The tumour-associated antigen L6 (L6-Ag) is recruited to the tetraspanin-enriched microdomains: implication for tumour cell motility

The role of Tetraspanins in digestive system tumor development: update and emerging evidence

Digestive system malignancies, including cancers of the esophagus, pancreas, stomach, liver, and colorectum, are the leading causes of cancer-related deaths worldwide due to their high morbidity and poor prognosis. The lack of effective early diagnosis methods is a significant factor contributing to the poor prognosis for these malignancies. Tetraspanins (Tspans) are a superfamily of 4-transmembrane proteins (TM4SF), classified as low-molecular-weight glycoproteins, with 33 Tspan family members identified in humans to date. They interact with other membrane proteins or TM4SF members to form a functional platform on the cytoplasmic membrane called Tspan-enriched microdomain and serve multiple functions including cell adhesion, migration, propagation and signal transduction. In this review, we summarize the various roles of Tspans in the progression of digestive system tumors and the underlying molecular mechanisms in recent years. Generally, the expression of CD9, CD151, Tspan1, Tspan5, Tspan8, Tspan12, Tspan15, and Tspan31 are upregulated, facilitating the migration and invasion of digestive system cancer cells. Conversely, Tspan7, CD82, CD63, Tspan7, and Tspan9 are downregulated, suppressing digestive system tumor cell metastasis. Furthermore, the connection between Tspans and the metastasis of malignant bone tumors is reviewed. We also summarize the potential role of Tspans as novel immunotherapy targets and as an approach to overcome drug resistance. Finally, we discuss the potential clinical value and therapeutic targets of Tspans in the treatments of digestive system malignancies and provide some guidance for future research.

Construction of CAR-T cells targeting TM4SF1 and its anti-tumor capacity in ovarian cancer

Ovarian cancer (OC) is the most lethal gynecological malignancy with a 5-year survival rate of 49.1% on average. In clinical practice, cytoreduction and chemotherapy remain the conventional treatment for advanced OC. However, the overall prognosis remains poor, which urges oncologists to develop new treatments. Chimeric antigen receptor (CAR)-T therapy as a branch of immunotherapy had gained a success in treating hematological malignancies. TM4SF1, a potential biomarker in many tumors, was validated highly expressed in ovarian cancer. Here we constructed a 3^rd generation CAR-T agent targeting TM4SF1 to treat ovarian cancer. CAR-T cells showed a specific cytotoxicity against TM4SF1 positive tumor cell lines in vitro and repressed SKOV3-derived tumor growth in vivo. This is the first time reporting a CAR-T therapy targeting TM4SF1 in ovarian cancer. Our results suggested that TM4SF1 could be a very promising target in curing OC and showed the possibility of TM4SF1-based immunotherapy.

TM4SF1 promotes esophageal squamous cell carcinoma metastasis by interacting with integrin α6

Transmembrane-4 L-six family member-1 (TM4SF1) is a member of the L6 family and functions as a signal transducer to regulate tumor cell behaviors. However, the function and mechanism of TM4SF1 in esophageal squamous cell carcinoma (ESCC) metastasis remains unclear. Here, we find that TM4SF1 expression is increased and positively correlated with clinical TNM stage, N classification, differentiation, tumor size, and poor prognosis in ESCC patients. Interestingly, we demonstrate that TM4SF1 promotes ESCC cell adhesion, spreading, migration, and invasion, but not cell proliferation, in a laminin-dependent manner by interacting with integrin α6. Mechanistically, the TM4SF1/integrin α6/FAK axis signal pathway mediates cell migration under laminin-coating condition. Inhibiting FAK or knocking down TM4SF1 can attenuate TM4SF1-mediated cell migration and lung metastasis. Clinically, the TM4SF1/integrin α6/FAK axis positively correlates with ESCC. Altogether, these findings reveal a new mechanism of TM4SF1 in promoting ESCC metastasis via binding to integrin α6 and suggest that the cross-talk between TM4SF1 and integrin α6 may serve as a therapeutic target for ESCC.

