JEAP, a novel component of tight junctions in exocrine cells

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.

SRSF3/AMOTL1 splicing axis promotes the tumorigenesis of nasopharyngeal carcinoma through regulating the nucleus translocation of YAP1

Dysregulation of serine/arginine splicing factors (SRSFs) and abnormal alternative splicing (AS) have been widely implicated in various cancers but scarcely investigated in nasopharyngeal carcinoma (NPC). Here we examine the expression of 12 classical SRSFs between 87 NPC and 10 control samples, revealing a significant upregulation of SRSF3 and its association with worse prognosis in NPC. Functional assays demonstrate that SRSF3 exerts an oncogenic function in NPC progression. Transcriptome analysis reveals 1,934 SRSF3-regulated AS events in genes related to cell cycle and mRNA metabolism. Among these events, we verify the generation of a long isoform of AMOTL1 (AMOTL1-L) through a direct bond of the SRSF3 RRM domain with the exon 12 of AMOTL1 to promote exon inclusion. Functional studies also reveal that AMOTL1-L promotes the proliferation and migration of NPC cells, while AMOTL1-S does not. Furthermore, overexpression of AMOTL1-L, but not -S, significantly rescues the inhibitory effects of SRSF3 knockdown. Additionally, compared with AMOTL1-S, AMOTL1-L has a localization preference in the intracellular than the cell membrane, leading to a more robust interaction with YAP1 to promote nucleus translocation. Our findings identify SRSF3/AMOTL1 as a novel alternative splicing axis with pivotal roles in NPC development, which could serve as promising prognostic biomarkers and therapeutic targets for NPC.

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.

CircAMOTL1 RNA and AMOTL1 Protein: Complex Functions of AMOTL1 Gene Products

The complexity of the cellular proteome facilitates the control of a wide range of cellular processes. Non-coding RNAs, including microRNAs and long non-coding RNAs, greatly contribute to the repertoire of tools used by cells to orchestrate various functions. Circular RNAs (circRNAs) constitute a specific class of non-coding RNAs that have recently emerged as a widely generated class of molecules produced from many eukaryotic genes that play essential roles in regulating cellular processes in health and disease. This review summarizes current knowledge about circRNAs and focuses on the functions of AMOTL1 circRNAs and AMOTL1 protein. Both products from the AMOTL1 gene have well-known functions in physiology, cancer, and other disorders. Using AMOTL1 as an example, we illustrate how focusing on both circRNAs and proteins produced from the same gene contributes to a better understanding of gene functions.

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.

Junctional Adhesion Molecules: Potential Proteins in Atherosclerosis

Junctional adhesion molecules (JAMs) are cell-cell adhesion molecules of the immunoglobulin superfamily and are involved in the regulation of diverse atherosclerosis-related processes such as endothelial barrier maintenance, leucocytes transendothelial migration, and angiogenesis. To combine and further broaden related results, this review concluded the recent progress in the roles of JAMs and predicted future studies of JAMs in the development of atherosclerosis.

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.

Endothelial permeability, LDL deposition, and cardiovascular risk factors-a review

Early atherosclerosis features functional and structural changes in the endothelial barrier function that affect the traffic of molecules and solutes between the vessel lumen and the vascular wall. Such changes are mechanistically related to the development of atherosclerosis. Proatherogenic stimuli and cardiovascular risk factors, such as dyslipidaemias, diabetes, obesity, and smoking, all increase endothelial permeability sharing a common signalling denominator: an imbalance in the production/disposal of reactive oxygen species (ROS), broadly termed oxidative stress. Mostly as a consequence of the activation of enzymatic systems leading to ROS overproduction, proatherogenic factors lead to a pro-inflammatory status that translates in changes in gene expression and functional rearrangements, including changes in the transendothelial transport of molecules, leading to the deposition of low-density lipoproteins (LDL) and the subsequent infiltration of circulating leucocytes in the intima. In this review, we focus on such early changes in atherogenesis and on the concept that proatherogenic stimuli and risk factors for cardiovascular disease, by altering the endothelial barrier properties, co-ordinately trigger the accumulation of LDL in the intima and ultimately plaque formation.

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.

VCAM-1 induces signals that stimulate ZO-1 serine phosphorylation and reduces ZO-1 localization at lung endothelial cell junctions

Endothelial cell VCAM-1 regulates recruitment of lymphocytes, eosinophils, mast cells, or dendritic cells during allergic inflammation. In this report, we demonstrated that, during allergic lung responses, there was reduced zonula occludens (ZO)-1 localization in lung endothelial cell junctions, whereas there was increased lung endothelial cell expression of VCAM-1, N-cadherin, and angiomotin. In vitro, leukocyte binding to VCAM-1 reduced ZO-1 in endothelial cell junctions. Using primary human endothelial cells and mouse endothelial cell lines, Ab crosslinking of VCAM-1 increased serine phosphorylation of ZO-1 and induced dissociation of ZO-1 from endothelial cell junctions, demonstrating that VCAM-1 regulates ZO-1. Moreover, VCAM-1 induction of ZO-1 phosphorylation and loss of ZO-1 localization at cell junctions was blocked by inhibition of VCAM-1 intracellular signals that regulate leukocyte transendothelial migration, including NOX2, PKCα, and PTP1B. Furthermore, exogenous addition of the VCAM-1 signaling intermediate H₂ O₂ (1 μM) stimulated PKCα-dependent and PTP1B-dependent serine phosphorylation of ZO-1 and loss of ZO-1 from junctions. Overexpression of ZO-1 blocked leukocyte transendothelial migration. In summary, leukocyte binding to VCAM-1 induces signals that stimulated ZO-1 serine phosphorylation and reduced ZO-1 localization at endothelial cell junctions during leukocyte transendothelial migration.

