The Angiomotins--from discovery to function

p97/VCP is required for piecemeal autophagy of aggresomes

Metazoan cells adapt to the exhaustion of protein quality control (PQC) systems by sequestering aggregation-prone proteins in large, pericentriolar structures termed aggresomes. Defects in both aggresome formation and clearance affect proteostasis and have been linked to neurodegenerative diseases, but aggresome clearance pathways are still underexplored. Here we show that aggresomes comprising endogenous proteins are cleared via selective autophagy requiring the cargo receptor TAX1BP1. TAX1BP1 proximitomes reveal the presence of various PQC systems at aggresomes, including Hsp70 chaperones, the 26S proteasome, and the ubiquitin-selective unfoldase p97/VCP. While Hsp70 and p97/VCP with its cofactors UFD1-NPL4 and FAF1 play key roles in aggresome disassembly, the 26S proteasome is dispensable. We identify aggresomal client proteins that are degraded via different routes, in part in a p97/VCP-dependent manner via aggrephagy. Upon acute inhibition of p97/VCP, aggresomes fail to disintegrate and cannot be incorporated into autophagosomes despite the presence of factors critical for aggrephagosome formation, including p62/SQSTM1, TAX1BP1, and WIPI2. We conclude that the p97/VCP-mediated removal of ubiquitylated aggresomal clients is essential for the disintegration and subsequent piecemeal autophagy of aggresomes.

PARylation-mediated post-transcriptional modifications in cancer immunity and immunotherapy

Poly-ADP-ribosylation (PARylation) is a post-translational modification in which ADP-ribose is added to substrate proteins. PARylation is mediated by a superfamily of ADP-ribosyl transferases known as PARPs and influences a wide range of cellular functions, including genome integrity maintenance, and the regulation of proliferation and differentiation. We and others have recently reported that PARylation of SH3 domain-binding protein 2 (3BP2) plays a role in bone metabolism, immune system regulation, and cytokine production. Additionally, PARylation has recently gained attention as a target for cancer treatment. In this review, we provide an overview of PARylation, its involvement in several signaling pathways related to cancer immunity, and the potential of combination therapies with PARP inhibitors and immune checkpoint inhibitors.

Angiomotin cleavage promotes leader formation and collective cell migration

Collective cell migration (CCM) is involved in multiple biological processes, including embryonic morphogenesis, angiogenesis, and cancer invasion. However, the molecular mechanisms underlying CCM, especially leader cell formation, are poorly understood. Here, we show that a signaling pathway regulating angiomotin (AMOT) cleavage plays a role in CCM, using mammalian epithelial cells and mouse models. In a confluent epithelial monolayer, full-length AMOT localizes at cell-cell junctions and limits cell motility. After cleavage, the C-terminal fragment of AMOT (AMOT-CT) translocates to the cell-matrix interface to promote the maturation of focal adhesions (FAs), generate traction force, and induce leader cell formation. Meanwhile, decreased full-length AMOT at cell-cell junctions leads to tissue fluidization and coherent migration of cell collectives. Hence, the cleavage of AMOT serves as a molecular switch to generate polarized contraction, promoting leader cell formation and CCM.

Biliary atresia: insights into mechanisms using a toxic model of the disease including Wnt and Hippo signaling pathways and microtubules

BACKGROUND

Mechanisms underlying bile duct injury in biliary atresia (BA) remain unclear and mechanisms of bile duct repair are unknown. This study aimed to explore the roles of microtubule instability and Wnt and Hippo signaling pathways in a biliatresone-induced BA model.

METHODS

Using primary murine neonatal cholangiocytes in both 2D and 3D cultures, and ex-vivo extra hepatic bile ducts (EHBD) which also has peri-cholangiocyte area, we analyzed injury and recovery processes. Injury was induced by the toxin biliatresone and recovery was induced by toxin wash-out.

RESULTS

Microtubule stabilizer paclitaxel prevented biliatresone-induced injury, both to cholangiocytes as well as reduced periductal αSMA stain, this process is mediated by decreased glutathione levels. RhoU and Wnt11 (Wnt signaling) and Pard6g and Amotl1 (Hippo signaling) are involved in both injury and recovery processes, with the latter acting upstream to Wnt signaling.

CONCLUSIONS

Early stages of biliatresone-induced EHBD injury in cholangiocytes and periductal structures are reversible. Wnt and Hippo signaling pathways play crucial roles in injury and recovery, providing insights into BA injury mechanisms and potential recovery avenues.

IMPACT

Microtubule stabilization prevents cholangiocyte injury and lumen obstruction in a toxic model of biliary atresia (biliatresone induced). Early stages of biliatresone-induced injury, affecting both cholangiocytes and periductal structures, are reversible. Both Wnt and Hippo signaling pathways play a crucial role in bile duct injury and recovery, with a noted interplay between the two. Understanding mechanisms of cholangiocyte recovery is imperative to unveil potential therapeutic avenues.

Association of low angiomotin-p130 and high YAP1 nuclear expression with adverse prognosis in epithelial ovarian cancer

OBJECTIVES

The aim of our study was to examine the association of Angiomotin (Amot-p130) and Yes-associated protein 1 (YAP1) expressions and their prognostic significance in epithelial ovarian cancer (EOC).

METHODS

A total of 100 primary EOC samples were obtained for immunohistochemical analysis of Amot-p130 and YAP1 expressions. Correlation analysis was performed between Amot-p130 or YAP1 and clinical factors. The overall survival time was calculated.

RESULTS

Low Amot-p130 and high YAP1 nuclear expression were identified in 34 and 56 of 100 EOC tissues, respectively. Both low Amot-p130 and high YAP1 nuclear expression were associated with advanced tumor stage, high-grade carcinoma, and non-response to chemotherapy (p<0.05). They were also associated with shorter overall survival time (p<0.05) by log-rank test. A marker of low Amot-p130 and high YAP1 expression was associated with high-grade ovarian carcinoma, late-stage disease, non-response to chemotherapy, and shorter overall survival time (p<0.05).

CONCLUSIONS

Low Amot-p130 and high YAP1 nuclear expression can provide additional prognostic information for patients with EOC. A marker of low Amot-p130 and high YAP1 expression may be a potent predictor of poor prognosis in patients with epithelial ovarian cancer.

The L27 domain of MPP7 enhances TAZ-YY1 cooperation to renew muscle stem cells

Stem cells regenerate differentiated cells to maintain and repair tissues and organs. They also replenish themselves, i.e. self-renew, to support a lifetime of regenerative capacity. Here we study the renewal of skeletal muscle stem cell (MuSC) during regeneration. The transcriptional co-factors TAZ/YAP (via the TEAD transcription factors) regulate cell cycle and growth while the transcription factor YY1 regulates metabolic programs for MuSC activation. We show that MPP7 and AMOT join TAZ and YY1 to regulate a selected number of common genes that harbor TEAD and YY1 binding sites. Among these common genes, Carm1 can direct MuSC renewal. We demonstrate that the L27 domain of MPP7 enhances the interaction as well as the transcriptional activity of TAZ and YY1, while AMOT acts as an intermediate to bridge them together. Furthermore, MPP7, TAZ and YY1 co-occupy the promoters of Carm1 and other common downstream genes. Our results define a renewal program comprised of two progenitor transcriptional programs, in which selected key genes are regulated by protein-protein interactions, dependent on promoter context.