Identification of three hub genes related to the prognosis of idiopathic pulmonary fibrosis using bioinformatics analysis

Background: Idiopathic pulmonary fibrosis (IPF) is a chronic respiratory disease characterized by peripheral distribution of bilateral pulmonary fibrosis that is more pronounced at the base. IPF has a short median survival time and a poor prognosis. Therefore, it is necessary to identify effective prognostic indicators to guide the treatment of patients with IPF. Methods: We downloaded microarray data of bronchoalveolar lavage cells from the Gene Expression Omnibus (GEO), containing 176 IPF patients and 20 controls. The top 5,000 genes in the median absolute deviation were classified into different color modules using weighted gene co-expression network analysis (WGCNA), and the modules significantly associated with both survival time and survival status were identified as prognostic modules. We used Lasso Cox regression and multivariate Cox regression to search for hub genes related to prognosis from the differentially expressed genes (DEGs) in the prognostic modules and constructed a risk model and nomogram accordingly. Moreover, based on the risk model, we divided IPF patients into high-risk and low-risk groups to determine the biological functions and immune cell subtypes associated with the prognosis of IPF using gene set enrichment analysis and immune cell infiltration analysis. Results: A total of 153 DEGs located in the prognostic modules, three (TPST1, MRVI1, and TM4SF1) of which were eventually defined as prognostic hub genes. A risk model was constructed based on the expression levels of the three hub genes, and the accuracy of the model was evaluated using time-dependent receiver operating characteristic (ROC) curves. The areas under the curve for 1-, 2-, and 3-year survival rates were 0.862, 0.885, and 0.833, respectively. The results of enrichment analysis showed that inflammation and immune processes significantly affected the prognosis of patients with IPF. The degree of mast and natural killer (NK) cell infiltration also increases the prognostic risk of IPF. Conclusions: We identified three hub genes as independent molecular markers to predict the prognosis of patients with IPF and constructed a prognostic model that may be helpful in promoting therapeutic gains for IPF patients.

Rapid Capture of Cancer Extracellular Vesicles by Lipid Patch Microarrays

Extracellular vesicles (EVs) contain various bioactive molecules such as DNA, RNA, and proteins, and play a key role in the regulation of cancer progression. Furthermore, cancer-associated EVs carry specific biomarkers and can be used in liquid biopsy for cancer detection. However, it is still technically challenging and time consuming to detect or isolate cancer-associated EVs from complex biofluids (e.g., blood). Here, a novel EV-capture strategy based on dip-pen nanolithography generated microarrays of supported lipid membranes is presented. These arrays carry specific antibodies recognizing EV- and cancer-specific surface biomarkers, enabling highly selective and efficient capture. Importantly, it is shown that the nucleic acid cargo of captured EVs is retained on the lipid array, providing the potential for downstream analysis. Finally, the feasibility of EV capture from patient sera is demonstrated. The demonstrated platform offers rapid capture, high specificity, and sensitivity, with only a small need in analyte volume and without additional purification steps. The platform is applied in context of cancer-associated EVs, but it can easily be adapted to other diagnostic EV targets by use of corresponding antibodies.

Single-cell Long Non-coding RNA Landscape of T Cells in Human Cancer Immunity

The development of new biomarkers or therapeutic targets for cancer immunotherapies requires deep understanding of T cells. To date, the complete landscape and systematic characterization of long noncoding RNAs (lncRNAs) in T cells in cancer immunity are lacking. Here, by systematically analyzing full-length single-cell RNA sequencing (scRNA-seq) data of more than 20,000 libraries of T cells across three cancer types, we provided the first comprehensive catalog and the functional repertoires of lncRNAs in human T cells. Specifically, we developed a custom pipeline for de novotranscriptome assembly and obtained a novel lncRNA catalog containing 9433 genes. This increased the number of current human lncRNA catalog by 16% and nearly doubled the number of lncRNAs expressed in T cells. We found that a portion of expressed genes in single T cells were lncRNAs which had been overlooked by the majority of previous studies. Based on metacell maps constructed by the MetaCell algorithm that partitions scRNA-seq datasets into disjointed and homogenous groups of cells (metacells), 154 signature lncRNA genes were identified. They were associated with effector, exhausted, and regulatory T cell states. Moreover, 84 of them were functionally annotated based on the co-expression networks, indicating that lncRNAs might broadly participate in the regulation of T cell functions. Our findings provide a new point of view and resource for investigating the mechanisms of T cell regulation in cancer immunity as well as for novel cancer-immune biomarker development and cancer immunotherapies

