Epithelial membrane protein-2 is expressed in discrete anatomical regions of the eye

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.

EMP2 Serves as a Functional Biomarker for Chemotherapy-Resistant Triple-Negative Breast Cancer

Breast cancer (BC) remains among the most commonly diagnosed cancers in women worldwide. Triple-negative BC (TNBC) is a subset of BC characterized by aggressive behavior, a high risk of distant recurrence, and poor overall survival rates. Chemotherapy is the backbone for treatment in patients with TNBC, but outcomes remain poor compared to other BC subtypes, in part due to the lack of recognized functional targets. In this study, the expression of the tetraspan protein epithelial membrane protein 2 (EMP2) was explored as a predictor of TNBC response to standard chemotherapy. We demonstrate that EMP2 functions as a prognostic biomarker for patients treated with taxane-based chemotherapy, with high expression at both transcriptomic and protein levels following treatment correlating with poor overall survival. Moreover, we show that targeting EMP2 in combination with docetaxel reduces tumor load in syngeneic and xenograft models of TNBC. These results provide support for the prognostic and therapeutic potential of this tetraspan protein, suggesting that anti-EMP2 therapy may be beneficial for the treatment of select chemotherapy-resistant TNBC tumors.

Epithelial membrane protein 2 (EMP2): A systematic review of its implications in pathogenesis

OBJECTIVES

Epithelial membrane protein 2 (EMP2) is a cell surface protein composed of approximately 160 amino acids and encoded by the growth arrest-specific 3 (GAS3)/peripheral myelin protein 22 kDa (PMP22) gene family. Although EMP2 expression has been investigated in several diseases, much remains unknown regarding its mechanism of action and the extent of its role in pathogenesis. Our aim was to perform a systematic review on the involvement of EMP2 in disease processes and the current usage of anti-EMP2 therapies.

METHODS

A Boolean search of the English-language medical literature was performed. PubMed, Scopus, Cochrane, and Web of Science were used to identify relevant citations. This study followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.

RESULTS

52 studies met the inclusion criteria for qualitative analysis. Of those, 28 (53.8%) were human-only studies, 11 (21.2%) were animal-only studies, and 13 (25%) studies included both human and animal models. Furthermore, 34 (65.4%) studies focused on EMP2's role in neoplasms, while the remaining 18 (34.6%) articles evaluated its role in other pathologies.

CONCLUSION

Overall, the evidence suggests the mechanisms of action of EMP2 are context dependent. Promising results have been produced by utilizing EMP2 as a biomarker and therapeutic target. More studies are warranted to better understand the mechanism and comprehend the role of EMP2 in the pathogenesis of diseases.

Epithelial membrane protein 2 (EMP2) regulates hypoxia-induced angiogenesis in the adult retinal pigment epithelial cell lines

Pathologic retinal neovascularization is a potentially blinding consequence seen in many common diseases including diabetic retinopathy, retinopathy of prematurity, and retinal vaso-occlusive diseases. This study investigates epithelial membrane protein 2 (EMP2) and its role as a possible modulator of angiogenesis in human retinal pigment epithelium (RPE) under hypoxic conditions. To study its effects, the RPE cell line ARPE-19 was genetically modified to either overexpress EMP2 or knock down its levels, and RNA sequencing and western blot analysis was performed to confirm the changes in expression at the RNA and protein level, respectively. Protein expression was evaluated under both normoxic conditions or hypoxic stress. Capillary tube formation assays with human umbilical vein endothelial cells (HUVEC) were used to evaluate functional responses. EMP2 expression was found to positively correlate with expression of pro-angiogenic factors HIF1α and VEGF at both mRNA and protein levels under hypoxic conditions. Mechanistically, EMP2 stabilized HIF1α expression through downregulation of von Hippel Lindau protein (pVHL). EMP2 mediated changes in ARPE-19 cells were also found to alter the secretion of a paracrine factor(s) in conditioned media that can regulate HUVEC migration and capillary tube formation in in vitro functional angiogenesis assays. This study identifies EMP2 as a potential mediator of angiogenesis in a human RPE cell line. EMP2 levels positively correlate with pro-angiogenic mediators HIF1α and VEGF, and mechanistically, EMP2 regulates HIF1α through downregulation of pVHL. This study supports further investigation of EMP2 as a promising novel target for therapeutic treatment of pathologic neovascularization in the retina.

