The RNF146 and tankyrase pathway maintains the junctional Crumbs complex through regulation of angiomotin

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.

The Hippo Pathway in Breast Cancer: The Extracellular Matrix and Hypoxia

As one of the most prevalent malignant neoplasms among women globally, the optimization of therapeutic strategies for breast cancer has perpetually been a research hotspot. The tumor microenvironment (TME) is of paramount importance in the progression of breast cancer, among which the extracellular matrix (ECM) and hypoxia are two crucial factors. The alterations of these two factors are predominantly regulated by the Hippo signaling pathway, which promotes tumor invasiveness, metastasis, therapeutic resistance, and susceptibility. Hence, this review focuses on the Hippo pathway in breast cancer, specifically, how the ECM and hypoxia impact the biological traits and therapeutic responses of breast cancer. Moreover, the role of miRNAs in modulating ECM constituents was investigated, and hsa-miR-33b-3p was identified as a potential therapeutic target for breast cancer. The review provides theoretical foundations and potential therapeutic direction for clinical treatment strategies in breast cancer, with the aspiration of attaining more precise and effective treatment alternatives in the future.

The cellular localization and oncogenic or tumor suppressive effects of angiomiotin-like protein 2 in tumor and normal cells

Angiomiotin (AMOT) family comprises three members: AMOT, AMOT-like protein 1 (AMOTL1), and AMOT-like protein 2 (AMOTL2). AMOTL2 is widely expressed in endothelial cells, epithelial cells, and various cancer cells. Specifically, AMOTL2 predominantly localizes in the cytoplasm and nucleus in human normal cells, whereas associates with cell-cell junctions and actin cytoskeleton in non-human cells, and locates at cell junctions or within the recycling endosomes in cancer cells. AMOTL2 is implicated in regulation of tube formation, cell polarity, and shape, although the specific impact on tumorigenesis remains to be conclusively determined. It has been shown that AMOTL2 enhances tumor growth and metastasis in pancreatic, breast, and colon cancer, however inhibits cell proliferation and migration in lung, hepatocellular cancer, and glioblastoma. In addition to its role in cell shape and cytoskeletal dynamics through co-localization with F-actin, AMOTL2 modulates the transcription of Yes-associated protein (YAP) by binding to it, thereby affecting its phosphorylation and cellular sequestration. Furthermore, the stability and cellular localization of AMOTL2, influenced by its phosphorylation and ubiquitination mediated by specific proteins, affects its cellular function. Additionally, we observe that AMOTL2 is predominantly downregulated in some tumors, but significantly elevated in colorectal adenocarcinoma (COAD). Moreover, overall analysis, GSEA and ROC curve analysis indicate that AMOTL2 exerts as an oncogenic protein in COAD by modulating Wnt pathway, participating in synthesis of collagen formation, and interacting with extracellular matrix receptor. In addition, AMOTL2 potentially regulates the distribution of immune cells infiltration in COAD. In summary, AMOTL2 probably functions as an oncogene in COAD. Consequently, further in-depth mechanistic research is required to elucidate the precise roles of AMOTL2 in various cancers.

A ligand discovery toolbox for the WWE domain family of human E3 ligases

The WWE domain is a relatively under-researched domain found in twelve human proteins and characterized by a conserved tryptophan-tryptophan-glutamate (WWE) sequence motif. Six of these WWE domain-containing proteins also contain domains with E3 ubiquitin ligase activity. The general recognition of poly-ADP-ribosylated substrates by WWE domains suggests a potential avenue for development of Proteolysis-Targeting Chimeras (PROTACs). Here, we present novel crystal structures of the HUWE1, TRIP12, and DTX1 WWE domains in complex with PAR building blocks and their analogs, thus enabling a comprehensive analysis of the PAR binding site structural diversity. Furthermore, we introduce a versatile toolbox of biophysical and biochemical assays for the discovery and characterization of novel WWE domain binders, including fluorescence polarization-based PAR binding and displacement assays, 15N-NMR-based binding affinity assays and 19F-NMR-based competition assays. Through these assays, we have characterized the binding of monomeric iso-ADP-ribose (iso-ADPr) and its nucleotide analogs with the aforementioned WWE proteins. Finally, we have utilized the assay toolbox to screen a small molecule fragment library leading to the successful discovery of novel ligands targeting the HUWE1 WWE domain.