Rapid and Electronic Identification and Quantification of Age-Specific Circulating Exosomes via Biologically Activated Graphene Transistors

Increasing access to modern clinical practices concomitantly extends lifespan, ironically revealing new classes of degenerative and inflammatory diseases of later years. Here, an electronic graphene field-effect transistor (gFET) is reported, termed EV-chip, for label-free, rapid identification and quantification of exosomes (EV) associated with aging through specific surface markers, CD63 and CD151. Studies suggest that blood-derived exosomes carry specific biomolecules that can be used toward diagnostic applications of age and health. However, to observe improvements in patient outcomes, earlier detection at the point-of-care (POC) is required. Unfortunately, conventional techniques and other electronic-based platforms for exosome sensing are burdensome and inept for the POC distinction of aged blood factors. It is shown that EV-chip can quantitatively detect purified exosomes from plasma, with a limit of detection (LOD) of 2 × 10⁴ particles mL^-1 and a limit of quantification (LOQ) of 6 × 10⁴ particles mL^-1 . The sensitivity and compact electronics of the EV-chip improves upon previously published electronic biosensors, making it ideal for a physician's office or a simple biological laboratory. The sensitivity, selectivity, and portability of the EV-chip demonstrate the potential of the biosensor as a powerful point-of-care diagnostic and prognostic tool for age-related diseases.

Metastatic behavior analyses of tetraspanin TM4SF5-expressing spheres in three-dimensional (3D) cell culture environment

Cancer metastasis involves diverse cellular functions via bidirectional communications between intracellular and extracellular spaces. To achieve development of the anti-metastatic drugs, one needs to consider the efficacy and mode of action (MOA) of the drug candidates to block the metastatic potentials of cancerous cells. Rather than under two-dimensional environment, investigation of the metastatic potentials under three-dimensional environment would be much pharmaceutically beneficent, since it can mimic the in vivo tumor lesions in cancer patients, leading to allowance of drug candidates analyzed in the 3D culture systems to lower failure rates during the anti-metastatic drug development. Here we have reviewed on the analyses of metastatic potentials of certain cancer models in 3D culture systems surrounded with extracellular matrix proteins, which could be supported by TM4SF5- and/or EMT-mediated actions. We particularly focused the initial events of the cancer metastasis, such as invasive outgrowth and dissemination from the cancer cell masses, spheroids, embedded in the 3D gel culture systems. This review summarizes the significance of tetraspanin TM4SF5 and Snail1 that are related to EMT in the metastatic potentials explored in the 3D gel systems.

Role of Transmembrane 4 L Six Family 1 in the Development and Progression of Cancer

Transmembrane 4 L six family 1 (TM4SF1) is a protein with four transmembrane domains that belongs to the transmembrane 4 L six family members (TM4SFs). Structurally, TM4SF1 consists of four transmembrane domains (TM1–4), N- and C-terminal intracellular domains, two extracellular domains, a smaller domain between TM1 and TM2, and a larger domain between TM3 and TM4. Within the cell, TM4SF1 is located at the cell surface where it transmits extracellular signals into the cytoplasm. TM4SF1 interacts with tetraspanins, integrin, receptor tyrosine kinases, and other proteins to form tetraspanin-enriched microdomains. This interaction affects the pro-migratory activity of the cells, and thus it plays important roles in the development and progression of cancer. TM4SF1 has been shown to be overexpressed in many malignant tumors, including gliomas; malignant melanomas; and liver, prostate, breast, pancreatic, bladder, colon, lung, gastric, ovarian, and thyroid cancers. TM4SF1 promotes the migration and invasion of cancer cells by inducing epithelial-mesenchymal transition, self-renewal ability, tumor angiogenesis, invadopodia formation, and regulating the related signaling pathway. TM4SF1 is an independent prognostic indicator and biomarker in several cancers. It also promotes drug resistance, which is a major cause of therapeutic failure. These characteristics make TM4SF1 an attractive target for antibody-based immunotherapy. Here, we review the many functions of TM4SF1 in malignant tumors, with the aim to understand the interaction between its expression and the biological behaviors of cancer and to supply a basis for exploring new therapeutic targets.

