Hsa_circ_0001278 Facilitates Colorectal Cancer Progression via Sponging miR-338-5p and Regulating AMOTL1 Expression

BACKGROUND

Colorectal cancer (CRC) ranks as the third most common cancer and is second in terms of mortality worldwide. Circular RNAs are involved in the occurrence and development of malignant tumors by functioning either as oncogenes or tumor suppressors.

METHOD

This study investigated the functions of hsa_circ_0001278 in CRC. We analyzed the expression of hsa_circ_0001278 in CRC tissues and adjacent normal tissues. In order to understand the roles of hsa_circ_0001278 in CRC in terms of cellular biological behavior, in vitro experiments were conducted. A mechanistic study was designed to investigate the regulatory effect of hsa_circ_0001278 on CRC.

RESULTS

Hsa_circ_0001278 was found to be significantly upregulated in CRC specimens. The functional analysis indicated that hsa_circ_0001278 promotes aggressive phenotypes of CRC cells. Further mechanistic studies revealed that hsa_circ_0001278 sponges miR-338-5p to regulate angiomotin-like 1 (AMOTL1), thereby facilitating CRC progression.

CONCLUSION

Our results demonstrate that hsa_circ_0001278 promotes malignant behaviors in CRC cells by sponging miR-338-5p to regulate AMOTL1 expression. This suggests that hsa_circ_0001278 may serve as a novel target for CRC treatment.

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.

Investigating whether exosomal miR-205-5p derived from tongue squamous cell carcinoma cells stimulates the angiogenic activity of HUVECs by targeting AMOT

BACKGROUND

Although exosomal microRNAs (exo-miRNAs) regulate angiogenesis, they are not sufficient for the development of anti-vascular drugs for tongue squamous cell carcinoma (TSCC). miR-205-5p is an exo-miRNA that is highly expressed in the saliva of patients with oral SCC.

OBJECTIVE

We aimed to clarify the role and molecular mechanism of exosomal miR-205-5p in regulating TSCC angiogenesis.

METHODS

Effect of exosomes derived from TSCC cells on human umbilical vein endothelial cell (HUVEC) function was determined using the CCK-8, Transwell, Transwell-Matrigel, and Matrigel-based tube formation assays. Protein levels were detected by western blot. The binding between miR-205-5p and the 3'UTR of AMOT was verified using a luciferase reporter assay.

RESULTS

Exosomal miR-205-5p (exo-miR-205-5p) promoted the proliferation, migration, and invasion of HUVECs, increased the number of tubes formed by HUVECs, and increased the vascular endothelial growth factor receptor 2 levels in HUVECs. Exo-miR-205-5p downregulated the AMOT level in HUVECs. Results of the luciferase reporter assay showed that miR-205-5p could bind to the 3'UTR of AMOT. AMOT overexpression blocked the effect of exo-miR-205-5p on HUVEC functions.

CONCLUSION

Exo-miR-205-5p derived from TSCC regulates the angiogenic activity of HUVECs by targeting AMOT and might be a new molecular target for the development of anti-vascular drugs for TSCC.

Multiphase coalescence mediates Hippo pathway activation

The function of biomolecular condensates is often restricted by condensate dissolution. Whether condensates can be suppressed without condensate dissolution is unclear. Here, we show that upstream regulators of the Hippo signaling pathway form functionally antagonizing condensates, and their coalescence into a common phase provides a mode of counteracting the function of biomolecular condensates without condensate dissolution. Specifically, the negative regulator SLMAP forms Hippo-inactivating condensates to facilitate pathway inhibition by the STRIPAK complex. In response to cell-cell contact or osmotic stress, the positive regulators AMOT and KIBRA form Hippo-activating condensates to facilitate pathway activation. The functionally antagonizing SLMAP and AMOT/KIBRA condensates further coalesce into a common phase to inhibit STRIPAK function. These findings provide a paradigm for restricting the activity of biomolecular condensates without condensate dissolution, shed light on the molecular principles of multiphase organization, and offer a conceptual framework for understanding upstream regulation of the Hippo signaling pathway.

