The tetraspan protein EMP2 modulates the surface expression of caveolins and glycosylphosphatidyl inositol-linked proteins

89Zr-ImmunoPET for the Specific Detection of EMP2-Positive Tumors

Epithelial membrane protein-2 (EMP2) is upregulated in a number of tumors and therefore remains a promising target for mAb-based therapy. In the current study, image-guided therapy for an anti-EMP2 mAb was evaluated by PET in both syngeneic and immunodeficient cancer models expressing different levels of EMP2 to enable a better understanding of its tumor uptake and off target accumulation and clearance. The therapeutic efficacy of the anti-EMP2 mAb was initially evaluated in high- and low-expressing tumors, and the mAb reduced tumor load for the high EMP2-expressing 4T1 and HEC-1-A tumors. To create an imaging agent, the anti-EMP2 mAb was conjugated to p-SCN-Bn-deferoxamine (DFO) and radiolabeled with 89Zr. Tumor targeting and tissue biodistribution were evaluated in syngeneic tumor models (4T1, CT26, and Panc02) and human tumor xenograft models (Ramos, HEC-1-A, and U87MG/EMP2). PET imaging revealed radioactive accumulation in EMP2-positive tumors within 24 hours after injection, and the signal was retained for 5 days. High specific uptake was observed in tumors with high EMP2 expression (4T1, CT26, HEC-1-A, and U87MG/EMP2), with less accumulation in tumors with low EMP2 expression (Panc02 and Ramos). Biodistribution at 5 days after injection revealed that the tumor uptake ranged from 2 to approximately 16%ID/cc. The results show that anti-EMP2 mAbs exhibit EMP2-dependent tumor uptake with low off-target accumulation in preclinical cancer models. The development of improved anti-EMP2 Ab fragments may be useful to track EMP2-positive tumors for subsequent therapeutic interventions.

Unraveling the structures, functions and mechanisms of epithelial membrane protein family in human cancers

Peripheral myelin protein 22 (PMP22) and epithelial membrane proteins (EMP-1, -2, and -3) belong to a small hydrophobic membrane protein subfamily, with four transmembrane structures. PMP22 and EMPs are widely expressed in various tissues and play important roles in cell growth, differentiation, programmed cell death, and metastasis. PMP22 presents its highest expression in the peripheral nerve and participates in normal physiological and pathological processes of the peripheral nervous system. The progress of molecular genetics has shown that the genetic changes of the PMP22 gene, including duplication, deletion, and point mutation, are behind various hereditary peripheral neuropathies. EMPs have different expression patterns in diverse tissues and are closely related to the risk of malignant tumor progression. In this review, we focus on the four members in this protein family which are related to disease pathogenesis and discuss gene mutations and post-translational modification of them. Further research into the interactions between structural alterations and function of PMP22 and EMPs will help understand their normal physiological function and role in diseases and might contribute to developing novel therapeutic tools.

Loss of EMP2 Inhibits Melanogenesis of MNT1 Melanoma Cells via Regulation of TRP-2

Melanogenesis is the production of melanin from tyrosine by a series of enzyme-catalyzed reactions, in which tyrosinase and DOPA oxidase play key roles. The melanin content in the skin determines skin pigmentation. Abnormalities in skin pigmentation lead to various skin pigmentation disorders. Recent research has shown that the expression of EMP2 is much lower in melanoma than in normal melanocytes, but its role in melanogenesis has not yet been elucidated. Therefore, we investigated the role of EMP2 in the melanogenesis of MNT1 human melanoma cells. We examined TRP-1, TRP-2, and TYR expression levels during melanogenesis in MNT1 melanoma cells by gene silencing of EMP2. Western blot and RT-PCR results confirmed that the expression levels of TYR and TRP-2 were decreased when EMP2 expression was knocked down by EMP2 siRNA in MNT1 cells, and these changes were reversed when EMP2 was overexpressed. We verified the EMP2 gene was knocked out of the cell line (EMP2 CRISPR/Cas9) by using a CRISPR/Cas9 system and found that the expression levels of TRP-2 and TYR were significantly lower in the EMP2 CRISPR/Cas9 cell lines. Loss of EMP2 also reduced migration and invasion of MNT1 melanoma cells. In addition, the melanosome transfer from the melanocytes to keratinocytes in the EMP2 KO cells cocultured with keratinocytes was reduced compared to the cells in the control coculture group. In conclusion, these results suggest that EMP2 is involved in melanogenesis via the regulation of TRP-2 expression.

Chip-Based Sensing of the Intercellular Transfer of Cell Surface Proteins: Regulation by the Metabolic State

Glycosylphosphatidylinositol (GPI)-anchored proteins (GPI-APs) are anchored at the surface of mammalian blood and tissue cells through a carboxy-terminal GPI glycolipid. Eventually, they are released into incubation medium in vitro and blood in vivo and subsequently inserted into neighboring cells, potentially leading to inappropriate surface expression or lysis. To obtain first insight into the potential (patho)physiological relevance of intercellular GPI-AP transfer and its biochemical characterization, a cell-free chip- and microfluidic channel-based sensing system was introduced. For this, rat or human adipocyte or erythrocyte plasma membranes (PM) were covalently captured by the TiO₂ chip surface operating as the acceptor PM. To measure transfer between PM, donor erythrocyte or adipocyte PM were injected into the channels of a flow chamber, incubated, and washed out, and the type and amount of proteins which had been transferred to acceptor PM evaluated with specific antibodies. Antibody binding was detected as phase shift of horizontal surface acoustic waves propagating over the chip surface. Time- and temperature-dependent transfer, which did not rely on fusion of donor and acceptor PM, was detected for GPI-APs, but not typical transmembrane proteins. Transfer of GPI-APs was found to be prevented by α-toxin, which binds to the glycan core of GPI anchors, and serum proteins in concentration-dependent fashion. Blockade of transfer, which was restored by synthetic phosphoinositolglycans mimicking the glycan core of GPI anchors, led to accumulation in the chip channels of full-length GPI-APs in association with phospholipids and cholesterol in non-membrane structures. Strikingly, efficacy of transfer between adipocytes and erythrocytes was determined by the metabolic state (genotype and feeding state) of the rats, which were used as source for the PM and sera, with upregulation in obese and diabetic rats and counterbalance by serum proteins. The novel chip-based sensing system for GPI-AP transfer may be useful for the prediction and stratification of metabolic diseases as well as elucidation of the putative role of intercellular transfer of cell surface proteins, such as GPI-APs, in (patho)physiological mechanisms.

Regulatory mechanisms of neutrophil migration from the circulation to the airspace

The neutrophil, a short-lived effector leukocyte of the innate immune system best known for its proteases and other degradative cargo, has unique, reciprocal physiological interactions with the lung. During health, large numbers of ‘marginated’ neutrophils reside within the pulmonary vasculature, where they patrol the endothelial surface for pathogens and complete their life cycle. Upon respiratory infection, rapid and sustained recruitment of neutrophils through the endothelial barrier, across the extravascular pulmonary interstitium, and again through the respiratory epithelium into the airspace lumen, is required for pathogen killing. Overexuberant neutrophil trafficking to the lung, however, causes bystander tissue injury and underlies several acute and chronic lung diseases. Due in part to the unique architecture of the lung’s capillary network, the neutrophil follows a microanatomic passage into the distal airspace unlike that observed in other end-organs that it infiltrates. Several of the regulatory mechanisms underlying the stepwise recruitment of circulating neutrophils to the infected lung have been defined over the past few decades; however, fundamental questions remain. In this article, we provide an updated review and perspective on emerging roles for the neutrophil in lung biology, on the molecular mechanisms that control the trafficking of neutrophils to the lung, and on past and ongoing efforts to design therapeutics to intervene upon pulmonary neutrophilia in lung disease.