MiRNA-206 suppresses PGE2-induced colorectal cancer cell proliferation, migration, and invasion by targetting TM4SF1

MiRNA (miR)-206 plays a tumor suppressor role in various cancer types. Here, we investigated whether miR-206 is involved in prostaglandin E2 (PGE2)-induced epithelial–mesenchymal transition (EMT) in colorectal cancer (CRC) cells through the targetting of transmembrane 4 L six family member 1 (TM4SF1).

The effect of PGE2 on growth and apoptosis of CRC cells was evaluated using the MTT assay and flow cytometry analysis, respectively. TM4SF1 and miR-206 expression levels were determined with quantitative polymerase chain reaction (qRT-PCR) in CRC tissues and cell lines. The concentration of PGE2 in the serum of CRC patients and healthy controls was measured with an ELISA kit. A miR-206 or TM4SF1 construct was transfected into cells with PGE2. Transwell migration and invasion assays were used to examine cell migration and invasion properties. Additionally, a luciferase assay was performed to determine whether TM4SF1 was directly targetted by miR-206.

We found that miR-206 was down-regulated and TM4SF1 was up-regulated in human CRC tissues and cell lines. Moreover, miR-206 was negatively correlated with TM4SF1 expression. Bioinformatics analysis and a luciferase reporter assay revealed that miR-206 directly targetted the 3′-untranslated region (UTR) of TM4SF1, and TM4SF1 expression was reduced by miR-206 overexpression at both the mRNA and protein levels. Additionally, PGE2 significantly suppressed the expression of miR-206 and increased the expression of TM4SF1 in CRC cells. PGE2 induction led to enhanced CRC cell proliferation, migration, and invasion. Moreover, the overexpression of miR-206 decreased CRC cell proliferation, migration, and invasion compared with control group in PGE2-induced cells, and these effects could be recovered by the overexpression of TM4SF1. Overexpression of miR-206 also suppressed the expression of β-catenin, VEGF, MMP-9, Snail, and Vimentin and enhanced E-cadherin expression in PGE2-induced cells. These results could be reversed by the overexpression of TM4SF1. At last, up-regulation of miR-206 suppressed expression of p-AKT and p-ERK by targetting TM4SF1 in PGE2-induced cells.

Our results provide further evidence that miR-206 has a protective effect on PGE2-induced colon carcinogenesis.

TM4SF1 inhibits apoptosis and promotes proliferation, migration and invasion in human gastric cancer cells

Gastric cancer (GC) is associated with poor patient prognosis, and so it crucial to investigate the molecular mechanisms underlying the progression of GC. The aim of the present study was to investigate the role of transmembrane-4 L6 family member 1 (TM4SF1) in the progression of GC. TM4SF1 small interfering RNA (siRNA) and TM4SF1-expressing plasmids were employed to regulate TM4SF1 expression. In vitro experiments were performed to determine the effect of TM4SF1 on the expression of apoptosis-associated molecules and determine the role of TM4SF1 in apoptosis, proliferation, migration and invasion using human GC cell lines MGC803 and MKN45. The data of the present study demonstrated that TM4SF1 may regulate the expression of apoptosis-associated molecules at the mRNA and protein levels. TM4SF1 silencing reduced B-cell lymphoma 2 (Bcl2) expression, whilst caspase-3 and Bcl2-associated X expression increased, and upregulating TM4SF1 reversed these changes in GC cells. Furthermore, TM4SF1 knockdown promoted apoptosis while inhibiting the proliferation, migration and invasion of GC cells. Rescue experiments demonstrated that TM4SF1 upregulation reversed the changes induced by transfection with TM4SF1 siRNA. In summary, TM4SF1 is an anti-apoptosis protein associated with the progression of GC. Additional in vivo experiments and clinical trials are required to confirm the possible use of TM4SF1 in tumor therapy.

