Hippo Core Kinase Research Articles

Hippo signaling in cancer: regulatory mechanisms and therapeutic strategies

As an evolutionarily conserved pathway, Hippo signaling not only plays a key role in embryonic development, but also regulates the initiation and progression of cancer. The upstream factors regulating the Hippo pathway are complex, including cell–cell contact, cell–extracellular matrix contact, membrane receptor–ligand binding, and cytoskeletal tension. In response to these mechanical or soluble cues, the Hippo core kinases are activated or inactivated, regulating the activity of key transcription co-factor YAP/TAZ thus yielding biological consequences. In the context of neoplasm, dysregulation of Hippo signaling contributes to cancer hallmarks such as sustained proliferation, stem-like properties, and metastasis. Importantly, targeting Hippo signaling by chemicals is emerging as a promising anticancer strategy. This article briefly introduces the discovery process of the Hippo pathway, summarizes the upstream signals regulating the Hippo pathway, discusses the relationship between Hippo inactivation and cancer development, and highlights the potential use of chemicals targeting Hippo signaling in cancer treatment.

Cellular feedback dynamics and multilevel regulation driven by the hippo pathway.

The Hippo pathway is a dynamic cellular signalling nexus that regulates differentiation and controls cell proliferation and death. If the Hippo pathway is not precisely regulated, the functionality of the upstream kinase module is impaired, which increases nuclear localisation and activity of the central effectors, the transcriptional co-regulators YAP and TAZ. Pathological YAP and TAZ hyperactivity consequently cause cancer, fibrosis and developmental defects. The Hippo pathway controls an array of fundamental cellular processes, including adhesion, migration, mitosis, polarity and secretion of a range of biologically active components. Recent studies highlight that spatio-temporal regulation of Hippo pathway components are central to precisely controlling its context-dependent dynamic activity. Several levels of feedback are integrated into the Hippo pathway, which is further synergized with interactors outside of the pathway that directly regulate specific Hippo pathway components. Likewise, Hippo core kinases also ‘moonlight’ by phosphorylating multiple substrates beyond the Hippo pathway and thereby integrates further flexibility and robustness in the cellular decision-making process. This topic is still in its infancy but promises to reveal new fundamental insights into the cellular regulation of this therapeutically important pathway. We here highlight recent advances emphasising feedback dynamics and multilevel regulation of the Hippo pathway with a focus on mitosis and cell migration, as well as discuss potential productive future research avenues that might reveal novel insights into the overall dynamics of the pathway.

CORO7 functions as a scaffold protein for the core kinase complex assembly of the Hippo pathway

The Hippo pathway controls organ size and tissue homeostasis through the regulation of cell proliferation and apoptosis. However, the exact molecular mechanisms underpinning Hippo pathway regulation are not fully understood. Here, we identify a new component of the Hippo pathway: coronin 7 (CORO7), a coronin protein family member that is involved in organization of the actin cytoskeleton. pod1, the Drosophila ortholog of CORO7, genetically interacts with key Hippo pathway genes in Drosophila. In mammalian cells, CORO7 is required for the activation of the Hippo pathway in response to cell–cell contact, serum deprivation, and cytoskeleton damage. CORO7 forms a complex with the core components of the pathway and functions as a scaffold for the Hippo core kinase complex. Collectively, these results demonstrate that CORO7 is a key scaffold controlling the Hippo pathway via modulating protein–protein interactions.

STRIPAK Is a Regulatory Hub Initiating Hippo Signaling

Signaling modules that integrate the diverse extra- and intracellular inputs to the Hippo pathway were previously unknown. By biochemical and molecular interrogation, Chen et al. established a molecular framework, the RhoA-RHPN-NF2/Kibra-STRIPAK axis, that regulates the status of Hippo core kinases and connects upstream signals to initiate and orchestrate the Hippo pathway.

Src-mediated crosstalk between FXR and YAP protects against renal fibrosis.