Epithelial membrane protein 2 governs transepithelial migration of neutrophils into the airspace

Whether respiratory epithelial cells regulate the final transit of extravasated neutrophils into the inflamed airspace or are a passive barrier is poorly understood. Alveolar epithelial type 1 (AT1) cells, best known for solute transport and gas exchange, have few established immune roles. Epithelial membrane protein 2 (EMP2), a tetraspan protein that promotes recruitment of integrins to lipid rafts, is highly expressed in AT1 cells but has no known function in lung biology. Here, we show that Emp2-/- mice exhibit reduced neutrophil influx into the airspace after a wide range of inhaled exposures. During bacterial pneumonia, Emp2-/- mice had attenuated neutrophilic lung injury and improved survival. Bone marrow chimeras, intravital neutrophil labeling, and in vitro assays suggested that defective transepithelial migration of neutrophils into the alveolar lumen occurs in Emp2-/- lungs. Emp2-/- AT1 cells had dysregulated surface display of multiple adhesion molecules, associated with reduced raft abundance. Epithelial raft abundance was dependent upon putative cholesterol-binding motifs in EMP2, whereas EMP2 supported adhesion molecule display and neutrophil transmigration through suppression of caveolins. Taken together, we propose that EMP2-dependent membrane organization ensures proper display on AT1 cells of a suite of proteins required to instruct paracellular neutrophil traffic into the alveolus.

High expression of EMP1 predicts a poor prognosis and correlates with immune infiltrates in bladder urothelial carcinoma

Epithelial membrane protein 1 (EMP1) is a key gene that regulates cell proliferation and metastatic capability in various types of cancer, and serves an important role in tumor-immune interactions. However, the association between EMP1 and clinical prognosis, as well as the presence of tumor-infiltrating lymphocytes in bladder urothelial carcinoma (BLCA) remains unclear. The present study aimed to explore the relationship between EMP1 expression and tumor immune cell infiltration in BLCA. In the present study, EMP1 expression in BLCA was analyzed using the Oncomine database, The Cancer Genome Atlas (TCGA) and the Tumor Immune Estimation Resource (TIMER). The effects of EMP1 on clinical prognosis were evaluated using the Kaplan-Meier plotter and Gene Expression Profiling Interactive Analysis. The correlations between EMP1, cancer immune infiltrates and lymphocyte abundance were determined using the TIMER and Tumor immune system interaction database. In addition, correlations between EMP1 expression and gene markers in immune infiltrates were analyzed using cBioportal. The results demonstrated that, compared with adjacent normal tissues, EMP1 was downregulated in BLCA tissues. High expression of EMP1 was significantly associated with poor overall survival (OS) in BLCA cases obtained from TCGA. Multivariate Cox analysis revealed that EMP1 was an independent predictor of OS in patients with BLCA. Gene set enrichment analysis revealed that EMP1 was associated with cancer-related pathways and was positively correlated with the levels of infiltrating CD8⁺ T cells, macrophages, neutrophils and dendritic cells in BLCA. Further analysis demonstrated that EMP1 was significantly associated with the enrichment of multiple types of lymphocyte. EMP1 expression exhibited a strong correlation with a range of immune markers in BLCA. In conclusion, the results of the present study demonstrated that EMP1 was associated with a poor prognosis in patients with BLCA, and that the levels of immune infiltration and multiple immunomarker groups were associated with EMP1 expression. These results suggested that EMP1 may be used as a predictive biomarker to determine the prognosis and immune infiltration in BLCA.

Patent highlights October-November 2019

A snapshot of noteworthy recent developments in the patent literature of relevance to pharmaceutical and medical research and development.

The Pivotal Roles of the Epithelial Membrane Protein Family in Cancer Invasiveness and Metastasis

The members of the family of epithelial membrane proteins (EMPs), EMP1, EMP2, and EMP3, possess four putative transmembrane domain structures and are composed of approximately 160 amino acid residues. EMPs are encoded by the growth arrest-specific 3 (GAS3)/peripheral myelin protein 22 kDa (PMP22) gene family. The GAS3/PMP22 family members play roles in cell migration, growth, and differentiation. Evidence indicates an association of these molecules with cancer progression and metastasis. Each EMP has pro- and anti-metastatic functions that are likely involved in the complex mechanisms of cancer progression. We have recently demonstrated that the upregulation of EMP1 expression facilitates cancer cell migration and invasion through the activation of a small GTPase, Rac1. The inoculation of prostate cancer cells overexpressing EMP1 into nude mice leads to metastasis to the lymph nodes and lungs, indicating that EMP1 contributes to metastasis. Pro-metastatic properties of EMP2 and EMP3 have also been proposed. Thus, targeting EMPs may provide new insights into their clinical utility. Here, we highlight the important aspects of EMPs in cancer biology, particularly invasiveness and metastasis, and describe recent therapeutic approaches.

EMP2 acts as a suppressor of melanoma and is negatively regulated by mTOR-mediated autophagy

Cutaneous melanoma is one of the most common malignant skin tumors and advanced melanoma is usually associated with a poor prognosis. In the current study, we demonstrated the tumor suppressing role of epithelial membrane protein-2 (EMP2) by inducing apoptosis in a A375 human melanoma cell line. Mechanistically, the low expression of EMP2 in melanoma is partially due to autophagic protein degradation mediated by the mTOR pathway. These results suggest there is regulation of autophagy as well as EMP2 levels might be an interesting novel targeted therapeutic strategy for melanoma. Although the further investigation is needed to deeply understand the regulatory mechanisms of EMP2 in melanoma progression and metastasis, our results clarify the functions and mechanisms of autophagy in melanoma, and shed new light on novel targeted therapeutics for melanoma.

Tissue microarray analysis for epithelial membrane protein-2 as a novel biomarker for gliomas

Epithelial membrane protein-2 (EMP2) expression is noted in many human cancers. We evaluated EMP2 as a biomarker in gliomas. A large tissue microarray of lower grade glioma (WHO grades II-III, n = 19 patients) and glioblastoma (GBM) (WHO grade IV, n = 50 patients) was stained for EMP2. EMP2 expression was dichotomized to low or high expression scores and correlated with clinical data. The mean EMP2 expression was 1.68 in lower grade gliomas versus 2.20 in GBMs (P = 0.01). The percentage of samples with high EMP2 expression was greater in GBMs than lower grade gliomas (90.0 vs. 52.6%, P = 0.001). No significant difference was found between median survival among patients with GBM tumors exhibiting high EMP2 expression and survival of those with low EMP2 expression (8.38 vs. 10.98 months, P = 0.39). However, EMP2 expression ≥2 correlated with decreased survival (r = -0.39, P = 0.001). The EMP2 expression level also correlated with Ki-67 positivity (r = 0.34, P = 0.008). The mortality hazard ratio for GBM patients with EMP2 score of 3 or higher was 1.92 (CI 0.69-5.30). Our findings suggest that elevated EMP2 expression is associated with GBM. With other biomarkers, EMP2 may have use as a molecular target for the diagnosis and treatment of gliomas.

