The cytoplasmic tyrosine kinase SRC controls cell growth, proliferation, adhesion, and motility. The current view is that SRC acts primarily downstream of cell-surface receptors to control ...intracellular signaling cascades. Here we reveal that SRC functions in cell-to-cell communication by controlling the biogenesis and the activity of exosomes. Exosomes are viral-like particles from endosomal origin that can reprogram recipient cells. By gain- and loss-of-function studies, we establish that SRC stimulates the secretion of exosomes having promigratory activity on endothelial cells and that syntenin is mandatory for SRC exosomal function. Mechanistically, SRC impacts on syndecan endocytosis and on syntenin–syndecan endosomal budding, upstream of ARF6 small GTPase and its effector phospholipase D2, directly phosphorylating the conserved juxtamembrane DEGSY motif of the syndecan cytosolic domain and syntenin tyrosine 46. Our study uncovers a function of SRC in cell–cell communication, supported by syntenin exosomes, which is likely to contribute to tumor–host interactions.
Cell motility depends on tight coordination between the microtubule (MT) and actin cytoskeletons, but the mechanisms underlying this MT-actin cross talk have remained poorly understood. Here, we show ...that the tumor suppressor protein adenomatous polyposis coli (APC), which is a known MT-associated protein, directly nucleates actin assembly to promote directed cell migration. By changing only two residues in APC, we generated a separation-of-function mutant, APC (m4), that abolishes actin nucleation activity without affecting MT interactions. Expression of full-length APC carrying the m4 mutation (APC (m4)) rescued cellular defects in MT organization, MT dynamics, and mitochondrial distribution caused by depletion of endogenous APC but failed to restore cell migration. Wild-type APC and APC (m4) localized to focal adhesions (FAs), and APC (m4) was defective in promoting actin assembly at FAs to facilitate MT-induced FA turnover. These results provide the first direct evidence for APC-mediated actin assembly in vivo and establish a role for APC in coordinating MTs and actin at FAs to direct cell migration.
Small molecules inducing protein degradation are important pharmacological tools to interrogate complex biology and are rapidly translating into clinical agents. However, to fully realise the ...potential of these molecules, selectivity remains a limiting challenge. Herein, we addressed the issue of selectivity in the design of CRL4CRBN recruiting PROteolysis TArgeting Chimeras (PROTACs). Thalidomide derivatives used to generate CRL4CRBN recruiting PROTACs have well described intrinsic monovalent degradation profiles by inducing the recruitment of neo‐substrates, such as GSPT1, Ikaros and Aiolos. We leveraged structural insights from known CRL4CRBN neo‐substrates to attenuate and indeed remove this monovalent degradation function in well‐known CRL4CRBN molecular glues degraders, namely CC‐885 and Pomalidomide. We then applied these design principles on a previously published BRD9 PROTAC (dBRD9‐A) and generated an analogue with improved selectivity profile. Finally, we implemented a computational modelling pipeline to show that our degron blocking design does not impact PROTAC‐induced ternary complex formation. We believe that the tools and principles presented in this work will be valuable to support the development of targeted protein degradation.
The use of phenotypic screening was central to the discovery and development of novel thalidomide analogs, the IMiDs (immunomodulatory drugs) agents. With the discovery that these agents bind the E3 ...ligase, CRL4CRBN, and alter its substrate specificity, there has been a great deal of endeavor to discover other small molecules that can modulate alternative E3 ligases. Furthermore, the chemical properties necessary for drug discovery and the rules by which neo-substrates are selected for degradation are being defined in the context of phenotypic alterations in specific cellular systems. This review gives a detailed summary of these recent advances and the methodologies being exploited to understand the mechanism of action of emerging protein degradation therapies.
Display omitted
In this review, Ege et al. provide a detailed overview of the role of phenotypic screening to the discovery and development of E3 ligase modulators. It further summarizes recent advances and methodologies being exploited to understand the mechanism of action of emerging protein degradation therapies.
Control of microtubule dynamics underlies several fundamental processes such as cell polarity, cell division, and cell motility. To gain insights into the mechanisms that control microtubule dynamics ...during cell motility, we investigated the interactome of the microtubule plus-end–binding protein end-binding 1 (EB1). Via molecular mapping and cross-linking mass spectrometry we identified and characterized a large complex associating a specific isoform of myomegalin termed “SMYLE” (for short myomegalin-like EB1 binding protein), the PKA scaffolding protein AKAP9, and the pericentrosomal protein CDK5RAP2. SMYLE was associated through an evolutionarily conserved N-terminal domain with AKAP9, which in turn was anchored at the centrosome via CDK5RAP2. SMYLE connected the pericentrosomal complex to the microtubule-nucleating complex (γ-TuRC) via Galectin-3–binding protein. SMYLE associated with nascent centrosomal microtubules to promote microtubule assembly and acetylation. Disruption of SMYLE interaction with EB1 or AKAP9 prevented microtubule nucleation and their stabilization at the leading edge of migrating cells. In addition, SMYLE depletion led to defective astral microtubules and abnormal orientation of the mitotic spindle and triggered G1 cell-cycle arrest, which might be due to defective centrosome integrity. As a consequence, SMYLE loss of function had a profound impact on tumor cell motility and proliferation, suggesting that SMYLE might be an important player in tumor progression.
E3 ligase mediated targeted protein degradation is an ever more important area in drug discovery. In the case of cereblon two avenues exist; either heterobifunctional PROTACs, or discrete cereblon ...ligands that induce a specific neosubstrate degron association to the complex. Here we present a degron blocking approach, whereby structural and in silico understandings of degron association has directed ligand design to block IMiD‐like binding of degron containing neosubstrates, thus enhancing PROTAC selectivity. More information can be found in the Research Article by H. Bouguenina, J. J. Caldwell et al.
Small molecules that induce protein degradation hold the potential to overcome several limitations of the currently available inhibitors. Monovalent or molecular glue degraders, in particular, enable ...the benefits of protein degradation without the disadvantages of high molecular weight and the resulting challenge in drug development that are associated with bivalent molecules like Proteolysis Targeting Chimeras. One key challenge in designing monovalent degraders is how to build in the degrader activityhow can we convert an inhibitor into a degrader? If degradation activity requires very specific molecular features, it will be difficult to find new degraders and challenging to optimize those degraders toward drugs. Herein, we demonstrate that an unexpectedly wide range of modifications to the degradation-inducing group of the cyclin K degrader CR8 are tolerated, including both aromatic and nonaromatic groups. We used these findings to convert the pan-CDK inhibitors dinaciclib and AT-7519 to Cyclin K degraders, leading to a novel dinaciclib-based compound with improved degradation activity compared to CR8 and confirm the mechanism of degradation. These results suggest that general design principles can be generated for the development and optimization of monovalent degraders.
PDF
