Targeting Human Hippo TEAD Binding Interface with YAP/TAZ-Derived, Flexibility-Reduced Peptides in Gastric Cancer

TAZ-hTrap: A Rationally Designed, Disulfide-Stapled Tead Helical Hairpin Trap to Selectively Capture Hippo Signaling Taz With Potent Antigynecological Tumor Activity

Transcriptional enhanced associate domain (Tead)-mediated Hippo signaling pathway regulates diverse physiological processes; its dysfunction has been implicated in an increasing number of human gynecological cancers. The transcriptional coactivator with PDZ-binding motif (Taz) binds to and then activates Tead through forming a three-helix bundle (THB) at their complex interface. The THB is defined by a double-helical hairpin from Tead and a single α-helix from Taz, serving as the key interaction hotspot between Tead and Taz. In the present study, the helical hairpin was derived from Tead protein to generate a hairpin segment, which is a 25-mer polypeptide consisting of a longer helical arm-1 and a shorter helical arm-2 as well as a flexible loop linker between them. Dynamics simulation and energetics characterization revealed that the hairpin peptide is intrinsically disordered when splitting from its protein context, thus incurring a large entropy penalty upon binding to Taz α-helix. A disulfide bridge was introduced across the two helical arms of hairpin peptide to obtain a strong binder termed TAZ-hTrap, which can maintain in a considerably structured, native-like conformation in unbound state, and the entropy penalty was minimized by disulfide stapling to effectively improve its affinity toward the α-helix. These computational findings can be further substantiated by circular dichroism and fluorescence polarization at molecular level, and viability assay also observed a potent cytotoxic effect on diverse human gynecological tumors at cellular level. In addition, we further demonstrated that the TAZ-hTrap has a good selectivity for its cognate Taz over other noncognate proteins that share a high conservation with the Taz α-helix.

Computational design and experimental confirmation of a disulfide-stapled YAP helixα1-trap derived from TEAD4 helical hairpin to selectively capture YAP α1-helix with potent antitumor activity

Human Hippo signaling pathway is an evolutionarily conserved regulator network that controls organ development and has been implicated in various cancers. Transcriptional enhanced associate domain-4 (TEAD4) is the final nuclear effector of Hippo pathway, which is activated by Yes-associated protein (YAP) through binding to two separated YAP regions of α1-helix and Ω-loop. Previous efforts have all been addressed on deriving peptide inhibitors from the YAP to target TEAD4. Instead, we herein attempted to rationally design a so-called 'YAP helixα1-trap' based on the TEAD4 to target YAP by using dynamics simulation and energetics analysis as well as experimental assays at molecular and cellular levels. The trap represents a native double-stranded helical hairpin covering a specific YAP-binding site on TEAD4 surface, which is expected to form a three-helix bundle with the α1-helical region of YAP, thus competitively disrupting TEAD4-YAP interaction. The hairpin was further stapled by a disulfide bridge across its two helical arms. Circular dichroism characterized that the stapling can effectively constrain the trap into a native-like structured conformation in free state, thus largely minimizing the entropy penalty upon its binding to YAP. Affinity assays revealed that the stapling can considerably improve the trap binding potency to YAP α1-helix by up to 8.5-fold at molecular level, which also exhibited a good tumor-suppressing effect at cellular level if fused with TAT cell permeation sequence. In this respect, it is considered that the YAP helixα1-trap-mediated blockade of Hippo pathway may be a new and promising therapeutic strategy against cancers.

Molecular Alterations in Malignant Pleural Mesothelioma: A Hope for Effective Treatment by Targeting YAP

Malignant pleural mesothelioma is a rare and aggressive neoplasm, which has primarily been attributed to the exposure to asbestos fibers (83% of cases); yet, despite a ban of using asbestos in many countries, the incidence of malignant pleural mesothelioma failed to decline worldwide. While little progress has been made in malignant pleural mesothelioma diagnosis, bevacizumab at first, then followed by double immunotherapy (nivolumab plus ipilumumab), were all shown to improve survival in large phase III randomized trials. The morphological analysis of the histological subtyping remains the primary indicator for therapeutic decision making at an advanced disease stage, while a platinum-based chemotherapy regimen combined with pemetrexed, either with or without bevacizumab, is still the main treatment option. Consequently, malignant pleural mesothelioma still represents a significant health concern owing to poor median survival (12-18 months). Given this context, both diagnosis and therapy improvements require better knowledge of the molecular mechanisms underlying malignant pleural mesothelioma's carcinogenesis and progression. Hence, the Hippo pathway in malignant pleural mesothelioma initiation and progression has recently received increasing attention, as the aberrant expression of its core components may be closely related to patient prognosis. The purpose of this review was to provide a critical analysis of our current knowledge on these topics, the main focus being on the available evidence concerning the role of each Hippo pathway's member as a promising biomarker, enabling detection of the disease at earlier stages and thus improving prognosis.