Epithelial membrane protein 2: Molecular interactions and clinical implications

Epithelial membrane protein 2 (EMP2) is a cell surface protein that has recently emerged as an object of neuro-oncological interest due to its potential to be utilized as a biomarker and target for antibody therapies. Preclinical studies have demonstrated that EMP2 is associated with disease prognosis in a number of human cancers, including glioblastoma. The four large extracellular domains of EMP2 and its association with the extracellular matrix makes it an attractive target for future cancer therapies. Translational research suggests that EMP2 may be targeted with antibodies to improve tumor control and survival in a variety of murine models and cancer types. However, in order to translate these preclinical findings into the clinic, future research will need to focus on elucidating the role EMP2 in the normal human body by better understanding its molecular and chemical interactions. The focus of this review is to provide a comprehensive insight into current research endeavors, discuss the potential for clinically translatable applications, and predict the future directions of such research.

Epithelial Membrane Protein-2 in Human Proliferative Vitreoretinopathy and Epiretinal Membranes

Purpose

To determine the level of epithelial membrane protein-2 (EMP2) expression in preretinal membranes from surgical patients with proliferative vitreoretinopathy (PVR) or epiretinal membranes (ERMs). EMP2, an integrin regulator, is expressed in the retinal pigment epithelium and understanding EMP2 expression in human retinal disease may help determine whether EMP2 is a potential therapeutic target.

Methods

Preretinal membranes were collected during surgical vitrectomies after obtaining consents. The membranes were fixed, processed, sectioned, and protein expression of EMP2 was evaluated by immunohistochemistry. The staining intensity (SI) and percentage of positive cells (PP) in membranes were compared by masked observers. Membranes were categorized by their cause and type including inflammatory and traumatic.

Results

All of the membranes stained positive for EMP2. Proliferative vitreoretinopathy–induced membranes (all causes) showed greater expression of EMP2 than ERMs with higher SI (1.81 vs. 1.38; P = 0.07) and PP (2.08 vs. 1.54; P = 0.09). However all the PVR subgroups had similar levels of EMP2 expression without statistically significant differences by Kruskal-Wallis test. Inflammatory PVR had higher expression of EMP2 than ERMs (SI of 2.58 vs. 1.38); however, this was not statistically significant. No correlation was found between duration of PVR membrane and EMP2 expression. EMP2 was detected by RT-PCR in all samples (n = 6) tested.

Conclusions

All studied ERMs and PVR membranes express EMP2. Levels of EMP2 trended higher in all PVR subgroups than in ERMs, especially in inflammatory and traumatic PVR. Future studies are needed to determine the role of EMP2 in the pathogenesis and treatment of various retinal conditions including PVR.

EMP1, EMP 2, and EMP3 as novel therapeutic targets in human cancer

The epithelial membrane protein genes 1, 2, and 3 (EMP1, EMP2, and EMP3) belong to the peripheral myelin protein 22-kDa (PMP22) gene family, which consists of at least seven members: PMP22, EMP1, EMP2, EMP3, PERP, brain cell membrane protein 1, and MP20. This review addresses the structural and functional features of EMPs, detailing their tissue distribution and functions in the human body, their expression pattern in a variety of tumors, and highlighting the underlying mechanisms involved in carcinogenesis. The implications in cancer biology, patient prognosis prediction, and potential application in disease therapy are discussed. For example, EMP1 was reported to be a biomarker of gefitinib resistance in lung cancer and contributes to prednisolone resistance in acute lymphoblastic leukemia patients. EMP2 functions as an oncogene in human endometrial and ovarian cancers; however, characteristics of EMP2 in urothelial cancer fulfill the criteria of a suppressor gene. Of particular interest, EMP3 overexpression in breast cancer is significantly related to strong HER-2 expression. Co-expression of HER-2 and EMP3 is the most important indicator of progression-free and metastasis-free survival for patients with urothelial carcinoma of the upper urinary tract. Altogether, discovery of pharmacological inhibitors and/or regulators of EMP protein activity could open novel strategies for enhanced therapy against EMP-mediated human diseases.

Interaction Between Peroxisome Proliferator Activated Receptor δ and Epithelial Membrane Protein 2 Polymorphisms Influences HDL-C Levels in the Chinese Population

Peroxisome proliferator activated receptors (PPARs) are transcription factors involved in the regulation of key metabolic pathways. Numerous in vivo and in vitro studies have established their important roles in lipid metabolism. A few SNPs in PPAR genes have been reported to be associated with lipid levels. In this study, we aimed to investigate the interactive effects between single nucleotide polymorphisms (SNPs) in three PPAR isoforms α/δ/γ and other genetic variants across the genome on plasma high-density lipoprotein-cholesterol (HDL-C) levels. Study subjects (N = 2003) were genotyped using Illumina HumanOmniZhongHua-8 Beadchip. Fifty-three tag SNPs ± 100 kb of PPAR α, δ, and γ (r(2) < 0.2) were selected. The effect of interactions between PPAR SNPs and those across the genome on HDL-C was tested using linear regression models. One statistically significant interaction influencing HDL-C was detected between PPARδ SNP rs2267668 and epithelial membrane protein 2 (EMP2) downstream SNP rs7191411 (N = 1993, β = 0.74, adjusted P = 0.022). This interaction was successfully replicated in the meta-analysis of two additional Chinese cohorts (N = 3948, P = 0.01). The present study showed a novel SNP × SNP interaction between rs2267668 in PPARδ and rs7191411 in EMP2 that has significant impact on circulating HDL-C levels in the Singaporean Chinese population.

Epithelial membrane protein 2 regulates sphingosylphosphorylcholine-induced keratin 8 phosphorylation and reorganization: Changes of PP2A expression by interaction with alpha4 and caveolin-1 in lung cancer cells

Sphingosylphosphorylcholine (SPC) is found at increased in the malignant ascites of tumor patients and induces perinuclear reorganization of keratin 8 (K8) filaments that contribute to the viscoelasticity of metastatic cancer cells. However, the detailed mechanism of SPC-induced K8 phosphorylation and reorganization is not clear. We observed that SPC dose-dependently reduced the expression of epithelial membrane protein 2 (EMP2) in lung cancer cells. Then, we examined the role of EMP2 in SPC-induced phosphorylation and reorganization of K8 in lung cancer cells. We found that SPC concentration-dependently reduced EMP2 in A549, H1299, and other lung cancer cells. This was verified at the mRNA level by RT-PCR and real-time PCR (qPCR), and intracellular variation through confocal microscopy. EMP2 gene silencing and stable lung cancer cell lines established using EMP2 lentiviral shRNA induced K8 phosphorylation and reorganization. EMP2 overexpression reduced K8 phosphorylation and reorganization. We also observed that SPC-induced loss of EMP2 induces phosphorylation of JNK and ERK via reduced expression of protein phosphatase 2A (PP2A). Loss of EMP2 induces ubiquitination of protein phosphatase 2A (PP2A). SPC induced caveolin-1 (cav-1) expression and EEA1 endosome marker protein but not cav-2. SPC treatment enhanced the binding of cav-1 and PP2A and lowered binding of PP2A and alpha4. Gene silencing of EMP2 increased and gene silencing of cav-1 reduced migration of A549 lung cancer cells. Overall, these results suggest that SPC induces EMP2 down-regulation which reduces the PP2A via ubiquitination induced by cav-1, which sequestered alpha4, leading to the activation of ERK and JNK.