Interactions between AMOT PPxY motifs and NEDD4L WW domains function in HIV-1 release

Like most enveloped viruses, HIV must acquire a lipid membrane as it assembles and buds through the plasma membrane of infected cells to spread infection. Several sets of host cell machinery facilitate this process, including proteins of the endosomal sorting complexes required for transport pathway, which mediates the membrane fission reaction required to complete viral budding, as well as angiomotin (AMOT) and NEDD4L, which bind one another and promote virion membrane envelopment. AMOT and NEDD4L interact through the four NEDD4L WW domains and three different AMOT Pro-Pro-x (any amino acid)-Tyr (PPxY) motifs, but these interactions are not yet well defined. Here, we report that individual AMOT PPxY and NEDD4L WW domains interact with the following general affinity hierarchies: AMOT PPxY1>PPxY2>PPxY3 and NEDD4L WW3>WW2>WW1∼WW4. The unusually high-affinity of the AMOT PPxY1–NEDD4L WW3 interaction accounts for most of the AMOT–NEDD4L binding and is critical for stimulating HIV-1 release. Comparative structural, binding, and virological analyses reveal that complementary ionic and hydrophobic contacts on both sides of the WW–PPxY core interaction account for the unusually high affinity of the AMOT PPxY1–NEDD4L WW3 interaction. Taken together, our studies reveal how the first AMOT PPxY1 motif binds the third NEDD4L WW domain to stimulate HIV-1 viral envelopment and promote infectivity.

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.

Angiomotins stimulate LATS kinase autophosphorylation and act as scaffolds that promote Hippo signaling

The Hippo pathway controls cell proliferation, differentiation, and survival by regulating the Yes-associated protein (YAP) transcriptional coactivator in response to various stimuli, including the mechanical environment. The major YAP regulators are the LATS1/2 kinases, which phosphorylate and inhibit YAP. LATS1/2 are activated by phosphorylation on a hydrophobic motif (HM) outside of the kinase domain by MST1/2 and other kinases. Phosphorylation of the HM motif then triggers autophosphorylation of the kinase in the activation loop to fully activate the kinase, a process facilitated by MOB1. The angiomotin family of proteins (AMOT, AMOTL1, and AMOTL2) bind LATS1/2 and promote its kinase activity and YAP phosphorylation through an unknown mechanism. Here we show that angiomotins increase Hippo signaling through multiple mechanisms. We found that, by binding LATS1/2, SAV1, and YAP, angiomotins function as a scaffold that connects LATS1/2 to both its activator SAV1-MST1 and its target YAP. Deletion of all three angiomotins reduced the association of LATS1 with SAV1-MST1 and decreased MST1/2-mediated LATS1/2-HM phosphorylation. Angiomotin deletion also reduced LATS1/2's ability to associate with and phosphorylate YAP. In addition, we found that angiomotins have an unexpected function along with MOB1 to promote autophosphorylation of LATS1/2 on the activation loop motif independent of HM phosphorylation. These results indicate that angiomotins enhance Hippo signaling by stimulating LATS1/2 autophosphorylation and by connecting LATS1/2 with both its activator SAV1-MST1/2 and its substrate YAP.

MiR-4463 inhibits the migration of human aortic smooth muscle cells by AMOT

Aberrant vascular smooth muscle cell (VSMC) migration has been implicated in a variety of vascular disorders, while the signal pathways governing this process remain unclear. Here, we investigated whether miRNAs, which are strong post-transcriptional regulators of gene expression, could alter VSMC migration. We detected the expression of miR-4463 in the plasma of patients with atherosclerosis and in human aortic smooth muscle cells under hypoxia–ischemia condition, and investigated the migration effect and its downstream pathways. The results have shown that whether in clinical AS patients or hypoxic cells, the expression of miR-4463 was lower than that of normal group, then the number of migrating cells in the miR-4463 mimic intervention group was significantly decreased compared with the normal group and miR-4463 inhibitor instead. Furthermore, the expression of angiomotin (AMOT) in gastrocnemius muscle and femoral artery of patients was significantly higher than that of the control group. The protein level of AMOT in miR-4463 mimic intervention group was significantly decreased, and its level was reversed by inhibiting miR-4463. In summary, these results indicate that miR-4463 is a novel modulator of VSMC migration by targetting AMOT expression. Regulating miR-4463 or its specific downstream target genes in VSMCs may represent an attractive approach for the treatment of vascular diseases.

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.

Conditional knockout of TFPI-1 in VSMCs of mice accelerates atherosclerosis by enhancing AMOT/YAP pathway

BACKGROUND

Tissue factor pathway inhibitor-1 (TFPI-1) has multiple functions and its precise role and molecular mechanism during the development of atherosclerosis are not clear.

OBJECTIVES

To determine the effect and molecular mechanism of TFPI-1 deficiency in vascular smooth muscle cells (VSMCs) in atherosclerosis in the apolipoprotein E knockout (ApoE^-/-) mouse.