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

Tankyrase Inhibitor Sensitizes Lung Cancer Cells to Endothelial Growth Factor Receptor (EGFR) Inhibition via Stabilizing Angiomotins and Inhibiting YAP Signaling

YAP signaling pathway plays critical roles in tissue homeostasis, and aberrant activation of YAP signaling has been implicated in cancers. To identify tractable targets of YAP pathway, we have performed a pathway-based pooled CRISPR screen and identified tankyrase and its associated E3 ligase RNF146 as positive regulators of YAP signaling. Genetic ablation or pharmacological inhibition of tankyrase prominently suppresses YAP activity and YAP target gene expression. Using a proteomic approach, we have identified angiomotin family proteins, which are known negative regulators of YAP signaling, as novel tankyrase substrates. Inhibition of tankyrase or depletion of RNF146 stabilizes angiomotins. Angiomotins physically interact with tankyrase through a highly conserved motif at their N terminus, and mutation of this motif leads to their stabilization. Tankyrase inhibitor-induced stabilization of angiomotins reduces YAP nuclear translocation and decreases downstream YAP signaling. We have further shown that knock-out of YAP sensitizes non-small cell lung cancer to EGFR inhibitor Erlotinib. Tankyrase inhibitor, but not porcupine inhibitor, which blocks Wnt secretion, enhances growth inhibitory activity of Erlotinib. This activity is mediated by YAP inhibition and not Wnt/β-catenin inhibition. Our data suggest that tankyrase inhibition could serve as a novel strategy to suppress YAP signaling for combinatorial targeted therapy.

Mitigation of tight junction protein dysfunction in lung microvascular endothelial cells with pitavastatin

BACKGROUND

Statin use in individuals with chronic obstructive pulmonary disease (COPD) with coexisting cardiovascular disease is associated with a reduced risk of exacerbations. The mechanisms by which statin plays a role in the pathophysiology of COPD have not been defined. To explore the mechanisms involved, we investigated the effect of statin on endothelial cell function, especially endothelial cell tight junctions.

METHOD

We primarily assessed whether pitavastatin could help mitigate the development of emphysema induced by continuous cigarette smoking (CS) exposure. We also investigated the activation of liver kinase B1 (LKB1)/AMP-activated protein kinase (AMPK) signaling, which plays a role in maintaining endothelial functions, important tight junction proteins, zonula occludens (ZO)-1 and claudin-5 expression, and lung microvascular endothelial cell permeability.

RESULTS

We found that pitavastatin prevented the CS-induced decrease in angiomotin-like protein 1 (AmotL1)-positive vessels via the activation of LKB1/AMPK signaling and IFN-γ-induced hyperpermeability of cultured human lung microvascular endothelial cells by maintaining the levels of AmotL1, ZO-1, and claudin-5 expression at the tight junctions.

CONCLUSION

Our results indicate that the maintenance of lung microvascular endothelial cells by pitavastatin prevents tight junction protein dysfunctions induced by CS. These findings may ultimately lead to new and novel therapeutic targets for patients with COPD.

MiR-124 represses vasculogenic mimicry and cell motility by targeting amotL1 in cervical cancer cells

miRNAs have extensive functions in differentiation, metabolism, programmed cell death, and tumor metastasis by post-transcriptional regulation. Vasculogenic mimicry is an important pathway in tumor metastasis. Many factors can regulate vasculogenic mimicry, including miRNAs. In previous studies, miR-124 was found to repress proliferation and metastasis in different types of cancers, but whether it functions in cervical cancer remained unknown. Here, we demonstrate that miR-124 can repress vasculogenic mimicry, migration and invasion in HeLa and C33A cells in vitro. Furthermore, we reveal that the effect of miR-124 on vasculogenic mimicry, migration and invasion results from its interaction with AmotL1. MiR-124 regulates AmotL1 negatively by targeting its 3'untranslated region (3'UTR). We found that miR-124 can repress the EMT process. Together, these results improve our understanding of the function of miR-124 in tumor metastasis and will help to provide new potential target sites for cervical cancer treatment.

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.

Non-coding-regulatory regions of human brain genes delineated by bacterial artificial chromosome knock-in mice

BACKGROUND

The next big challenge in human genetics is understanding the 98% of the genome that comprises non-coding DNA. Hidden in this DNA are sequences critical for gene regulation, and new experimental strategies are needed to understand the functional role of gene-regulation sequences in health and disease. In this study, we build upon our HuGX ('high-throughput human genes on the X chromosome') strategy to expand our understanding of human gene regulation in vivo.

RESULTS

In all, ten human genes known to express in therapeutically important brain regions were chosen for study. For eight of these genes, human bacterial artificial chromosome clones were identified, retrofitted with a reporter, knocked single-copy into the Hprt locus in mouse embryonic stem cells, and mouse strains derived. Five of these human genes expressed in mouse, and all expressed in the adult brain region for which they were chosen. This defined the boundaries of the genomic DNA sufficient for brain expression, and refined our knowledge regarding the complexity of gene regulation. We also characterized for the first time the expression of human MAOA and NR2F2, two genes for which the mouse homologs have been extensively studied in the central nervous system (CNS), and AMOTL1 and NOV, for which roles in CNS have been unclear.

CONCLUSIONS

We have demonstrated the use of the HuGX strategy to functionally delineate non-coding-regulatory regions of therapeutically important human brain genes. Our results also show that a careful investigation, using publicly available resources and bioinformatics, can lead to accurate predictions of gene expression.

The role of tumor necrosis factor-α and interferon-γ in regulating angiomotin-like protein 1 expression in lung microvascular endothelial cells

BACKGROUND

Angiogenesis in the alveolar septa is thought be a critical factor in pulmonary emphysema. Angiomotin-like protein 1 (AmotL1) is involved in angiogenesis via regulating endothelial cell function. However, the role of AmotL1 in the pathogenesis of pulmonary emphysema has not been elucidated. The objective of this study is to evaluate the expression of AmotL1 in lung tissues from a murine model with emphysema, as well as from patients with chronic obstructive pulmonary disease (COPD). Furthermore, we analyzed the regulation of AmotL1 expression by TNF-α and IFN-γ in endothelial cells in vitro.