Changes in AmotL2 Expression in Cells of the Human Enteral Nervous System in Oxaliplatin-Induced Enteric Neuropathy

Gastrointestinal (GI) toxicity is a common side effect in patients undergoing oxaliplatin (OxPt)-based chemotherapy for colorectal cancer (CRC). Frequently, this complication persists in the long term and could affect the efficacy of the treatment and the patient's life quality. This long-term GI toxicity is thought to be related to OxPt-induced enteral neuropathy. AmotL2 is a member of the Angiomotin family of proteins, which play a role in cell survival, neurite outgrowth, synaptic maturation, oxidative stress protection, and inflammation. In order to assess the role of AmotL2 in OxPt-induced enteral neuropathy, we studied the expression of AmotL2 in cells of the enteric nervous system (ENS) of untreated and OxPt-treated CRC patients and its relationship with inflammation, using immunofluorescence confocal microscopy. Our results in human samples show that the total number of neurons and glial cells decreased in OxPt-treated patients, and TNF-α and AmotL2 expression was increased and colocalized in both neurons and glia. AmotL2 differential expression between OxPt-treated and untreated CRC patients shows the involvement of this scaffold protein in the inflammatory component and toxicity by OxPt in the ENS.

Angiomotin family proteins in the Hippo signaling pathway

The Motin family proteins (Motins) are a class of scaffolding proteins consisting of Angiomotin (AMOT), AMOT-like protein 1 (AMOTL1), and AMOT-like protein 2 (AMOTL2). Motins play a pivotal role in angiogenesis, tumorigenesis, and neurogenesis by modulating multiple cellular signaling pathways. Recent findings indicate that Motins are components of the Hippo pathway, a signaling cascade involved in development and cancer. This review discusses how Motins are integrated into the Hippo signaling network, as either upstream regulators or downstream effectors, to modulate cell proliferation and migration. The repression of YAP/TAZ by Motins contributes to growth inhibition, whereas subcellular localization of Motins and their interactions with actin fibers are critical in regulating cell migration. The net effect of Motins on cell proliferation and migration may contribute to their diverse biological functions.

Genome-Wide CRISPR Screen Identifies an NF2-Adherens Junction Mechanistic Dependency for Cardiac Lineage

BACKGROUND

Cardiomyocyte differentiation involves a stepwise clearance of repressors and fate-restricting regulators through the modulation of BMP (bone morphogenic protein)/Wnt-signaling pathways. However, the mechanisms and how regulatory roadblocks are removed with specific developmental signaling pathways remain unclear.

METHODS

We conducted a genome-wide CRISPR screen to uncover essential regulators of cardiomyocyte specification in human embryonic stem cells using a myosin heavy chain 6 (MYH6)-GFP (green fluorescence protein) reporter system. After an independent secondary single guide ribonucleic acid validation of 25 candidates, we identified NF2 (neurofibromin 2), a moesin-ezrin-radixin like (MERLIN) tumor suppressor, as an upstream driver of early cardiomyocyte lineage specification. Independent monoclonal NF2 knockouts were generated using CRISPR-Cas9, and cell states were inferred through bulk RNA sequencing and protein expression analysis across differentiation time points. Terminal lineage differentiation was assessed by using an in vitro 2-dimensional-micropatterned gastruloid model, trilineage differentiation, and cardiomyocyte differentiation. Protein interaction and post-translation modification of NF2 with its interacting partners were assessed using site-directed mutagenesis, coimmunoprecipitation, and proximity ligation assays.

RESULTS

Transcriptional regulation and trajectory inference from NF2-null cells reveal the loss of cardiomyocyte identity and the acquisition of nonmesodermal identity. Sustained elevation of early mesoderm lineage repressor SOX2 and upregulation of late anticardiac regulators CDX2 and MSX1 in NF2 knockout cells reflect a necessary role for NF2 in removing regulatory roadblocks. Furthermore, we found that NF2 and AMOT (angiomotin) cooperatively bind to YAP (yes-associated protein) during mesendoderm formation, thereby preventing YAP activation, independent of canonical MST (mammalian sterile 20-like serine-threonine protein kinase)-LATS (large tumor suppressor serine-threonine protein kinase) signaling. Mechanistically, cardiomyocyte lineage identity was rescued by wild-type and NF2 serine-518 phosphomutants, but not NF2 FERM (ezrin-radixin-meosin homology protein) domain blue-box mutants, demonstrating that the critical FERM domain-dependent formation of the AMOT-NF2-YAP scaffold complex at the adherens junction is required for early cardiomyocyte lineage differentiation.

CONCLUSIONS

These results provide mechanistic insight into the essential role of NF2 during early epithelial-mesenchymal transition by sequestering the repressive effect of YAP and relieving regulatory roadblocks en route to cardiomyocytes.

The L27 Domain of MPP7 enhances TAZ-YY1 Cooperation to Renew Muscle Stem Cells

Stem cells regenerate differentiated cells to maintain and repair tissues and organs. They also replenish themselves, i.e. self-renewal, for the regenerative process to last a lifetime. How stem cells renew is of critical biological and medical significance. Here we use the skeletal muscle stem cell (MuSC) to study this process. Using a combination of genetic, molecular, and biochemical approaches, we show that MPP7, AMOT, and TAZ/YAP form a complex that activates a common set of target genes. Among these targets, Carm1 can direct MuSC renewal. In the absence of MPP7, TAZ can support regenerative progenitors and activate Carm1 expression, but not to a level needed for self-renewal. Facilitated by the actin polymerization-responsive AMOT, TAZ recruits the L27 domain of MPP7 to up-regulate Carm1 to the level necessary to drive MuSC renewal. The promoter of Carm1, and those of other common downstream genes, also contain binding site(s) for YY1. We further demonstrate that the L27 domain of MPP7 enhances the interaction between TAZ and YY1 to activate Carm1. Our results define a renewal transcriptional program embedded within the progenitor program, by selectively up-regulating key gene(s) within the latter, through the combination of protein interactions and in a manner dependent on the promoter context.

The L27 Domain of MPP7 enhances TAZ-YY1 Cooperation to Renew Muscle Stem Cells

Stem cells regenerate differentiated cells to maintain and repair tissues and organs. They also replenish themselves, i.e. self-renewal, for the regenerative process to last a lifetime. How stem cells renew is of critical biological and medical significance. Here we use the skeletal muscle stem cell (MuSC) to study this process. Using a combination of genetic, molecular, and biochemical approaches, we show that MPP7, AMOT, and TAZ/YAP form a complex that activates a common set of target genes. Among these targets, Carm1 can direct MuSC renewal. In the absence of MPP7, TAZ can support regenerative progenitors and activate Carm1 expression, but not to a level needed for self-renewal. Facilitated by the actin polymerization-responsive AMOT, TAZ recruits the L27 domain of MPP7 to up-regulate Carm1 to the level necessary to drive MuSC renewal. The promoter of Carm1, and those of other common downstream genes, also contain binding site(s) for YY1. We further demonstrate that the L27 domain of MPP7 enhances the interaction between TAZ and YY1 to activate Carm1. Our results define a renewal transcriptional program embedded within the progenitor program, by selectively up-regulating key gene(s) within the latter, through the combination of protein interactions and in a manner dependent on the promoter context.

Proteolytic activation of angiomotin by DDI2 promotes angiogenesis

The scaffolding protein angiomotin (AMOT) is indispensable for vertebrate embryonic angiogenesis. Here, we report that AMOT undergoes cleavage in the presence of lysophosphatidic acid (LPA), a lipid growth factor also involved in angiogenesis. AMOT cleavage is mediated by aspartic protease DNA damage-inducible 1 homolog 2 (DDI2), and the process is tightly regulated by a signaling axis including neurofibromin 2 (NF2), tankyrase 1/2 (TNKS1/2), and RING finger protein 146 (RNF146), which induce AMOT membrane localization, poly ADP ribosylation, and ubiquitination, respectively. In both zebrafish and mice, the genetic inactivation of AMOT cleavage regulators leads to defective angiogenesis, and the phenotype is rescued by the overexpression of AMOT-CT, a C-terminal AMOT cleavage product. In either physiological or pathological angiogenesis, AMOT-CT is required for vascular expansion, whereas uncleavable AMOT represses this process. Thus, our work uncovers a signaling pathway that regulates angiogenesis by modulating a cleavage-dependent activation of AMOT.

