Structural Basis for alpha-Helix Mimicry and Inhibition of Protein-Protein Interactions with Oligourea Foldamers

Efficient optimization of a peptide lead into a drug candidate frequently needs further transformation to augment properties such as bioavailability. Among the different options, foldamers, which are sequence-based oligomers with precise folded conformation, have emerged as a promising technology. We introduce oligourea foldamers to reduce the peptide character of inhibitors of protein-protein interactions (PPI). However, the precise design of such mimics is currently limited by the lack of structural information on how these foldamers adapt to protein surfaces. We report a collection of X-ray structures of peptide-oligourea hybrids in complex with ubiquitin ligase MDM2 and vitamin D receptor and show how such hybrid oligomers can be designed to bind with high affinity to protein targets. This work should enable the generation of more effective foldamer-based disruptors of PPIs in the context of peptide lead optimization

Etude structure-fonction du complexe du récepteur nucléaire de la Vitamine D avec le coactivateur MED1

Le récepteur de la vitamine D (VDR) est un facteur de transcription activé par la forme active de la vitamine D3. VDR est une cible thérapeutique potentielle pour de multiples pathologies telles que les maladies auto-immunes et neurodégénératives et certains cancers. VDR module l’expression de gènes par le recrutement sélectif de corégulateurs. Les données structurales disponibles à ce jour pour des complexes de récepteur nucléaire-corégulateurs sont très limitées. Cette étude se focalise sur l’architecture du complexe formé par VDR et un grand fragment du coactivateur MED1, une sous-unité du complexe Médiateur qui fait le lien entre les récepteurs nucléaires et la machinerie basale de transcription. Les résultats obtenus nous sont permis de caractériser l'interaction du récepteur avec le coactivateur et de révéler l'architecture globale du complexe. Ce travail fournit une base solide pour la détermination structurale d’autres complexes impliqués dans le contrôle de la transcription.The vitamin D nuclear receptor (VDR) is a transcription factor activated by the biologically active form of vitamin D3. VDR is a potential candidate to treat neurodegenerative and autoimmune disorders, and cancer. VDR modulates the expression of vitamin D3-regulated genes by selective recruitment of coregulators of transcription which are, in turn, attractive targets in epigenetic-oriented drug discovery. Available structural data for receptor-coregulator complexes are limited; investigation of such complexes is highly important. The present work focuses on the architecture of the complex between VDR and a large part of the coactivator MED1, a subunit of the Mediator complex linking nuclear receptors to the basal transcription machinery. Obtained results revealed important details of the interaction, as well as the overall organization of the complex. This work provides a solid background for the structural investigation of similar complexes involved in the transcriptional control

Etude structure-fonction du complexe du récepteur nucléaire de la Vitamine D avec le coactivateur MED1

Le récepteur de la vitamine D (VDR) est un facteur de transcription activé par la forme active de la vitamine D3. VDR est une cible thérapeutique potentielle pour de multiples pathologies telles que les maladies auto-immunes et neurodégénératives et certains cancers. VDR module l’expression de gènes par le recrutement sélectif de corégulateurs. Les données structurales disponibles à ce jour pour des complexes de récepteur nucléaire-corégulateurs sont très limitées. Cette étude se focalise sur l’architecture du complexe formé par VDR et un grand fragment du coactivateur MED1, une sous-unité du complexe Médiateur qui fait le lien entre les récepteurs nucléaires et la machinerie basale de transcription. Les résultats obtenus nous sont permis de caractériser l'interaction du récepteur avec le coactivateur et de révéler l'architecture globale du complexe. Ce travail fournit une base solide pour la détermination structurale d’autres complexes impliqués dans le contrôle de la transcription.The vitamin D nuclear receptor (VDR) is a transcription factor activated by the biologically active form of vitamin D3. VDR is a potential candidate to treat neurodegenerative and autoimmune disorders, and cancer. VDR modulates the expression of vitamin D3-regulated genes by selective recruitment of coregulators of transcription which are, in turn, attractive targets in epigenetic-oriented drug discovery. Available structural data for receptor-coregulator complexes are limited; investigation of such complexes is highly important. The present work focuses on the architecture of the complex between VDR and a large part of the coactivator MED1, a subunit of the Mediator complex linking nuclear receptors to the basal transcription machinery. Obtained results revealed important details of the interaction, as well as the overall organization of the complex. This work provides a solid background for the structural investigation of similar complexes involved in the transcriptional control

Cytosolic sequestration of the vitamin D receptor as a therapeutic option for vitamin D-induced hypercalcemia

International audienceThe bioactive vitamin D3, 1α,25(OH)2D3, plays a central role in calcium homeostasis by controlling the activity of the vitamin D receptor (VDR) in various tissues. Hypercalcemia secondary to high circulating levels of vitamin D3 leads to hypercalciuria, nephrocalcinosis and renal dysfunctions. Current therapeutic strategies aim at limiting calcium intake, absorption and resorption, or 1α,25(OH)2D3 synthesis, but are poorly efficient. In this study, we identify WBP4 as a new VDR interactant, and demonstrate that it controls VDR subcellular localization. Moreover, we show that the vitamin D analogue ZK168281 enhances the interaction between VDR and WBP4 in the cytosol, and normalizes the expression of VDR target genes and serum calcium levels in 1α,25(OH)2D3-intoxicated mice. As ZK168281 also blunts 1α,25(OH)2D3-induced VDR signaling in fibroblasts of a patient with impaired vitamin D degradation, this VDR antagonist represents a promising therapeutic option for 1α,25(OH)2D3-induced hypercalcemia