Renal fibrosis is the common pathway of chronic kidney disease progression. The nuclear receptor farnesoid X receptor [FXR, NR1H4 (nuclear receptor subfamily 1 group member 4)], a multifunctional transcription factor, plays a pivotal role in protecting against fibrosis. However, the mechanisms underlying these antifibrotic actions of FXR in kidney disease are largely unknown. Here, we show that agonist GW4064-mediated FXR activation inhibits the activity of the nonreceptor tyrosine kinase Src (proto-oncogene tyrosine-protein kinase), which is critical for regulation of yes-associated protein (YAP) phosphorylation and nuclear localization in renal fibrosis. Activation of FXR suppressed renal fibrosis and Tyr416-Src phosphorylation in TGF-β-treated human renal proximal tubule epithelial (HK2) cells. Moreover, GW4064 treatment in HK2 cells increased Ser127 phosphorylation, cytosolic accumulation of YAP, and interaction of the hippo core kinases (Ste20-like kinase 1, large tumor suppressor kinase 1, and salvador homolog 1). Inhibition of Src using PP2 (Src kinase inhibitor) prevented renal fibrosis and increased Ser127 phosphorylation and cytosolic accumulation of YAP. The expression of fibrosis markers, inflammatory genes, and YAP target genes was increased in the kidneys of FXR knockout mice compared with those of wild-type mice. In addition, GW4064 or WAY-362450 (turofexorate isopropyl) treatment protected against unilateral ureteral obstruction-induced renal fibrosis. Collectively, our data support the novel conclusion that Src-mediated crosstalk between FXR and YAP protects against renal fibrosis, making this pathway a possible therapeutic target for chronic kidney disease.-Kim, D.-H., Choi, H.-I., Park, J. S., Kim, C. S., Bae, E. H., Ma, S. K., Kim, S. W. Src-mediated crosstalk between FXR and YAP protects against renal fibrosis.

Abstract 2693: Targeting the Hippo-YAP pathway with novel small-molecule inhibitors of the YAP-TEAD transcription activity

Abstract We have discovered and are developing multiple novel small molecule medicines targeting the Hippo-YAP pathway. Consisting of upstream regulatory components, the Hippo core kinase components (MST1/2, MAP4K1-7, and LATS1/2), and the downstream transcriptional machinery (YAP, TAZ, and TEAD), the mammalian Hippo-YAP pathway is involved in the regulation of cell proliferation, survival, and cell migration. It functions normally to control tissue regeneration and homeostasis and limit organ size/shape. Genetic alterations of pathway components have been reported in a variety of human malignancies. YAP activity is also linked to resistance to targeted therapies and cancer relapse. Through high-throughput phenotypic screens, we have identified novel classes of small molecule compounds that inhibit the YAP-TEAD transcription activity. Medicinal chemistry efforts on lead optimization resulted in highly potent inhibitors that block YAP-TEAD transcription activity at single digit nM. The classes of inhibitors that were demonstrated to interact directly with the TEAD transcription factors by thermal shift assay, co-crystal structures, and inhibition of autopalmitoylation of purified recombinant TEAD proteins will be presented. In cell-based assays, these inhibitors block TEAD palmitoylation in cells and selectively inhibit proliferation of NF2-deficient mesothelioma. In vivo, complete growth inhibition of NF2 mutant xenograft tumors can be achieved at doses that are well tolerated in mice without adverse effect on body weight. With the discovery and development of potent TEAD inhibitors, we bring forth a new generation of cancer therapeutics targeting a thus far undruggable pathway that is dysregulated in many cancers and critically associated with targeted therapy resistance. Citation Format: Tracy T. Tang, Andrei W. Konradi, Ying Feng, Xiao Peng, Sofie Qiao, Leonard Post. Targeting the Hippo-YAP pathway with novel small-molecule inhibitors of the YAP-TEAD transcription activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2693.

MiR-7977 inhibits the Hippo-YAP signaling pathway in bone marrow mesenchymal stromal cells.