METHODS

Nrf2 knockout mice were exposed to cigarette smoke (CS) for 4 weeks, and the down-regulated genes affecting vascularity in the whole lung were identified by microarray analysis. This analysis revealed that the mRNA expression of AmotL1 decreased in response to CS when compared with air exposure. To confirm the protein levels that were indicated in the microarray data, we determined the expression of AmotL1 in lung tissues obtained from patients with COPD and also determined the expression of AmotL1, NFκB and IκBα in cultured normal human lung microvascular endothelial cells (HLMVECs) that were stimulated by TNF-α and IFN-γ.

RESULTS

We found that the number of AmotL1-positive vessels decreased in the emphysema lungs compared with the normal and bronchial asthmatic lungs. IFN-γ pretreatment diminished the TNF-α-induced AmotL1 in the cultured HLMVECs by blocking the degradation of IκBα.

CONCLUSIONS

These results suggested that IFN-γ exhibits anti-angiogenesis effects by regulating the expression of TNF-α-induced AmotL1 via NFκB in emphysema lungs.

Opposing roles of angiomotin-like-1 and zona occludens-2 on pro-apoptotic function of YAP

YAP (Yes-associated protein) oncogene has been found to form a stable complex with members of the Angiomotin (Amot) family of proteins, which bind WW domains of YAP and sequester the protein in the cytoplasm and junctional complexes. The Amot-mediated retention of YAP in the cytoplasm results in the inhibition of its proliferative function. Using apoptotic 'read-out' of YAP in HEK293 cells, we confirmed the molecular mode by which Amot regulates YAP. We showed that a representative member of the Amot family, AmotL1 (Angiomotin-like-1), uses its PPxY motifs to bind WW domains of YAP and inhibit YAP's nuclear translocation and pro-apoptotic function. Recently we also showed that YAP uses its PDZ-binding motif to interact with zona occludens-2 (ZO-2) protein, which promotes YAP's translocation to the nucleus. We also asked if AmotL1, YAP and ZO-2 signal together. We report here that AmotL1 and ZO-2 form a tripartite complex with YAP and regulate its function in HEK293 cells in opposite directions. AmotL1 inhibits pro-apoptotic function of YAP, whereas ZO-2 enhances it. As YAP is a potent oncogene, the identification and characterization of its regulators is important. AmotL1 and ZO-2 are two candidates that could be harnessed to control the oncogenic function of YAP.

Epithelial cell polarity and tumorigenesis: new perspectives for cancer detection and treatment

Loss of cell-cell adhesion and cell polarity is commonly observed in tumors of epithelial origin and correlates with their invasion into adjacent tissues and formation of metastases. Growing evidence indicates that loss of cell polarity and cell-cell adhesion may also be important in early stage of cancer. In first part of this review, we delineate the current understanding of the mechanisms that establish and maintain the polarity of epithelial tissues and discuss the involvement of cell polarity and apical junctional complex components in tumor pathogenesis. In the second part we address the clinical significance of cell polarity and junctional complex components in cancer diagnosis and prognosis. Finally, we explore their potential use as therapeutic targets in the treatment of cancer.

LSR defines cell corners for tricellular tight junction formation in epithelial cells

Epithelial cell contacts consist of not only bicellular contacts but also tricellular contacts, where the corners of three cells meet. At tricellular contacts, tight junctions (TJs) generate specialized structures termed tricellular TJs (tTJs) to seal the intercellular space. Tricellulin is the only known molecular component of tTJs and is involved in the formation of tTJs, as well as in the normal epithelial barrier function. However, the detailed molecular mechanism of how tTJs are formed and maintained remains elusive. Using a localization-based expression cloning method, we identified a novel tTJ-associated protein known as lipolysis-stimulated lipoprotein receptor (LSR). Upon LSR knockdown in epithelial cells, tTJ formation was affected and the epithelial barrier function was diminished. Tricellulin accumulation at the tricellular contacts was also diminished in these cells. By contrast, LSR still accumulated at the tricellular contacts upon tricellulin knockdown. Analyses of deletion mutants revealed that the cytoplasmic domain of LSR was responsible for the recruitment of tricellulin. On the basis of these observations, we propose that LSR defines tricellular contacts in epithelial cellular sheets by acting as a landmark to recruit tricellulin for tTJ formation.

PIV5 M protein interaction with host protein angiomotin-like 1

Paramyxovirus matrix (M) proteins organize virus assembly, functioning as adapters that link together viral ribonucleoprotein complexes and viral glycoproteins at infected cell plasma membranes. M proteins may also function to recruit and manipulate host factors to assist virus budding, similar to retroviral Gag proteins. By yeast two-hybrid screening, angiomotin-like 1 (AmotL1) was identified as a host factor that interacts with the M protein of parainfluenza virus 5 (PIV5). AmotL1-M protein interaction was observed in yeast, in transfected mammalian cells, and in virus-infected cells. Binding was mapped to a 83-amino acid region derived from the C-terminal portion of AmotL1. Overexpression of M-binding AmotL1-derived polypeptides potently inhibited production of PIV5 VLPs and impaired virus budding. Expression of these polypeptides moderately inhibited production of mumps VLPs, but had no effect on production of Nipah VLPs. siRNA-mediated depletion of AmotL1 protein reduced PIV5 budding, suggesting that this interaction is beneficial to paramyxovirus infection.

Tight junctions: a barrier to the initiation and progression of breast cancer?

Breast cancer is a complex and heterogeneous disease that arises from epithelial cells lining the breast ducts and lobules. Correct adhesion between adjacent epithelial cells is important in determining the normal structure and function of epithelial tissues, and there is accumulating evidence that dysregulated cell-cell adhesion is associated with many cancers. This review will focus on one cell-cell adhesion complex, the tight junction (TJ), and summarize recent evidence that TJs may participate in breast cancer development or progression. We will first outline the protein composition of TJs and discuss the functions of the TJ complex. Secondly we will examine how alterations in these functions might facilitate breast cancer initiation or progression; by focussing on the regulatory influence of TJs on cell polarity, cell fate and cell migration. Finally we will outline how pharmacological targeting of TJ proteins may be useful in limiting breast cancer progression. Overall we hope to illustrate that the relationship between TJ alterations and breast cancer is a complex one; but that this area offers promise in uncovering fundamental mechanisms linked to breast cancer progression.