Role of angiomotin family members in human diseases (Review)

Angiomotin (Amot) family members, including Amot, Amot-like protein 1 (Amotl1) and Amot-like protein 2 (Amotl2), have been found to interact with angiostatins. In addition, Amot family members are involved in various physiological and pathological functions such as embryonic development, angiogenesis and tumorigenesis. Some studies have also demonstrated its regulation in signaling pathways such as the Hippo signaling pathway, AMPK signaling pathway and mTOR signaling pathways. Amot family members play an important role in neural stem cell differentiation, dendritic formation and synaptic maturation. In addition, an increasing number of studies have focused on their function in promoting and/or suppressing cancer, but the underlying mechanisms remain to be elucidated. The present review integrated relevant studies on upstream regulation and downstream signals of Amot family members, as well as the latest progress in physiological and pathological functions and clinical applications, hoping to offer important ideas for further research.

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.

Identification of new candidate genes for spina bifida through exome sequencing

PURPOSE

Neural tube defects are a group of birth defects caused by failure of neural tube closure during development. The etiology of NTD, requiring a complex interaction between environmental and genetic factors, is not well understood.

METHODS

We performed whole-exome sequencing (WES) in six trios, with a single affected proband with spina bifida, to identify rare/novel variants as potential causes of the NTD.

RESULTS

Our analysis identified four de novo and ten X-linked recessive variants in four of the six probands, all of them in genes previously never implicated in NTD. Among the 14 variants, we ruled out six of them, based on different criteria and pursued the evaluation of eight potential candidates in the following genes: RXRγ, DTX1, COL15A1, ARHGAP36, TKTL1, AMOT, GPR50, and NKRF. The de novo variants where located in the RXRγ, DTX1, and COL15A1 genes while ARHGAP36, TKTL1, AMOT, GPR50, and NKRF carry X-linked recessive variants. This analysis also revealed that four patients presented multiple variants, while we were unable to identify any significant variant in two patients.

CONCLUSIONS

Our preliminary conclusion support a major role for the de novo variants with respect to the X-linked recessive variants where the X-linked could represent a contribution to the phenotype in an oligogenic model.

Tankyrase regulates epithelial lumen formation via suppression of Rab11 GEFs

Rab11 GTPase proteins are required for cytokinesis, ciliogenesis, and lumenogenesis. Rab11a is critical for apical delivery of podocalyxin (PODXL) during lumen formation in epithelial cells. SH3BP5 and SH3BP5L are guanine nucleotide exchange factors (GEFs) for Rab11. We show that SH3BP5 and SH3BP5L are required for activation of Rab11a and cyst lumen formation. Using proximity-dependent biotin identification (BioID) interaction proteomics, we have identified SH3BP5 and its paralogue SH3BP5L as new substrates of the poly-ADP-ribose polymerase Tankyrase and the E3 ligase RNF146. We provide data demonstrating that epithelial polarity via cyst lumen formation is governed by Tankyrase, which inhibits Rab11a activation through the suppression of SH3BP5 and SH3BP5L. RNF146 reduces Tankyrase protein abundance and restores Rab11a activation and lumen formation. Thus, Rab11a activation is controlled by a signaling pathway composed of the sequential inhibition of SH3BP5 paralogues by Tankyrase, which is itself suppressed by RNF146.

First body of evidence suggesting a role of a tankyrase-binding motif (TBM) of vinculin (VCL) in epithelial cells

BACKGROUND

Adherens junctions (AJ) are involved in cancer, infections and neurodegeneration. Still, their composition has not been completely disclosed. Poly(ADP-ribose) polymerases (PARPs) catalyze the synthesis of poly(ADP-ribose) (PAR) as a posttranslational modification. Four PARPs synthesize PAR, namely PARP-1/2 and Tankyrase-1/2 (TNKS). In the epithelial belt, AJ are accompanied by a PAR belt and a subcortical F-actin ring. F-actin depolymerization alters the AJ and PAR belts while PARP inhibitors prevent the assembly of the AJ belt and cortical actin. We wondered which PARP synthesizes the belt and which is the PARylation target protein. Vinculin (VCL) participates in the anchorage of F-actin to the AJ, regulating its functions, and colocalized with the PAR belt. TNKS has been formerly involved in the assembly of epithelial cell junctions.

