Inhibition of hsa_circ_0002570 suppresses high-glucose-induced angiogenesis and inflammation in retinal microvascular endothelial cells through miR-1243/angiomotin axis

Diabetic retinopathy (DR) is the most severe microvascular complication of diabetes and a major cause of visual impairment and blindness. However, the treatment for DR is still limited. Our study aimed to explore the role of circular RNA_0002570 in DR. First, we predicted the potential microRNA and mRNA that could bind to circ_0002570 and identified the miR-1243 and angiomotin gene; then, we used RT-PCR and Western blot to measure their expression. Next, we evaluated the abilities of proliferation, migration, and angiogenesis in vitro in human retinal microvascular endothelial cells (hRMECs) by CCK-8, transwell assay, and tube formation assay, respectively. To analyze the relationship among miR-1243, circ_0002570, and angiomotin, RNA pull-down and luciferase assay were performed. Our results showed that, in DR patients and high-glucose-induced hRMECs, miR-1243, circ_0002570, and angiomotin were all abnormally expressed. MiR-1243 could directly and competitively bind to both circ_0002570 and angiomotin mRNA to inhibit their expression. Moreover, circ_0002570 suppressed the abilities of proliferation, migration, and angiogenesis in hRMECs induced by high glucose, which was dependent on miR-1243-angiomotin axis. Furthermore, circ_0002570 could upregulate angiomotin by targeting miR-1243 to mediate the dysfunction of hRMECs induced by high glucose. In conclusion, circ_0002570 might serve as a potential target for diagnosis and treatment for DR.

Angiomotin promotes renal epithelial and carcinoma cell proliferation by retaining the nuclear YAP

Renal cell carcinoma (RCC) is one of the common tumors in the urinary system without effective therapies. Angiomotin (Amot) can interact with Yes-associated protein (YAP) to either stimulate or inhibit YAP activity, playing a potential role in cell proliferation. However, the role of Amot in regulating the proliferation of renal epithelial and RCC cells is unknown. Here, we show that Amot is expressed predominantly in the nucleus of RCC cells and tissues, and in the cytoplasm and nucleus of renal epithelial cells and paracancerous tissues. Furthermore, Amot silencing inhibited proliferation of HK-2 and 786-O cells while Amot upregulation promoted proliferation of ACHN cells. Interestingly, the location of Amot and YAP in RCC clinical samples and cells was similar. Amot interacted with YAP in HK-2 and 786-O cells, particularly in the nucleus. Moreover, Amot silencing mitigated the levels of nuclear YAP in HK-2 and 786-O cells and reduced YAP-related CTGF and Cyr61 expression in 786-O cells. Amot upregulation slightly increased the nuclear YAP and YAP-related gene expression in ACHN cells. Finally, enhanced YAP expression restored proliferation of Amot-silencing 786-O cells. Together, these data indicate that Amot is crucial for the maintenance of nuclear YAP to promote renal epithelial and RCC proliferation.

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.

Regulation of localization and function of the transcriptional co-activator YAP by angiomotin

The Hippo-YAP pathway is a central regulator of cell contact inhibition, proliferation and death. There are conflicting reports regarding the role of Angiomotin (Amot) in regulating this pathway. While some studies suggest a YAP-inhibitory function other studies indicate Amot is required for YAP activity. Here, we describe an Amot-dependent complex comprised of Amot, YAP and Merlin. The phosphorylation of Amot at Serine 176 shifts localization of this complex to the plasma membrane, where it associates with the tight-junction proteins Pals1/PATJ and E-cadherin. Conversely, hypophosphorylated Amot shifts localization of the complex to the nucleus, where it facilitates the association of YAP and TEAD, induces transcriptional activation of YAP target genes and promotes YAP-dependent cell proliferation. We propose that phosphorylation of Amot^S176 is a critical post-translational modification that suppresses YAP’s ability to promote cell proliferation and tumorigenesis by altering the subcellular localization of an essential YAP co-factor.

DOI:http://dx.doi.org/10.7554/eLife.23966.001

Cells in animals and other multi-cellular organisms need to know when and where they should grow and divide. Individual cells communicate with their surrounding environment and each other via signaling pathways such as the Hippo-YAP pathway, which stimulates cells to grow and therefore influences the size of organs. When the Hippo part of the pathway is active it causes a protein known as YAP to move out of a compartment in the cell called the nucleus. Inside the nucleus, YAP helps to activate genes that promote cell growth. If the Hippo pathway can no longer respond to cues from the environment, YAP becomes over-active and can contribute to the development of various cancers. Therefore researchers are trying to better understand how it is regulated.

Many signals both from inside and outside the cell influence YAP activity. For example, some signals block YAP from entering the nucleus, whereas others cause YAP to be broken down entirely. Several studies have recently identified a signal protein called angiomotin as a regulator of YAP. However, the studies provide conflicting reports as to whether angiomotin promotes or inhibits cell growth.

Like many other proteins, angiomotin can be tagged with a small molecule called a phosphate group that can alter its activity. Moleirinho, Hoxha et al. studied human cells containing versions of angiomotin that mimic different forms of the protein with or without the phosphate. The experiments indicate that when a phosphate is attached at a particular position (known as serine 176), angiomotin predominantly interacts with YAP and another protein called Merlin at the cell surface. On the other hand, when angiomotin does not have a phosphate attached to it, all three proteins can move into the nucleus, where YAP is able to activate genes and promote cell growth.

Overall, these findings indicate that adding a phosphate group to angiomotin can act as a switch to regulate where in the cell it and YAP are found and thus, whether YAP is active. Future experiments will investigate which enzymes add the phosphate group to serine 176, and when they are able to do so.