Modulation of E-Cadherin Function through the AmotL2 Isoforms Promotes Ameboid Cell Invasion

The spread of tumor cells and the formation of distant metastasis remain the main causes of mortality in cancer patients. However, the mechanisms governing the release of cells from micro-environmental constraints remain unclear. E-cadherin negatively controls the invasion of epithelial cells by maintaining cell-cell contacts. Furthermore, the inactivation of E-cadherin triggers invasion in vitro. However, the role of E-cadherin is complex, as metastasizing cells maintain E-cadherin expression, which appears to have a positive role in the survival of tumor cells. In this report, we present a novel mechanism delineating how E-cadherin function is modulated to promote invasion. We have previously shown that E-cadherin is associated with p100AmotL2, which is required for radial actin formation and the transmission of mechanical force. Here, we present evidence that p60AmotL2, which is expressed in invading tumor cells, binds to the p100AmotL2 isoform and uncouples the mechanical constraint of radial actin filaments. We show for the first time that the coupling of E-cadherin to the actin cytoskeleton via p100AmotL2 is directly connected to the nuclear membrane. The expression of p60AmotL2 inactivates this connection and alters the properties of the nuclear lamina, potentiating the invasion of cells into micropores of the extracellular matrix. In summary, we propose that the balance of the two AmotL2 isoforms is important in the modulation of E-cadherin function and that an imbalance of this axis promotes ameboid cell invasion.

The X-factor in ART: does the use of assisted reproductive technologies influence DNA methylation on the X chromosome?

BACKGROUND

Assisted reproductive technologies (ART) may perturb DNA methylation (DNAm) in early embryonic development. Although a handful of epigenome-wide association studies of ART have been published, none have investigated CpGs on the X chromosome. To bridge this knowledge gap, we leveraged one of the largest collections of mother-father-newborn trios of ART and non-ART (natural) conceptions to date to investigate sex-specific DNAm differences on the X chromosome. The discovery cohort consisted of 982 ART and 963 non-ART trios from the Norwegian Mother, Father, and Child Cohort Study (MoBa). To verify our results from the MoBa cohort, we used an external cohort of 149 ART and 58 non-ART neonates from the Australian 'Clinical review of the Health of adults conceived following Assisted Reproductive Technologies' (CHART) study. The Illumina EPIC array was used to measure DNAm in both datasets. In the MoBa cohort, we performed a set of X-chromosome-wide association studies ('XWASs' hereafter) to search for sex-specific DNAm differences between ART and non-ART newborns. We tested several models to investigate the influence of various confounders, including parental DNAm. We also searched for differentially methylated regions (DMRs) and regions of co-methylation flanking the most significant CpGs. Additionally, we ran an analogous model to our main model on the external CHART dataset.

RESULTS

In the MoBa cohort, we found more differentially methylated CpGs and DMRs in girls than boys. Most of the associations persisted after controlling for parental DNAm and other confounders. Many of the significant CpGs and DMRs were in gene-promoter regions, and several of the genes linked to these CpGs are expressed in tissues relevant for both ART and sex (testis, placenta, and fallopian tube). We found no support for parental DNAm-dependent features as an explanation for the observed associations in the newborns. The most significant CpG in the boys-only analysis was in UBE2DNL, which is expressed in testes but with unknown function. The most significant CpGs in the girls-only analysis were in EIF2S3 and AMOT. These three loci also displayed differential DNAm in the CHART cohort.

CONCLUSIONS

Genes that co-localized with the significant CpGs and DMRs associated with ART are implicated in several key biological processes (e.g., neurodevelopment) and disorders (e.g., intellectual disability and autism). These connections are particularly compelling in light of previous findings indicating that neurodevelopmental outcomes differ in ART-conceived children compared to those naturally conceived.

The role of Motin family proteins in tumorigenesis-an update

The Motin protein family consists of three members: AMOT (p80 and p130 isoforms), AMOT-like protein 1 (AMOTL1), and AMOT-like protein 2 (AMOTL2). The family members play an important role in processes such as cell proliferation, migration, angiogenesis, tight junction formation, and cell polarity. These functions are mediated through the involvement of the Motins in the regulation of different signal transduction pathways, including those regulated by small G-proteins and the Hippo-YAP pathway. One of the more characterized aspects of Motin family function is their role in regulating signaling through the Hippo-YAP pathway, and while some studies suggest a YAP-inhibitory function other studies indicate the Motins are required for YAP activity. This duality is also reflected in previous reports, often contradictory, that suggest the Motin proteins can function as oncogenes or tumor suppressors in tumorigenesis. In this review we summarize recent findings and integrate that with the existing work describing the multifunctional role of the Motins in different cancers. The emerging picture suggests that the Motin protein function is cell-type and context dependent and that further investigation in relevant cell types and whole organism models is required for the elucidation of the function of this protein family.

Clinical report: Chronic liver dysfunction in an individual with an AMOTL1 variant

AMOTL1 is a member of the Motin protein family and localizes to tight junctions and is involved in cell polarity and paracellular permeability. Pathological variants have been reported in three patients from two separate families in recent years. The clinical spectrum includes cleft lip and palate along with a high incidence of congenital cardiac disease and ear malformations. We report a case of AMOTL1 pathogenic variant in a 11-year-old male patient with nonspecific and chronic liver dysfunction accompanied by persistently elevated liver enzymes since early infancy. Liver biopsy at 8 years of age revealed a mildly dilated central vein and sinusoid with no specific etiology. Liver dysfunction is not a known clinical feature of AMOTL1 malfunction. However, given that the protein is known to be involved in angiogenesis, it may be inferred that abnormalities in this process may lead to liver dysfunction. This is the first report of liver dysfunction identified in a patient with AMOTL1 malfunction, which will shed light on other putative functions of the protein.

Circular RNAs: New Players in Cardiomyopathy

Cardiomyopathies comprise a heterogeneous group of cardiac diseases identified by myocardium disorders and diminished cardiac function. They often lead to heart failure or heart transplantation and constitute one of the principal causes of morbidity and mortality worldwide. Circular RNAs (circRNAs) are a novel type of noncoding RNAs. They are covalently closed and single-stranded and derived from the exons and introns of genes by alternative splicing. This specific structure renders them resistant to exonuclease digestion. Many recent studies have demonstrated that circRNAs are highly abundant and conserved and can play central roles in biological functions such as microRNA (miRNA) sponging, splicing, and transcription regulation. Emerging evidence indicates that circRNAs can play significant roles in cardiovascular diseases, including cardiomyopathies. In this review, we briefly describe the current understanding regarding the classification, nomenclature, characteristics, and function of circRNAs and report recent significant findings concerning the roles of circRNAs in cardiomyopathies. Furthermore, we discuss the clinical application potential of circRNAs as the therapeutic targets and diagnostic biomarkers of cardiomyopathies.

O-GlcNAcylation: An Emerging Protein Modification Regulating the Hippo Pathway

Simple Summary

The contact point between the Hippo pathway, which serves as a central hub for various external environments, and O-GlcNAcylation, which is a non-canonical glycosylation process acting as a dynamic regulator in various signal transduction pathways, has recently been identified. This review aims to summarize the function of O-GlcNAcylation as an intrinsic and extrinsic regulator of the Hippo pathway.

