Hippo Kinase Cascade Research Articles

HPV18 E7 inhibits LATS1 kinase and activates YAP1 by degrading PTPN14.

High-risk human papillomavirus (HPV) oncoproteins inactivate cellular tumor suppressors to reprogram host cell signaling pathways. HPV E7 proteins bind and degrade the tumor suppressor PTPN14, thereby promoting the nuclear localization of the YAP1 oncoprotein and inhibiting keratinocyte differentiation. YAP1 is a transcriptional coactivator that drives epithelial cell stemness and self-renewal. YAP1 activity is inhibited by the highly conserved Hippo pathway, which is frequently inactivated in human cancers. MST1/2 and LATS1/2 kinases form the core of the Hippo kinase cascade. Active LATS1 kinase is phosphorylated on threonine 1079 and inhibits YAP1 by phosphorylating it on amino acids including serine 127. Here, we tested the effect of high-risk (carcinogenic) HPV18 E7 on Hippo pathway activity. We found that either PTPN14 knockout or PTPN14 degradation by HPV18 E7 decreased the phosphorylation of LATS1 T1079 and YAP1 S127 in human keratinocytes and inhibited keratinocyte differentiation. Conversely, PTPN14-dependent differentiation required LATS kinases and certain PPxY motifs in PTPN14. Neither MST1/2 kinases nor the putative PTPN14 phosphatase active sites were required for PTPN14 to promote differentiation. Together, these data support that PTPN14 inactivation or degradation of PTPN14 by HPV18 E7 reduce LATS1 activity, promoting active YAP1 and inhibiting keratinocyte differentiation.IMPORTANCEThe Hippo kinase cascade inhibits YAP1, an oncoprotein and driver of cell stemness and self-renewal. There is mounting evidence that the Hippo pathway is targeted by tumor viruses including human papillomavirus. The high-risk HPV E7 oncoprotein promotes YAP1 nuclear localization and the carcinogenic activity of high-risk HPV E7 requires YAP1 activity. Blocking HPV E7-dependent YAP1 activation could inhibit HPV-mediated carcinogenesis, but the mechanism by which HPV E7 activates YAP1 has not been elucidated. Here we report that by degrading the tumor suppressor PTPN14, HPV18 E7 inhibits LATS1 kinase, reducing inhibitory phosphorylation on YAP1. These data support that an HPV oncoprotein can inhibit Hippo signaling to activate YAP1 and strengthen the link between PTPN14 and Hippo signaling in human epithelial cells.

HPV18 E7 inhibits LATS1 kinase and activates YAP1 by degrading PTPN14.

High-risk human papillomavirus (HPV) oncoproteins inactivate cellular tumor suppressors to reprogram host cell signaling pathways. HPV E7 proteins bind and degrade the tumor suppressor PTPN14, thereby promoting the nuclear localization of the YAP1 oncoprotein and inhibiting keratinocyte differentiation. YAP1 is a transcriptional coactivator that drives epithelial cell stemness and self-renewal. YAP1 activity is inhibited by the highly conserved Hippo pathway, which is frequently inactivated in human cancers. MST1/2 and LATS1/2 kinases form the core of the Hippo kinase cascade. Active LATS1 kinase is phosphorylated on threonine 1079 and inhibits YAP1 by phosphorylating it on amino acids including serine 127. Here, we tested the effect of high-risk (carcinogenic) HPV18 E7 on Hippo pathway activity. We found that either PTPN14 knockout or PTPN14 degradation by HPV18 E7 decreased phosphorylation of LATS1 T1079 and YAP1 S127 in human keratinocytes and inhibited keratinocyte differentiation. Conversely, PTPN14-dependent differentiation required LATS kinases and certain PPxY motifs in PTPN14. Neither MST1/2 kinases nor the putative PTPN14 phosphatase active site were required for PTPN14 to promote differentiation. Taken together, these data support that PTPN14 inactivation or degradation of PTPN14 by HPV18 E7 reduce LATS1 activity, promoting active YAP1 and inhibiting keratinocyte differentiation.