We and others have demonstrated that various abnormalities of the bone marrow (BM) mesenchymal stromal cells (MSCs) such as aberrant cytokine expression, abnormal hedgehog signaling, and impaired miRNA biogenesis are observed in patients with acute myeloid leukemia (AML). However, underlying mechanisms to induce the dysfunction of BM MSCs have not yet been clarified. We previously showed that AML cells release abundant exosomal miR-7977, which, in turn, enters BM mesenchymal stromal cells (MSCs). However, the precise function of miR-7977 is not known. In this study, we performed transduction of a miR-7977 mimic into MSCs, compared transcriptomes between control-transduced (n = 3) and miR-7977-transduced MSCs (n = 3), and conducted pathway analysis. The array data revealed that the expression of 0.05% of genes was reduced 2-fold and the expression of 0.01% of genes was increased 2-fold. Interestingly, approximately half of these genes possessed a miR-7977 target site, while the other genes did not, suggesting that miR-7977 regulates the gene expression level directly and indirectly. Gene set enrichment analysis showed that the gene sets of Yes-associated protein 1 (YAP1) _up were significantly enriched (p<0.001, q<0.25), suggesting that miR-7977 modulates the Hippo-YAP signaling pathway. Visualization of pathway and network showed that miR-7977 significantly reduced the expression of Hippo core kinase, STK4. miR-7977 inactivated the Hippo-YAP signaling pathway as proven by GFP-tagged YAP nuclear trans localization and TEAD reporter assay. The miR-7977-transduced MSC cell line, HTS-5, showed elevated saturation density and enhanced entry into the cell cycle. These results suggest that miR-7977 is a critical factor that regulates the Hippo-YAP signaling pathway in BM-MSCs and may be involved in the upregulation of leukemia-supporting stroma growth.

Extravesicular Mir-7977 Released from Leukemic Cells Inhibites the PCBP1-Mediated mRNA Stabilization and Hippo-YAP Signaling Pathway in Bone Marrow Mesenchymal Stromal Cells

[Background] We and others have revealed that various abnormalities of the bone marrow (BM) environment such as aberrant cytokine expression and impaired microRNA (miRNA) biogenesis are observed in patients with myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). However, underlying mechanisms to induce BM stromal dysfunction have not yet been clarified. Recently, we have found that abundant extracellular vesicles including exosomes, were detected in the BM interstitial fluid. Furthermore, we have shown that exosomal miR-7977 was highly released from AML cells (GSE64029) and was taken up by BM mesenchymal stem cells (MSCs). Based on these findings, we hypothesized that exosomal miR-7977 could be involved in the alteration of BM stromal function of MDS/AML.[Materials and Methods] To gain an insight into the function of exosomal miR-7977 in BM, we firstly performed transduction of a miR-7977 mimic into BM MSCs and compared transcriptomes between control-transduced and miR-7977-transduced MSCs (GSE108186). Subsequently, we selected the differentially expressed genes (DEGs) and conduced gene set enrichment analysis (GSEA).[Results] Regarding DEGs, we focused on poly(rC) binding protein 1 (PCBP1), since PCBP1 was predicted to be a target gene of miR-7977 by an online database for miRNA target prediction using miRDB. The reductions in PCBP1 mRNA and protein were confirmed in MSCs after miR-7977 transfer by real time PCR. Because PCBP1 is known to be involved in splicing, and the expression levels of several genes, we analyzed the expression of several hematopoietic factors and found that expression level of stem cell factor (SCF), angiopoietin-1 (ANGPT1) and Jagged-1 (JAG1) were remarkably decreased. Regarding the pathway analysis, GSEA showed that the gene sets of Yes-associated protein 1 (YAP1)_up were significantly enriched (p<0.001, q<0.25), suggesting that miR-7977 modulates the Hippo-YAP signaling pathway. Visualization of pathway and network showed that miR-7977 significantly reduced the expression of Hippo core kinase, STK4. The transfer of miR-7977 mimic inactivated the Hippo-YAP signaling pathway as proven by GFP-tagged YAP nuclear trans localization and TEAD reporter assay. The miR-7977-transduced MSCs showed elevated saturation density and enhanced entry into the cell cycle.[Conclusion] Collectively, these results indicated that miR-7977 is an important factor that inhibits normal hematopoiesis via PCBP1 reduction and up-regulate the growth of functionally-disturbed MSCs via inactivation of Hippo-YAP signaling pathway in MDS/AML. DisclosuresNo relevant conflicts of interest to declare.