Angiomotin-Like Protein 1 Controls Endothelial Polarity and Junction Stability During Sprouting Angiogenesis

Rationale: We have previously shown that angiomotin (Amot) is essential for endothelial cell migration during mouse embryogenesis. However, ≈5% of Amot knockout mice survived without any detectable vascular defects. Angiomotin-like protein 1 (AmotL1) potentially compensates for the absence of Amot as it is 62% homologous to Amot and exhibits similar expression pattern in endothelial cells.

Objective: Here, we report the identification of a novel isoform of AmotL1 that controls endothelial cell polarization and directional migration.

Methods and Results: Small interfering RNA–mediated silencing of AmotL1 in mouse aortic endothelial cells caused a significant reduction in migration. In confluent mouse pancreatic islet endothelial cells (MS-1), AmotL1 colocalized with Amot to tight junctions. Small interfering RNA knockdown of both Amot and AmotL1 in MS-1 cells exhibited an additive effect on increasing paracellular permeability compared to that of knocking down either Amot or AmotL1, indicating both proteins were required for proper tight junction activity. Moreover, as visualized using high-resolution 2-photon microscopy, the morpholino-mediated knockdown of amotl1 during zebrafish embryogenesis resulted in vascular migratory defect of intersegmental vessels with strikingly decreased junction stability between the stalk cells and the aorta. However, the phenotype was quite distinct from that of amot knockdown which affected polarization of the tip cells of intersegmental vessels. Double knockdown resulted in an additive phenotype of depolarized tip cells with no or decreased connection of the stalk cells to the dorsal aorta.

Conclusions: These results cumulatively validate that Amot and AmotL1 have similar effects on endothelial migration and tight junction formation in vitro. However, in vivo Amot appears to control the polarity of vascular tip cells whereas AmotL1 mainly affects the stability of cell–cell junctions of the stalk cells.

The Amot/Patj/Syx signaling complex spatially controls RhoA GTPase activity in migrating endothelial cells

Controlled regulation of Rho GTPase activity is an essential component mediating growth factor-stimulated migration. We have previously shown that angiomotin (Amot), a membrane-associated scaffold protein, plays a critical role during vascular patterning and endothelial migration during embryogenesis. However, the signaling pathways by which Amot controls directional migration are not known. Here we have used peptide pull-down and yeast 2-hybrid (Y2H) screening to identify proteins that interact with the C-terminal PDZ-binding motifs of Amot and its related proteins AmotL1 and 2. We report that Amot and its related proteins bind to the RhoA GTPase exchange factor (RhoGEF) protein Syx. We show that Amot forms a ternary complex together with Patj (or its paralogue Mupp1) and Syx. Using FRET analysis, we provide evidence that Amot controls targeting of RhoA activity to lamellipodia in vitro. We also report that, similar to Amot, morpholino knockdown of Syx in zebrafish results in inhibition of migration of intersegmental arteries. Taken together, our results indicate that the directional migration of capillaries in the embryo is governed by the Amot:Patj/Mupp1:Syx signaling that controls local GTPase activity.

Mass spectrometric analysis of microtubule co-sedimented proteins from rat brain

Microtubules (MTs) play crucial roles in a variety of cell functions, such as mitosis, vesicle transport and cell motility. MTs also compose specialized structures, such as centrosomes, spindles and cilia. However, molecular mechanisms of these MT-based functions and structures are not fully understood. Here, we analyzed MT co-sedimented proteins from rat brain by tandem mass spectrometry (MS) upon ion exchange column chromatography. We identified a total of 391 proteins. These proteins were grouped into 12 categories: 57 MT cytoskeletal proteins, including MT-associated proteins (MAPs) and motor proteins; 66 other cytoskeletal proteins; 4 centrosomal proteins; 10 chaperons; 5 Golgi proteins; 7 mitochondrial proteins; 62 nucleic acid-binding proteins; 14 nuclear proteins; 13 ribosomal proteins; 28 vesicle transport proteins; 83 proteins with diverse function and/or localization; and 42 uncharacterized proteins. Of these uncharacterized proteins, six proteins were expressed in cultured cells, resulting in the identification of three novel components of centrosomes and cilia. Our present method is not specific for MAPs, but is useful for identifying low abundant novel MAPs and components of MT-based structures. Our analysis provides an extensive list of potential candidates for future study of the molecular mechanisms of MT-based functions and structures.

Organization of multiprotein complexes at cell-cell junctions

The formation of stable cell–cell contacts is required for the generation of barrier-forming sheets of epithelial and endothelial cells. During various physiological processes like tissue development, wound healing or tumorigenesis, cellular junctions are reorganized to allow the release or the incorporation of individual cells. Cell–cell contact formation is regulated by multiprotein complexes which are localized at specific structures along the lateral cell junctions like the tight junctions and adherens junctions and which are targeted to these site through their association with cell adhesion molecules. Recent evidence indicates that several major protein complexes exist which have distinct functions during junction formation. However, this evidence also indicates that their composition is dynamic and subject to changes depending on the state of junction maturation. Thus, cell–cell contact formation and integrity is regulated by a complex network of protein complexes. Imbalancing this network by oncogenic proteins or pathogens results in barrier breakdown and eventually in cancer. Here, I will review the molecular organization of the major multiprotein complexes at junctions of epithelial cells and discuss their function in cell–cell contact formation and maintenance.

Claudin expression in pancreatic endocrine tumors as compared with ductal adenocarcinomas

Altered expression of recently described claudins (CLDNs) as members of tight junction (TJ) transmembrane proteins was noted in several malignancies. We aimed to analyze protein and messenger RNA (mRNA) expressions of different CLDNs in human pancreatic endocrine tumors (PET) and ductal adenocarcinomas. A total of 45 formalin-fixed, paraffin-embedded samples were studied. Immunohistochemistry and real-time reverse transcriptase polymerase chain reaction analysis were carried out for quantification of CLDN 1, -2, -3, -4, and -7 expressions. Normal acini and ducts showed strong CLDNs 1, -3, -4, and -7 and scattered CLDN 2 protein expressions, while Langerhans islands revealed only CLDN 3 and -7 expressions. CLDN 2 expression was found in the half of ductal adenocarcinomas, while the vast majority of endocrine tumors were negative. CLDN 1, -4, and -7 immunohistochemistry was positive in all adenocarcinomas, whereas endocrine tumors were completely negative for CLDNs 1 and -4. CLDN 3 and -7 proteins were detected in all endocrine tumors, while CLDN 3 in ductal adenocarcinomas was negative. The mRNA expression of CLDNs showed differences between endocrine tumors and ductal adenocarcinomas, similar as found for protein expression. Our findings support that PET and ductal carcinomas are specifically characterized by different expression pattern of CLDNs. High expressions of CLDN 3 in endocrine tumors and CLDN 4 in ductal carcinomas might attract them as targets for adjuvant therapy.