Clinical significance of TM4SF1 as a tumor suppressor gene in gastric cancer

Transmembrane‐4‐L‐six‐family member‐1 (TM4SF1), a tumor‐associated antigen, is overexpressed in most epithelial cell carcinomas and a potential target for antibody‐mediated therapy. However, the role of TM4SF1 in gastric cancer has not been elucidated. The aim of this study was to investigate the clinical significance of TM4SF1 expression in gastric carcinoma (GC) tissues using 152 GC tissue samples and matched adjacent nontumor tissue samples analyzed by immunohistochemistry, and 13 fresh GC tissue samples analyzed by Western blotting. The results showed that TM4SF1 was heterogeneously expressed in normal gastric mucosa, with a high expression rate in fundus mucosa. Higher levels and strong expression rate of TM4SF1 were associated with GC tissues of higher‐grade differentiation. TM4SF1 levels were lower in gastric cancer tissues than gastric noncancerous tissues. Expression of TM4SF1 was not correlated with USP10 (P = 0.157), S100A12 (P = 0.479), p53 (P = 0.249), or Ki67 (P = 0.166) in GC. The expression of TM4SF1 was significantly and negatively correlated with depth of invasion (P = 0.031), nodal metastasis (P = 0.042), TNM stage (P = 0.030), and Lauren classification (P = 0.026). There was no significant correlation between TM4SF1 expression and age, gender, tumor size, or distant metastasis (P > 0.05). The expression of TM4SF1 was associated with well overall survival (P = 0.0164). The 5‐year survival rate for patients with GC showing TM4SF1 positive was 58.82% (10/17), and the median survival time was 78 months, higher than that (12.90%, 12/93) of patients who were TM4SF1 negative, whose median survival time was 62 months. These data suggested that low expression of TM4SF1 is associated with carcinogenesis and development, tumor progression and invasion of gastric cancer, and poor overall survival of patients with GC. TM4SF1 is a tumor suppressor for GC and a novel prognostic marker for patients with GC.

Upregulation of transmembrane 4 L6 family member 1 predicts poor prognosis in invasive breast cancer: A STROBE-compliant article

Transmembrane 4 L6 family member 1 (TM4SF1) belongs to the 4-transmembrane-domain family and functions as an oncogene in multiple human cancers. In this work, we aim to determine TM4SF1 expression and its prognostic impact on patients with invasive breast cancer.Overall, we enrolled 209 invasive breast cancer patients and immunohistochemically examined the expression of TM4SF1 in tumor specimens. The relationship between TM4SF1 expression and clinicopathological parameter and patient survival of breast cancer patients was analyzed.Among the 209 cases, 137 (65.6%) exhibited high expression of TM4SF1. High TM4SF1 expression was significantly associated with advanced histological grade and negative estrogen receptor and progesterone receptor status. Triple-negative breast cancer (TNBC) tumors were more likely to express high levels of TM4SF1 than non-TNBC cases. Patients with high tumoral expression of TM4SF1 had a significantly shorter disease-free survival (DFS; P = .00) and overall survival (OS; P = .01) than those with low expression of TM4SF1. When survival analysis was restricted to the 167 patients (79.9%) receiving adjuvant chemotherapy, TM4SF1 expression was also correlated with poorer DFS and OS (P = .00). In multiple Cox regression analysis TM4SF1 expression remained an independent prognostic indicator for OS and DFS.TM4SF1 is upregulated and serves as an independent poor prognostic indicator in invasive breast cancer.

Integrative radiogenomic analysis for multicentric radiophenotype in glioblastoma

We postulated that multicentric glioblastoma (GBM) represents more invasiveness form than solitary GBM and has their own genomic characteristics. From May 2004 to June 2010 we retrospectively identified 51 treatment-naïve GBM patients with available clinical information from the Samsung Medical Center data registry. Multicentricity of the tumor was defined as the presence of multiple foci on the T1 contrast enhancement of MR images or having high signal for multiple lesions without contiguity of each other on the FLAIR image. Kaplan-Meier survival analysis demonstrated that multicentric GBM had worse prognosis than solitary GBM (median, 16.03 vs. 20.57 months, p < 0.05). Copy number variation (CNV) analysis revealed there was an increase in 11 regions, and a decrease in 17 regions, in the multicentric GBM. Gene expression profiling identified 738 genes to be increased and 623 genes to be decreased in the multicentric radiophenotype (p < 0.001). Integration of the CNV and expression datasets identified twelve representative genes: CPM, LANCL2, LAMP1, GAS6, DCUN1D2, CDK4, AGAP2, TSPAN33, PDLIM1, CLDN12, and GTPBP10 having high correlation across CNV, gene expression and patient outcome. Network and enrichment analyses showed that the multicentric tumor had elevated fibrotic signaling pathways compared with a more proliferative and mitogenic signal in the solitary tumors. Noninvasive radiological imaging together with integrative radiogenomic analysis can provide an important tool in helping to advance personalized therapy for the more clinically aggressive subset of GBM.