Stable MOB1 interaction with Hippo/MST is not essential for development and tissue growth control

The Hippo tumor suppressor pathway is essential for development and tissue growth control, encompassing a core cassette consisting of the Hippo (MST1/2), Warts (LATS1/2), and Tricornered (NDR1/2) kinases together with MOB1 as an important signaling adaptor. However, it remains unclear which regulatory interactions between MOB1 and the different Hippo core kinases coordinate development, tissue growth, and tumor suppression. Here, we report the crystal structure of the MOB1/NDR2 complex and define key MOB1 residues mediating MOB1’s differential binding to Hippo core kinases, thereby establishing MOB1 variants with selective loss-of-interaction. By studying these variants in human cancer cells and Drosophila, we uncovered that MOB1/Warts binding is essential for tumor suppression, tissue growth control, and development, while stable MOB1/Hippo binding is dispensable and MOB1/Trc binding alone is insufficient. Collectively, we decrypt molecularly, cell biologically, and genetically the importance of the diverse interactions of Hippo core kinases with the pivotal MOB1 signal transducer.

Impaired liver regeneration in aged mice can be rescued by silencing Hippo core kinases MST1 and MST2

The liver has an intrinsic capacity to regenerate in response to injury or surgical resection. Nevertheless, circumstances in which hepatocytes are unresponsive to proliferative signals result in impaired regeneration and hepatic failure. As the Hippo pathway has a canonical role in the maintenance of liver size, we investigated whether it could serve as a therapeutic target to support regeneration. Using a standard two‐thirds partial hepatectomy (PH) model in young and aged mice, we demonstrate that the Hippo pathway is modulated across the phases of liver regeneration. The activity of the core kinases MST1 and LATS1 increased during the early hypertrophic phase and returned to steady state levels in the proliferative phase, coinciding with activation of YAP1 target genes and hepatocyte proliferation. Moreover, following PH in aged mice, we demonstrate that Hippo signaling is anomalous in non‐regenerating livers. We provide pre‐clinical evidence that silencing the Hippo core kinases MST1 and MST2 with siRNA provokes hepatocyte proliferation in quiescent livers and rescues liver regeneration in aged mice following PH. Our data suggest that targeting the Hippo core kinases MST1/2 has therapeutic potential to improve regeneration in non‐regenerative disorders.

AJUBA LIM Proteins Limit Hippo Activity in Proliferating Cells by Sequestering the Hippo Core Kinase Complex in the Cytosol.

The Hippo pathway controls organ growth and is implicated in cancer development. Whether and how Hippo pathway activity is limited to sustain or initiate cell growth when needed is not understood. The members of the AJUBA family of LIM proteins are negative regulators of the Hippo pathway. In mammalian epithelial cells, we found that AJUBA LIM proteins limit Hippo regulation of YAP, in proliferating cells only, by sequestering a cytosolic Hippo kinase complex in which LATS kinase is inhibited. At the plasma membranes of growth-arrested cells, AJUBA LIM proteins do not inhibit or associate with the Hippo kinase complex. The ability of AJUBA LIM proteins to inhibit YAP regulation by Hippo and to associate with the kinase complex directly correlate with their capacity to limit Hippo signaling during Drosophila wing development. AJUBA LIM proteins did not influence YAP activity in response to cell-extrinsic or cell-intrinsic mechanical signals. Thus, AJUBA LIM proteins limit Hippo pathway activity in contexts where cell proliferation is needed.