Molecular characterization of angiomotin/JEAP family proteins: interaction with MUPP1/Patj and their endogenous properties

We have previously shown that MUPP1, which has an MRE domain and 13 PDZ domains, is expressed in epithelial cells and localize at tight junctions (TJs) and apical membranes. Using yeast two-hybrid screening, we found here that MUPP1 interacts with angiomotin (Amot), JEAP/Amot-like 1 and MASCOT/Amot-like 2, which we refer to as Amot/JEAP family proteins. PDZ2 and -3 were responsible for MUPP1's interaction with Amot and MASCOT, whereas only PDZ3 was responsible for its interaction with JEAP. All the Amot/JEAP family proteins also interacted with Patj, a close relative of MUPP1. The C-terminal PDZ-binding motives of the Amot/JEAP family were required for these interactions. We successfully generated specific antibodies for these proteins and analyzed the endogenous molecular properties of the family in parallel. Immunofluorescence microscopy of cultured epithelial cells showed that in subcellular distribution, the Amot/JEAP family proteins were indistinguishable; they were apparent at TJs as well as apical membranes, and mostly co-localized with MUPP1. They were also located at TJs in several mouse tissues, but each protein showed a distinct tissue distribution. In biochemical fractionation assays, the Amot/JEAP family behaved not as transmembrane but as peripheral membrane proteins. Unexpectedly, the PDZ-binding motives were not necessarily required for their localization to TJs, and dominant negative MUPP1 or Patj did not affect the localization of Amot/JEAP family proteins, suggesting that the interaction with MUPP1/Patj is not necessarily responsible for their proper subcellular distribution.

Normal establishment of epithelial tight junctions in mice and cultured cells lacking expression of ZO-3, a tight-junction MAGUK protein

ZO-1, ZO-2, and ZO-3 are closely related MAGUK family proteins that localize at the cytoplasmic surface of tight junctions (TJs). ZO-1 and ZO-2 are expressed in both epithelia and endothelia, whereas ZO-3 is exclusively expressed in epithelia. In spite of intensive studies of these TJ MAGUKs, our knowledge of their functions in vivo, especially those of ZO-3, is still fragmentary. Here, we have generated mice, as well as F9 teratocarcinoma cell lines, that do not express ZO-3 by homologous recombination. Unexpectedly, ZO-3(-/-) mice were viable and fertile, and rigorous phenotypic analyses identified no significant abnormalities. Moreover, ZO-3-deficient F9 teratocarcinoma cells differentiated normally into visceral endoderm epithelium-like cells in the presence of retinoic acid. These cells had a normal epithelial appearance, and the molecular architecture of their TJs did not appear to be affected, except that TJ localization of ZO-2 was upregulated. Suppression of ZO-2 expression by RNA interference in ZO-3(-/-) cells, however, did not affect the architecture of TJs. Furthermore, the speed with which TJs formed after a Ca(2+) switch was indistinguishable between wild-type and ZO-3(-/-) cells. These findings indicate that ZO-3 is dispensable in vivo in terms of individual viability, epithelial differentiation, and the establishment of TJs, at least in the laboratory environment.

A Rich1/Amot complex regulates the Cdc42 GTPase and apical-polarity proteins in epithelial cells

Using functional and proteomic screens of proteins that regulate the Cdc42 GTPase, we have identified a network of protein interactions that center around the Cdc42 RhoGAP Rich1 and organize apical polarity in MDCK epithelial cells. Rich1 binds the scaffolding protein angiomotin (Amot) and is thereby targeted to a protein complex at tight junctions (TJs) containing the PDZ-domain proteins Pals1, Patj, and Par-3. Regulation of Cdc42 by Rich1 is necessary for maintenance of TJs, and Rich1 is therefore an important mediator of this polarity complex. Furthermore, the coiled-coil domain of Amot, with which it binds Rich1, is necessary for localization to apical membranes and is required for Amot to relocalize Pals1 and Par-3 to internal puncta. We propose that Rich1 and Amot maintain TJ integrity by the coordinate regulation of Cdc42 and by linking specific components of the TJ to intracellular protein trafficking.

p130-Angiomotin associates to actin and controls endothelial cell shape

Angiomotin, an 80 kDa protein expressed in endothelial cells, promotes cell migration and invasion, and stabilizes tube formation in vitro. Angiomotin belongs to a new protein family with two additional members, Amotl-1 and Amotl-2, which are characterized by conserved coiled-coil domains and C-terminal PDZ binding motifs. Here, we report the identification of a 130 kDa splice isoform of angiomotin that is expressed in different cell types including vascular endothelial cells, as well as cytotrophoblasts of the placenta. p130-Angiomotin consists of a cytoplasmic N-terminal extension that mediates its association with F-actin. Transfection of p130-angiomotin into endothelial cells induces actin fiber formation and changes cell shape. The p130-angiomotin protein remained associated with actin after destabilization of actin fibers with cytochalasin B. In contrast to p80-angiomotin, p130-angiomotin does not promote cell migration and did not respond to angiostatin. We propose that p80- and p130-angiomotin play coordinating roles in tube formation by affecting cell migration and cell shape, respectively.