Loss of Epithelial Membrane Protein 2 Aggravates Podocyte Injury via Upregulation of Caveolin-1

Nephrotic syndrome is a CKD defined by proteinuria with subsequent hypoalbuminemia, hyperlipidemia, and edema caused by impaired renal glomerular filtration barrier function. We previously identified mutations in epithelial membrane protein 2 (EMP2) as a monogenic cause of this disease. Here, we generated an emp2-knockout zebrafish model using transcription activator-like effector nuclease-based genome editing. We found that loss of emp2 in zebrafish upregulated caveolin-1 (cav1), a major component of caveolae, in embryos and adult mesonephric glomeruli and exacerbated podocyte injury. This phenotype was partially rescued by glucocorticoids. Furthermore, overexpression of cav1 in zebrafish podocytes was sufficient to induce the same phenotype observed in emp2 homozygous mutants, which was also treatable with glucocorticoids. Similarly, knockdown of EMP2 in cultured human podocytes resulted in increased CAV1 expression and decreased podocyte survival in the presence of puromycin aminonucleoside, whereas glucocorticoid treatment ameliorated this phenotype. Taken together, we have established excessive CAV1 as a mediator of the predisposition to podocyte injury because of loss of EMP2, suggesting CAV1 could be a novel therapeutic target in nephrotic syndrome and podocyte injury.

Review of the GAS3 Family of Proteins and their Relevance to Cancer

The GAS3 family of tetraspan proteins has recently been implicated in the progression of cancer. Currently, six members of the GAS3 family have been identified in humans and mice, and while their expressions in disease vary, data suggest that they play a role in epithelial cell structure and function. In this review, we highlight the studies implicating four of the members in disease pathogenesis as well as probe the structural similarities between the family members. Finally, the impact of targeting select members of the family such as PMP22 and EMP2 is discussed.

The lung-specific proteome defined by integration of transcriptomics and antibody-based profiling

The combined action of multiple cell types is essential for the physiological function of the lung, and increased awareness of the molecular constituents characterizing each cell type is likely to advance the understanding of lung biology and disease. In the current study, we used genome-wide RNA sequencing of normal lung parenchyma and 26 additional tissue types, combined with antibody-based protein profiling, to localize the expression to specific cell types. Altogether, 221 genes were found to be elevated in the lung compared with their expression in other analyzed tissues. Among the gene products were several well-known markers, but also several proteins previously not described in the context of the lung. To link the lung-specific molecular repertoire to human disease, survival associations of pneumocyte-specific genes were assessed by using transcriptomics data from 7 non-small-cell lung cancer (NSCLC) cohorts. Transcript levels of 10 genes (SFTPB, SFTPC, SFTPD, SLC34A2, LAMP3, CACNA2D2, AGER, EMP2, NKX2-1, and NAPSA) were significantly associated with survival in the adenocarcinoma subgroup, thus qualifying as promising biomarker candidates. In summary, based on an integrated omics approach, we identified genes with elevated expression in lung and localized corresponding protein expression to different cell types. As biomarker candidates, these proteins may represent intriguing starting points for further exploration in health and disease.

Mutations in EMP2 cause childhood-onset nephrotic syndrome

Nephrotic syndrome (NS) is a genetically heterogeneous group of diseases that are divided into steroid-sensitive NS (SSNS) and steroid-resistant NS (SRNS). SRNS inevitably leads to end-stage kidney disease, and no curative treatment is available. To date, mutations in more than 24 genes have been described in Mendelian forms of SRNS; however, no Mendelian form of SSNS has been described. To identify a genetic form of SSNS, we performed homozygosity mapping, whole-exome sequencing, and multiplex PCR followed by next-generation sequencing. We thereby detected biallelic mutations in EMP2 (epithelial membrane protein 2) in four individuals from three unrelated families affected by SRNS or SSNS. We showed that EMP2 exclusively localized to glomeruli in the kidney. Knockdown of emp2 in zebrafish resulted in pericardial effusion, supporting the pathogenic role of mutated EMP2 in human NS. At the cellular level, we showed that knockdown of EMP2 in podocytes and endothelial cells resulted in an increased amount of CAVEOLIN-1 and decreased cell proliferation. Our data therefore identify EMP2 mutations as causing a recessive Mendelian form of SSNS.

Significance of caveolin-1 regulators in pancreatic cancer

Caveolin-1 is a scaffold protein on the cell membrane. As the main component of caveolae, caveolin-1 is involved in many biological processes that include substance uptake and transmembrane signaling. Many of these processes and thus caveolin-1 contribute to cell transformation, tumorigenesis, and metastasis. Of particular interest are the dual rolesof tumor suppressor and oncogene that caveolin-1 appear to play in different malignancies, including pancreatic cancer. Therefore, analyzing caveolin-1 regulators and understanding their mechanisms of actionis key to identifying novel diagnostic and therapeutic tools for pancreatic cancer. This review details the mechanisms of action of caveolin-1 regulators and the potential significance for pancreatic cancer treatment.

Positron emission tomography imaging of endometrial cancer using engineered anti-EMP2 antibody fragments

Purpose

As imaging of the cell surface tetraspan protein epithelial membrane protein-2 (EMP2) expression in malignant tumors may provide important prognostic and predictive diagnostic information, the goal of this study is to determine if antibody fragments to EMP2 may be useful for imaging EMP2 positive tumors.

Procedures

The normal tissue distribution of EMP2 protein expression was evaluated by immunohistochemistry and found to be discretely expressed in both mouse and human tissues. To detect EMP2 in tumors, a recombinant human anti-EMP2 minibody (scFv-hinge-C_H3 dimer; 80 kDa) was designed to recognize a common epitope in mice and humans and characterized. In human tumor cell lines, the antibody binding induced EMP2 internalization and degradation, prompting the need for a residualizing imaging strategy. Following conjugation to DOTA (1,4,7,10-tetraazacyclododecane-N,N′,N′,N′″-tetraacetic acid), the minibody was radiolabeled with ⁶⁴Cu (t_1/2 = 12.7 h) and evaluated in mice as a positron emission tomography (PET) imaging agent for human EMP2-expressing endometrial tumor xenografts.

Results

The residualizing agent, ⁶⁴Cu-DOTA anti-EMP2 minibody, achieved high uptake in endometrial cancer xenografts overexpressing EMP2 (10.2 ± 2.6, percent injected dose per gram (%ID/g) ± SD) with moderate uptake in wild-type HEC1A tumors (6.0 ± 0.1). In both cases, precise tumor delineation was observed from the PET images. In contrast, low uptake was observed with anti-EMP2 minibodies in EMP2-negative tumors (1.9 ± 0.5).

Conclusions

This new immune-PET agent may be useful for preclinical assessment of anti-EMP2 targeting in vivo. It may also have value for imaging of tumor localization and therapeutic response in patients with EMP2-positive malignancies.

