Biology subjects

Margolis, S. S.

Publications and source records attributed to Margolis, S. S..

3 recordsLinked to original sources

bioRxiv2025

Rapaprotin is Activated by an Endopeptidase to Disassemble 26S Proteasome

The 19S regulatory particle (RP) associates with the 20S core particle (CP) to form the 26S proteasome, an evolutionarily conserved holoenzyme that plays key roles in both physiological and pathological processes. Proteasome inhibitors that target the catalytic subunits within the 20S have proven to be valuable research tools and therapeutics for various cancers. Herein we report the discovery of rapaprotin, a 26S proteasome assembly inhibitor from our natural product-inspired hybrid macrocycle rapafucin library. Rapaprotin induces apoptosis in both myeloma and leukemia cell lines. Genome-wide CRISPR-Cas9 screen identified a cytosolic enzyme, prolyl endopeptidase (PREP) that is required for the pro-apoptotic activity of rapaprotin. Further mechanistic studies revealed that rapaprotin acts as a molecular transformer, changing from an inactive cyclic form into an active linear form, rapaprotin-L, upon PREP cleavage, to block 26S proteasome activity. Time-resolved cryogenic electron microscopy (cryo-EM) revealed that rapaprotin-L induces dissociation of the 19S RP from the 26S holoenzyme, which was verified in cells. Furthermore, rapaprotin exhibits a marked synergistic effect with FDA-approved proteasome inhibitors and resensitizes drug-resistant multiple myeloma cells from patients to bortezomib. Taken together, these results suggest that rapaprotin is a new chemical tool to probe the dynamics of the 26S proteasome assembly and a promising anticancer drug lead.

pharmacology and toxicology↗

bioRxiv2022

Neuronal membrane proteasomes homeostatically regulate neural circuit activity in vivo and are required for learning-induced behavioral plasticity

Protein degradation is critical for brain function through processes that remain poorly understood. Here we investigated the in vivo function of a recently reported neuronal membrane-associated proteasome (NMP) in the brain of Xenopus laevis tadpoles. We demonstrated that NMPs are present in the tadpole brain with biochemistry and electron microscopy, and showed that they actively degrade neuronal activity-induced nascent proteins. Using in vivo calcium imaging in the optic tectum, we showed that acute inhibition of NMP function rapidly increased spontaneous neuronal activity, resulting in hyper-synchronization among tectal neurons. At the circuit level, inhibiting NMPs abolished learning-dependent improvement in a visuomotor behavior paradigm in live animals. Our data provide the first in vivo characterization of NMP functions in the vertebrate nervous system and suggest that NMP-mediated degradation of activity-induced nascent proteins may serve as a homeostatic modulatory mechanism in neurons that is critical for regulating neuronal activity and experience-dependent circuit plasticity.

neuroscience↗

bioRxiv2019

YAP controls cell migration and invasion through a Rho-GTPase switch

Delineating the mechanisms controlling the invasive spread of non-diseased and transformed cells is central to understanding diverse processes including cancer progression. Here, we found that Yes-associated protein (YAP), a central transcriptional regulator implicated in controlling organ and body size, modulated a Rho-GTPase switch that drives cellular migration by transactivating the Rac1-GEF protein TRIO through direct modulation of its intronic enhancer. Additionally, YAP and TRIO may promote invasive behavior through putative crosstalk with STAT3 signaling, a potential downstream target. Although we found this YAP-dependent infiltrative program in many cell types, it was particularly enhanced in a patient-specific manner in the most common malignant brain tumor, glioblastoma (GBM), where hyperactivation of the YAP, TRIO, and STAT3 signatures also conferred poor clinical outcome. Our analysis suggests that the YAP-TRIO-Rho-GTPase signaling network identified in this study is a ubiquitous regulator of invasive cell spread in both physiological and pathological contexts.

cancer biology↗