Angiomotin and angiomotin like proteins, their expression and correlation with angiogenesis and clinical outcome in human breast cancer

Backgound

Angiomotin is a newly discovered molecule that regulates the migration and tubule formation of endothelial cells. It therefore has been implicated in the control of angiogenesis under physiological and pathological conditions. This study examined the expression of angiomotin and its analogues, angiomotin-like 1 (L1) and -like 2 (L2) in breast tumour tissues, and analysed their correlation with angiogenesis and clinical outcomes.

Methods

Human breast tissues (normal n = 32 and tumours n = 120) were used. The levels of expression of angiomotin, L1 and L2 were determined using reverse transcription PCR. Microvessels were stained using antibodies against PECAM, von Willebrand factor (factor 8, or vWF) and VE-cadherin. The transcript levels of angiomotin and its analogues were assessed against the clinical and pathological background, including long term survival (120 months).

Results

Breast cancer tissues expressed significantly higher levels of angiomotin transcript, compared with normal mammary tissues (33.1 ± 11 in normal versus 86.5 ± 13.7 in tumour tissues, p = 0.003). Both L1 and L2 were seen at marginally higher levels in tumour than normal tissues but the difference was not statistically significant. Levels of angiomotin were at significantly higher levels in grade 2 and grade 3 tumours compared with grade 1 (p < 0.01 and p = 0.05 respectively). The levels of angiomotin in tumours from patients who had metastatic disease were also significantly higher than those patients who remained disease free (p = 0.03). Multivariate analysis indicated that angiomotin transcript was an independent prognostic factor (p = 0.031). No significant correlations were seen between angiomotin-L1 and L2 with the clinical outcome. Furthermore, high levels of angiomotin transcript were associated with shorter overall survival (p < 0.05). There was a high degree of correlation between levels of vW factor and that of angiomotin (p < 0.05), but not angiomotin-L1 and angiomotin-L2.

Conclusion

Angiomotin, a putative endothelial motility factor, is highly expressed in human breast tumour tissues and linked to angiogenesis. It links to the aggressive nature of breast tumours and the long term survival of the patients. These data point angiomotin as being a potential therapeutic target.

Tight junctions: molecular architecture and function

Tight junctions are the most apical component of the epithelial junctional complex and are crucial for the formation and functioning of epithelial and endothelial barriers. They regulate selective diffusion of ions and solutes along the paracellular pathway and restrict apical/basolateral intramembrane diffusion of lipids. Research over the past years provided much insight into the molecular composition of tight junctions, and we are starting to understand the mechanisms that permit selective paracellular diffusion. Moreover, a complex network of proteins has been identified at tight junctions that is based on cytoskeleton-linked adaptors that recruit and thereby often regulate different types of signaling components that regulate epithelial proliferation, differentiation, and polarization.

Angiomotin Regulates Endothelial Cell-Cell Junctions and Cell Motility

We have previously identified angiomotin by its ability to bind to and mediate the anti-angiogenic properties of angiostatin. In vivo and in vitro data indicate an essential role of angiomotin in endothelial cell motility. Here we show that angiostatin binds angiomotin on the cell surface and provide evidence for a transmembrane model for the topology of both p80 and p130 angiomotin isoforms. Immunofluorescence analysis shows that angiomotin co-localized with ZO-1 in cell-cell contacts in endothelial cells in vitro and in angiogenic blood vessels of the postnatal mouse retina in vivo. Transfection of p80 as well as p130 angiomotin in Chinese hamster ovary cells resulted in junctional localization of both isoforms. Furthermore, p130 angiomotin could recruit ZO-1 to actin stress fibers. The p130 but not p80 isoform could be coprecipitated with MAGI-1b, a component of endothelial tight junctions. Paracellular permeability, as measured by diffusion of fluorescein isothiocyanate-dextran, was reduced by p80 and p130 angiomotin expression with 70 and 88%, respectively, compared with control. Angiostatin did not have any effect on cell permeability but inhibited the migration of angiomotin-expressing cells in the Boyden chamber assay. We conclude that angiomotin, in addition to controlling cell motility, may play a role in the assembly of endothelial cell-cell junctions.

Bves modulates epithelial integrity through an interaction at the tight junction

We first identified Bves (blood vessel/epicardial substance) as a transmembrane protein that localized to the lateral compartment of the epithelial epicardium. Bves traffics to sites of cell-cell contact in cultured epicardial cells and promotes adhesion following transfection into non-adherent fibroblastic L-cells, reminiscent of a cell adhesion molecule. Currently, no function for Bves in relation to epithelial cell adhesion has been identified. We hypothesize that Bves plays a role at cell junctions to establish and/or modulate cell adhesion or cell-cell interactions in epithelial cell types. In this study, we demonstrate that Bves regulates epithelial integrity and that this function may be associated with a role at the tight junction (TJ). We report that Bves localizes with ZO-1 and occludin, markers of the TJ, in polarized epithelial cell lines and in vivo. We find that the behavior of Bves following low Ca2+ challenge or TPA treatment mimics that observed for ZO-1 and is distinct from adherens junction proteins such as E-cadherin. Furthermore, GST pull-down experiments show an interaction between ZO-1 and the intracellular C-terminal tail of Bves. Finally, we demonstrate that Bves modulates tight junction integrity, as indicated by the loss of transepithelial resistance and junction protein localization at the membrane following Bves knock-down in cultured cells. This study is the first to identify a function for Bves in epithelia and supports the hypothesis that Bves contributes to establishment and/or maintenance of epithelial cell integrity.

The blood-brain barrier/neurovascular unit in health and disease

The blood-brain barrier (BBB) is the regulated interface between the peripheral circulation and the central nervous system (CNS). Although originally observed by Paul Ehrlich in 1885, the nature of the BBB was debated well into the 20th century. The anatomical substrate of the BBB is the cerebral microvascular endothelium, which, together with astrocytes, pericytes, neurons, and the extracellular matrix, constitute a "neurovascular unit" that is essential for the health and function of the CNS. Tight junctions (TJ) between endothelial cells of the BBB restrict paracellular diffusion of water-soluble substances from blood to brain. The TJ is an intricate complex of transmembrane (junctional adhesion molecule-1, occludin, and claudins) and cytoplasmic (zonula occludens-1 and -2, cingulin, AF-6, and 7H6) proteins linked to the actin cytoskeleton. The expression and subcellular localization of TJ proteins are modulated by several intrinsic signaling pathways, including those involving calcium, phosphorylation, and G-proteins. Disruption of BBB TJ by disease or drugs can lead to impaired BBB function and thus compromise the CNS. Therefore, understanding how BBB TJ might be affected by various factors holds significant promise for the prevention and treatment of neurological diseases.