Differential regulation of cellular functions by the C-termini of transmembrane 4 L six family proteins in 2- or 3-dimensional environment

The transmembrane 4 L six family proteins TM4SF1, TM4SF4, and TM4SF5 share 40-50% overall sequence identity, but their C-terminus identity is limited. It may be likely that the C-termini of the members are important and unique for own regulatory functions. We thus examined how the TM4SF5 C-terminus affected cellular functions differentially from other family members. Using colon cancer cells expressing wildtype (WT), C-terminus-deleted, or chimeric mutants, diverse cellular functions were explored in 2-dimensional (2D) and 3-dimensional (3D) condition. The C-termini of the proteins were relatively comparable with respect to 2D cell proliferation, although each C-terminal-deletion mutant exhibited increased proliferation relative to the WT. Using chimeric constructs, we found that the TM4SF5 C-terminus was critical for regulating the diverse metastatic functions of TM4SF5, and could positively replace the C-termini of other family members. Replacement of the TM4SF1 or TM4SF4 C-terminus with that of TM4SF5 increased spheroids growth, transwell migration, and invasive dissemination from spheroids in 3D collagen gels. TM4SF5-mediated effects required its extracellular loop 2 linked to the C-terminus via the transmembrane domain 4, with causing c-Src activation. Altogether, the C-terminus of TM4SF5 appears to mediate pro-migratory roles, depending on a structural relay from the second extracellular loop to the C-terminus.

MicroRNA-30a-5p (miR-30a) regulates cell motility and EMT by directly targeting oncogenic TM4SF1 in colorectal cancer

PURPOSE

Colorectal cancer (CRC) is one of the leading causes of cancer death worldwide, and many oncogenes and tumor suppressor genes are involved in CRC. MicroRNAs (miRNAs) are small non-coding RNAs that can negatively regulate gene expression. Previous studies have revealed that miRNAs regulate the development and progression of many cancers. In this study, we investigated the role of microRNA-30a-5p (miR-30a) in CRC and its unknown mechanisms.

METHODS

qRT-PCR was used to detect miR-30a and TM4SF1 mRNA expression in CRC specimens and cell lines. CRC cell migration and invasion were assessed after transfection with miR-30a or TM4SF1 using wound healing and trans-well migration and invasion assays. Transmembrane-4-L-six-family protein (TM4SF1) was validated as a target of miR-30a in CRC through luciferase reporter assay and bioinformatics algorithms. Moreover, two EMT regulators, E-cadherin and VEGF, were also identified using Western blotting and immunohistochemistry.

RESULTS

We found that miR-30a was down-regulated in CRC tumor tissues and cell lines, and miR-30a was inversely associated with advanced stage and lymph node metastatic status compared with normal tissues. miR-30a decreased migration and invasion in CRC cell lines, and miR-30a overexpression not only down-regulated TM4SF1 mRNA and protein expression, but also inhibited the expression of VEGF and enhanced expression of E-cadherin. We also showed that TM4SF1 was up-regulated in CRC tumor specimens compared with adjacent normal tissues, and TM4SF1 expression was significantly associated with advanced stage and lymph node status compared with adjacent normal tissues.

CONCLUSIONS

These results suggest that miR-30a is an important regulator of TM4SF1, VEGF, and E-cadherin for CRC lymph node metastasis, a potential new therapeutic target in CRC.

TM4SF1 Promotes Proliferation, Invasion, and Metastasis in Human Liver Cancer Cells

Transmembrane 4 superfamily member 1 (TM4SF1) is a member of tetraspanin family, which mediates signal transduction events regulating cell development, activation, growth and motility. Our previous studies showed that TM4SF1 is highly expressed in liver cancer. HepG2 cells were transfected with TM4SFl siRNA and TM4SF1-expressing plasmids and their biological functions were analyzed in vitro and in vivo. HepG2 cells overexpressing TM4SF1 showed reduced apoptosis and increased cell migration in vitro and enhanced tumor growth and metastasis in vivo, whereas siRNA-mediated silencing of TM4SF1 had the opposite effect. TM4SF1 exerts its effect by regulating a few apoptosis- and migration-related genes including caspase-3, caspase-9, MMP-2, MMP-9 and VEGF. These results indicate that TM4SF1 is associated with liver tumor growth and progression, suggesting that TM4SF1 may be a potential target for treatment of liver cancer in future.