Abstract 4585: Discovery of ETS-006, a highly potent YAP/TEADs PPI inhibitor with broad anti-tumor activity as a single agent

Abstract The transcription co-activators YAP, pairing with the TEAD family of transcription factors, serve as essential effectors of the conserved Hippo signaling pathway. Hippo kinase cascade controls YAP nuclear entry and binding with TEADs by modulating its phosphorylation and stability. Overexpression and activation of YAP/TAZ are frequently observed in a variety of cancers. It has been well established that YAP aberration contributes to cancer development, metastasis, immunosurveillance escape and drug resistance. Disruption of YAP/TEADs PPI is an effective approach to inhibit YAP transcriptional activity. We previously have reported the identification of YAP/TEADs PPI hit compound through the fragment-based screen and advanced the hit to lead compound ETS-003. Here we reported the preclinical candidate of YAP/TEADs PPI inhibitor ETS-006 with much more potent anti-tumor activity and favorable safety profile. Compared to TEAD palmitoylation inhibitor, ETS-006 could completely disrupt the interaction of YAP/TEADs, resulting in a more profound downregulation of YAP target gene expression. ETS-006 demonstrated more robust anti-tumor activity than the competitor’s YAP/TEADs PPI inhibitor in MPM CDX model with favorable ADME properties. Notably, ETS-006 showed promising efficacy across multiple solid tumor types, including head and neck squamous cell carcinoma, osteosarcoma, and triple-negative breast cancer with urgent unmet clinical needs. In conclusion, ETS-006 is a highly potent and orally available YAP/TEADs PPI inhibitor with broad anti-tumor activity as a single agent. Citation Format: Jiajun Lu, Ming Gao, Wenpei Du, Xiaofei Fan, Jinping Li, Mengya Wang, Lijian Feng, Yingjie Li, Jiaqi Yao, Jiting Lu, Wenqi Cui, Qiangang Zheng, Jidong Zhu. Discovery of ETS-006, a highly potent YAP/TEADs PPI inhibitor with broad anti-tumor activity as a single agent [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4585.

The Hippo kinase cascade regulates a contractile cell behavior and cell density in a close unicellular relative of animals.

The genomes of close unicellular relatives of animals encode orthologs of many genes that regulate animal development. However, little is known about the function of such genes in unicellular organisms or the evolutionary process by which these genes came to function in multicellular development. The Hippo pathway, which regulates cell proliferation and tissue size in animals, is present in some of the closest unicellular relatives of animals, including the amoeboid organism Capsaspora owczarzaki. We previously showed that the Capsaspora ortholog of the Hippo pathway nuclear effector Yorkie/YAP/TAZ (coYki) regulates actin dynamics and the three-dimensional morphology of Capsaspora cell aggregates, but is dispensable for cell proliferation control (Phillips et al., 2022). However, the function of upstream Hippo pathway components, and whether and how they regulate coYki in Capsaspora, remained unknown. Here, we analyze the function of the upstream Hippo pathway kinases coHpo and coWts in Capsaspora by generating mutant lines for each gene. Loss of either kinase results in increased nuclear localization of coYki, indicating an ancient, premetazoan origin of this Hippo pathway regulatory mechanism. Strikingly, we find that loss of either kinase causes a contractile cell behavior and increased density of cell packing within Capsaspora aggregates. We further show that this increased cell density is not due to differences in proliferation, but rather actomyosin-dependent changes in the multicellular architecture of aggregates. Given its well-established role in cell density-regulated proliferation in animals, the increased density of cell packing in coHpo and coWts mutants suggests a shared and possibly ancient and conserved function of the Hippo pathway in cell density control. Together, these results implicate cytoskeletal regulation but not proliferation as an ancestral function of the Hippo pathway kinase cascade and uncover a novel role for Hippo signaling in regulating cell density in a proliferation-independent manner.

The Hippo kinase cascade regulates a contractile cell behavior and cell density in a close unicellular relative of animals