Identification and characterization of a novel tight junction-associated family of proteins that interacts with a WW domain of MAGI-1

The membrane-associated guanylate kinase protein, MAGI-1, has been shown to be a component of epithelial tight junctions in both Madin-Darby canine kidney cells and in intestinal epithelium. Because we have previously observed MAGI-1 expression in glomerular visceral epithelial cells (podocytes) of the kidney, we screened a glomerular cDNA library to identify the potential binding partners of MAGI-1 and isolated a partial cDNA encoding a novel protein. The partial cDNA exhibited a high degree of identity to an uncharacterized human cDNA clone, KIAA0989, which encodes a protein of 780 amino acids and contains a predicted coiled-coil domain in the middle of the protein. In vitro binding assays using the partial cDNA as a GST fusion protein confirm the binding to full-length MAGI-1 expressed in HEK293 cells, as well as endogenous MAGI-1, and also identified the first WW domain of MAGI-1 as the domain responsible for binding to this novel protein. Although a conventional PPxY binding motif for WW domains was not present in the partial cDNA clone, a variant WW binding motif was identified, LPxY, and found to be necessary for interacting with MAGI-1. When expressed in Madin-Darby canine kidney cells, the full-length novel protein was found to colocalize with MAGI-1 at the tight junction of these cells and the coiled-coil domain was found to be necessary for this localization. Because of its interaction with MAGI-1 and its localization to cell-cell junctions, this novel protein has been given the name MAGI-1-associated coiled-coil tight junction protein (MASCOT).

Sublingual Delivery of Insulin: Effects of Enhancers on the Mucosal Lipid Fluidity and Protein Conformation, Transport, and in Vivo Hypoglycemic Activity

The purposes of this study were to evaluate effects of enhancers for sublingual delivering insulin on the mucosal lipid fluidity and protein conformation, transport, and in vivo hypoglycemic activity in normal rats. The effects on sublingual mucosa, and aggregation states of insulin were estimated using fluorescence polarization, and circular dichroism method, respectively. The human immortalized oral epithelial cell monolayer was used for evaluating transport of insulin. Hydroxylpropyl-beta-cyclodextrin (HP-beta-CD), chitosan, polyethylene-polypropylene glycol, polyoxyethylene lauryl ether, polysorbate 80, egg lecithin, or oleic acid, was used as a penetration enhancer, respectively. The fluidity of sublingual mucosal lipid was markedly reduced by these enhancers excluding polysorbate 80, and the secondary structure of the mucosal proteins was also influenced by these enhancers. The hexamers of insulin were dissociated to monomers only by chitosan, polyoxyethylene lauryl ether, and egg lecithin. Nonetheless, plasma glucose levels in normal rats were significantly lowered after sublingual administration of insulin with an enhancer compared with those without an enhancer at the same time-point. The enhancing effects may be due to one or multiple factors: increasing the mucosal lipid fluidity, directly loosing the tight junction of epithelia, and dissociating the hexamers of insulin to monomers. Among these, the opened tight junction may correlate most with the enhancing effect in the mucosal permeability. Because the aggregates of insulin exist, the dissociation of the aggregates by an enhancer would benefit the permeability.

Androgen-regulated transcripts in the neonatal mouse testis as determined through microarray analysis

Androgens are required for normal spermatogenesis in mammalian testes. These hormones directly regulate testicular somatic cells that, in turn, support germ cell differentiation. However, the identity of genes under androgen regulation in the testis are not well known. In the present study, neonatal male mice (8 days postpartum) treated by testosterone propionate (TP) were used to study androgen action in the testis as evidenced by alterations in gene expression. Mice were treated with 0.5 mg of TP or dihydrotestosterone (DHT) or vehicle (oil), and testes were harvested 4, 8, and 16 h after treatment. Global gene expression was monitored by microarray analysis. Real-time reverse transcription-polymerase chain reaction was performed to confirm the microarray results. The methodology was verified by confirming the presence of previously characterized TP-regulated genes, including Pem in Sertoli cells and Cyp17a1 in Leydig cells. No significant differences in gene expression were found between TP- and DHT-treated samples. Microarray analysis identified 141, 119, and 109 up-regulated genes at 4, 8 and 16 h after TP treatment, respectively, and 83, 99, and 111 down-regulated genes at the same corresponding time points. The androgen regulation of the selected gene was verified further using testes from flutamide-treated adult mice and isolated Sertoli cells in culture. The data generated in the present study may serve as a foundation for hypothesis-driven research and provide insights regarding gene networks and pathways under androgen control in the testis.

Barriers built on claudins

The fundamental functions of epithelia and endothelia in multicellular organisms are to separate compositionally distinct compartments and regulate the exchange of small solutes and other substances between them. Tight junctions (TJs) between adjacent cells constitute the barrier to the passage of ions and molecules through the paracellular pathway and function as a 'fence' within the plasma membrane to create and maintain apical and basolateral membrane domains. How TJs achieve this is only beginning to be understood. Recently identified components of TJs include the claudins, a family of four-transmembrane-span proteins that are prime candidates for molecules that function in TJ permeability. Their identification and characterization have provided new insight into the diversity of different TJs and heterogeneity of barrier functions in different epithelia and endothelia.

Cell Adhesion, Polarity, and Epithelia in the Dawn of Metazoans

Transporting epithelia posed formidable conundrums right from the moment that Du Bois Raymond discovered their asymmetric behavior, a century and a half ago. It took a century and a half to start unraveling the mechanisms of occluding junctions and polarity, but we now face another puzzle: lest its cells died in minutes, the first high metazoa (i.e., higher than a sponge) needed a transporting epithelium, but a transporting epithelium is an incredibly improbable combination of occluding junctions and cell polarity. How could these coincide in the same individual organism and within minutes? We review occluding junctions (tight and septate) as well as the polarized distribution of Na+-K+-ATPase both at the molecular and the cell level. Junctions and polarity depend on hosts of molecular species and cellular processes, which are briefly reviewed whenever they are suspected to have played a role in the dawn of epithelia and metazoan. We come to the conclusion that most of the molecules needed were already present in early protozoan and discuss a few plausible alternatives to solve the riddle described above.