METHODS AND RESULTS

A mouse model with a conditional knockout of TFPI-1 in VSMCs in an atherosclerosis-prone background (ApoE^-/-) was generated. Mice were fed a high fat diet for 18weeks and were then euthanized. Arterial trees and aortas were stained with Sudan IV and were labeled via immunohistochemistry. Cell proliferation and migration of VSMCs in atherosclerotic plaques were assessed. More atherosclerotic lesions and higher levels of proliferation and migration of VSMCs were observed in TFPI-1^fl/fl/Sma-Cre⁺ApoE^-/-mice. An interaction between TFPI-1 and angiomotin (AMOT) was identified in human VSMCs by mass spectrometry, immunoprecipitation and co-localization analyses. Signal pathway changes were detected by Western blot analysis, and the expression levels of target genes were determined by real-time PCR. Decreased phosphorylation of AMOT and Yes-associated protein 1 (YAP) in TFPI-1^fl/fl/Sma-Cre⁺ApoE^-/- mice resulted in increased expression levels of snail family zinc finger 2 (SLUG) and connective tissue growth factor (CTGF), which are target genes of the Hippo signaling pathway that have been verified as atherosclerosis candidate genes.

CONCLUSION

Deficiency in TFPI-1 in the VSMCs of ApoE^-/- mice accelerated the development of atherosclerosis by promoting the proliferation and migration of VSMCs which may be caused by the decreased phosphorylation of AMOT and YAP.

SIGNIFICANCE

TFPI-1 has been found to has an anticoagulant activity, induce cell apoptosis and prevent cell proliferation. For the first time, we constructed a line of conditional knockout mice in which the TPFI-1 gene is deleted in VSMCs. We found that TFPI-1 deficiency clearly promoted the development of atherosclerosis when these mice were crossed into an ApoE^-/-background. One notable feature of atherosclerosis is the proliferation and migration of smooth muscle cells. Previous reports involved TFPI-1 do not completely explain the proliferation and migration of VSMCs because heterozygous TF deficient (TF^±) mice bred in an ApoE^-/- background did not show diminished atherosclerosis compared to TF^+/+ mice bred in the same background. Our results first confirmed that TFPI-1 interacts with AMOT, which led to a decrease in the phosphorylation of YAP and further increased the genes expression of the proliferation and migration involved. Our results further confirmed that atherosclerosis was a localized disease.

Long non-coding RNA small nucleolar RNA host gene 12 (SNHG12) promotes cell proliferation and migration by upregulating angiomotin gene expression in human osteosarcoma cells

The long non-coding RNA (lncRNA) small nucleolar RNA host gene 12 (SNHG12) has a role in cell proliferation and migration. Angiomotin, encoded by the AMOT gene, is a protein that regulates the migration and organization of endothelial cells. SNHG12 and AMOT have been shown to play a role in a variety of human cancers but have yet to be studied in detail in human osteosarcoma. Tissue samples from primary osteosarcoma (n = 20) and adjacent normal tissues (n = 20), the osteosarcoma cell lines, SAOS-2, MG-63, U-2 OS, and the human osteoblast cell line hFOB (OB3) were studied using Western blot for angiomotin, and quantitative real-time polymerase chain reaction for the expression of SNHG12 and AMOT. The expression of SNHG12 was knocked down using RNA interference. Cell migration assays were performed. Cell apoptosis was studied using flow cytometry. SNHG12 and AMOT messenger RNA (mRNA) expression was upregulated in osteosarcoma tissues and cell lines when compared with normal tissues and cells. Upregulation of AMOT mRNA was associated with upregulation of SNHG12. Knockdown of SNHG12 reduced the expression of angiomotin in osteosarcoma cells and suppressed cell proliferation and migration but did not affect cell apoptosis. This preliminary study has shown that the lncRNA SNHG12 promotes cell proliferation and migration by upregulating AMOT gene expression in osteosarcoma cells in vivo and in vitro. Further studies are recommended to investigate the role of SNHG12 and AMOT expression in tumor cell proliferation and migration and angiogenesis in osteosarcoma and a range of malignant mesenchymal tumors.

Phosphorylation of angiomotin by Lats1/2 kinases inhibits F-actin binding, cell migration, and angiogenesis

The Hippo tumor suppressor pathway plays important roles in organ size control through Lats1/2 mediated phosphorylation of the YAP/TAZ transcription co-activators. However, YAP/TAZ independent functions of the Hippo pathway are largely unknown. Here we report a novel role of the Hippo pathway in angiogenesis. Angiomotin p130 isoform (AMOTp130) is phosphorylated on a conserved HXRXXS motif by Lats1/2 downstream of GPCR signaling. Phosphorylation disrupts AMOT interaction with F-actin and correlates with reduced F-actin stress fibers and focal adhesions. Furthermore, phosphorylation of AMOT by Lats1/2 inhibits endothelial cell migration in vitro and angiogenesis in zebrafish embryos in vivo. Thus AMOT is a direct substrate of Lats1/2 mediating functions of the Hippo pathway in endothelial cell migration and angiogenesis.