HYPOTHESIS

TNKS poly(ADP-ribosylates) (PARylates) epithelial belt VCL, affecting its functions in AJ, including cell shape maintenance.

MATERIALS AND METHODS

Tankyrase-binding motif (TBM) sequences in hVCL gene were identified and VCL sequences from various vertebrates, Drosophila melanogaster and Caenorhabditis elegans were aligned and compared. Plasma membrane-associated PAR was tested by immunocytofluorescence (ICF) and subcellular fractionation in Vero cells while TNKS role in this structure and cell junction assembly was evaluated using specific inhibitors. The identity of the PARylated proteins was tested by affinity precipitation with PAR-binding reagent followed by western blots. Finally, MCF-7 human breast cancer epithelial cells were subjected to transfection with Tol2-plasmids, carrying a dicistronic expression sequence including Gallus gallus wt VCL (Tol-2-GgVCL), or the same VCL gene with a point mutation in TBM-II (Tol2-GgVCL/*TBM) under the control of a β-actin promoter, plus green fluorescent protein following an internal ribosome entry site (IRES-GFP) to allow the identification of transfected cells without modifying the transfected protein of interest.

RESULTS AND DISCUSSION

In this work, some of the hypothesis predictions have been tested. We have demonstrated that: (1) VCL TBMs were conserved in vertebrate evolution while absent in C. elegans; (2) TNKS inhibitors disrupted the PAR belt synthesis, while PAR and an endogenous TNKS pool were associated to the plasma membrane; (3) a VCL pool was covalently PARylated; (4) transfection of MCF-7 cells leading to overexpression of Gg-VCL/*TBM induced mesenchymal-like cell shape changes. This last point deserves further investigation, bypassing the limits of our transient transfection and overexpression system. In fact, a 5th testable prediction would be that a single point mutation in VCL TBM-II under endogenous expression control would induce an epithelial to mesenchymal transition (EMT). To check this, a CRISPR/Cas9 substitution approach followed by migration, invasion, gene expression and chemo-resistance assays should be performed.

MAGI1 inhibits the AMOTL2/p38 stress pathway and prevents luminal breast tumorigenesis

Alterations to cell polarization or to intercellular junctions are often associated with epithelial cancer progression, including breast cancers (BCa). We show here that the loss of the junctional scaffold protein MAGI1 is associated with bad prognosis in luminal BCa, and promotes tumorigenesis. E-cadherin and the actin binding scaffold AMOTL2 accumulate in MAGI1 deficient cells which are subjected to increased stiffness. These alterations are associated with low YAP activity, the terminal Hippo-pathway effector, but with an elevated ROCK and p38 Stress Activated Protein Kinase activities. Blocking ROCK prevented p38 activation, suggesting that MAGI1 limits p38 activity in part through releasing actin strength. Importantly, the increased tumorigenicity of MAGI1 deficient cells is rescued in the absence of AMOTL2 or after inhibition of p38, demonstrating that MAGI1 acts as a tumor-suppressor in luminal BCa by inhibiting an AMOTL2/p38 stress pathway.

Tankyrase Mediates K63-Linked Ubiquitination of JNK to Confer Stress Tolerance and Influence Lifespan in Drosophila

Tankyrase (Tnks) transfers poly(ADP-ribose) on substrates. Whereas studies have highlighted the pivotal roles of Tnks in cancer, cherubism, systemic sclerosis, and viral infection, the requirement for Tnks under physiological contexts remains unclear. Here, we report that the loss of Tnks or its muscle-specific knockdown impairs lifespan, stress tolerance, and energy homeostasis in adult Drosophila. We find that Tnks is a positive regulator in the JNK signaling pathway, and modest alterations in the activity of JNK signaling can strengthen or suppress the Tnks mutant phenotypes. We further identify JNK as a direct substrate of Tnks. Although Tnks-dependent poly-ADP-ribosylation is tightly coupled to proteolysis in the proteasome, we demonstrate that Tnks initiates degradation-independent ubiquitination on two lysine residues of JNK to promote its kinase activity and in vivo functions. Our study uncovers a type of posttranslational modification of Tnks substrates and provides insights into Tnks-mediated physiological roles.

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.