The genomes of close unicellular relatives of animals encode orthologs of many genes that regulate animal development. However, little is known about the function of such genes in unicellular organisms or the evolutionary process by which these genes came to function in multicellular development. The Hippo pathway, which regulates cell proliferation and tissue size in animals, is present in some of the closest unicellular relatives of animals, including the amoeboid organism Capsaspora owczarzaki. We previously showed that the Capsaspora ortholog of the Hippo pathway nuclear effector Yorkie/YAP/TAZ (coYki) regulates actin dynamics and the three-dimensional morphology of Capsaspora cell aggregates, but is dispensable for cell proliferation control (Phillips et al., 2022). However, the function of upstream Hippo pathway components, and whether and how they regulate coYki in Capsaspora, remained unknown. Here, we analyze the function of the upstream Hippo pathway kinases coHpo and coWts in Capsaspora by generating mutant lines for each gene. Loss of either kinase results in increased nuclear localization of coYki, indicating an ancient, premetazoan origin of this Hippo pathway regulatory mechanism. Strikingly, we find that loss of either kinase causes a contractile cell behavior and increased density of cell packing within Capsaspora aggregates. We further show that this increased cell density is not due to differences in proliferation, but rather actomyosin-dependent changes in the multicellular architecture of aggregates. Given its well-established role in cell density-regulated proliferation in animals, the increased density of cell packing in coHpo and coWts mutants suggests a shared and possibly ancient and conserved function of the Hippo pathway in cell density control. Together, these results implicate cytoskeletal regulation but not proliferation as an ancestral function of the Hippo pathway kinase cascade and uncover a novel role for Hippo signaling in regulating cell density in a proliferation-independent manner.

The TGFβ→TAK1→LATS→YAP1 Pathway Regulates the Spatiotemporal Dynamics of YAP1.

The Hippo kinase cascade functions as a central hub that relays input from the "outside world" of the cell and translates it into specific cellular responses by regulating the activity of Yes-associated protein 1 (YAP1). How Hippo translates input from the extracellular signals into specific intracellular responses remains unclear. Here, we show that transforming growth factor β (TGFβ)-activated TAK1 activates LATS1/2, which then phosphorylates YAP1. Phosphorylated YAP1 (p-YAP1) associates with RUNX3, but not with TEAD4, to form a TGFβ-stimulated restriction (R)-point-associated complex which activates target chromatin loci in the nucleus. Soon after, p-YAP1 is exported to the cytoplasm. Attenuation of TGFβ signaling results in re-localization of unphosphorylated YAP1 to the nucleus, where it forms a YAP1/TEAD4/SMAD3/AP1/p300 complex. The TGFβ-stimulated spatiotemporal dynamics of YAP1 are abrogated in many cancer cells. These results identify a new pathway that integrates TGFβ signals and the Hippo pathway (TGFβ→TAK1→LATS1/2→YAP1 cascade) with a novel dynamic nuclear role for p-YAP1.

A tale of two Hippo pathway modules.

The Hippo pathway is an evolutionarily conserved pathway with crucial roles in development, organ size control, tissue homeostasis and cancer. Over two decades of research have elucidated the core Hippo pathway kinase cascade, but its precise organization has not been fully understood. In this issue of The EMBO Journal, Qi etal(2023) report a new model of two modules for the Hippo kinase cascade, providing new insights into this long-standing question.

Non-hippo kinases: indispensable roles in YAP/TAZ signaling and implications in cancer therapy.

The transcriptional co-activators Yes-associated protein (YAP) and PDZ-binding domain (TAZ) are the known downstream effectors of the Hippo kinase cascade. YAP/TAZ have been shown to play important roles in cellular growth and differentiation, tissue development and carcinogenesis. Recent studies have found that, in addition to the Hippo kinase cascade, multiple non-Hippo kinases also regulate the YAP/TAZ cellular signaling and produce important effects on cellular functions, particularly on tumorigenesis and progression. In this article, we will review the multifaceted regulation of the YAP/TAZ signaling by the non-Hippo kinases and discuss the potential application of the non-Hippo kinase-regulated YAP/TAZ signaling for cancer therapy.

Chlamydia trachomatis induces the transcriptional activity of host YAP in a Hippo-independent fashion.