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.

miR-340-5p mediates the therapeutic effect of mesenchymal stem cells on corneal neovascularization

BACKGROUND

Our previous study revealed that mesenchymal stem cells (MSCs) inhibited angiogenesis via miRNA-mediated repression of prospero homeobox 1 (PROX1). This study aimed to verify whether miR-340-5p participates in the therapeutic effect of MSCs on corneal neovascularization (CNV) via repressing PROX1 and epithelial membrane protein 2 (EMP2).

MATERIALS AND METHODS

The rat CNV model was established by corneal alkali burn. The binding relationship between miR-340-5p and 3'-untranslational regions (3'UTRs) of EMP2 and PROX1 was confirmed using dual-luciferase reporter assay. After culturing corneal epithelial cells (CECs) using MSC supernatants, the vascular endothelial growth factor (VEGF) level in CEC supernatants and the CEC viability were detected. The role of miR-340-5p in the therapeutic effect of MSC on CNV was determined via lentivirus-mediated miR-340-5p intervention in vivo.

RESULTS

The expression of miR-340-5p was reduced and EMP2 and PROX1 were increased in CNV corneal tissues. The lentivirus-mediated overexpression of miR-340-5p inhibited the expressions of EMP2 and PROX1. The dual-luciferase reporter assay confirmed that miR-340-5p could bind with the 3'UTRs of EMP2 and PROX1. miR-340-5p was enriched in MSC supernatants and the culture of CECs using MSC supernatants increased the miR-340-5p expression in CECs. After being cultured in miR-340-5p-knocking down MSC supernatants, the expressions of EMP2 and PROX1 were increased, and the VEGF level and CEC viability were restored. The in vivo experiments also indicated that the therapeutic effect of MSCs was mediated by miR-340-5p.

CONCLUSIONS

miR-340-5p mediates the therapeutic effect of MSCs on CNV via binding and repressing the expressions of EMP2 and PROX1.

Epithelial Membrane Protein 2 Suppresses Non-Small Cell Lung Cancer Cell Growth by Inhibition of MAPK Pathway

Epithelial membrane proteins (EMP1-3) are involved in epithelial differentiation and carcinogenesis. Dysregulated expression of EMP2 was observed in various cancers, but its role in human lung cancer is not yet clarified. In this study, we analyzed the expression of EMP1-3 and investigated the biological function of EMP2 in non-small cell lung cancer (NSCLC). The results showed that lower expression of EMP1 was significantly correlated with tumor size in primary lung tumors (p = 0.004). Overexpression of EMP2 suppressed tumor cell growth, migration, and invasion, resulting in a G1 cell cycle arrest, with knockdown of EMP2 leading to enhanced cell migration, related to MAPK pathway alterations and disruption of cell cycle regulatory genes. Exosomes isolated from transfected cells were taken up by tumor cells, carrying EMP2-downregulated microRNAs (miRNAs) which participated in regulation of the tumor microenvironment. Our data suggest that decreased EMP1 expression is significantly related to increased tumor size in NSCLC. EMP2 suppresses NSCLC cell growth mainly by inhibiting the MAPK pathway. EMP2 might further affect the tumor microenvironment by regulating tumor microenvironment-associated miRNAs.

Epithelial Membrane Protein 2 (EMP2) Promotes VEGF-Induced Pathological Neovascularization in Murine Oxygen-Induced Retinopathy

Purpose

Retinopathy of prematurity (ROP) is a leading cause of childhood blindness. ROP occurs as a consequence of postnatal hyperoxia exposure in premature infants, resulting in vasoproliferation in the retina. The tetraspan protein epithelial membrane protein-2 (EMP2) is highly expressed in the retinal pigment epithelium (RPE) in adults, and it controls vascular endothelial growth factor (VEGF) production in the ARPE-19 cell line. We, therefore, hypothesized that Emp2 knockout (Emp2 KO) protects against neovascularization in murine oxygen-induced retinopathy (OIR).