Epithelial membrane protein 2 is a prognostic indictor for patients with urothelial carcinoma of the upper urinary tract

Upper urinary tract urothelial carcinoma is a relatively uncommon disease and is diagnosed more frequently at advanced stages. The prognosis of these patients mainly has been related to tumor stage and grade. As a result, the definition of prognostic indicators enabling precise patient selection is mandatory for neoadjuvant or adjuvant therapies. The epithelial membrane protein (EMP2) was identified as one of the up-regulated genes by isoflavones. EMP2 overexpression suppressed foci formation, anchorage-independent growth in vitro, and tumorigenicity in severe combined immunodeficiency mice (all P < 0.05). In addition, a cross-talk between EMP2 and integrins αV and β3 was shown in the regulation of cell adhesion and migration. Higher EMP2 expression was associated with a better progression-free survival (P = 0.008) and cancer-related death (P < 0.001). EMP2 was identified as a tumor-suppressor gene in urinary tract urothelial carcinoma and may be an innovative co-targeting candidate for designing integrin-based cancer therapy.

Epithelial membrane protein 2 controls VEGF expression in ARPE-19 cells

PURPOSE

VEGF production by RPE cells has been shown to be important in regulating aberrant angiogenesis in the retina, which is responsible for multiple types of ocular pathology. EMP2 is highly expressed in the RPE and has been shown to regulate FAK activation, which is implicated in VEGF expression in other cell lines. The purpose of this study was to determine whether EMP2 regulates VEGF expression in the RPE cell line, ARPE-19.

METHODS

ARPE-19 cells were engineered to overexpress EMP2. EMP2 siRNA was used to decrease EMP2 expression. The small molecule inhibitor PP2 was used to inhibit FAK activation. VEGF levels were measured by Western blot and ELISA. Functional differences in secreted VEGF were assayed using HUVEC migration.

RESULTS

VEGF expression levels correlated with levels of EMP2. An increase of VEGF by 150% was observed in EMP2 overexpressing cells as compared with ARPE-19 cells. Concordantly, EMP2 knockdown resulted in a 57% decrease in VEGF expression. HUVEC migration (P = 0.01) and vessel tube formation (P < 0.01) were significantly increased when exposed to cell culture supernatants from EMP2 overexpressing cells.

CONCLUSIONS

This study establishes a novel connection between EMP2 and VEGF and may reflect either a direct effect through the tetraspan web or an indirect change through FAK activation. This connection is functionally significant. In addition to the direct use of anti-VEGF antibodies, modulation of EMP2 with impact on VEGF is potentially a distinct therapeutic target for the treatment of neovascularization associated with retinal diseases that involve pathologic angiogenesis.

Anti-EMP2 diabody blocks epithelial membrane protein 2 (EMP2) and FAK mediated collagen gel contraction in ARPE-19 cells

Epithelial membrane protein 2 (EMP2) regulates collagen gel contraction by the retinal pigment epithelium cell line ARPE-19 by modulating FAK activation. Collagen gel contraction is one in vitro model for an aberrant wound healing response, proliferative vitreoretinopathy (PVR), which occurs as a complication of severe ocular trauma. The purpose of this study is to investigate whether EMP2 specific recombinant diabody decreases activation of FAK and collagen gel contraction in ARPE-19. Anti-EMP2 diabody was recombinantly constructed from a human phage library-derived clone selected for reactivity against an extracellular domain of human EMP2. ARPE-19 cells were exposed to an anti-EMP2 or control diabody, and toxicity, adhesion, and migration were assessed respectively through toluidine blue exclusion, binding to collagen type 1, and a migration assay. Collagen gel contraction was assessed using an in vitro assay. FAK activation was evaluated using Western blot. Exposure to anti-EMP2 diabody, resulted in a 75% reduction in EMP2 protein levels at 4 h. No significant toxicity was observed with anti-EMP2 diabody at levels that maximally reduced EMP2. Anti-EMP2 diabody, but not control diabody, significantly reduced collagen gel contraction (p < 0.001), without changes in adhesion or migration. Concordantly, anti-EMP2 diabody as compared to a control diabody reduced collagen stimulated FAK activation (p = 0.01). Anti-EMP2 diabody decreases EMP2 protein levels, FAK activation, and collagen gel contraction by ARPE-19 cells without an adverse effect on cell survival. Modulation of EMP2 using anti-EMP2 diabody could be a new approach for targeting EMP2 and pathologic consequences associated with EMP2.

Loss of epithelial membrane protein-2 expression confers an independent prognosticator in nasopharyngeal carcinoma: a cohort study

OBJECTIVE

To evaluate the expression of epithelial membrane protein-2 (EMP2) protein and its clinicopathological associations in patients with nasopharyngeal carcinoma.

DESIGN

Retrospective population-based cohort study.

SETTING

This study was based on a biobank in Chi-Mei Medical Center (Tainan, Taiwan) from 1993 to 2002.

PARTICIPANTS

Biopsies of 124 consecutive nasopharyngeal carcinoma patients without initial distant metastasis and treated with consistent guidelines were assessed. Immunoexpressions of EMP2 were analysed and the outcomes were correlated with clinicopathological features and patient survivals.

PRIMARY AND SECONDARY OUTCOME MEASURES

Immunoexpressions of EMP2 were analyzed and the outcomes were correlated with clinicopathological features and patient survivals.

RESULTS

Loss of EMP2 expression (49.2%) was correlated with advanced primary tumour (p=0.044), nodal status (p=0.045) and the 7th American Joint Committee on Cancer stage (p=0.027). In multivariate analyses, loss of EMP2 expression emerged as an independent prognosticator for worse disease-specific survival (DSS; p=0.015) and local recurrence-free survival (LRFS; p=0.030), along with the American Joint Committee on Cancer stages III-IV (p=0.034, DSS; p=0.023, LRFS).

CONCLUSIONS

Loss of EMP2 expression is common and associated with adverse prognosticators and might confer tumour aggressiveness through hampering its interaction with specific membrane protein(s) and hence the downstream signal transduction pathway(s).

Molecular signature and pathway analysis of human primary squamous and adenocarcinoma lung cancers

Non-small cell lung cancer (NSCLC) is the most common type of lung cancer, with a poor response to chemotherapy and low survival rate. This unfavorable treatment response is likely to derive from both late diagnosis and from complex, incompletely understood biology, and heterogeneity among NSCLC subtypes. To define the relative contributions of major cellular pathways to the biogenesis of NSCLC and highlight major differences between NSCLC subtypes, we studied the molecular signatures of lung adenocarcinoma (ADC) and squamous cell carcinoma (SCC), based on analysis of gene expression and comparison of tumor samples with normal lung tissue. Our results suggest the existence of specific molecular networks and subtype-specific differences between lung ADC and SCC subtypes, mostly found in cell cycle, DNA repair, and metabolic pathways. However, we also observed similarities across major gene interaction networks and pathways in ADC and SCC. These data provide a new insight into the biology of ADC and SCC and can be used to explore novel therapeutic interventions in lung cancer chemoprevention and treatment.

Rewiring integrin-mediated signaling and cellular response with the peripheral myelin protein 22 and epithelial membrane protein 2 components of the tetraspan web

PURPOSE

Integrin-mediated collagen gel contraction by ARPE-19 is an in vitro model for proliferative vitreoretinopathy (PVR), an aberrant wound healing response after retinal detachment or ocular trauma. Expression of the tetraspan protein epithelial membrane protein 2 (EMP2) controls gel contraction through FAK activation. Peripheral myelin protein 22 (PMP22), another member of the tetraspan web, is closely related to EMP2. The purpose of this study was to determine whether PMP22 also controls the contractile phase associated with PVR.