The obligate intracellular pathogen Chlamydia trachomatis is the causative agent of the most common bacterial sexually transmitted disease worldwide. While the host response to infection by this pathogen has been well characterized, it remains unclear to what extent host gene expression during infection is the product of Chlamydia-directed modulation of host transcription factors. To identify transcription factors potentially modulated by Chlamydia during infection, we infected immortalized endocervical epithelial cells (End1/E6E7) with the anogenital C. trachomatis serovar L2, harvesting polyadenylated RNA for bulk RNA-sequencing. Subsequent experiments elucidating the mechanism of infection-mediated YAP activation assayed YAP target gene expression via qRT-PCR, YAP nuclear translocation via quantitative immunofluorescence, and YAP phosphorylation via Western blotting. RNA sequencing of Chlamydia-infected endocervical epithelial cells revealed gene expression consistent with activity of YAP, a transcriptional coactivator implicated in cell proliferation, wound healing, and fibrosis. After confirming induction of YAP target genes during infection, we observed an infection-dependent increase in YAP nuclear translocation sensitive to inhibition of bacterial protein synthesis. While Hippo-mediated phosphoinhibition of YAP at S127 was unaffected by C. trachomatis infection, Hippo-independent phosphorylation at Y357 was increased. Infection did not enhance nuclear translocation of Y357F mutant YAP, illustrating a requirement for phosphorylation at this residue. Pharmacological inhibition of host Src-family kinase activity attenuated YAP Y357 phosphorylation, but not nuclear translocation - which was instead sensitive to inhibition of Abl. Our results define a transcriptome-altering mechanism of pathogen-directed YAP activation that bypasses canonical inhibition by the Hippo kinase cascade, with a potential link to chlamydial fibrosis and other advanced disease sequelae. Additional study is required to determine the specific role of infection-associated Y357 phosphorylation and Abl activity in chlamydial induction of YAP.

The deubiquitinase USP7 promotes HNSCC progression via deubiquitinating and stabilizing TAZ

Dysregulated abundance, location and transcriptional output of Hippo signaling effector TAZ have been increasingly linked to human cancers including head neck squamous cell carcinoma (HNSCC). TAZ is subjected to ubiquitination and degradation mediated by E3 ligase β-TRCP. However, the deubiquitinating enzymes and mechanisms responsible for its protein stability remain underexplored. Here, we exploited customized deubiquitinases siRNA and cDNA library screen strategies and identified USP7 as a bona fide TAZ deubiquitinase in HNSCC. USP7 promoted cell proliferation, migration, invasion in vitro and tumor growth by stabilizing TAZ. Mechanistically, USP7 interacted with, deubiquitinated and stabilized TAZ by selectively removing its K48-linked ubiquitination chain independent of canonical Hippo kinase cascade. USP7 potently antagonized β-TRCP-mediated ubiquitin-proteasomal degradation of TAZ and enhanced its nuclear retention and transcriptional output. Importantly, overexpression of USP7 correlated with TAZ upregulation, tumor aggressiveness and unfavorable prognosis in HNSCC patients. Pharmacological inhibition of USP7 significantly suppressed tumor growth in both xenograft and PDX models. Collectively, these findings identify USP7 as an essential regulator of TAZ and define USP7-TAZ signaling axis as a novel biomarker and potential therapeutic target for HNSCC.

The role of Hippo-YAP/TAZ signaling in brain development.

In order for our complex nervous system to develop normally, both precise spatial and temporal regulation of a number of different signaling pathways is critical. During both early embryogenesis and in organ development, one pathway that has been repeatedly implicated is the Hippo-YAP/TAZ signaling pathway. The paralogs YAP and TAZ are transcriptional co-activators that play an important role in cell proliferation, cell differentiation, and organ growth. Regulation of these proteins by the Hippo kinase cascade is therefore important for normal development. In this article, we review the growing field of research surrounding the role of Hippo-YAP/TAZ signaling in normal and atypical brain development. Starting from the development of the neural tube to the development and refinement of the cerebral cortex, cerebellum, and ventricular system, we address the typical role of these transcriptional co-activators, the functional consequences that manipulation of YAP/TAZ and their upstream regulators have on brain development, and where further research may be of benefit.

KMT5A-methylated SNIP1 promotes triple-negative breast cancer metastasis by activating YAP signaling

Smad nuclear-interacting protein 1 (SNIP1) is a transcription repressor related to the TGF-β signaling pathway and associates with c-MYC, a key regulator of cell proliferation and tumor development. Currently, the mechanism by which SNIP1 regulates tumorigenesis and cancer metastasis is unknown. Here, we identify that SNIP1 is a non-histone substrate of lysine methyltransferase KMT5A, which undergoes KMT5A-mediated mono-methylation to promote breast cancer cell growth, invasion and lung metastasis. Mechanistically, we show KMT5A-mediated K301 methylation of SNIP1 represents a sensing signal to release histone acetyltransferase KAT2A and promotes the interaction of c-MYC and KAT2A, and the recruitment of c-MYC/KAT2A complex to promoter of c-MYC targets. This event ultimately inhibits the Hippo kinase cascade to enhance triple-negative breast cancer (TNBC) metastasis by transcriptionally activating MARK4. Co-inhibition of KMT5A catalytic activity and YAP in TNBC xenograft-bearing animals attenuates breast cancer metastasis and increases survival. Collectively, this study presents an KMT5A methylation-dependent regulatory mechanism governing oncogenic function of SNIP1.