Methods

Eyes were obtained from wildtype (WT) and Emp2 KO mouse pups at P7, P12, P17, and P21 after normoxia or hyperoxia (P7-P12) exposure. Following hyperoxia exposure, RNA sequencing was performed using the retina/choroid layers obtained from WT and Emp2 KO at P17. Retinal sections from P7, P12, P17, and P21 were evaluated for Emp2, hypoxia-inducible factor 1α (Hif1α), and VEGF expression. Whole mount images were generated to assess vaso-obliteration at P12 and neovascularization at P17.

Results

Emp2 KO OIR mice demonstrated a decrease in pathologic neovascularization at P17 compared with WT OIR mice through evaluation of retinal vascular whole mount images. This protection was accompanied by a decrease in Hif1α at P12 and VEGFA expression at P17 in Emp2 KO animals compared with the WT animals in OIR conditions. Collectively, our results suggest that EMP2 enhances the effects of neovascularization through modulation of angiogenic signaling.

Conclusions

The protection of Emp2 KO mice against pathologic neovascularization through attenuation of HIF and VEGF upregulation in OIR suggests that hypoxia-induced upregulation of EMP2 expression in the neuroretina modulates HIF-mediated neuroretinal VEGF expression.

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.

Genetic Deletion of Emp2 Does Not Cause Proteinuric Kidney Disease in Mice

Nephrotic syndrome is one of the most common glomerular diseases in children and can be classified on the basis of steroid responsiveness. While multiple genetic causes have been discovered for steroid resistant nephrotic syndrome, the genetics of steroid sensitive nephrotic syndrome remains elusive. Mutations in Epithelial Membrane Protein 2 (EMP2), a member of the GAS3/PMP22 tetraspan family of proteins, were recently implicated as putative monogenic cause of steroid sensitive nephrotic syndrome. We investigated this hypothesis by developing Emp2 reporter and knockout mouse models. In lacZ reporter mice (engineered to drive expression of the enzyme β-galactosidase under the control of the endogenous murine Emp2 promoter), Emp2 promoter activity was not observed in podocytes but was particularly prominent in medium- and large-caliber arterial vessels in the kidney and other tissues where it localizes specifically in vascular smooth muscle cells (vSMCs) but not in the endothelium. Strong Emp2 expression was also found in non-vascular smooth muscle cells found in other organs like the stomach, bladder, and uterus. Global and podocyte-specific Emp2 knockout mice were viable and did not develop nephrotic syndrome showing no evidence of abnormal glomerular histology or ultrastructure. Altogether, our results do not support that loss of function of EMP2 represent a monogenic cause of proteinuric kidney disease. However, the expression pattern of Emp2 indicates that it may be relevant in smooth muscle function in various organs and tissues including the vasculature.

Epithelial Membrane Protein-2 (EMP2) Antibody Blockade Reduces Corneal Neovascularization in an In Vivo Model

Purpose

Pathologic corneal neovascularization is a major cause of blindness worldwide, and treatment options are currently limited. VEGF is one of the critical mediators of corneal neovascularization but current anti-VEGF therapies have produced limited results in the cornea. Thus, additional therapeutic agents are needed to enhance the antiangiogenic arsenal. Our group previously demonstrated epithelial membrane protein-2 (EMP2) involvement in pathologic angiogenesis in multiple cancer models including breast cancer and glioblastoma. In this paper, we investigate the efficacy of anti-EMP2 immunotherapy in the prevention of corneal neovascularization.

Methods

An in vivo murine cornea alkali burn model was used to study pathologic neovascularization. A unilateral corneal burn was induced using NaOH, and subconjunctival injection of either anti-EMP2 antibody, control antibody, or sterile saline was performed after corneal burn. Neovascularization was clinically scored at 7 days postalkali burn, and eyes were enucleated for histologic analysis and immunostaining including VEGF, CD31, and CD34 expression.