Sertoli-Sertoli and Sertoli-germ cell interactions and their significance in germ cell movement in the seminiferous epithelium during spermatogenesis

Spermatogenesis is the process by which a single spermatogonium develops into 256 spermatozoa, one of which will fertilize the ovum. Since the 1950s when the stages of the epithelial cycle were first described, reproductive biologists have been in pursuit of one question: How can a spermatogonium traverse the epithelium, while at the same time differentiating into elongate spermatids that remain attached to the Sertoli cell throughout their development? Although it was generally agreed upon that junction restructuring was involved, at that time the types of junctions present in the testis were not even discerned. Today, it is known that tight, anchoring, and gap junctions are found in the testis. The testis also has two unique anchoring junction types, the ectoplasmic specialization and tubulobulbar complex. However, attention has recently shifted on identifying the regulatory molecules that "open" and "close" junctions, because this information will be useful in elucidating the mechanism of germ cell movement. For instance, cytokines have been shown to induce Sertoli cell tight junction disassembly by shutting down the production of tight junction proteins. Other factors such as proteases, protease inhibitors, GTPases, kinases, and phosphatases also come into play. In this review, we focus on this cellular phenomenon, recapping recent developments in the field.

Endothelial cell-to-cell junctions: molecular organization and role in vascular homeostasis

Intercellular junctions mediate adhesion and communication between adjoining endothelial and epithelial cells. In the endothelium, junctional complexes comprise tight junctions, adherens junctions, and gap junctions. The expression and organization of these complexes depend on the type of vessels and the permeability requirements of perfused organs. Gap junctions are communication structures, which allow the passage of small molecular weight solutes between neighboring cells. Tight junctions serve the major functional purpose of providing a "barrier" and a "fence" within the membrane, by regulating paracellular permeability and maintaining cell polarity. Adherens junctions play an important role in contact inhibition of endothelial cell growth, paracellular permeability to circulating leukocytes and solutes. In addition, they are required for a correct organization of new vessels in angiogenesis. Extensive research in the past decade has identified several molecular components of the tight and adherens junctions, including integral membrane and intracellular proteins. These proteins interact both among themselves and with other molecules. Here, we review the individual molecules of junctions and their complex network of interactions. We also emphasize how the molecular architectures and interactions may represent a mechanistic basis for the function and regulation of junctions, focusing on junction assembly and permeability regulation. Finally, we analyze in vivo studies and highlight information that specifically relates to the role of junctions in vascular endothelial cells.

JACOP, a novel plaque protein localizing at the apical junctional complex with sequence similarity to cingulin

The apical junctional complex is composed of various cell adhesion molecules and cytoplasmic plaque proteins. Using a monoclonal antibody that recognizes a chicken 155-kDa cytoplasmic antigen (p155) localizing at the apical junctional complex, we have cloned a cDNA of its mouse homologue. The full-length cDNA of mouse p155 encoded a 148-kDa polypeptide containing a coiled-coil domain with sequence similarity to cingulin, a tight junction (TJ)-associated plaque protein. We designated this protein JACOP (junction-associated coiled-coil protein). Immunofluorescence staining showed that JACOP was concentrated in the junctional complex in various types of epithelial and endothelial cells. Furthermore, in the liver and kidney, JACOP was also distributed along non-junctional actin filaments. Upon immunoelectron microscopy, JACOP was found to be localized to the undercoat of TJs in the liver, but in some tissues, its distribution was not restricted to TJs but extended to the area of adherens junctions. Overexpression studies have revealed that JACOP was recruited to the junctional complex in epithelial cells and to cell-cell contacts and stress fibers in fibroblasts. These findings suggest that JACOP is involved in anchoring the apical junctional complex, especially TJs, to actin-based cytoskeletons.

A novel role of nectins in inhibition of the E-cadherin-induced activation of Rac and formation of cell-cell adherens junctions

Nectins are Ca(2+)-independent immunoglobulin (Ig)-like cell-cell adhesion molecules. The trans-interactions of nectins recruit cadherins to the nectin-based cell-cell adhesion, resulting in formation of cell-cell adherens junctions (AJs) in epithelial cells and fibroblasts. The trans-interaction of E-cadherin induces activation of Rac small G protein, whereas the trans-interactions of nectins induce activation of not only Rac but also Cdc42 small G protein. We showed by the fluorescent resonance energy transfer (FRET) imaging that the trans-interaction of E-cadherin induced dynamic activation and inactivation of Rac, which led to dynamic formation and retraction of lamellipodia. Moreover, we found here that the nectins, which did not trans-interact with other nectins (non-trans-interacting nectins), inhibited the E-cadherin-induced activation of Rac and reduced the velocity of the formation of the E-cadherin-based cell-cell AJs. The inhibitory effect of non-trans-interacting nectins was suppressed by the activation of Cdc42 induced by the trans-interactions of nectins. These results indicate a novel role of nectins in regulation of the E-cadherin-induced activation of Rac and formation of cell-cell AJs.

The organization of tight junctions in epithelia: implications for mammary gland biology and breast tumorigenesis

Tight junctions (TJs), the most apical components of the cell-cell junctional complexes, play a crucial role in the establishment and maintenance of cell polarity within tissues. In secretory glandular tissues, such as the mammary gland, TJs are crucial for separating apical and basolateral domains. TJs also create the variable barrier regulating paracellular movement of molecules through epithelial sheets, thereby maintaining tissue homeostasis. Recent advances reveal that TJs exist as macromolecular complexes comprised of several types of membrane proteins, cytoskeletal proteins, and signaling molecules. Many of these components are regulated during mammary gland development and pregnancy cycles, and several have received much attention as possible "tumor suppressors" during progression to breast cancer.