METHODS

Integrin expression, adhesion, and protein expression were assessed, respectively, through flow cytometry, binding to collagen types I and IV, and Western blot analysis. Collagen gel contraction was assessed using an in vitro assay.

RESULTS

Overexpression of PMP22 in ARPE-19 cells (ARPE-19/PMP22) resulted in increased collagen adhesion. Gel contraction, however, was reduced by greater than 50% in ARPE-19/PMP22 cells (P < 0.001). In contrast to the FAK activation observed by increasing EMP2 expression, PMP22 overexpression led to increased AKT activation. The decrease in gel contraction by the ARPE-19/PMP22 cells was partially reversed through either PMP22 siRNA or by blockade of AKT.

CONCLUSIONS

Relative expression of EMP2 or PMP22 within the tetraspan web drives a cellular response toward a FAK- or AKT-dependent pathway, respectively. EMP2 and PMP22 differentially regulate collagen gel contraction in the ARPE-19 cell line. The implication of this finding adds a new dimension to the concept of the tetraspan web, in which the abundance of individual tetraspan family members differentially regulates signal transduction and the downstream cellular response.

Epithelial membrane protein-2 (EMP2) and experimental proliferative vitreoretinopathy (PVR)

PURPOSE

Proliferative vitreoretinopathy (PVR) is believed to result in part from de-differentiation of retinal pigment epithelium (RPE) with cellular migration in the vitreous cavity, membrane formation, and contraction in an aberrant wound-healing strategy. In an in vitro collagen-gel contraction assay, epithelial membrane protein 2 (EMP2) controls contraction through activation of focal adhesion kinase (FAK) in a RPE cell line (ARPE-19). The purpose of this study was to investigate how blocking or altering the level of EMP2 expression changed clinical PVR in an in vivo model.

METHODS

Using the ARPE-19 cell line, the levels of EMP2 modulated through stable transfections of an EMP2 overexpressing construct, EMP2 ribozyme, or vector alone. These transfected cell lines were used in a rabbit model of PVR. The severity of PVR was classified by two masked observers. An EMP2 blocking antibody was also used to decrease functional EMP2 in the PVR model. Immunohistochemistry was used to evaluate EMP2 expression in vivo.

RESULTS

The transfectants with lower levels of EMP2 had significantly less PVR severity than the degree of PVR induced by wild-type cells (p = 0.05). Also, the transfectants with a low-level of EMP2 expression showed a strong trend of less PVR severity than the high-levels EMP2 transfectants (p = 0.06). Blocking EMP2 with a specific polyclonal antibody significantly decreased the level of PVR severity (p = 0.02). PVR membranes were found to be positive for EMP2 expression.

CONCLUSIONS

These in vivo studies support a direct correlation between EMP2 expression and severity of PVR. These results validate the potential for controlling RPE biology through a change in EMP2 expression, and provide a potential therapeutic target for this disease.

Epithelial membrane protein-2 promotes endometrial tumor formation through activation of FAK and Src

Endometrial cancer is the most common gynecologic malignancy diagnosed among women in developed countries. One recent biomarker strongly associated with disease progression and survival is epithelial membrane protein-2 (EMP2), a tetraspan protein known to associate with and modify surface expression of certain integrin isoforms. In this study, we show using a xenograft model system that EMP2 expression is necessary for efficient endometrial tumor formation, and we have started to characterize the mechanism by which EMP2 contributes to this malignant phenotype. In endometrial cancer cells, the focal adhesion kinase (FAK)/Src pathway appears to regulate migration as measured through wound healing assays. Manipulation of EMP2 levels in endometrial cancer cells regulates the phosphorylation of FAK and Src, and promotes their distribution into lipid raft domains. Notably, cells with low levels of EMP2 fail to migrate and poorly form tumors in vivo. These findings reveal the pivotal role of EMP2 in endometrial cancer carcinogenesis, and suggest that the association of elevated EMP2 levels with endometrial cancer prognosis may be causally linked to its effect on integrin-mediated signaling.

Epithelial membrane protein-2 is a novel therapeutic target in ovarian cancer

PURPOSE

The tetraspan protein epithelial membrane protein-2 (EMP2) has been shown to regulate the surface display and signaling from select integrin pairs, and it was recently identified as a prognostic biomarker in human endometrial cancer. In this study, we assessed the role of EMP2 in human ovarian cancer.

EXPERIMENTAL DESIGN

We examined the expression of EMP2 within a population of women with ovarian cancer using tissue microarray assay technology. We evaluated the efficacy of EMP2-directed antibody therapy using a fully human recombinant bivalent antibody fragment (diabody) in vitro and ovarian cancer xenograft models in vivo.

RESULTS

EMP2 was found to be highly expressed in >70% of serous and endometrioid ovarian tumors compared with nonmalignant ovarian epithelium using a human ovarian cancer tissue microarray. Using anti-EMP2 diabody, we evaluated the in vitro response of nine human ovarian cancer cell lines with detectable EMP2 expression. Treatment of human ovarian cancer cell lines with anti-EMP2 diabodies induced cell death and retarded cell growth, and these response rates correlated with cellular EMP2 expression. We next assessed the effects of anti-EMP2 diabodies in mice bearing xenografts from the ovarian endometrioid carcinoma cell line OVCAR5. Anti-EMP2 diabodies significantly suppressed tumor growth and induced cell death in OVCAR5 xenografts.

CONCLUSIONS

These findings indicate that EMP2 is expressed in the majority of ovarian tumors and may be a feasible target in vivo.

Epithelial membrane protein-2 expression is an early predictor of endometrial cancer development

BACKGROUND

Endometrial cancer (EC) is a common malignancy worldwide. It is often preceded by endometrial hyperplasia, whose management and risk of neoplastic progression vary. Previously, the authors have shown that the tetraspan protein epithelial membrane protein-2 (EMP2) is a prognostic indicator for EC aggressiveness and survival. Here the authors validate the expression of EMP2 in EC, and further examine whether EMP2 expression within preneoplastic lesions is an early prognostic biomarker for EC development.

METHODS

A tissue microarray (TMA) was constructed with a wide representation of benign and malignant endometrial samples. The TMA contains a metachronous cohort of cases from individuals who either developed or did not develop EC. Intensity and frequency of EMP2 expression were assessed using immunohistochemistry.

RESULTS

There was a stepwise, statistically significant increase in the average EMP2 expression from benign to hyperplasia to atypia to EC. Furthermore, detailed analysis of EMP2 expression in potentially premalignant cases demonstrated that EMP2 positivity was a strong predictor for EC development.

CONCLUSIONS

EMP2 is an early predictor of EC development in preneoplastic lesions. In addition, combined with our previous findings, these results validate EMP2 as a novel biomarker for EC development.

Functional consequences of interactions between FAK and epithelial membrane protein 2 (EMP2)

PURPOSE

Collagen gel contraction by ARPE-19 is controlled by epithelial membrane protein 2 (EMP2) through focal adhesion kinase (FAK) activation. The purpose of this study was to test the role of EMP2 in the cellular context of FAK activation.

METHODS

The ARPE-19 cell line was recombinantly modified to increase the expression of EMP2 and was used in this study. Quantification of FAK and Src phosphorylation was determined with Western blot analysis of whole cell lysates with the use of specific antibodies for different target sites of phosphorylation. Coimmunoprecipitation of whole cell lysates with an antibody against EMP2, followed by Western blot analysis and identification of FAK, was performed. Focal adhesions and their relationship to EMP2 were identified with immunofluorescence and confocal microscopy. F-actin distribution was identified using fluorescence microscopy, and alpha- smooth muscle actin (alpha-SMA) expression was quantified with Western blot analysis and specific antibodies. Adhesion to collagen type I was determined with a binding assay.

