Repurposing of Drugs Targeting YAP-TEAD Functions

Abstract

Drug repurposing is a fast and consolidated approach for the research of new active compounds bypassing the long streamline of the drug discovery process. Several drugs in clinical practice have been reported for modulating the major Hippo pathway's terminal effectors, namely YAP (Yes1-associated protein), TAZ (transcriptional co-activator with PDZ-binding motif) and TEAD (transcriptional enhanced associate domains), which are directly involved in the regulation of cell growth and tissue homeostasis. Since this pathway is known to have many cross-talking phenomena with cell signaling pathways, many efforts have been made to understand its importance in oncology. Moreover, this could be relevant to obtain new molecular tools and potential therapeutic assets. In this review, we discuss the main mechanisms of action of the best-known compounds, clinically approved or investigational drugs, able to cross-talk and modulate the Hippo pathway, as an attractive strategy for the discovery of new potential lead compounds.

Keywords: Hippo pathway; YAP-TEAD disruption; cell signaling; drug repurposing; protein-protein interactions.

Figure 1

Hippo pathway upstream modulation. Upstream modulators in the blue field regulate Hippo core kinases in the green field, namely MST (mammalian STE20-like protein kinase) 1-2 and LATS (large tumor suppressor) 1-2 [1]. Once phosphorylated, these kinases inhibit YAP (Yes1-associated protein)/TAZ (transcriptional co-activator with PDZ-binding motif) nuclear translocation through serine-phosphorylation, ensuring cytoplasmic compartmentalization and promoting degradation mechanisms. The Hippo pathway induces an onco-protective signal by impairing antiapoptotic and cell proliferation-related genes transcription by the final effectors. G-protein coupled receptors with Gs promote LATS1-2 activation, while other coupling-type mechanisms promote actin cytoskeleton dynamics that impair Hippo kinases activity [12]. The Ras-association domain family (RASSF) proteins generally promote Hippo kinases phosphorylation and activation, while phosphatase promotes the opposite. Other upstream modulators such as FRMD6/WWC1-2/NF2 complex activate Hippo kinases in response to cytomechanical response. Ajuba inactivates MST1-2 and LATS1-2 when it is up-regulated [13,14], while apicobasal cell polarity control complexes, such as the Scribble complex, have been proved to display a tumor-suppressive role [15].

Figure 2

YAP principal interactors and phosphorylation sites. YAP phosphorylation main site is on S127 with consequent 14-3-3σ proteins recruitment, YAP cytoplasmic sequestration and phosphorylation site shielding from phosphatases. LATS1-2 also promotes phosphorylation on other sites (yellow glow), namely S397 phosphorylation which in turn promotes S400 and S403 phosphorylations (green glow) by Casein Kinase 1 family, isoforms δ and ε (CK1δ/ε), overall forming the phosphodegron site responsible for ubiquitination system recruitment [17]. Y407 is phosphorylated by C-Abl and Yes-1 (blue glow) prompting opposite effect according to the involved tyrosine kinase. While C-Abl has onco-protective relevance, promoting binding with p73, Yes-1 promotes nuclear translocation through cross-talking with Wnt/β-catenin pathway (paragraph 2.3.3). The first WW domain (tryptophan tryptophan domain) is responsible for N-terminal AMOT PPXY motif binding, while the second one is only conserved in YAP1-2 isoforms. WW1 domain also permits LATS1-2 binding, but it is unclear if this binding is needed for S127 phosphorylation [18]. The terminal motif binds PDZ domain, anchoring YAP to tight junction proteins, such as Zonula Occludens-1/2 (ZO-1/2) [19]. Sequence consensus boxes of the interactors are colored according to the protein to which it belongs [1,20,21].

Figure 3

Repurposing of drugs on YAP (Yes-1 associated protein)-TEAD (transcriptional enhanced associate domain) system through cross-talking pathways. Hippo pathway core kinases (in blue) and final effector YAP are modulated by approved drugs through different cross-talking pathways. Dobutamine binds β₁-adrenergic receptor and promotes LATS (large tumor suppressor) 1/2 phosphorylation through PKA (protein kinase A) signaling, while melatonin is believed to modulate YAP through pleiotropic mechanisms (GPCRs (G-protein coupled receptors) signaling in red). Statins, as HMG-CoA (3-hydroxy-3-methylglutaryl CoA) reductase inhibitors, impair Rho signaling in orange and modulate actin cytoskeleton, impairing LATS1/2 activation altogether. Tyrosine kinase inhibitors target growth factors signaling in cerulean (PI3K-AKT pathway), green (MAPK (mitogen-activated protein kinase) pathway) and black and purple (MAPK pathway final effectors) according to the proper interested drug. Receptor autophosphorylation inhibitors, such as Gefitinib, Erlotinib, and Pazopanib, hit an ATP-binding site. Instead, Dasatinib is a Src/Bcr-abl dual inhibitor, while Losmapimod and Trametinib target downstream components of MAPK pathway. Dimethylfumarate inhibits GSK3β phosphorylation, preventing APC β-catenin destruction complex formation and undermining oncogenic β-catenin pathway in the process. Metformin, through AMPK phosphorylation and consequent half-time AMOT (Angiomotin) prolongment, promotes phosphorylation-independent YAP cytoplasmic sequestration by AMOT in yellow. Digitoxin, Verteporfin and Flufenamic acid and derivatives modulate YAP/TEAD interaction, as better discussed in paragraphs 3 and 4.

Figure 4

Superposition of hTEAD2 (as part of the PDB structure 5DQ8, in cyan) and hTEAD1 in complex with YAP2 (in blue and red, respectively, as part of the PDB structure 3KYS). The β1 strand of YAP is displayed on the left, the α1 helix in the center, and the Ω-loop on the right of the figure. The cysteines which are the sites of palmitoylation for the two TEAD isoforms are evidenced.

Figure 5

Flufenamic acid (in purple as part of the PDB structure 5DQ8, in cyan) and palmitate (in green as part of the PDB structure 5EMV, in orange) share the same binding pocket as shown by superposition of co-crystallized hTEAD2 structures. The surface of the amino acid residues lining the binding pocket of hTEAD2 is represented in orange.