A novel EHD1/CD44/Hippo/SP1 positive feedback loop potentiates stemness and metastasis in lung adenocarcinoma.

There is growing evidence that endocytosis plays a pivotal role in cancer metastasis. In this study, we first identified endocytic and metastasis-associated genes (EMGs) and then investigated the biological functions and mechanisms of EMGs. Cancer stem cells (CSCs)-like characteristics were evaluated by tumour limiting dilution assays, three-dimensional (3D) spheroid cancer models. Microarray analysis was used to identify the pathways significantly regulated by mammalian Eps15 homology domain protein 1 (EHD1) knockdown. Mass spectrometry (MS) was performed to identify EHD1-interacting proteins. The function of EHD1 as a regulator of cluster of differentiation 44 (CD44) endocytic recycling and lysosomal degradation was determined by CD44 biotinylation and recycling assays. EHD1 was identified as a significant EMG. Knockdown of EHD1 suppressed CSCs-like characteristics, epithelial-mesenchymal transition (EMT), migration and invasion of lung adenocarcinoma (LUAD) cells by increasing Hippo kinase cascade activation. Conversely, EHD1 overexpression inhibited the Hippo pathway to promote cancer stemness and metastasis. Notably, utilising MS analysis, the CD44 protein was identified as a potential binding partner of EHD1. Furthermore, EHD1 enhanced CD44 recycling and stability. Indeed, silencing of CD44 or disruption of the EHD1/CD44 interaction enhanced Hippo pathway activity and reduced CSCs-like traits, EMT and metastasis. Interestingly, specificity protein 1 (SP1), a known downstream target gene of the Hippo-TEA-domain family members 1 (TEAD1) pathway, was found to directly bind to the EHD1 promoter region and induce its expression. Among clinical specimens, the EHD1 expression level in LUAD tissues of metastatic patients was higher than that of non-metastatic patients. Our findings emphasise that EHD1 might be a potent anti-metastatic target and present a novel regulatory mechanism by which the EHD1/CD44/Hippo/SP1 positive feedback circuit plays pivotal roles in coupling modules of CSCs-like properties and EMT in LUAD. Targeting this loop may serve as a remedy for patients with advanced metastatic LUAD.

Calmodulin activates the Hippo signaling pathway by promoting LATS1 kinase–mediated inhibitory phosphorylation of the transcriptional coactivator YAP

The Hippo signaling pathway regulates tissue growth and cell fate, and its dysregulation can induce tumorigenesis. When Hippo is activated by cell–cell contact, extracellular signals, or cell polarity among others, the large tumor suppressor 1 (LATS1) kinase catalyzes inhibitory phosphorylation of the transcriptional coactivator Yes-associated protein (YAP) to maintain YAP in the cytoplasm or promote its degradation. Separately, calmodulin is a Ca2+-dependent protein that modulates the activity of target proteins and regulates several signaling cascades; however, its potential role in the Hippo pathway has not been identified. Here, using diverse experimental approaches, including in vitro binding analyses, kinase assays, RT–PCR, and confocal microscopy, we reveal that calmodulin promotes Hippo signaling. We show that purified YAP and LATS1 bind directly to calmodulin and form a Ca2+-dependent ternary complex in vitro. Importantly, Ca2+/calmodulin directly stimulated the activity of LATS1 kinase. In cultured mammalian cells, we demonstrated that endogenous YAP and LATS1 coimmunoprecipitate with endogenous calmodulin. In cells with activated Hippo signaling, we show that calmodulin antagonism significantly (i) decreases YAP phosphorylation, (ii) increases expression of two Hippo target genes (connective tissue growth factor [CTGF] and cysteine-rich angiogenic inducer 61 [CYR61]) that regulate cell proliferation and tumor progression, and (iii) enhances the interaction of YAP with its major transcription factor, thereby facilitating transcription of target genes. Collectively, our data demonstrate that calmodulin activates the Hippo kinase cascade and inhibits YAP activity via a direct interaction with LATS1 and YAP, thereby uncovering previously unidentified crosstalk between the Ca2+/calmodulin and Hippo signaling pathways.