Abstract 3305: Hippo kinases LATS1/2 control human breast cell fate

Abstract Cellular differentiation and lineage commitment in adult tissues is a tightly regulated, yet highly dynamic process. It is of crucial importance to understand how different cell fates are maintained and how cellular plasticity is regulated: In the context of normal development but also in the light of the fact that perturbations acting as cell fate switches are the underlining cause for many human diseases. Still, the regulation of cell fate in many tissues, including the breast, remains largely elusive. We performed a high-content confocal image-based loss-of-function screen for regulators of primary breast cell fate. We infected primary human breast cells with a shRNA tumor suppressor library in serum-free suspension culture in an arrayed format and assessed a variety of phenotypic parameters using automated confocal imaging. We found that removal of tumor-suppressor genes increased the number of progenitor cells and promoted self-renewal potential. Unexpectedly, these effects were particularly linked to an increase in the number of cells of the luminal lineage. Redundant shRNA activity (RSA) and pathway analysis revealed that activation of the Hippo pathway was significantly associated with this increase in self-renewal and the luminal phenotype. We focused on the Hippo core kinases LATS1/2 (LATS), which were among the highest scored hits in the initial screen. Depletion of LATS in normal breast cells derived from several independent donors promoted self-renewal, luminal fate and increased the numbers of luminal progenitors. Luminal progenitors have been shown to include the cell-of-origin of most human breast cancers and supporting this hypothesis, we found that LATS protein expression was low or absent in most human breast cancers. Furthermore, we generated a gene signature of LATS depleted primary breast cells, which revealed a high enrichment in genes belonging to luminal A and B subtypes of breast cancer. Surprisingly, endogenous activation of the Hippo pathway via removal of its core kinases LATS only resulted in modest upregulation of its canonical targets YAP/TAZ, but rather triggered a pronounced increase in the expression of luminal and luminal progenitor genes. These findings challenge the current observation that Hippo effectors YAP/TAZ are associated with mammary basal cell fate and uncover a novel YAP/TAZ-independent role of LATS in the regulation on breast cell fate. Citation Format: Adrian Britschgi, Stephan Duss, Sungeun Kim, Heike Brinkhaus, Joana Pinto Couto, Duvini De Silva, Loren Miraglia, Michael B. Stadler, Anthony P. Orth, Ghislain M.C. Bonamy, Venkateshwar A. Reddy, Mohamed Bentires-Alj. Hippo kinases LATS1/2 control human breast cell fate. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3305.

Abstract 2274: Deregulated Hippo pathway is a potential therapeutic target for advanced gallbladder cancer

Abstract Gallbladder cancer (GBC) is lethal and aggressive disease characterized by late diagnosis, poor prognosis and lack of effective therapeutic options. An excellent candidate for targeting therapy in cancer is the Hippo signaling pathway that has been reported to be deregulated in different types of cancer and recently has emerged as a master regulator that plays a critical role in multiple processes such as tumorigenesis, apoptosis, tumor stem cell phenotype, drug cell resistance and metastatic potential. However, little is known about the status of the Hippo kinase pathway in human GBC. The aim of this study is determinate the Hippo pathway activity in GBC and evaluate the potential therapeutic role of YAP1 siRNA and the pharmacological inhibitor Verteporfin, a small molecule that inhibit TEAD-YAP interaction. Immunohistochemistry was used to analyze the expression of YAP1 and Survivin, a major downstream effector and transcriptional target gene of Hippo signaling pathway, in tissue microarray containing 198 advanced GBC samples. Then, we performed an exploratory analysis of Hippo pathway activity by qRT- PCR in advanced GBC and cholecystitis samples. The levels of expression of the Hippo core kinase proteins in GBC cell lines was studied by western blot and the inhibition of YAP1 was performed thought specific siRNA and Verteporfin. Immunohistochemistry showed high nuclear expression of YAP1 in vast majority of advanced GBC, which is correlated significantly with nuclear Survivin expression. The 5-year survival rates of patients with survivin-positive cancer were significantly lower compared with survivin-negative cancer patients (p&amp;lt;0.05, Log-rank test). The gene expression analysis showed a significant down-regulation of the Hippo kinase core suppressor genes STK3 (MST2), STK4 (MST1), SAV1, LATS2 and up-regulation of GPCR5A and BIRC5 in GBC tissues compared with cholecystitis. In addition, western blot analysis show high levels of nuclear YAP1 in 4 GBC cells and its expression were associated with a reduction in the phosphorylation status of LATS1 and MOB. Our findings indicate that targeting YAP1 with siRNA reduced mRNA and protein levels of this oncogene in almost 80% and inhibited the clonogenic capacity of GBC cell lines. Otherwise, the in vitro pharmacological inhibition of YAP1 with Verterporfin reduces YAP1 protein in a dose-dependent manner and was associated with down-regulation of survivin. Our results showed that the Hippo- pathway is deregulated in advanced GBC and mediates its oncogenic effects through of attenuation of their suppressor core components, nuclear translocation of YAP1 and up-regulation of survivin expression. Targeting YAP1 by siRNA and Verteporfin leads to inactivation of YAP1 and survivin affecting cancer cell survival capacity. Targeting the Hippo/YAP has the potential to provide a novel strategy for GBC therapy. Research supported by FONDECYT 3140426, 1130204, 11130515, 3140308. Citation Format: Carolina Bizama, Patricia García, Jaime A Espinoza, Nicole Elgueta, Ismael Riquelme, Francisca Alfaro, Diego Romero, Helga Weber, Pamela Leal, Javier Retamal, Lorena Rosa, Juan Carlos Roa. Deregulated Hippo pathway is a potential therapeutic target for advanced gallbladder cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2274.