DOI:http://dx.doi.org/10.7554/eLife.23966.002

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

The Crumbs complex is an important determinant of epithelial apical-basal polarity that functions in regulation of tight junctions, resistance to epithelial-to-mesenchymal transitions and as a tumour suppressor. Although the functional role of the Crumbs complex is being elucidated, its regulation is poorly understood. Here, we show that suppression of RNF146, an E3 ubiquitin ligase that recognizes ADP-ribosylated substrates, and tankyrase, a poly(ADP-ribose) polymerase, disrupts the junctional Crumbs complex and disturbs the function of tight junctions. We show that RNF146 binds a number of polarity-associated proteins, in particular members of the angiomotin (AMOT) family. Accordingly, AMOT proteins are ADP-ribosylated by TNKS2, which drives ubiquitylation by RNF146 and subsequent degradation. Ablation of RNF146 or tankyrase, as well as overexpression of AMOT, led to the relocation of PALS1 (a Crumbs complex component) from the apical membrane to internal puncta, a phenotype that is rescued by AMOTL2 knockdown. We thus reveal a new function of RNF146 and tankyrase in stabilizing the Crumbs complex through downregulation of AMOT proteins at the apical membrane.

Rho-associated protein kinase regulates subcellular localisation of Angiomotin and Hippo-signalling during preimplantation mouse embryo development

The differential activity of the Hippo-signalling pathway between the outer- and inner-cell populations of the developing preimplantation mouse embryo directs appropriate formation of trophectoderm and inner cell mass (ICM) lineages. Such distinct signalling activity is under control of intracellular polarization, whereby Hippo-signalling is either supressed in polarized outer cells or activated in apolar inner cells. The central role of apical-basolateral polarization to such differential Hippo-signalling regulation prompted us to reinvestigate the role of potential upstream molecular regulators affecting apical-basolateral polarity. This study reports that the chemical inhibition of Rho-associated kinase (Rock) is associated with failure to form morphologically distinct blastocysts, indicative of compromised trophectoderm differentiation, and defects in the localization of both apical and basolateral polarity factors associated with malformation of tight junctions. Moreover, Rock-inhibition mediates mislocalization of the Hippo-signalling activator Angiomotin (Amot), to the basolateral regions of outer cells and is concomitant with aberrant activation of the pathway. The Rock-inhibition phenotype is mediated by Amot, as RNAi-based Amot knockdown totally rescues the normal suppression of Hippo-signalling in outer cells. In conclusion, Rock, via regulating appropriate apical-basolateral polarization in outer cells, regulates the appropriate activity of the Hippo-signalling pathway, by ensuring correct subcellular localization of Amot protein in outer cells.

Multimodal biopanning of T7 phage-displayed peptides reveals angiomotin as a potential receptor of the anti-angiogenic macrolide Roxithromycin

Roxithromycin (RXM) is a semi-synthetic fourteen-membered macrolide antibiotic that shows anti-angiogenic activity in solid tumors. In the present study, we conducted biopanning of T7 phage-displayed peptides either on a 96-well formatted microplate, a flow injection-type quartz-crystal microbalance (QCM) biosensor, or a cuvette-type QCM. RXM-selected peptides of different sequence, length and number were obtained from each mode of screening. Subsequent bioinformatics analysis of the RXM-selected peptides consistently gave positive scores for the extracellular domain (E458-T596) of angiomotin (Amot), indicating that this may comprise a binding region for RXM. Bead pull down assay and QCM analysis confirmed that RXM directly interacts with Amot via the screen-guided region, which also corresponds to the binding site for the endogenous anti-angiogenic inhibitor angiostatin (Anst). Thus, multimodal biopanning of T7PD revealed that RXM binds to the extracellular domain on Amot as a common binding site with Anst, leading to inhibition of angiogenesis-dependent tumor growth and metastasis. These data might explain the molecular basis underlying the mechanism of action for the anti-angiogenic activity of RXM.

The Angiomotins--from discovery to function

Angiomotins were originally identified as angiostatin binding proteins and implicated in the regulation of endothelial cell migration. Recent studies have shed light on the role of Angiomotins and other members of the Motin protein family in epithelial cells and in pathways directly linked to the pathogenesis of cancer. In particular, Motins have been shown to play a role in signaling pathways regulated by small G-proteins and the Hippo-YAP pathway. In this review the role of the Motin protein family in these signaling pathways will be described and open questions will be discussed.

Actin-binding and cell proliferation activities of angiomotin family members are regulated by Hippo pathway-mediated phosphorylation

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

Amot130 adapts atrophin-1 interacting protein 4 to inhibit yes-associated protein signaling and cell growth

The adaptor protein Amot130 scaffolds components of the Hippo pathway to promote the inhibition of cell growth. This study describes how Amot130 through binding and activating the ubiquitin ligase AIP4/Itch achieves these effects. AIP4 is found to bind and ubiquitinate Amot130 at residue Lys-481. This both stabilizes Amot130 and promotes its residence at the plasma membrane. Furthermore, Amot130 is shown to scaffold a complex containing overexpressed AIP4 and the transcriptional co-activator Yes-associated protein (YAP). Consequently, Amot130 promotes the ubiquitination of YAP by AIP4 and prevents AIP4 from binding to large tumor suppressor 1. Amot130 is found to reduce YAP stability. Importantly, Amot130 inhibition of YAP dependent transcription is reversed by AIP4 silencing, whereas Amot130 and AIP4 expression interdependently suppress cell growth. Thus, Amot130 repurposes AIP4 from its previously described role in degrading large tumor suppressor 1 to the inhibition of YAP and cell growth.