MicroRNA-9 suppresses cell migration and invasion through downregulation of TM4SF1 in colorectal cancer

Transmembrane-4-L6 family 1 (TM4SF1) is upregulated in colorectal carcinoma (CRC). However, the mechanism leading to inhibition of the TM4SF1 is not known. In the present study, we investigated the regulation of TM4SF1 and function of microRNAs (miRNAs) in CRC invasion and metastasis. We analyzed 60 colon cancers and paired normal specimens for TM4SF1 and miRNA-9 (miR-9) expression using quantitative real-time PCR. A bioinformatics analysis identified a putative miR-9 binding site within the 3'-UTR of TM4SF1. We also found that TM4SF1 was upregulated in CRC tissues and CRC cell lines. The expression of TM4SF1 was positively correlated with clinical advanced stage and lymph node metastasis. Moreover, a luciferase assay revealed that miR-9 directly targeted 3'-UTR-TM4SF1. Overexpression of miR-9 inhibited expression of TM4SF1 mRNA and protein, wound healing, transwell migration and invasion of SW480 cells, whereas, overexpression of anti-miR-9 and siRNA-TM4SF1 inversely regulated the TM4SF1 mRNA and protein level in HCT116 cells. Furthermore, miR-9 suppressed not only TM4SF1 expression but also MMP-2, MMP-9 and VEGF expression. In clinical specimens, miR-9 was generally down-regulated in CRC and inversely correlated with TM4SF1 expression. These results suggest that miR-9 functions as a tumor-suppressor in CRC, and that its suppressive effects mediate invasion and metastasis by inhibition of TM4SF1 expression. Our results also indicate that miR-9 might be a novel target for the treatment of CRC invasion and metastasis.

TM4SF1 Promotes Gemcitabine Resistance of Pancreatic Cancer In Vitro and In Vivo

Background

TM4SF1 is overexpressed in pancreatic ductal adenocarcinoma (PDAC) and affects the development of this cancer. Also, multidrug resistance (MDR) is generally associated with tumor chemoresistance in pancreatic cancer. However, the correlation between TM4SF1 and MDR remains unknown. This research aims to investigate the effect of TM4SF1 on gemcitabine resistance in PDAC and explore the possible molecular mechanism between TM4SF1 and MDR.

Methods

The expression of TM4SF1 was evaluated in pancreatic cancer cell lines and human pancreatic duct epithelial (HPDE) cell lines by quantitative RT-PCR. TM4SF1 siRNA transfection was carried out using Hiperfect transfection reagent to knock down TM4SF1. The transcripts were analyzed by quantitative RT-PCR, RT-PCR and western blotting for further study. The cell proliferation and apoptosis were obtained to investigate the sensitivity to gemcitabine of pancreatic cancer cells after silencing TM4SF1 in vitro. We demonstrated that cell signaling of TM4SF1 mediated chemoresistance in cancer cells by assessing the expression of multidrug resistance (MDR) genes using quantitative RT-PCR. In vivo, we used orthotopic pancreatic tumor models to investigate the effect of proliferation after silencing TM4SF1 by a lentivirus-mediated shRNA in MIA PaCa-2 cell lines.

Results

The mRNA expression of TM4SF1 was higher in seven pancreatic cancer cell lines than in HPDE cell lines. In three gemcitabine-sensitive cell lines (L3.6pl, BxPC-3, SU86.86), the expression of TM4SF1 was lower than that in four gemcitabine-resistant cell lines (MIA PaCa-2, PANC-1, Hs766T, AsPC-1). We evaluated that TM4SF1 was a putative target for gemcitabine resistance in pancreatic cancer cells. Using AsPC-1, MIA PaCa-2 and PANC-1, we investigated that TM4SF1 silencing affected cell proliferation and increased the percentages of cell apoptosis mediated by treatment with gemcitabine compared with cells which were treated with negative control. This resistance was associated with the expression of multidrug resistance genes including ABCB1 and ABCC1. In vivo, silencing of TM4SF1 in MIA PaCa-2 cell lines increased the effectiveness of gemcitabine-based treatment in orthotopic pancreatic tumor models evaluated using noninvasive bioluminescent imaging.