Abstract

The balance between cellular proliferation and apoptosis and the regulation of cell differentiation must be established to maintain tissue homeostasis. These cellular responses involve the kinase cascade-mediated Hippo pathway as a crucial regulator. Hence, Hippo pathway dysregulation is implicated in diverse diseases, including cancer. O-GlcNAcylation is a non-canonical glycosylation that affects multiple signaling pathways through its interplay with phosphorylation in the nucleus and cytoplasm. An abnormal increase in the O-GlcNAcylation levels in various cancer cells is a potent factor in Hippo pathway dysregulation. Intriguingly, Hippo pathway dysregulation also disrupts O-GlcNAc homeostasis, leading to a persistent elevation of O-GlcNAcylation levels, which is potentially pathogenic in several diseases. Therefore, O-GlcNAcylation is gaining attention as a protein modification that regulates the Hippo pathway. This review presents a framework on how O-GlcNAcylation regulates the Hippo pathway and forms a self-perpetuating cycle with it. The pathological significance of this self-perpetuating cycle and clinical strategies for targeting O-GlcNAcylation that causes Hippo pathway dysregulation are also discussed.

Angiomotin isoform 2 promotes binding of PALS1 to KIF13B at primary cilia and regulates ciliary length and signaling

The kinesin-3 motor KIF13B functions in endocytosis, vesicle transport and regulation of ciliary length and signaling. Direct binding of the membrane-associated guanylate kinase (MAGUK) DLG1 to the MAGUK-binding stalk domain of KIF13B relieves motor autoinhibition and promotes microtubule plus-end-directed cargo transport. Here, we characterize angiomotin (AMOT) isoform 2 (p80, referred to as Ap80) as a novel KIF13B interactor that promotes binding of another MAGUK, the polarity protein and Crumbs complex component PALS1, to KIF13B. Live-cell imaging analysis indicated that Ap80 is concentrated at and recruits PALS1 to the base of the primary cilium, but is not a cargo of KIF13B itself. Consistent with a ciliary function for Ap80, its depletion led to elongated primary cilia and reduced agonist-induced ciliary accumulation of SMO, a key component of the Hedgehog signaling pathway, whereas Ap80 overexpression caused ciliary shortening. Our results suggest that Ap80 activates KIF13B cargo binding at the base of the primary cilium to regulate ciliary length, composition and signaling.

Multivalent Angiomotin-like 1 and Yes-associated protein form a dynamic complex

Multivalent complexes formed between the cancer-promoting transcriptional co-activator, Yes-associated protein (YAP), and proteins containing short linear motifs of type PPxY modulate cell proliferation and are attractive therapeutic targets. However, challenges producing PPxY polypeptides containing the full binding domain has limited understanding of the assembly process. Here, we successfully produced a polypeptide containing the complete set of three PPxY binding sites of Angiomotin-like 1 (AMOTL1), a scaffolding protein that regulates the nucleo-cytoplasmic shuttling of YAP via WW-PPxY interactions. Using an array of biophysical techniques including isothermal titration calorimetry, size-exclusion chromatography coupled to multi-angle light scattering, and solution nuclear magnetic resonance spectroscopy, we show that the AMOTL1 polypeptide is partially disordered, and binds the YAP WW domains to form an ensemble of complexes of varying stabilities. The binding process is initiated by the binding of one YAP WW domain to one AMOTL1 PPxY motif and is completed by transient interactions of the second YAP WW domain with a second AMOTL1 PPxY motif to form an equilibrating mixture composed of various species having two YAP sites bound to two conjugate AMOTL1 sites. We rationalize that the transient interactions fine-tune the stability of the complex for rapid assembly and disassembly in response to changes in the local cellular environment.

WWOX-Mediated Degradation of AMOTp130 Negatively Affects Egress of Filovirus VP40 VLPs

Ebola (EBOV) and Marburg (MARV) viruses continue to emerge and cause severe hemorrhagic disease in humans. A comprehensive understanding of the filovirus-host interplay will be crucial for identifying and developing antiviral strategies. The filoviral VP40 matrix protein drives virion assembly and egress, in part by recruiting specific WW-domain-containing host interactors via its conserved PPxY Late (L) domain motif to positively regulate virus egress and spread. In contrast to these positive regulators of virus budding, a growing list of WW-domain-containing interactors that negatively regulate virus egress and spread have been identified, including BAG3, YAP/TAZ and WWOX. In addition to host WW-domain regulators of virus budding, host PPxY-containing proteins also contribute to regulating this late stage of filovirus replication. For example, angiomotin (AMOT) is a multi-PPxY-containing host protein that functionally interacts with many of the same WW-domain-containing proteins that regulate virus egress and spread. In this report, we demonstrate that host WWOX, which negatively regulates egress of VP40 VLPs and recombinant VSV-M40 virus, interacts with and suppresses the expression of AMOT. We found that WWOX disrupts AMOT's scaffold-like tubular distribution and reduces AMOT localization at the plasma membrane via lysosomal degradation. In sum, our findings reveal an indirect and novel mechanism by which modular PPxY/WW-domain interactions between AMOT and WWOX regulate PPxY-mediated egress of filovirus VP40 VLPs. A better understanding of this modular network and competitive nature of protein-protein interactions will help to identify new antiviral targets and therapeutic strategies. IMPORTANCE Filoviruses (Ebola [EBOV] and Marburg [MARV]) are zoonotic, emerging pathogens that cause outbreaks of severe hemorrhagic fever in humans. A fundamental understanding of the virus-host interface is critical for understanding the biology of these viruses and for developing future strategies for therapeutic intervention. Here, we reveal a novel mechanism by which host proteins WWOX and AMOTp130 interact with each other and with the EBOV matrix protein VP40 to regulate VP40-mediated egress of virus like particles (VLPs). Our results highlight the biological impact of competitive interplay of modular virus-host interactions on both the virus lifecycle and the host cell.

The Roles of Tricellular Tight Junction Protein Angulin-1/Lipolysis-Stimulated Lipoprotein Receptor (LSR) in Endometriosis and Endometrioid-Endometrial Carcinoma

Tight junction proteins play roles beyond permeability barriers functions and control cell proliferation and differentiation. The relation between tight junctions and the signal transduction pathways affects cell growth, invasion and migration. Abnormality of tight junction proteins closely contributes to epithelial mesenchymal transition (EMT) and malignancy of various cancers. Angulin-1/lipolysis-stimulated lipoprotein receptor (LSR) forms tricellular contacts that has a barrier function. Downregulation of angulin-1/LSR correlates with the malignancy in various cancers, including endometrioid-endometrial carcinoma (EEC). These alterations have been shown to link to not only multiple signaling pathways such as Hippo/YAP, HDAC, AMPK, but also cell metabolism in ECC cell line Sawano. Moreover, loss of angulin-1/LSR upregulates claudin-1, and loss of apoptosis stimulating p53 protein 2 (ASPP2) downregulates angulin-1/LSR. Angulin-1/LSR and ASPP2 concentrate at both midbody and centrosome in cytokinesis. In EEC tissues, angulin-1/LSR and ASPP2 are reduced and claudin-2 is overexpressed during malignancy, while in the tissues of endometriosis changes in localization of angulin-1/LSR and claudin-2 are seen. This review highlights how downregulation of angulin-1/LSR promotes development of endometriosis and EEC and discusses about the roles of angulin-1/LSR and its related proteins, including claudins and ASPP2.

Stabilization of Motin family proteins in NF2-deficient cells prevents full activation of YAP/TAZ and rapid tumorigenesis

Germline alterations of the NF2 gene cause neurofibromatosis type 2, a syndrome manifested with benign tumors, and Nf2 deletion in mice also results in slow tumorigenesis. As a regulator of the Hippo signaling pathway, NF2 induces LATS1/2 kinases and consequently represses YAP/TAZ. YAP/TAZ oncoproteins are also inhibited by motin family proteins (Motins). Here, we show that the Hippo signaling is fine-tuned by Motins in a NF2-dependent manner, in which NF2 recruits E3 ligase RNF146 to facilitate ubiquitination and subsequent degradation of Motins. In the absence of NF2, Motins robustly accumulate to restrict full activation of YAP/TAZ and prevent rapid tumorigenesis. Hence, NF2 deficiency not only activates YAP/TAZ by inhibiting LATS1/2 but also stabilizes Motins to keep YAP/TAZ activity in check. The upregulation of Motins upon NF2 deletion serves as a strategy for avoiding uncontrolled perturbation of the Hippo signaling and may contribute to the benign nature of most NF2-mutated tumors.