THU-459 - Deletion of the Hippo Core Kinases MST1 and MST2 by SIRNA Rescued Liver Regeneration in Aged Mice

THU-459 - Deletion of the Hippo Core Kinases MST1 and MST2 by SIRNA Rescued Liver Regeneration in Aged Mice

Upregulation of miR-181c contributes to chemoresistance in pancreatic cancer by inactivating the Hippo signaling pathway.

The Hippo signaling pathway plays a crucial role in regulating tissue homeostasis, organ size, tumorigenesis and cancer chemoresistance when deregulated. Physiologically, the Hippo core kinase cassette that consists of mamma-lian STE20-like protein kinase 1/2 (MST1/2), and large tumour suppressor 1/2 (LATS1/2), together with the adaptor proteins Salvador homologue 1 (SAV1) and MOB kinase activator 1 (MOB1), tightly restricts the activities of homologous oncoproteins Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ) to low levels. However, how the Hippo kinase cassette core components are simultaneously inhibited, to exhibit constitutively inactivated Hippo signaling and activated YAP/TAZ in cancer remains puzzling. Herein, we reported that miR-181c directly repressed MST1, LATS2, MOB1 and SAV1 expression in human pancreatic cancer cells. Overexpression of miR-181c induced hyperactivation of the YAP/TAZ and enhanced expression of the Hippo signaling downstream genes CTGF, BIRC5 and BLC2L1, leading to pancreatic cancer cell survival and chemoresistance in vitro and in vivo. Importantly, high miR-181c levels were significantly correlated with Hippo signaling inactivation in pancreatic cancer samples, and predicted a poor patient overall survival. These findings provide a novel mechanism for Hippo signaling inactivation in cancer, indicating not only a potentially pivotal role for miR-181c in the progression of pancreatic cancer, but also may represent a new therapeutic target and prognostic marker.

Actin-binding and Cell Proliferation Activities of Angiomotin Family Members Are Regulated by Hippo Pathway-mediated Phosphorylation

Whether the Hippo pathway has downstream targets other than YAP and TAZ is unknown. In this report, we have identified angiomotin (Amot) family members as novel substrates of Hippo core kinases. The N-terminal regions of Amot proteins contain a conserved HXRXXS consensus site for LATS1/2-mediated phosphorylation. Phospho-specific antibodies showed that Hippo core kinases could mediate phosphorylation of endogenous as well as exogenous Amot family members. Knockdown of LATS1 and LATS2 endogenously reduced the phosphorylation of Amots detected by the phospho-specific antibodies. Mutation of the serine to alanine within this HXRXXS site in Amot and AmotL2 established that this site was essential for Hippo core kinase-mediated phosphorylation. Wild-type and non-phosphorylated Amot (Amot-S175A) were targeted to actin filaments, whereas phospho-mimic Amot (Amot-S175D) failed to be localized with actin. Overexpression of LATS2 caused dissociation of Amot from actin but not Amot-S175A. Mapping of the actin-binding site of Amot showed that serine 175 of Amot was important for the actin-binding activity. Amot-S175A promoted, whereas Amot and Amot-S175D inhibited, cell proliferation. These results collectively suggest that the Hippo pathway negatively regulates the actin-binding activity of Amot family members through direct phosphorylation.