Molecular determinants of MED1 interaction with the DNA bound VDR–RXR heterodimer

International audienceThe MED1 subunit of the Mediator complex is an essential coactivator of nuclear receptor-mediated transcriptional activation. While structural requirements for ligand-dependent binding of classical coactivator motifs of MED1 to numerous nuclear receptor ligand-binding domains have been fully elucidated, the recognition of the full-length or truncated coactivator by full nuclear receptor complexes remain unknown. Here we present structural details of the interaction between a large part of MED1 comprising its structured N-terminal and the flexible receptor-interacting domains and the mutual heterodimer of the vitamin D receptor (VDR) and the retinoid X receptor (RXR) bound to their cognate DNA response element. Using a combination of structural and biophysical methods we show that the ligand-dependent interaction between VDR and the second coactivator motif of MED1 is crucial for complex formation and we identify additional, previously unseen, interaction details. In particular, we identified RXR regions involved in the interaction with the structured N-terminal domain of MED1, as well as VDR regions outside the classical coactivator binding cleft affected by coactivator recruitment. These findings highlight important roles of each receptor within the heterodimer in selective recognition of MED1 and contribute to our understanding of the nuclear receptor-coregulator complexes

Vitamin D Analogs Bearing C-20 Modifications Stabilize the Agonistic Conformation of Non-Responsive Vitamin D Receptor Variants

International audienceThe Vitamin D receptor (VDR) plays a key role in calcium homeostasis, as well as in cell proliferation and differentiation. Among the large number of VDR ligands that have been developed, we have previously shown that BXL-62 and Gemini-72, two C-20-modified vitamin D analogs are highly potent VDR agonists. In this study, we show that both VDR ligands restore the transcriptional activities of VDR variants unresponsive to the natural ligand and identified in patients with rickets. The elucidated mechanisms of action underlying the activities of these C-20-modified analogs emphasize the mutual adaptation of the ligand and the VDR ligand-binding pocket

Structural Insights into the Molecular Mechanism of Vitamin D Receptor Activation by Lithocholic Acid Involving a New Mode of Ligand Recognition

The vitamin D receptor (VDR), an endocrine nuclear receptor for 1α,25-dihydroxyvitamin D3, acts also as a bile acid sensor by binding lithocholic acid (LCA). The crystal structure of the zebrafish VDR ligand binding domain in complex with LCA and the SRC-2 coactivator peptide reveals the binding of two LCA molecules by VDR. One LCA binds to the canonical ligand-binding pocket, and the second one, which is not fully buried, is anchored to a site located on the VDR surface. Despite the low affinity of the alternative site, the binding of the second molecule promotes stabilization of the active receptor conformation. Biological activity assays, structural analysis, and molecular dynamics simulations indicate that the recognition of two ligand molecules is crucial for VDR agonism by LCA. The unique binding mode of LCA provides clues for the development of new chemical compounds that target alternative binding sites for therapeutic applications

A Vitamin D Receptor Selectively Activated by Gemini Analogs Reveals Ligand Dependent and Independent Effects

The bioactive form of vitamin D [1,25(OH)2D3] regulates mineral and bone homeostasis and exerts potent anti-inflammatory and antiproliferative properties through binding to the vitamin D receptor (VDR). The 3D structures of the VDR ligand-binding domain with 1,25(OH)2D3 or gemini analogs unveiled the molecular mechanism underlying ligand recognition. On the basis of structure-function correlations, we generated a point-mutated VDR (VDRgem) that is unresponsive to 1,25(OH)2D3, but the activity of which is efficiently induced by the gemini ligands. Moreover, we show that many VDR target genes are repressed by unliganded VDRgem and that mineral ion and bone homeostasis are more impaired in VDRgem mice than in VDR null mice, demonstrating that mutations abolishing VDR ligand binding result in more severe skeletal defects than VDR null mutations. As gemini ligands induce VDRgem transcriptional activity in mice and normalize their serum calcium levels, VDRgem is a powerful tool to further unravel both liganded and unliganded VDR signaling

A vitamin D‐based strategy overcomes chemoresistance in prostate cancer

International audienceBackground and purpose Castration‐resistant prostate cancer (CRPC) is a common male malignancy that requires new therapeutic strategies due to acquired resistance to its first‐line treatment, docetaxel. The benefits of vitamin D on prostate cancer (PCa) progression have been previously reported. This study aimed to investigate the effects of vitamin D on chemoresistance in CRPC. Experimental approach Structure function relationships of potent vitamin D analogues were determined. The combination of the most potent analogue and docetaxel was explored in chemoresistant primary PCa spheroids and in a xenograft mouse model derived from a patient with a chemoresistant CRPC. Key results Here, we show that Xe4MeCF3 is more potent than the natural ligand to induce vitamin D receptor (VDR) transcriptional activities and that it has a larger therapeutic window. Moreover, we demonstrate that VDR agonists restore docetaxel sensitivity in PCa spheroids. Importantly, Xe4MeCF3 reduces tumour growth in a chemoresistant CRPC patient‐derived xenograft. In addition, this treatment targets signalling pathways associated with cancer progression in the remaining cells. Conclusion and implications Taken together, these results unravel the potency of VDR agonists to overcome chemoresistance in CRPC and open new avenues for the clinical management of PCa