Poly(ADP-ribose)-dependent ubiquitination and its clinical implications

ADP-ribosylation-the addition of one or multiple ADP-ribose units onto proteins-is a therapeutically important post-translational modification implicated in cancer, neurodegeneration, and infectious diseases. The protein modification regulates a broad range of biological processes, including DNA repair, transcription, RNA metabolism, and the structural integrity of nonmembranous structures. The polymeric form of ADP-ribose, poly(ADP-ribose), was recently identified as a signal for triggering protein degradation through the ubiquitin-proteasome system. Using informatics analyses, we found that these ubiquitinated substrates tend to be low abundance proteins, which may serve as rate-limiting factors within signaling networks or metabolic processes. In this review, we summarize the current literature on poly(ADP-ribose)-dependent ubiquitination (PARdU) regarding its biological mechanisms, substrates, and relevance to diseases.

Angiomotin-p130 inhibits β-catenin stability by competing with Axin for binding to tankyrase in breast cancer

Growing evidence indicates that Angiomotin (Amot)-p130 and Amot-p80 have different physiological functions. We hypothesized that Amot-p130 is a tumor suppressor gene in breast cancer, in contrast with the canonical oncogenicity of Amot-p80 or total Amot. To clarify the role of Amot-p130 in breast cancer, we performed real-time quantitative PCR, western blotting, flow cytometry, microarray, immunofluorescence, immunoprecipitation, and tumor sphere-formation assays in vitro, as well as tumorigenesis and limited-dilution analysis in vivo. In this study, we showed that Amot-p130 inhibited the proliferation, migration, and invasion of breast cancer cells. Interestingly, transcriptional profiles indicated that genes differentially expressed in response to Amot-p130 knockdown were mostly related to β-catenin signaling in MCF7 cells. More importantly, most of the downstream partners of β-catenin were associated with stemness. In a further validation, Amot-p130 inhibited the cancer stem cell potential of breast cancer cells both in vitro and in vivo. Mechanistically, Amot-p130 decreased β-catenin stability by competing with Axin for binding to tankyrase, leading to a further inhibition of the WNT pathway. In conclusions, Amot-p130 functions as a tumor suppressor gene in breast cancer, disrupting β-catenin stability by competing with Axin for binding to tankyrase. Amot-p130 was identified as a potential target for WNT pathway-targeted therapies in breast cancer.

Structural basis for tankyrase-RNF146 interaction reveals noncanonical tankyrase-binding motifs

Poly(ADP-ribosyl)ation (PARylation) catalyzed by the tankyrase enzymes (Tankyrase-1 and -2; a.k.a. PARP-5a and -5b) is involved in mitosis, telomere length regulation, GLUT-4 vesicle transport, and cell growth and differentiation. Together with the E3 ubiquitin ligase RNF146 (a.k.a. Iduna), tankyrases regulate the cellular levels of several important proteins including Axin, 3BP2, and angiomotins, which are key regulators of Wnt, Src and Hippo signaling, respectively. These tankyrase substrates are first PARylated and then ubiquitylated by RNF146, which is allosterically activated by binding to PAR polymer. Each tankyrase substrate is recognized by a tankyrase-binding motif (TBM). Here we show that RNF146 binds directly to tankyrases via motifs in its C-terminal region. Four of these RNF146 motifs represent novel, extended TBMs, that have one or two additional amino acids between the most conserved Arg and Gly residues. The individual RNF146 motifs display weak binding, but together mediate a strong multivalent interaction with the substrate-binding region of TNKS, forming a robust one-to-one complex. A crystal structure of the first RNF146 noncanonical TBM in complex with the second ankyrin repeat domain of TNKS shows how an extended motif can be accommodated in a peptide-binding groove on tankyrases. Overall, our work demonstrates the existence of a new class of extended TBMs that exist in previously uncharacterized tankyrase-binding proteins including those of IF4A1 and NELFE.

The physiological role of Motin family and its dysregulation in tumorigenesis

Members in Motin family, or Angiomotins (AMOTs), are adaptor proteins that localize in the membranous, cytoplasmic or nuclear fraction in a cell context-dependent manner. They control the bioprocesses such as migration, tight junction formation, cell polarity, and angiogenesis. Emerging evidences have demonstrated that AMOTs participate in cancer initiation and progression. Many of the previous studies have focused on the involvement of AMOTs in Hippo-YAP1 pathway. However, it has been controversial for years that AMOTs serve as either positive or negative growth regulators in different cancer types because of the various cellular origins. The molecular mechanisms of these opposite roles of AMOTs remain elusive. This review comprehensively summarized how AMOTs function physiologically and how their dysregulation promotes or inhibits tumorigenesis. Better understanding the functional roles of AMOTs in cancers may lead to an improvement of clinical interventions as well as development of novel therapeutic strategies for cancer patients.