Results

Anti-EMP2 antibody, compared to control antibody or vehicle, significantly reduced neovascularization as measured by clinical score and central cornea thickness, as well as by histologic reduction of neovascularization, decreased CD34 staining, and decreased CD31 staining. Incubation of corneal limbal cells in vitro with anti-EMP2 blocking antibody significantly decreased EMP2 expression, VEGF expression and secretion, and cell migration.

Conclusions

This work demonstrates the effectiveness of EMP2 as a novel target in pathologic corneal neovascularization in an animal model and supports additional investigation into EMP2 antibody blockade as a potential new therapeutic option.

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.

Epithelial membrane protein 2 (EMP2) deficiency alters placental angiogenesis, mimicking features of human placental insufficiency

Epithelial membrane protein-2 (EMP2) is a tetraspan protein predicted to regulate placental development. Highly expressed in secretory endometrium and trophectoderm cells, previous studies suggest that it may regulate implantation by orchestrating the surface expression of integrins and other membrane proteins. In order to test the role of EMP2 in pregnancy, mice lacking EMP2 (Emp2^-/- ) were generated. Emp2^-/- females are fertile but have reduced litter sizes when carrying Emp2^-/- but not Emp2^+/- fetuses. Placentas of Emp2^-/- fetuses exhibit dysregulation in pathways related to neoangiogenesis, coagulation, and oxidative stress, and have increased fibrin deposition and altered vasculature. Given that these findings often occur due to placental insufficiency resulting in an oxygen-poor environment, the expression of hypoxia-inducible factor-1 alpha (HIF-1α) was examined. Placentas from Emp2^-/- fetuses had increased total HIF-1α expression in large part through an increase in uterine NK (uNK) cells, demonstrating a unique interplay between uNK cells and trophoblasts modulated through EMP2. To determine if these results translated to human pregnancy, placentas from normal, term deliveries or those complicated by placental insufficiency resulting in intrauterine growth restriction (IUGR) were stained for EMP2. EMP2 was significantly reduced in both villous and extravillous trophoblast populations in IUGR placentas. Experiments in vitro using human trophoblast cells lines indicate that EMP2 modulates angiogenesis by altering HIF-1α expression. Our results reveal a novel role for EMP2 in regulating trophoblast function and vascular development in mice and humans, and suggest that it may be a new biomarker for placental insufficiency. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

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.

The cAMP responsive element binding protein 1 transactivates epithelial membrane protein 2, a potential tumor suppressor in the urinary bladder urothelial carcinoma

In this study, we report that EMP2 plays a tumor suppressor role by inducing G₂/M cell cycle arrest, suppressing cell viability, proliferation, colony formation/anchorage-independent cell growth via regulation of G₂/M checkpoints in distinct urinary bladder urothelial carcinoma (UBUC)-derived cell lines. Genistein treatment or exogenous expression of the cAMP responsive element binding protein 1 (CREB1) gene in different UBUC-derived cell lines induced EMP2 transcription and subsequent translation. Mutagenesis on either or both cAMP-responsive element(s) dramatically decreased the EMP2 promoter activity with, without genistein treatment or exogenous CREB1 expression, respectively. Significantly correlation between the EMP2 immunointensity and primary tumor, nodal status, histological grade, vascular invasion and mitotic activity was identified. Multivariate analysis further demonstrated that low EMP2 immunoexpression is an independent prognostic factor for poor disease-specific survival. Genistein treatments, knockdown of EMP2 gene and double knockdown of CREB1 and EMP2 genes significantly inhibited tumor growth and notably downregulated CREB1 and EMP2 protein levels in the mice xenograft models. Therefore, genistein induced CREB1 transcription, translation and upregulated pCREB1(S133) protein level. Afterward, pCREB1(S133) transactivated the tumor suppressor gene, EMP2, in vitro and in vivo. Our study identified a novel transcriptional target, which plays a tumor suppressor role, of CREB1.