The Hippo Pathway Effectors YAP and TAZ Regulate LH Release by Pituitary Gonadotrope Cells in Mice.

The Hippo transcriptional coactivators YAP and TAZ exert critical roles in morphogenesis, organ size determination and tumorigenesis in many tissues. Although Hippo kinase cascade activity was recently reported in the anterior pituitary gland in mice, the role of the Hippo effectors in regulating gonadotropin production remains unknown. The objective of this study was therefore to characterize the roles of YAP and TAZ in gonadotropin synthesis and secretion. Using a conditional gene targeting approach (cKO), we found that gonadotrope-specific inactivation of Yap and Taz resulted in increased circulating levels of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in adult male mice, along with increased testosterone levels and testis weight. Female cKO mice had increased circulating LH (but not FSH) levels, which were associated with a hyperfertility phenotype characterized by higher ovulation rates and larger litter sizes. Unexpectedly, the loss of YAP/TAZ did not appear to affect the expression of gonadotropin subunit genes, yet both basal and GnRH-induced LH secretion were increased in cultured pituitary cells from cKO mice. Likewise, pharmacologic inhibition of YAP binding to the TEAD family of transcription factors increased both basal and GnRH-induced LH secretion in LβT2 gonadotrope-like cells in vitro without affecting Lhb expression. Conversely, mRNA levels of ChgA and SgII, which encode key secretory granule cargo proteins, were decreased following pharmacologic inhibition of YAP/TAZ, suggesting a mechanism whereby YAP/TAZ regulate the LH secretion machinery in gonadotrope cells. Together, these findings represent the first evidence that Hippo signaling may play a role in regulating pituitary LH secretion.

Lipid-Raft-Targeted Molecular Self-Assembly Inactivates YAP to Treat Ovarian Cancer.

The Yes-associated protein (YAP) is a major oncoprotein responsible for cell proliferation control. YAP's oncogenic activity is regulated by both the Hippo kinase cascade and uniquely by a mechanical-force-induced actin remodeling process. Inspired by reports that ovarian cancer cells specifically accumulate the phosphatase protein ALPP on lipid rafts that physically link to actin cytoskeleton, we developed a molecular self-assembly (MSA) technology that selectively halts cancer cell proliferation by inactivating YAP. We designed a ruthenium-complex-peptide precursor molecule that, upon cleavage of phosphate groups, undergoes self-assembly to form nanostructures specifically on lipid rafts of ovarian cancer cells. The MSAs exert potent, cancer-cell-specific antiproliferative effects in multiple cancer cell lines and in mouse xenograft tumor models. Our work illustrates how basic biochemical insights can be exploited as the basis for a nanobiointerface fabrication technology which links nanoscale protein activities at specific subcellular locations to molecular biological activities to suppress cancer cell proliferation.

Hepatic Hippo signaling inhibits development of hepatocellular carcinoma.

Primary liver cancer is one of the most common cancer worldwide. Hepatocellular carcinoma (HCC) in particular, is the second leading cause of cancer deaths in the world. The Hippo signaling pathway has emerged as a major oncosuppressive pathway that plays critical roles inhibiting hepatocyte proliferation, survival, and HCC formation. A key component of the Hippo pathway is the inhibition of yes-associated protein (YAP)/transcriptional co-activator with PDZ-binding motif (TAZ) transcription factors by the Hippo kinase cascade. Aberrant activation of YAP or TAZ has been found in several human cancers including HCC. It is also well established that YAP/TAZ activation in hepatocytes causes HCC in mouse models, indicating that YAP/TAZ are potential therapeutic targets for human liver cancer. In this review, we summarize the recent findings regarding the multifarious roles of Hippo/YAP/TAZ in HCC development, and focus on their cell autonomous roles in controlling hepatocyte proliferation, differentiation, survival and metabolism as well as their non-cell autonomous in shaping the tumor microenvironment.