RESULTS

EMP2 overexpression led to increased FAK phosphorylation at all measured phosphorylation sites. Coimmunoprecipitation and confocal microscopy provided evidence for a physical association between EMP2 and FAK. Increased EMP2 was also associated with altered distribution of focal adhesions, changes in actin organization, increased alpha-SMA expression, and increased adherence to a collagen-coated surface.

CONCLUSIONS

The EMP2-FAK association represents a novel protein-protein interaction, not previously reported, that demonstrates significant functional cellular responses in the context of in vitro models of proliferative vitreoretinopathy (PVR).

Blockade of epithelial membrane protein 2 (EMP2) abrogates infection of Chlamydia muridarum murine genital infection model

New methods are needed to eradicate or prevent Chlamydia trachomatis infections. Blockade of epithelial membrane protein 2 (EMP2) by genetic silencing or neutralizing polyclonal antibody reduced chlamydial infectivity in vitro. This study tests the prediction that recombinant anti-EMP2 diabody could reduce early chlamydial infection of the genital tract in vivo. In a murine infection model, pretreatment with anti-EMP2 diabody, as compared with control diabody, significantly reduced bacterial load, tissue production of inflammatory cytokines, recruitment of polymorphonuclear leukocytes, and local tissue inflammation. These findings support EMP2 as a potential preventative and therapeutic target for genital chlamydial infection.

Diabodies targeting epithelial membrane protein 2 reduce tumorigenicity of human endometrial cancer cell lines

PURPOSE

Endometrial cancer is the most common gynecologic malignancy. One promising biomarker is epithelial membrane protein 2 (EMP2), and its expression is an independent prognostic indicator for tumors with poor clinical outcome expression. The present study assesses the suitability of EMP2 as a therapeutic target.

EXPERIMENTAL DESIGN

Human monovalent anti-EMP2 antibody fragments were isolated from a human phage display library and engineered as bivalent antibody fragments (diabodies) with specificity and avidity to both EMP2 peptides and native cell-surface EMP2 protein. Diabodies were assessed using cell death and apoptosis assays. In addition, the efficacy of EMP2 diabodies on endometrial cancer tumors was determined using mouse xenograft models.

RESULTS

Treatment of human endometrial adenocarcinoma cell lines with anti-EMP2 diabodies induced significant cell death and caspase-3 cleavage in vitro. These responses correlated with cellular EMP2 expression and were augmented by progesterone, which physiologically induces EMP2 expression. In vivo, treatment of subcutaneous human xenografts of HEC-1A cell lines with anti-EMP2 diabodies suppressed tumor growth and induced cell death in the xenograft.

CONCLUSIONS

These findings suggest that EMP2 may be a potential pharmacologic target for human endometrial cancer.

FAK activation and the role of epithelial membrane protein 2 (EMP2) in collagen gel contraction

PURPOSE

Proliferative vitreoretinopathy (PVR) occurs in approximately 10% of patients after retinal detachment. PVR results from a multiphase process that leads to an aberrant wound-healing strategy with contractile cellular forces and tractional retinal detachment (TRD). Epithelial membrane protein (EMP) 2 controls cell surface expression and function of integrin isoforms associated with cellular contraction in many cell types. Since EMP2 is highly expressed in retinal pigment epithelium, this study investigates the role of EMP2 in collagen gel contraction.

METHODS

EMP2 expression was recombinantly modified in the ARPE-19 cell line. Cell surface integrin expression was assessed by flow cytometry. Collagen gel contraction was assessed by using an in vitro assay and the percentage of contraction was quantified. Proliferation and migration were measured by BrdU incorporation and a wound-healing assay, respectively. Cellular invasion was investigated with polycarbonate membranes coated with collagen.

RESULTS

EMP2 expression levels correlated positively with the ability to contract collagen gels. Compared with wild-type ARPE-19 cells, the cells with increased EMP2 expression exhibited enhanced contraction (P = 0.02), and decreased EMP2 expression concomitantly resulted in decreased contraction (P = 0.002). EMP2 overexpression resulted in reduced proliferation, migration, and integrin alpha1 and alpha2 integrin expression. EMP2 overexpression was associated with a 70% increase in FAK activation (P = 0.0003) and relative resistance of gel contraction to inhibitors of FAK/Src activation.

CONCLUSIONS

ARPE-19-mediated collagen gel contraction is a multistep process that requires integrin ligation and activation of the FAK/Src complex. EMP2 positively modulates collagen gel contraction by ARPE-19 cells through increased FAK activation.

Steroid hormone regulation of EMP2 expression and localization in the endometrium

BACKGROUND

The tetraspan protein epithelial membrane protein-2 (EMP2), which mediates surface display of diverse proteins, is required for endometrial competence in blastocyst implantation, and is uniquely correlated with poor survival from endometrial adenocarcinoma tumors. Because EMP2 is differentially expressed in the various stages of the murine and human estrous cycle, we tested the hypothesis that the steroid hormones progesterone and estrogen influence EMP2 expression and localization.

METHODS

Frozen human proliferative and secretory endometrium were collected and analyzed for EMP2 expression using SDS-PAGE/Western blot analysis. The response of EMP2 to progesterone and estradiol was determined using a combination of real-time PCR, SDS-PAGE/Western blot analysis, and confocal immunofluorescence in the human endometrial carcinoma cell line RL95-2. To confirm the in vitro results, ovariectomized mice were treated with progesterone or estradiol, and EMP2 expression was analyzed using immunohistochemistry.

RESULTS

Within normal human endometrium, EMP2 expression is upregulated in the secretory phase relative to the proliferative phase. To understand the role of steroid hormones on EMP2 expression, we utilized RL95-2 cells, which express both estrogen and progesterone receptors. In RL95-2 cells, both estradiol and progesterone induced EMP2 mRNA expression, but only progesterone induced EMP2 protein expression. To compare steroid hormone regulation of EMP2 between humans and mice, we analyzed EMP2 expression in ovarectomized mice. Similar to results observed in humans, progesterone upregulated endometrial EMP2 expression and induced EMP2 translocation to the plasma membrane. Estradiol did not promote translocation to the cell surface, but moderately induced EMP2 expression in cytoplasmic compartments in vivo.

CONCLUSION

These findings suggest that targeting of EMP2 to specific locations under the influence of these steroid hormones may be important for integrating the molecular responses required for implantation competence.

The tetraspan protein EMP2 regulates expression of caveolin-1

Caveolin-1 is the primary component of caveolae and functions in a variety of intracellular activities, including membrane trafficking and signal transduction. EMP2 (epithelial membrane protein 2) is a tetraspan protein recently identified as a novel regulator of caveolin-1 expression. In this study, we analyzed the mechanism of EMP2-mediated caveolin-1 regulation. In NIH 3T3 cells and in the human retinal pigment epithelium cell line (ARPE-19), EMP2 regulates caveolin-1 transcription and more substantially its protein levels. EMP2-mediated down-regulation of caveolin-1 does not affect caveolin-1 translational efficiency, phosphorylation, or proteasome-mediated degradation. Analysis of caveolin-1 protein half-life indicates the EMP2-mediated loss of caveolin-1 occurs rapidly. Protease inhibition and laser confocal microscopy associates this fate with specific intracellular compartmentalization, including early lysosomal delivery. These findings elucidate a new mechanism of caveolin-1 regulation and define an additional role for EMP2 as a key regulator of cell membrane composition.