Regulation of FAK Activity by Tetraspan Proteins: Potential Clinical Implications in Cancer

Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase that regulates multiple cell signaling pathways in both physiological and pathological conditions. Overexpression and activation of FAK is associated with many advanced stage cancers through promoting cancer cell tumorigenicity and progression as well as by regulating the tumor microenvironment. FAK has multiple binding partners through which FAK exerts its functions including RhoGEF, Src family, talin, cortactin, and paxilin. Over the last few years, it has been proposed that a novel group of four transmembrane proteins can interact with FAK and regulate its activity. These include select tetraspanins such as CD151 and CD9 as well as the GAS3 family members epithelial membrane protein-2 (EMP2) and peripheral myelin protein-22 (PMP22). In this review, we discuss the current knowledge of the interaction between FAK and tetraspan proteins in physiological and pathological conditions, with an emphasis on the potential of tetraspan family members as therapeutic targets in cancer.

Epithelial membrane protein-2 (EMP2) activates Src protein and is a novel therapeutic target for glioblastoma

Despite recent advances in molecular classification, surgery, radiotherapy, and targeted therapies, the clinical outcome of patients with malignant brain tumors remains extremely poor. In this study, we have identified the tetraspan protein epithelial membrane protein-2 (EMP2) as a potential target for glioblastoma (GBM) killing. EMP2 had low or undetectable expression in normal brain but was highly expressed in GBM as 95% of patients showed some expression of the protein. In GBM cells, EMP2 enhanced tumor growth in vivo in part by up-regulating αvβ3 integrin surface expression, activating focal adhesion kinase and Src kinases, and promoting cell migration and invasion. Consistent with these findings, EMP2 expression significantly correlated with activated Src kinase in patient samples and promoted tumor cell invasion using intracranial mouse models. As a proof of principle to determine whether EMP2 could serve as a target for therapy, cells were treated using specific anti-EMP2 antibody reagents. These reagents were effective in killing GBM cells in vitro and in reducing tumor load in subcutaneous mouse models. These results support the role of EMP2 in the pathogenesis of GBM and suggest that anti-EMP2 treatment may be a novel therapeutic treatment.

Rationale and preclinical efficacy of a novel anti-EMP2 antibody for the treatment of invasive breast cancer

Despite significant advances in biology and medicine, the incidence and mortality due to breast cancer worldwide is still unacceptably high. Thus, there is an urgent need to discover new molecular targets. In this article, we show evidence for a novel target in human breast cancer, the tetraspan protein epithelial membrane protein-2 (EMP2). Using tissue tumor arrays, protein expression of EMP2 was measured and found to be minimal in normal mammary tissue, but it was upregulated in 63% of invasive breast cancer tumors and in 73% of triple-negative tumors tested. To test the hypothesis that EMP2 may be a suitable target for therapy, we constructed a fully human immunoglobulin G1 (IgG1) antibody specific for a conserved domain of human and murine EMP2. Treatment of breast cancer cells with the anti-EMP2 IgG1 significantly inhibited EMP2-mediated signaling, blocked FAK/Src signaling, inhibited invasion, and promoted apoptosis in vitro. In both human xenograft and syngeneic metastatic tumor monotherapy models, anti-EMP2 IgG1 retarded tumor growth without detectable systemic toxicity. This antitumor effect was, in part, attributable to a potent antibody-dependent cell-mediated cytotoxicity response as well as direct cytotoxicity induced by the monoclonal antibody. Together, these results identify EMP2 as a novel therapeutic target for invasive breast cancer.

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).

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.

Peripheral myelin protein-22 (PMP22) modulates alpha 6 integrin expression in the human endometrium

BACKGROUND

PMP22, a member of the GAS3 family of tetraspan proteins, is associated with a variety of neurological diseases. Previous studies have shown that PMP22 is expressed in proliferative endometrium, but its function within this tissue is poorly understood. In this study, we first characterized the expression of PMP22 in the human menstrual cycle and began to characterize its function in the endometrium.