Casein kinase 1 family proteins promote Slimb-dependent Expanded degradation.

Hippo signalling integrates diverse stimuli related to epithelial architecture to regulate tissue growth and cell fate decisions. The Hippo kinase cascade represses the growth-promoting transcription co-activator Yorkie. The FERM protein Expanded is one of the main upstream Hippo signalling regulators in Drosophila as it promotes Hippo kinase signalling and directly inhibits Yorkie. To fulfil its function, Expanded is recruited to the plasma membrane by the polarity protein Crumbs. However, Crumbs-mediated recruitment also promotes Expanded turnover via a phosphodegron-mediated interaction with a Slimb/β-TrCP SCF E3 ligase complex. Here, we show that the Casein Kinase 1 (CKI) family is required for Expanded phosphorylation. CKI expression promotes Expanded phosphorylation and interaction with Slimb/β-TrCP. Conversely, CKI depletion in S2 cells impairs Expanded degradation downstream of Crumbs. In wing imaginal discs, CKI loss leads to elevated Expanded and Crumbs levels. Thus, phospho-dependent Expanded turnover ensures a tight coupling of Hippo pathway activity to epithelial architecture.

VGLL3 operates via TEAD1, TEAD3 and TEAD4 to influence myogenesis in skeletal muscle.

ABSTRACTVGLL proteins are transcriptional co-factors that bind TEAD family transcription factors to regulate events ranging from wing development in fly, to muscle fibre composition and immune function in mice. Here, we characterise Vgll3 in skeletal muscle. We found that mouse Vgll3 was expressed at low levels in healthy muscle but that its levels increased during hypertrophy or regeneration; in humans, VGLL3 was highly expressed in tissues from patients with various muscle diseases, such as in dystrophic muscle and alveolar rhabdomyosarcoma. Interaction proteomics revealed that VGLL3 bound TEAD1, TEAD3 and TEAD4 in myoblasts and/or myotubes. However, there was no interaction with proteins from major regulatory systems such as the Hippo kinase cascade, unlike what is found for the TEAD co-factors YAP (encoded by YAP1) and TAZ (encoded by WWTR1). Vgll3 overexpression reduced the activity of the Hippo negative-feedback loop, affecting expression of muscle-regulating genes including Myf5, Pitx2 and Pitx3, and genes encoding certain Wnts and IGFBPs. VGLL3 mainly repressed gene expression, regulating similar genes to those regulated by YAP and TAZ. siRNA-mediated Vgll3 knockdown suppressed myoblast proliferation, whereas Vgll3 overexpression strongly promoted myogenic differentiation. However, skeletal muscle was overtly normal in Vgll3-null mice, presumably due to feedback signalling and/or redundancy. This work identifies VGLL3 as a transcriptional co-factor operating with the Hippo signal transduction network to control myogenesis.

Intercalated discs: cellular adhesion and signaling in heart health and diseases.

Intercalated discs (ICDs) are highly orchestrated structures that connect neighboring cardiomyocytes in the heart. Three major complexes are distinguished in ICD: desmosome, adherens junction (AJ), and gap junction (GJ). Desmosomes are major cell adhesion junctions that anchor cell membrane to the intermediate filament network; AJs connect the actin cytoskeleton of adjacent cells; and gap junctions metabolically and electrically connect the cytoplasm of adjacent cardiomyocytes. All these complexes work as a single unit, the so-called area composita, interdependently rather than individually. Mutation or altered expression of ICD proteins results in various cardiac diseases, such as ARVC (arrhythmogenic right ventricular cardiomyopathy), dilated cardiomyopathy, and hypotrophy cardiomyopathy, eventually leading to heart failure. In this article, we first review the recent findings on the structural organization of ICD and their functions and then focus on the recent advances in molecular pathogenesis of the ICD-related heart diseases, which include two major areas: i) the ICD gene mutations in cardiac diseases, and ii) the involvement of ICD proteins in signal transduction pathways leading to myocardium remodeling and eventual heart failure. These major ICD-related signaling pathways include Wnt/β-catenin pathway, p38 MAPK cascade, Rho-dependent serum response factor (SRF) signaling, calcineurin/NFAT signaling, Hippo kinase cascade, etc., which are differentially regulated in pathological conditions.