Epithelial membrane protein 2 modulates infectivity of Chlamydia muridarum (MoPn)

Chlamydiae are bacterial pathogens which have evolved efficient strategies to enter, replicate, and survive inside host epithelial cells, resulting in acute and chronic diseases in humans and other animals. Several candidate molecules in the host receptor complex have been identified, but the precise mechanisms of infection have not been elucidated. Epithelial membrane protein-2 (EMP2), a 4-transmembrane protein, is highly expressed in epithelial cells in sites of chlamydial infections. Here we show that infectivity of the Chlamydia muridarum (MoPn) is associated with host cellular expression of EMP2 in multiple cell lines. Recombinant knockdown of EMP2 impairs infectivity, whereas infectivity is augmented in cells recombinantly modified to over-express EMP2. An epithelial cell line without native expression of EMP2 is relatively resistant to MoPn infection, whereas infectivity is markedly increased by recombinant expression of EMP2 in that cell line. Blockade of surface EMP2 using a specific anti-EMP2 antibody significantly reduces chlamydial infection efficiency. In addition, MoPn infectivity as measured in the EMP2 overexpressing cell line is not heparin-dependent, suggesting a possible role for EMP2 in the non-reversible phase of early infection. These findings identify EMP2 as a candidate host protein involved in infection of C. muridarum (MoPn).

Claudins--key pieces in the tight junction puzzle

Tight junctions restrict the flow of ions and aqueous molecules between cells by forming a selective barrier to the paracellular pathway. Permeability of the tight junction barrier is determined by a class of transmembrane proteins known as claudins. The relationship between claudins and paracellular permeability is complex and determined not only by the profile of claudin expression but also by the arrangement of claudins and other proteins into tight junction strands. This review summarizes progress in understanding how claudins are assembled into tight junctions and how they interact with other tight junction proteins.

White Matter Rafting––Membrane Microdomains in Myelin

The myelin membrane comprises a plethora of regions that are compositionally, ultrastructurally, and functionally distinct. Biochemical dissection of oligodendrocytes, Schwann cells, and central and peripheral nervous system myelin by means such as cold-detergent extraction and differential fractionation has led to the identification of a variety of detergent-resistant membrane assemblies, some of which represent putative signalling platforms. We review here the different microdomains that have hitherto been identified in the myelin membrane, particularly lipid rafts, caveolae, and cellular junctions such as the tight junctions that are found in the radial component of the CNS myelin sheath.

Expression of epithelial membrane protein-2 is associated with endometrial adenocarcinoma of unfavorable outcome

BACKGROUND

Epithelial membrane protein 2 (EMP2) is an estrus-regulated tetraspan protein that is required for endometrial competence in blastocyst implantation. EMP2 controls surface levels of several classes of integrin and other cell-interaction molecules, and their trafficking to glycolipid-enriched lipid raft domains is important in receptor signaling. These features suggest that EMP2 may contribute to neoplastic traits of endometrial cancer. The objective of this study was to determine the prevalence of EMP2 expression in endometrial neoplasms and its clinical significance.

METHODS

EMP2 immunophenotype, histologic diagnosis, grade, the presence of lymphovascular invasion, disease stage, and clinical follow-up were determined for 99 endometrial cancers.

RESULTS

Significant EMP2 expression (EMP2 positive) was observed in 12 of 99 cancers (9 endometrioid [6 International Federation of Gynecology and Obstetrics Grade 3], 1 serous, 1 mixed endometrioid and serous, and 1 mixed endometrioid and clear cell), and weak EMP2 expression was observed in 11 cancers. EMP2-positive tumors were more likely than others to be myometrium invasive, high stage, and recurrent, persistent, or fatal. The overall median survival for patients with EMP2-positive tumor was only 23 months, whereas the medial survival was not reached for patients with EMP2-weak and EMP2-negative tumors. The median disease-free interval was only 11 months for patients with EMP2-positive tumors and was not reached for patients with EMP2-weak and EMP2-negative tumors. A multivariate analysis of disease-free survival demonstrated independent, negative prognostic significance for EMP2 expression, high stage, and high-risk histologic subtypes.

CONCLUSIONS

EMP2 expression is a feature of some prognostically unfavorable endometrial cancers. Its utility for clinical decision making and its biologic role in endometrial cancer deserves further study in a larger series of patients.

Knockdown of the tetraspan protein epithelial membrane protein-2 inhibits implantation in the mouse

The establishment of pregnancy requires a successful molecular interaction between the trophectoderm cells of the blastocyst stage embryo and the endometrial cells of the uterus. These interactions are complex and require synchronous development and coordinated endocrine, paracrine, and autocrine communication. In this study, we demonstrate that the tetraspan protein epithelial membrane protein-2 (EMP2) is involved in these molecular interactions during implantation. EMP2, which is highly expressed in the uterus, translocates from an intracellular location to the apical surface of the endometrial epithelium during the window of implantation and is expressed in decidualized stromal cells. We developed plasmid constructs that utilized either ribozyme-mediated or short hairpin RNA-mediated mechanisms to target endometrial EMP2 mRNA for destruction. These constructs were transfected into the mouse uterus on day 1 of pregnancy using the technique of in vivo reproductive tract gene transfer. Reduction in EMP2 expression by either method resulted in a significant decrease in the number of implantation sites in the treated uterine horns as compared to control horns. These studies indicate a previously unknown function of tetraspan proteins in implantation and could provide a molecular framework for the development of therapeutic modalities for both contraception and fertility.

Epithelial membrane protein-2 regulates surface expression of alphavbeta3 integrin in the endometrium

The four-transmembrane protein epithelial membrane protein-2 (EMP2) was recently identified as an endometrial protein necessary for blastocyst implantation, but the mechanism of this role is uncertain. In other cell types, EMP2 controls delivery of certain classes of proteins to the cell surface, including various integrin isoforms (a class of receptors implicated in endometrial-blastocyst interaction). Since alphavbeta3 integrin is an important endometrial molecule involved in blastocyst interaction, we evaluated the role of EMP2 in modulating integrin expression in the HEC1A endometrial cell line and endometrial epithelium in vivo. Elevation of EMP2 expression in HEC1A cells selectively increased the expression of alphavbeta3 integrin on the plasma membrane and was functional as judged by increased cell binding to an alphavbeta3 ligand, fibronectin. Conversely, reduction in EMP2 expression using an EMP2 specific ribozyme decreased the cell alphavbeta3 surface expression. The influence of EMP2 on alphavbeta3 integrin was also observed in vivo as reduction of EMP2 using ribozymes or short hairpin RNA diminished alphavbeta3 integrin expression in glandular and luminal uterine epithelium. Colocalization and coimmunoprecipitation studies suggested that EMP2 and alphavbeta3 integrin predominantly exist in a physically associated state. This study demonstrates for the first time the influence of EMP2 on alphavbeta3 surface expression and suggests that surface trafficking of integrin alphavbeta3 by EMP2 during the window of implantation may be a mechanism for its requirement in endometrial-blastocyst interaction.