METHODS

Using a combination of immunohistochemistry and quantitative PCR, we characterized the expression of PMP22 in both proliferative and secretory endometrium. Differences in PMP22 expression between proliferative and secretory endometrium were determined using a Mann-Whitney U test. In order to investigate the influence of PMP22 on α6 integrin expression, cells were created that ectopically overexpressed PMP22 or expressed a siRNA to inhibit its expression. These cells were analyzed for changes in integrins and binding to extracellular matrices.

RESULTS

In this study, we show that PMP22 expression is higher in proliferative phase than secretory phase. Functionally, we have begun to characterize the functional significance of this expression. Previous studies have suggested a link between PMP22 and α6 integrin, and therefore we asked whether PMP22 could associate or potentially modulate the expression of α6 integrin. Expression of both PMP22 and α6 integrin were detectable in endometrial epithelial and stromal cells, and we show that both proteins can associate and colocalize with each other. To understand if PMP22 directly altered the expression of a6 integrin, we examined cell lines with modulated levels of the protein. Overexpression of PMP22 was sufficient to increase α6 integrin surface expression with a concominant increase in binding to the extracellular matrix laminin, while a reduction in PMP22 suppressed α6 integrin surface expression.

CONCLUSION

These findings suggest a physiologic role for PMP22 on the expression of α6 integrin. We predict that this may be important for the maintainence of endometrial integrity and to the disease biology associated with altered levels of α6 integrin expression in the endometrium.

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).

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.

Differential gene expression patterns of the developing and adult mouse cornea compared to the lens and tendon

The cornea continues to mature after birth to develop a fully functional, refractive and protective barrier tissue. Here we investigated the complex biological events underlying this process by profiling global genome-wide gene expression patterns of the immature postnatal day 10 and 7-week old adult mouse cornea. The lens and tendon were included in the study to increase the specificity of genes identified as upregulated in the corneal samples. Notable similarities in gene expression between the cornea and the tendon were in the mesenchymal extracellular matrix collagen (types I, III, V, VI) and proteoglycan (lumican, decorin and biglycan) genes. Expression similarities in the cornea and lens were limited to certain epithelial genes and the crystallins. Approximately 76 genes were over expressed in the cornea samples that showed basal expression levels in the lens and tendon. Thirty-two of these were novel with no known functions in the cornea. These include genes with a potential role in protection against oxidative stress (Dhcr24, Cdo1, Akr1b7, Prdx6), inflammation (Ltb4dh, Wdr1), ion transport (Pdzk1ip1, Slc12a2, Slc25a17) and transcription (Zfp36l3, Pdzk1ip1). Direct comparison of the cornea of two ages showed selective upregulation of 50 and 12 genes in the P10 and adult cornea, respectively. Of the upregulated P10 genes several encode extracellular matrix collagens and proteoglycans that are stable components of the adult cornea and their high transcriptional activity at P10 indicate a period of actie corneal growth and matrix deposition in the young cornea. Much less is known about the genes selectively over expressed in the adult cornea; some relate to immune response and innervations (Npy), and possibly to electron transport (Cyp24a1, Cyp2f2) and others of yet unknown functions in the cornea (Rgs10, Psmb8, Xlr4). This study detected expression of genes with known functions in the cornea, providing additional validation of the microarray experiments. Importantly, it identified several novel genes whose functions have not been investigated in the cornea.

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.

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).

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.

Identification of genes differentially expressed in rat alveolar type I cells

Although approximately 98% of the internal surface area of the lung is lined by alveolar type I cells, little is known about the functions of this cell type. Using freshly isolated rat type I and type II cells, we created a subtraction library by suppression subtractive hybridization to identify genes differentially expressed by type I cells. We identified twelve genes of known function that are differentially expressed by type I cells. Differential expression of all 12 genes was confirmed by Northern blotting; we confirmed differential expression by immunocytochemistry for 3 genes for which suitable antibodies were available. Most of the genes code for proteins that are multifunctional. From the known functions of these genes, we infer that type I cells may play a role in the maintenance of normal alveolar homeostasis and protection from injury, lung development and remodeling, host defense, tumor/growth suppression, and surfactant metabolism, among other functions.