AMOTL2 mono-ubiquitination by WWP1 promotes contact inhibition by facilitating LATS activation

This work reveals a novel function of WWP1 E3 ligase in the mono-ubiquitination of AMOTL2, which enables the binding and activation of LATS kinases upon contact inhibition.

Contact inhibition is a key cellular phenomenon that prevents cells from hyper-proliferating upon reaching confluence. Although not fully characterized, a critical driver of this process is the Hippo signaling pathway, whose downstream effector yes-associated protein plays pivotal roles in cell growth and differentiation. Here, we provide evidence that the E3 ligase WWP1 (WW-domain containing protein 1) mono-ubiquitinates AMOTL2 (angiomotin-like 2) at K347 and K408. Mono-ubiquitinated AMOTL2, in turn, interacts with the kinase LATS2, which facilitates recruitment of the upstream Hippo pathway component SAV1 and ultimately promotes yes-associated protein phosphorylation and subsequent cytoplasmic sequestration and/or degradation. Furthermore, contact inhibition induced by high cell density promoted the localization and stabilization of WWP1 at cell junctions, where it interacted with Crumbs polarity proteins. Notably, the Crumbs complex was functionally important for AMOTL2 mono-ubiquitination and LATS activation under high cell density conditions. These findings delineate a functionally important molecular mechanism in which AMOTL2 mono-ubiquitination by WWP1 at cell junctions and LATS activation are tightly coupled to upstream cell density cues.

Abnormally increased DNA methylation in chorionic tissue might play an important role in development of ectopic pregnancy

BACKGROUND

Human Ectopic Pregnancy (hEP) is the second most common cause of pregnancy-related deaths in the first trimester. Without timely detection, EPs can lead to an increased rate of infertility and an elevated risk for future tubal EPs. In addition, most studies in the field focus on the effect of the fallopian tube (maternal factors) and ignore epigenetic changes in genes and proteins of the embryo, which may also cause EPs. Therefore, the present study hypothesized that embryos also play an important role in the development of EP. The study also speculated that DNA methylation is associated with ectopic pregnancy. Consequently, the effects of DNA methylation on the occurrence and development of ectopic pregnancy were investigated. Moreover, genome-wide DNA methylation of chorionic tissue from ectopic and intrauterine pregnancies was detected using Illumina HumanMethylation450 arrays.

RESULTS

Forty-three hypermethylated genes involved in the regulation of adhesion as well as gene transcription and translation were identified. Furthermore, the PPI network showed that AMOTL1, SDR42E1, CAMTA1, PIP5K1C, KIAA1614, TSTD1 and DNER may play important roles in the occurrence and development of ectopic pregnancy. In addition, SDR42E1, CAMTA1 and TSTD1 displayed higher levels of methylation in ectopic pregnancy while PIP5K1C and DNER showed low degrees of methylation.

CONCLUSIONS

The study reveals that abnormal increase in methylation may be an early indicator or an inducer of ectopic pregnancy. In addition, AMOTL1, SDR42E1, CAMTA1, PIP5K1C, KIAA1614, TSTD1 and DNER might play important roles in the occurrence and development of ectopic pregnancy. However, the specific molecular mechanisms are still unclear and require further studies.

Full assembly of HIV-1 particles requires assistance of the membrane curvature factor IRSp53

During HIV-1 particle formation, the requisite plasma membrane curvature is thought to be solely driven by the retroviral Gag protein. Here, we reveal that the cellular I-BAR protein IRSp53 is required for the progression of HIV-1 membrane curvature to complete particle assembly. siRNA-mediated knockdown of IRSp53 gene expression induces a decrease in viral particle production and a viral bud arrest at half completion. Single-molecule localization microscopy at the cell plasma membrane shows a preferential localization of IRSp53 around HIV-1 Gag assembly sites. In addition, we observe the presence of IRSp53 in purified HIV-1 particles. Finally, HIV-1 Gag protein preferentially localizes to curved membranes induced by IRSp53 I-BAR domain on giant unilamellar vesicles. Overall, our data reveal a strong interplay between IRSp53 I-BAR and Gag at membranes during virus assembly. This highlights IRSp53 as a crucial host factor in HIV-1 membrane curvature and its requirement for full HIV-1 particle assembly.

Regulation of MST complexes and activity via SARAH domain modifications

Three elements of the Hippo tumor suppressor pathway - MST1/2, SAV1, and RASSF1-6 - share in common a C-terminal interaction motif termed the SARAH domain. Proteins containing this domain are capable of self-association as homodimers and also of trans-association with other SARAH domain containing proteins as well as selected additional proteins that lack this domain. Recently, the association of MST1/2 with itself or with other proteins has been shown to be regulated by phosphorylation at sites near or within the SARAH domain. In this review, we focus on recent findings regarding the regulation of such MST1/2 interactions, with an emphasis on the effects of these events on Hippo pathway activity.

Angiomotin Counteracts the Negative Regulatory Effect of Host WWOX on Viral PPxY-Mediated Egress

Filoviridae family members Ebola (EBOV) and Marburg (MARV) viruses and Arenaviridae family member Lassa virus (LASV) are emerging pathogens that can cause hemorrhagic fever and high rates of mortality in humans. A better understanding of the interplay between these viruses and the host will inform about the biology of these pathogens, and may lead to the identification of new targets for therapeutic development. Notably, expression of the filovirus VP40 and LASV Z matrix proteins alone drives assembly and egress of virus-like particles (VLPs). The conserved PPxY Late (L) domain motifs in the filovirus VP40 and LASV Z proteins play a key role in the budding process by mediating interactions with select host WW-domain containing proteins that then regulate virus egress and spread. To identify the full complement of host WW-domain interactors, we utilized WT and PPxY mutant peptides from EBOV and MARV VP40 and LASV Z proteins to screen an array of GST-WW-domain fusion proteins. We identified WW domain-containing oxidoreductase (WWOX) as a novel PPxY-dependent interactor, and we went on to show that full-length WWOX physically interacts with eVP40, mVP40 and LASV Z to negatively regulate egress of VLPs and of a live VSV/Ebola recombinant virus (M40). Interestingly, WWOX is a versatile host protein that regulates multiple signaling pathways and cellular processes via modular interactions between its WW-domains and PPxY motifs of select interacting partners, including host angiomotin (AMOT). Notably, we demonstrated recently that expression of endogenous AMOT not only positively regulates egress of VLPs, but also promotes egress and spread of live EBOV and MARV. Toward the mechanism of action, we show that the competitive and modular interplay among WWOX-AMOT-VP40/Z regulates VLP and M40 virus egress. Thus, WWOX is the newest member of an emerging group of host WW-domain interactors (e.g. BAG3; YAP/TAZ) that negatively regulate viral egress. These findings further highlight the complex interplay of virus-host PPxY/WW-domain interactions and their potential impact on the biology of both the virus and the host during infection.Author Summary Filoviruses (Ebola [EBOV] and Marburg [MARV]) and arenavirus (Lassa virus; LASV) are zoonotic, emerging pathogens that cause outbreaks of severe hemorrhagic fever in humans. A fundamental understanding of the virus-host interface is critical for understanding the biology of these viruses and for developing future strategies for therapeutic intervention. Here, we identified host WW-domain containing protein WWOX as a novel interactor with VP40 and Z, and showed that WWOX inhibited budding of VP40/Z virus-like particles (VLPs) and live virus in a PPxY/WW-domain dependent manner. Our findings are important to the field as they expand the repertoire of host interactors found to regulate PPxY-mediated budding of RNA viruses, and further highlight the competitive interplay and modular virus-host interactions that impact both the virus lifecycle and the host cell.