The RNF146 E3 ubiquitin ligase is required for the control of Wnt signaling and body pattern formation in Xenopus

The RING finger protein Rnf146 encodes an E3 ubiquitin ligase capable of targeting poly-ADP-ribosylated substrates for proteasomal degradation. Rnf146 has been identified as a critical regulator of Axin1 and thus of Wnt/β-catenin signaling. However its physiological significance in vertebrate embryonic development remains to be demonstrated. In this study, we take advantages of early Xenopus embryos to demonstrate that Rnf146 is essential for embryonic pattern formation. Depletion of zygotic Rnf146 using a translation blocking morpholino oligo (MO) results in anteriorized development and increased expression the anterior marker gene Otx2, consistent the notion that Rnf146 is a positive regulator of Wnt/β-catenin signaling through negatively regulating Axin1 expression. This notion is further supported by examination of the role of maternal Rnf146 in the context of Spemann organizer formation and dorsal axis development. Depletion of maternal Rnf146 using an antisense oligodeoxynucleic acid (ODN) leads to ventralized development and diminished expression of organizer genes. Together, we have provided evidence for the first time that Rnf146 is a critical regulator of embryonic pattern formation in vertebrates.

EPEC effector EspF promotes Crumbs3 endocytosis and disrupts epithelial cell polarity

Enteropathogenic Escherichia coli (EPEC) uses a type III secretion system to inject effector proteins into host intestinal epithelial cells causing diarrhoea. EPEC infection redistributes basolateral proteins β1-integrin and Na⁺ /K⁺ ATPase to the apical membrane of host cells. The Crumbs (Crb) polarity complex (Crb3/Pals1/Patj) is essential for epithelial cell polarisation and tight junction (TJ) assembly. Here, we demonstrate that EPEC displaces Crb3 and Pals1 from the apical membrane to the cytoplasm of cultured intestinal epithelial cells and colonocytes of infected mice. In vitro studies show that EspF, but not Map, alters Crb3, whereas both effectors modulate Pals1. EspF perturbs polarity formation in cyst morphogenesis assays and induces endocytosis and apical redistribution of Na⁺ /K⁺ ATPase. EspF binds to sorting nexin 9 (SNX9) causing membrane remodelling in host cells. Infection with ΔespF/pespFD3, a mutant strain that ablates EspF binding to SNX9, or inhibition of dynamin, attenuates Crb3 endocytosis caused by EPEC. In addition, infection with ΔespF/pespFD3 has no impact on Na⁺ /K⁺ ATPase endocytosis. These data support the hypothesis that EPEC perturbs apical-basal polarity in an EspF-dependent manner, which would contribute to EPEC-associated diarrhoea by disruption of TJ and altering the crucial positioning of membrane transporters involved in the absorption of ions and solutes.

Angiomotin Family Members: Oncogenes or Tumor Suppressors?

Angiomotin (Amot) family contains three members: Amot (p80 and p130 isoforms), Amot-like protein 1 (Amotl1), and Amot-like protein 2 (Amotl2). Amot proteins play an important role in tube formation and migration of endothelial cells and the regulation of tight junctions, polarity, and epithelial-mesenchymal transition in epithelial cells. Moreover, these proteins regulate the proliferation and migration of cancer cells. In most cancers, Amot family members promote the proliferation and invasion of cancer cells, including breast cancer, osteosarcoma, colon cancer, prostate cancer, head and neck squamous cell carcinoma, cervical cancer, liver cancer, and renal cell cancer. However, in glioblastoma, ovarian cancer, and lung cancer, Amot inhibits the growth of cancer cells. In addition, there are controversies on the regulation of Yes-associated protein (YAP) by Amot. Amot promotes either the internalization of YAP into the nucleus or the retention of YAP in the cytoplasm of different cell types. Moreover, Amot regulates the AMPK, mTOR, Wnt, and MAPK signaling pathways. However, it is unclear whether Amot is an oncogene or a tumor suppressor gene in different cellular processes. This review focuses on the multifunctional roles of Amot in cancers.