proteasome inhibitors. Because of their highly secretory nature, the proteasomes of MM cells can be burdened in a load-versus-capacity tug-of-war. This renders MM cells sensitive to proteasome inhibitors. Unfortunately, single agent therapies against the proteasome do not provide a cure, as tumor cells often acquire resistance. Because of this, we sought to understand how MM cancer cells respond and adapt to proteasome inhibition. Utilizing ultra-complex shRNA libraries, we screened several MM cell lines exposed to the proteasome inhibitor bortezomib. In these screens, we identified several genes that either sensitize or protect MM cells towards bortezomib intoxication. Unexpectedly we found that, contrary to knockdown of genes encoding subunits of the 20S core particle of the proteasome, knockdown of genes encoding subunits of the 19S regulatory particle of the proteasome lead to bortezomib desensitization. To understand the nature of this phenotype, we queried proteome changes in bortezomib treated cells where we ablated a single 19S subunit. By performing ubiquitin-remnant profiling and total proteome SILAC experiments, we identified several proteins involved in autophagy and NF-κB signaling as potential mediators of the protective phenotype. We are currently investigating the roles of components of these pathways in tailoring the response towards bortezomib. We surmise that some of these will be amenable for pharmacological targeting in developing novel combination therapies. Citation Format: Min Y. Cho, Diego Acosta-Alvear, Martin Kampmann, Thomas Wild, Chuna Ram Choudhary, Jonathan S. Weissman, Peter Walter. Opposing roles of the 19S regulatory and 20S core proteasomal subunits in controlling sensitivity to proteasome inhibitors. [abstract]. In: Proceedings of the AACR Special Conference on Translation of the Cancer Genome; Feb 7-9, 2015; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2015;75(22 Suppl 1):Abstract nr A2-12.