The Hippo pathway: Horizons for innovative treatments of peripheral nerve diseases

Initially identified in Drosophila, the Hippo signaling pathway regulates how cells respond to their environment by controlling proliferation, migration and differentiation. Many recent studies have focused on characterizing Hippo pathway function and regulation in mammalian cells. Here, we present a brief overview of the major components of the Hippo pathway, as well as their regulation and function. We comprehensively review the studies that have contributed to our understanding of the Hippo pathway in the function of the peripheral nervous system and in peripheral nerve diseases. Finally, we discuss innovative approaches that aim to modulate Hippo pathway components in diseases of the peripheral nervous system.

WWC Proteins: Important Regulators of Hippo Signaling in Cancer

Simple Summary

The conserved Hippo pathway regulates cell proliferation and apoptosis via a complex interplay of transcriptional activities, post-translational protein modifications, specific protein–protein interactions and cellular transport processes. Deregulating this highly balanced system can lead to hyperproliferation, organ overgrowth and cancer. Although WWC proteins are known as components of the Hippo signaling pathway, their association with tumorigenesis is often neglected. This review aims to summarize the current knowledge on WWC proteins and their contribution to Hippo signaling in the context of cancer.

Abstract

The Hippo signaling pathway is known to regulate cell differentiation, proliferation and apoptosis. Whereas activation of the Hippo signaling pathway leads to phosphorylation and cytoplasmic retention of the transcriptional coactivator YAP, decreased Hippo signaling results in nuclear import of YAP and subsequent transcription of pro-proliferative genes. Hence, a dynamic and precise regulation of the Hippo signaling pathway is crucial for organ size control and the prevention of tumor formation. The transcriptional activity of YAP is controlled by a growing number of upstream regulators including the family of WWC proteins. WWC1, WWC2 and WWC3 represent cytosolic scaffolding proteins involved in intracellular transport processes and different signal transduction pathways. Earlier in vitro experiments demonstrated that WWC proteins positively regulate the Hippo pathway via the activation of large tumor suppressor kinases 1/2 (LATS1/2) kinases and the subsequent cytoplasmic accumulation of phosphorylated YAP. Later, reduced WWC expression and subsequent high YAP activity were shown to correlate with the progression of human cancer in different organs. Although the function of WWC proteins as upstream regulators of Hippo signaling was confirmed in various studies, their important role as tumor modulators is often overlooked. This review has been designed to provide an update on the published data linking WWC1, WWC2 and WWC3 to cancer, with a focus on Hippo pathway-dependent mechanisms.

Emerging roles for angiomotin in the nervous system

Angiomotins are a family of molecular scaffolding proteins that function to organize contact points (called tight junctions in vertebrates) between adjacent cells. Some angiomotin isoforms bind to the actin cytoskeleton and are part of signaling pathways that influence cell morphology and migration. Others cooperate with components of the Hippo signaling pathway and the associated networks to control organ growth. The 130-kDa isoform, AMOT-p130, has critical roles in neural stem cell differentiation, dendritic patterning, and synaptic maturation-attributes that are essential for normal brain development and are consistent with its association with autism. Here, we review and discuss the evidence that supports a role for AMOT-p130 in neuronal development in the central nervous system.

De novo variant in AMOTL1 in infant with cleft lip and palate, imperforate anus and dysmorphic features

AMOTL1 belongs to the Motin family of proteins that are involved in organogenesis and tumorigenesis through regulation of cellular migration, tube formation, and angiogenesis. While involvement of all AMOTs in development or suppression of cancers is relatively well described, little is known about the congenital phenotype of pathogenic variants in these genes in humans. Recently, a heterozygous variant in AMOTL1 was published in association with orofacial clefts and cardiac abnormalities in an affected father and his daughter. However, studies in mice did not recapitulate the human phenotype and the case was summarized as inconclusive. We present a female infant with cleft lip and palate, imperforate anus and dysmorphic features, in whom trio exome sequencing revealed a de novo variant in AMOTL1 affecting a highly conserved amino acid (c.479C>T; p.[Pro160Leu]). Bioinformatic predictions and in silico modeling supported pathogenicity. This case reinforces the conjecture regarding the disruptive effect of pathogenic variants in AMOTL1 on organ formation in humans. Studies of additional families will reveal the full phenotypic spectrum associated with this multiple malformation syndrome.

Angiomotin regulates budding and spread of Ebola virus

The Ebola virus (EBOV) VP40 matrix protein (eVP40) orchestrates assembly and budding of virions in part by hijacking select WW-domain-bearing host proteins via its PPxY late (L)-domain motif. Angiomotin (Amot) is a multifunctional PPxY-containing adaptor protein that regulates angiogenesis, actin dynamics, and cell migration/motility. Amot also regulates the Hippo signaling pathway via interactions with the WW-domain-containing Hippo effector protein Yes-associated protein (YAP). In this report, we demonstrate that endogenous Amot is crucial for positively regulating egress of eVP40 virus-like particles (VLPs) and for egress and spread of authentic EBOV. Mechanistically, we show that ectopic YAP expression inhibits eVP40 VLP egress and that Amot co-expression rescues budding of eVP40 VLPs in a dose-dependent and PPxY-dependent manner. Moreover, results obtained with confocal and total internal reflection fluorescence microscopy suggested that Amot's role in actin organization and dynamics also contributes to promoting eVP40-mediated egress. In summary, these findings reveal a functional and competitive interplay between virus and host proteins involving the multifunctional PPxY-containing adaptor Amot, which regulates both the Hippo pathway and actin dynamics. We propose that our results have wide-ranging implications for understanding the biology and pathology of EBOV infections.

ASPP2 suppression promotes malignancy via LSR and YAP in human endometrial cancer

Apoptosis-stimulating p53 protein 2 (ASPP2) is an apoptosis inducer that acts via binding with p53 and epithelial polarity molecule PAR3. Lipolysis-stimulated lipoprotein receptor (LSR) is an important molecule at tricellular contacts, and loss of LSR promotes cell migration and invasion via Yes-associated protein (YAP) in human endometrial cancer cells. In the present study, to find how ASPP2 suppression promotes malignancy in human endometrial cancer, we investigated its mechanisms including the relationship with LSR. In endometriosis and endometrial cancers (G1 and G2), ASPP2 was observed as well as PAR3 and LSR in the subapical region. ASPP2 decreased in G3 endometrial cancer compared to G1. In human endometrial cancer cell line Sawano, ASPP2 was colocalized with LSR and tricellulin at tricellular contacts and binding to PAR3, LSR, and tricellulin in the confluent state. ASPP2 suppression promoted cell migration and invasion, decreased LSR expression, and induced expression of phosphorylated YAP, claudin-1, -4, and -7 as effectively as the loss of LSR. Knockdown of YAP prevented the upregulation of pYAP, cell migration and invasion induced by the ASPP2 suppression. Treatment with a specific antibody against ASPP2 downregulated ASPP2 and LSR, affected F-actin at tricellular contacts, upregulated expression of pYAP and claudin-1, and induced cell migration and invasion via YAP. In normal human endometrial epithelial cells, ASPP2 was in part colocalized with LSR at tricellular contacts and knockdown of ASPP2 or LSR induced expression of claudin-1 and claudin-4. ASPP2 suppression promoted cell invasion and migration via LSR and YAP in human endometrial cancer cells.