Interfacial Peptides as Affinity Modulating Agents of Protein-Protein Interactions

The identification of disease-related protein-protein interactions (PPIs) creates objective conditions for their pharmacological modulation. The contact area (interfaces) of the vast majority of PPIs has some features, such as geometrical and biochemical complementarities, "hot spots", as well as an extremely low mutation rate that give us key knowledge to influence these PPIs. Exogenous regulation of PPIs is aimed at both inhibiting the assembly and/or destabilization of protein complexes. Often, the design of such modulators is associated with some specific problems in targeted delivery, cell penetration and proteolytic stability, as well as selective binding to cellular targets. Recent progress in interfacial peptide design has been achieved in solving all these difficulties and has provided a good efficiency in preclinical models (in vitro and in vivo). The most promising peptide-containing therapeutic formulations are under investigation in clinical trials. In this review, we update the current state-of-the-art in the field of interfacial peptides as potent modulators of a number of disease-related PPIs. Over the past years, the scientific interest has been focused on following clinically significant heterodimeric PPIs MDM2/p53, PD-1/PD-L1, HIF/HIF, NRF2/KEAP1, RbAp48/MTA1, HSP90/CDC37, BIRC5/CRM1, BIRC5/XIAP, YAP/TAZ-TEAD, TWEAK/FN14, Bcl-2/Bax, YY1/AKT, CD40/CD40L and MINT2/APP.

Systematic profiling and identification of the peptide-mediated interactions between human Yes-associated protein and its partners in esophageal cancer

Human Yes-associated protein (YAP) is involved in the Hippo signaling pathway and serves as a coactivator to modulate gene expression, which contains a transactivation domain (TD) responsible for binding to the downstream TEA domain family (TEAD) of transcription factors and two WW1/2 domains that recognize the proline-rich motifs (PRMs) present in a variety of upstream protein partners through peptide-mediated interactions (PMIs). The downstream YAP TD-TEAD interactions are closely associated with gastric cancer, and a number of therapeutic agents have been developed to target the interactions. In contrast, the upstream YAP WW1/2-partner interactions are thought to be involved in esophageal cancer but still remain largely unexplored. Here, we attempted to elucidate the complicated PMIs between the YAP WW1/2 domains and various PRMs of YAP-interacting proteins. A total of 106 peptide segments carrying the class I WW-binding motif [P/L]Px[Y/P] were extracted from 22 partner candidates, which are potential recognition sites of YAP WW1/2 domains. Structural and energetic analyses of the intermolecular interactions between the domains and peptides created a systematic domain-peptide binding profile, from which a number of biologically functional PMIs were identified and then substantiated in vitro using fluorescence spectroscopy assays. It is revealed that: (a) The sequence requirement for the partner recognition site binding to YAP WW1/2 domains is a decapeptide segment that contains a core PRM motif as well as two three-residue extensions from each side of the motif; the core motif and extended sections are responsible for the binding stability and recognition specificity of domain-peptide interaction, respectively. (b) There is an exquisite difference in the recognition specificity of the two domains; the LPxP and PPxP appear to more prefer WW1 than WW2, whereas the WW2 can bind more effectively to LPxY and PPxY than WW1. (c) WW2 generally exhibits a higher affinity to the panel of recognition site candidates than WW1. In addition, a number of partner peptides were found as promising recognition sites of the two domains and/or to have a good selectivity between the two domains. For example, the DVL1 peptide was determined to have moderate affinity to WW2 and strong selectivity for WW2 over WW1. Hydrogen bonds play a central role in selectivity.

Recent Therapeutic Approaches to Modulate the Hippo Pathway in Oncology and Regenerative Medicine

The Hippo pathway is an evolutionary conserved signaling network that regulates essential processes such as organ size, cell proliferation, migration, stemness and apoptosis. Alterations in this pathway are commonly found in solid tumors and can lead to hyperproliferation, resistance to chemotherapy, compensation for mKRAS and tumor immune evasion. As the terminal effectors of the Hippo pathway, the transcriptional coactivators YAP1/TAZ and the transcription factors TEAD1–4 present exciting opportunities to pharmacologically modulate the Hippo biology in cancer settings, inflammation and regenerative medicine. This review will provide an overview of the progress and current strategies to directly and indirectly target the YAP1/TAZ protein–protein interaction (PPI) with TEAD1–4 across multiple modalities, with focus on recent small molecules able to selectively bind to TEAD, block its autopalmitoylation and inhibit YAP1/TAZ–TEAD-dependent transcription in cancer.