Modular mimicry and engagement of the Hippo pathway by Marburg virus VP40: Implications for filovirus biology and budding

Ebola (EBOV) and Marburg (MARV) are members of the Filoviridae family, which continue to emerge and cause sporadic outbreaks of hemorrhagic fever with high mortality rates. Filoviruses utilize their VP40 matrix protein to drive virion assembly and budding, in part, by recruitment of specific WW-domain-bearing host proteins via its conserved PPxY Late (L) domain motif. Here, we screened an array of 115 mammalian, bacterially expressed and purified WW-domains using a PPxY-containing peptide from MARV VP40 (mVP40) to identify novel host interactors. Using this unbiased approach, we identified Yes Associated Protein (YAP) and Transcriptional co-Activator with PDZ-binding motif (TAZ) as novel mVP40 PPxY interactors. YAP and TAZ function as downstream transcriptional effectors of the Hippo signaling pathway that regulates cell proliferation, migration and apoptosis. We demonstrate that ectopic expression of YAP or TAZ along with mVP40 leads to significant inhibition of budding of mVP40 VLPs in a WW-domain/PPxY dependent manner. Moreover, YAP colocalized with mVP40 in the cytoplasm, and inhibition of mVP40 VLP budding was more pronounced when YAP was localized predominantly in the cytoplasm rather than in the nucleus. A key regulator of YAP nuclear/cytoplasmic localization and function is angiomotin (Amot); a multi-PPxY containing protein that strongly interacts with YAP WW-domains. Interestingly, we found that expression of PPxY-containing Amot rescued mVP40 VLP egress from either YAP- or TAZ-mediated inhibition in a PPxY-dependent manner. Importantly, using a stable Amot-knockdown cell line, we found that expression of Amot was critical for efficient egress of mVP40 VLPs as well as egress and spread of authentic MARV in infected cell cultures. In sum, we identified novel negative (YAP/TAZ) and positive (Amot) regulators of MARV VP40-mediated egress, that likely function in part, via competition between host and viral PPxY motifs binding to modular host WW-domains. These findings not only impact our mechanistic understanding of virus budding and spread, but also may impact the development of new antiviral strategies.

By screening an array of 115 mammalian WW-domains with the PPxY motif from MARV VP40 (mVP40), we identified YAP1 and TAZ, transcriptional effectors of the Hippo pathway, as mVP40 interactors, and demonstrated that ectopically expressed YAP1 or TAZ inhibited budding of mVP40 virus-like particles (VLPs) in a WW-domain/PPxY dependent manner. Angiomotin (Amot), a multi-PPxY containing regulator of YAP1 nuclear/cytoplasmic localization and function, rescued mVP40 VLP egress from either YAP1- or TAZ-mediated inhibition in a PPxY-dependent manner. Indeed, endogenous Amot expression was critical for egress of mVP40 VLPs and authentic MARV. In sum, we have revealed a link between the Hippo pathway and filovirus egress by identifying negative (YAP/TAZ) and positive (Amot) regulators of MARV VP40-mediated egress.

AMOT130 drives BMP-SMAD signaling at the apical membrane in polarized cells

The large isoform of the transmembrane protein angiomotin (AMOT130) controls cell proliferation and migration of many cell types. AMOT130 associates to the actin cytoskeleton and regulates tight-junction maintenance and signaling often via endosomal uptake of polarity proteins at tight junctions. AMOT130 is highly polarized and present only at the apical side of polarized cells. Here we show that bone morphogenetic protein (BMP) growth factor signaling and AMOT function are interlinked in apical-basal polarized cells. BMP6 controls AMOT internalization and endosomal trafficking in epithelial cells. AMOT130 interacts with the BMP receptor BMPR2 and facilitates SMAD activation and target gene expression. We further demonstrate that this effect of AMOT on BMP-SMAD signaling is dependent on endocytosis and specific to the apical side of polarized epithelial and endothelial cells. Knockdown of AMOT reduces SMAD signaling only from the apical side of polarized cells, while basolateral BMP-SMAD signaling is unaffected. This allows for the first time interference with BMP signaling in a polarized manner and identifies AMOT130 as a novel BMP signaling regulator.

Structural Features of Tight-Junction Proteins

Tight junctions are complex supramolecular entities composed of integral membrane proteins, membrane-associated and soluble cytoplasmic proteins engaging in an intricate and dynamic system of protein-protein interactions. Three-dimensional structures of several tight-junction proteins or their isolated domains have been determined by X-ray crystallography, nuclear magnetic resonance spectroscopy, and cryo-electron microscopy. These structures provide direct insight into molecular interactions that contribute to the formation, integrity, or function of tight junctions. In addition, the known experimental structures have allowed the modeling of ligand-binding events involving tight-junction proteins. Here, we review the published structures of tight-junction proteins. We show that these proteins are composed of a limited set of structural motifs and highlight common types of interactions between tight-junction proteins and their ligands involving these motifs.

circAMOTL1 Motivates AMOTL1 Expression to Facilitate Cervical Cancer Growth

Cervical cancer is acknowledged as the most prevalent gynecological tumor and a severe public issue that threatens female health, resulting from its high incidence and fatality rate. Surging evidence have shown that circular RNAs (circRNAs) play significant roles in the initiation and progression of various malignancies. Although circAMOTL1 has been testified to execute oncogenic properties in breast cancer and prostate cancer, literature on its function and regulatory mechanism in cervical cancer development is still scanty. Using a bioinformatics analysis, we found circ_0004214 was a circular form of AMOTL1. Through qRT-PCR analysis, circAMOTL1 and its host gene AMOTL1 were both upregulated in cervical cancer tissues and closely correlated with poor prognosis of cervical cancer. Gain- or loss-of-function assays and in vivo experiments demonstrated that AMOTL1 promoted cervical cancer cell growth both in vitro and in vivo. Mechanically, circAMOTL1 served as a competing endogenous RNA (ceRNA) to prompt the expression of AMOTL1 through sponging miR-485-5p. Rescue assays revealed that miR-485-5p/AMOTL1 axis was involved in circ_AMOTL1-mediated cervical cancer progression. Our findings provide a better understanding of the molecular mechanism underlying circAMOTL1 in cervical cancer and indicated circAMOTL1/miR-485-5p/AMOTL1 as a promising novel therapeutic strategy for the treatment of this disease.

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.

Apatinib suppresses breast cancer cells proliferation and invasion via angiomotin inhibition

Breast cancer is a leading cause of cancer-related death in the women worldwide. Apatinib is a novel tyrosine kinase inhibitor that selectively binds and inhibits vascular endothelial growth factor receptor 2 (VEGFR-2). The clinical trials have demonstrated the objective efficacy of Apatinib against metastatic breast cancer. However, the underlying mechanism is not well established. In the present study, the breast cell lines, BT-474 and MCF-7, were investigated. The effect of Apatinib on the cell viability was determined using CCK-8 assay. The migration, invasion, cell cycle distribution and the downstream signaling of VEGFR-2 in the cells were determined after 48 h treatment with this drug. Subsequently, Vector of angiomotin (AMOT) cDNA was transfected into MCF-7 cells. The cells were either exposed to Apatinib or vehicle and then examined for cell viabilities, migration, invasion, cell cycle distribution and the downstream signaling of VEGFR-2. Apatinib demonstrated a dose-dependent, significant inhibition of cell viabilities, migration and invasion of BT-474 and MCF-7 cells, with an increase in the percentage of cells in G1 phase and a decrease in S phase. In addition, in MCF-7 cells, Apatinib decreased AMOT expression, accompanied with the decreased expression of LATS1/2, YAP, ERK1/2 phosphorylation and cyclin D1. The inhibitory effect of Apatinib on the cell activities and protein expressions were significantly suppressed by AMOT overexpression. The results of this study indicated that Apatinib inhibited MCF-7 cell proliferation and invasion through AMOT/VEGFR-2 pathway.

Identification of Specific Lysines and Arginines That Mediate Angiomotin Membrane Association

The family of Angiomotin (Amot) proteins regulate several biological pathways associated with cellular differentiation, proliferation, and migration. These adaptor proteins target proteins to the apical membrane, actin fibers, or the nucleus. A major function of the Amot coiled-coil homology (ACCH) domain is to initiate protein interactions with the cellular membrane, particularly those containing phosphatidylinositol lipids. The work presented in this article uses several ACCH domain lysine/arginine mutants to probe the relative importance of individual residues for lipid binding. This identified four lysine and three arginine residues that mediate full lipid binding. Based on these findings, three of these residues were mutated to glutamates in the Angiomotin 80 kDa splice form and were incorporated into human mammary cell lines. Results show that mutating three of these residues in the context of full-length Angiomotin reduced the residence of the protein at the apical membrane. These findings provide new insight into how the ACCH domain mediates lipid binding to enable Amot proteins to control epithelial cell growth.

Faulty oxygen sensing disrupts angiomotin function in trophoblast cell migration and predisposes to preeclampsia

Human placenta development and a successful pregnancy is incumbent upon precise oxygen-dependent control of trophoblast migration/invasion. Persistent low oxygen leading to failed trophoblast invasion promotes inadequate spiral artery remodeling, a characteristic of preeclampsia. Angiomotin (AMOT) is a multifaceted scaffolding protein involved in cell polarity and migration, yet its upstream regulation and significance in the human placenta remain unknown. Herein, we show that AMOT is primarily expressed in migratory extravillous trophoblast cells (EVTs) of the intermediate and distal anchoring column. Its expression increases after 10 weeks of gestation when oxygen tension rises and EVT migration/invasion peaks. Time-lapse imaging confirmed that the AMOT 80-kDa isoform promotes migration of trophoblastic JEG3 and HTR-8/SVneo cells. In preeclampsia, however, AMOT expression is decreased and its localization to migratory fetomaternal interface EVTs is disrupted. We demonstrate that Jumonji C domain-containing protein 6 (JMJD6), an oxygen sensor, positively regulates AMOT via oxygen-dependent lysyl hydroxylation. Furthermore, in vitro and ex vivo studies show that transforming growth factor-β (TGF-β) regulates AMOT expression, its interaction with polarity protein PAR6, and its subcellular redistribution from tight junctions to cytoskeleton. Our data reveal an oxygen- and TGF-β-driven migratory function for AMOT in the human placenta, and implicate its deficiency in impaired trophoblast migration that plagues preeclampsia.

Angiomotin Regulates YAP Localization during Neural Differentiation of Human Pluripotent Stem Cells

Leveraging the extraordinary potential of human pluripotent stem cells (hPSCs) requires an understanding of the mechanisms underlying cell-fate decisions. Substrate elasticity can induce differentiation by signaling through the transcriptional coactivator Yes-associated protein (YAP). Cells cultured on surfaces mimicking brain elasticity exclude YAP from their nuclei and differentiate to neurons. How YAP localization is controlled during neural differentiation has been unclear. We employed CRISPR/Cas9 to tag endogenous YAP in hPSCs and used this fusion protein to identify YAP's interaction partners. This engineered cell line revealed that neural differentiation promotes a change in YAP interactors, including a dramatic increase in angiomotin (AMOT) interaction with YAP. AMOT regulates YAP localization during differentiation. AMOT expression increases during neural differentiation and leads to YAP nuclear exclusion. Our findings that AMOT-dependent regulation of YAP helps direct hPSC fate provide insight into the molecular mechanisms by which the microenvironment can induce neural differentiation.

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Endogenous tagging reveals YAP interactors in hPSCs

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AMOT-YAP complex concentration increases during neural differentiation

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AMOT regulates YAP localization in hPSCs

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hPSC cytoskeleton influences YAP localization via AMOT

Angiomotin-Like 1 Links Paramyxovirus M Proteins to NEDD4 Family Ubiquitin Ligases

To define the links between paramyxovirus budding and cellular ESCRT machinery, we previously identified angiomotin-like 1 (AMOTL1) in a screen for host factors that bind to the matrix (M) protein of parainfluenza virus 5 (PIV5). This protein harbors three L/PPXY sequences, allowing it to interact with WW domain containing proteins including NEDD4 family members. We hypothesize that paramyxoviruses use AMOTL1 as a linker to indirectly recruit the same NEDD4 ubiquitin ligases for budding that other enveloped viruses recruit directly through their PPXY late domains. In support of this hypothesis, we found that AMOTL1 could link together M proteins and NEDD4 family proteins in three-way co-IP experiments. Both PIV5 and mumps virus M proteins could be linked to the NEDD4 family proteins NEDD4-1, NEDD4L, and NEDL1, provided that AMOTL1 was co-expressed as a bridging protein. AMOT and AMOTL2 could not substitute for AMOTL1, as they lacked the ability to bind with paramyxovirus M proteins. Attachment of a PPXY late domain sequence to PIV5 M protein obviated the need for AMOTL1 as a linker between M and NEDD4 proteins. Together, these results suggest a novel host factor recruitment strategy for paramyxoviruses to achieve particle release.

Reorganization of Ternary Lipid Mixtures of Nonphosphorylated Phosphatidylinositol Interacting with Angiomotin

Phosphatidylinositol (PI) lipids are necessary for many cellular signaling pathways of membrane associated proteins, such as angiomotin (Amot). The Amot family regulates cellular polarity, growth, and migration. Given the low concentration of PI lipids in these membranes, it is likely that such protein-membrane interactions are stabilized by lipid domains or small lipid clusters. By small-angle X-ray scattering, we show that nonphosphorylated PI lipids induce lipid demixing in ternary mixtures of phosphatidylcholine (PC) and phosphatidylethanolamine (PE), likely because of preferential interactions between the head groups of PE and PI. These results were obtained in the presence of buffer containing tris(hydroxymethyl)aminomethane, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, NaCl, ethylenediaminetetraacetic acid, dithiothreitol, and benzamidine at pH 8.0 that in previous work showed an ability to cause PC to phase separate but are necessary to stabilize Amot for in vitro experimentation. Collectively, this provided a framework for determining the effect of Amot on lipid organization. Using fluorescence spectroscopy, we were able to show that the association of Amot with this lipid platform causes significant reorganization of the lipid into a more homogenous structure. This reorganization mechanism could be the basis for Amot membrane association and fusogenic activity previously described in the literature and should be taken into consideration in future protein-membrane interaction studies.

Hippo-YAP/TAZ signaling in angiogenesis

Angiogenesis is a complex, multistep process involving dynamic changes in endothelial cell (EC) shapes and behaviors, especially in specialized cell types such as tip cells (with active filopodial extensions), stalk cells (with less motility) and phalanx cells (with stable junction connections). The Hippo-Yes-associated protein (YAP)/ transcription activator with PDZ binding motif (TAZ) signaling plays a critical role in development, regeneration and organ size by regulating cell-cell contact and actin cytoskeleton dynamics. Recently, with the finding that YAP is expressed in the front edge of the developing retinal vessels, Hippo-YAP/TAZ signaling has emerged as a new pathway for blood vessel development. Intriguingly, the LATS1/2-mediated angiomotin (AMOT) family and YAP/TAZ activities contribute to EC shapes and behaviors by spatiotemporally modulating actin cytoskeleton dynamics and EC junction stability. Herein, we summarize the recent understanding of the role of Hippo-YAP/TAZ signaling in the processes of EC sprouting and junction maturation in angiogenesis.

Cell Junctions in Hippo Signaling

The Hippo signal transduction pathway is an important regulator of organ growth and cell differentiation, and its deregulation contributes to the development of cancer. The activity of the Hippo pathway is strongly dependent on cell junctions, cellular architecture, and the mechanical properties of the microenvironment. In this review, we discuss recent advances in our understanding of how cell junctions transduce signals from the microenvironment and control the activity of the Hippo pathway. We also discuss how these mechanisms may control organ growth during development and regeneration, and how defects in them deregulate Hippo signaling in cancer cells.