Computational design and experimental substantiation of conformationally constrained peptides from the complex interfaces of transcriptional enhanced associate domains with their cofactors in gastric cancer

Transcriptional enhanced associate domains (Teads) are the downstream effectors of the hippo signaling pathway and have been recognized as attractive druggable targets of gastric cancer. The biological function of Teads is regulated by diverse cofactors. In this study, the intermolecular interactions of Teads with their cognate cofactors were systematically characterized at structural, thermodynamic and dynamic levels. The Teads possess a double-stranded helical hairpin that is surrounded by three independent structural elements β-sheet, α-helix and Ω-loop of cofactor proteins and plays a central role in recognition and association with cofactors. A number of functional peptides were split from the hairpin region at Tead-cofactor complex interfaces, which, however, cannot maintain in native conformation without the support of protein context and would therefore incur a considerable entropy penalty upon competitively rebinding to the interfaces. Here, we further used disulfide and hydrocarbon bridges to cyclize and staple the hairpin and helical peptides, respectively. The chemical modification strategies were demonstrated to effectively constrain peptide conformation into active state and to largely reduce peptide flexibility in free state, thus considerably improving their affinity. Since the cyclization and stapling only minimize the indirect entropy cost but do not influence the direct enthalpy effect upon peptide binding, the designed conformationally constrained peptides can retain in their native selectivity over different cofactors. This is particularly interesting because it means that the cyclized/stapled, affinity-improved peptides can specifically compete with their parent Teads for the cofactor arrays as they share consistent target specificity.

Hippo pathway: Regulation, deregulation and potential therapeutic targets in cancer

Hippo pathway is a master regulator of development, cell proliferation, stem cell function, tissue regeneration, homeostasis, and organ size control. Hippo pathway relays signals from different extracellular and intracellular events to regulate cell behavior and functions. Hippo pathway is conserved from Protista to eukaryotes. Deregulation of the Hippo pathway is associated with numerous cancers. Alteration of the Hippo pathway results in cell invasion, migration, disease progression, and therapy resistance in cancers. However, the function of the various components of the mammalian Hippo pathway is yet to be elucidated in detail especially concerning tumor biology. In the present review, we focused on the Hippo pathway in different model organisms, its regulation and deregulation, and possible therapeutic targets for cancer treatment.

Rational design and chemical modification of TEAD coactivator peptides to target hippo signaling pathway against gastrointestinal cancers

Human Hippo signaling pathway has been recognized as a new and promising therapeutic target of gastrointestinal cancers, which is regulated by the intermolecular recognition between the TEA domain (TEAD) transcription factor and its prime coactivators. The coactivator proteins adopt two hotspot sites, namely α-helix and Ω-loop, to interact with TEAD. Here, we demonstrate that both the α-helix and Ω-loop peptides cannot maintain in structured state when splitting from the full-length coactivator proteins; they exhibit a large intrinsic disorder in free state that prevents the coactivator peptide recognition by TEAD. Rational design is used to optimize the interfacial residues of coactivator α-helix peptides, which can effectively improve the favorable direct readout effect upon the peptide binding to TEAD. Chemical modification is employed to constrain the free α-helix peptide into native ordered conformation. The method introduces an all-hydrocarbon bridge across i and i + 4 residues to stabilize the helical structure of a free coactivator peptide, which can considerably reduce the unfavorable indirect readout effect upon the peptide binding to TEAD. The all-hydrocarbon bridge is designed to point out of the TEAD-peptide complex interface, which would not disrupt the direct intermolecular interaction between the TEAD and peptide. Therefore, the stapling only improves peptide affinity, but does not alter peptide specificity, to TEAD. Affinity assay confirms that the binding potency of coactivator α-helix peptides is improved substantially by >5-fold upon the rational design and chemical modification. Structural analysis reveals that the optimized/stapled peptides can form diverse nonbonded interactions such as hydrogen bonds and hydrophobic contacts with TEAD, thus conferring stability and specificity to the TEAD-peptide complex systems.