Conclusion

These findings suggest that TM4SF1 is a surface membrane antigen that is highly expressed in pancreatic cancer cells and increases the chemoresistance to gemcitabine. Thus, TM4SF1 may be a promising target to overcome the chemoresistance of pancreatic cancer.

Expression and Subcellular Distribution of GFP-Tagged Human Tetraspanin Proteins in Saccharomyces cerevisiae

Tetraspanins are integral membrane proteins that function as organizers of multimolecular complexes and modulate function of associated proteins. Mammalian genomes encode approximately 30 different members of this family and remotely related eukaryotic species also contain conserved tetraspanin homologs. Tetraspanins are involved in a number of fundamental processes such as regulation of cell migration, fusion, immunity and signaling. Moreover, they are implied in numerous pathological states including mental disorders, infectious diseases or cancer. Despite the great interest in tetraspanins, the structural and biochemical basis of their activity is still largely unknown. A major bottleneck lies in the difficulty of obtaining stable and homogeneous protein samples in large quantities. Here we report expression screening of 15 members of the human tetraspanin superfamily and successful protocols for the production in S. cerevisiae of a subset of tetraspanins involved in human cancer development. We have demonstrated the subcellular localization of overexpressed tetraspanin-green fluorescent protein fusion proteins in S. cerevisiae and found that despite being mislocalized, the fusion proteins are not degraded. The recombinantly produced tetraspanins are dispersed within the endoplasmic reticulum membranes or localized in granule-like structures in yeast cells. The recombinantly produced tetraspanins can be extracted from the membrane fraction and purified with detergents or the poly (styrene-co-maleic acid) polymer technique for use in further biochemical or biophysical studies.

Transmembrane 4 L Six Family Member 5 (TM4SF5)-Mediated Epithelial-Mesenchymal Transition in Liver Diseases

The membrane protein TM4SF5, a member of the transmembrane 4L six family, forms a tetraspanin-enriched microdomain (TEM) on the cell surface, where many different membrane proteins and receptors form a massive protein-protein complex to regulate cellular functions including transdifferentiation, migration, and invasion. We recently reported that TM4SF5 causes epithelial-mesenchymal transition (EMT), eventually contributing to aberrant multilayer cellular growth, drug resistance, enhanced migration, invasion, its circulation in the blood, tumor initiation for successful metastasis, and muscle development in zebrafish. In this review, I summarize the information on the role of TM4SF5 in EMT-related functions at TM4SF5-enriched microdomain (T5EM) on cell surface, where proteins such as TM4SF5, CD151, CD44, integrins, and epidermal growth factor receptor (EGFR) can form numerous protein complexes. TM4SF5-mediated EMT contributes to diverse cellular functions, leading to fibrotic phenotypes and initiating and maintaining tumors in primary and/or metastatic regions, in addition to its role in muscle development in zebrafish. Anti-TM4SF5 strategies for addressing the protein networks can lead to regulation of the fibrotic, tumorigenic, and tumor-maintaining functions of TM4SF5-positive hepatic cells. This review is for us to (re)consider the antifibrotic or antitumorigenic (i.e., anti-EMT-related diseases) strategies of dealing with protein networks that would be involved in cross-talks to regulate various cellular functions during TM4SF5-dependent progression from fibrotic to cancerous hepatic cells.

Therapeutic effect of a TM4SF5-specific monoclonal antibody against colon cancer in a mouse model

Transmembrane 4 superfamily member 5 protein (TM4SF5) is presumed to serve as a molecular target to prevent or treat hepatocellular carcinoma (HCC) and colon cancer in a mouse model. Previously, we reported the efficacy of anti-cancer peptide vaccine targeting TM4SF5. In addition, we reported an anti-proliferative effect of anti-TM4SF5 monoclonal antibody in HCC. Here, we investigated expression of TM4SF5 in 45 primary colon cancer tissues. Almost all of the colon cancer tissues expressed TM4SF5 based on immunohistochemistry using anti-TM4SF5 monoclonal antibody. The treatment of human colon cancer cells with anti-TM4SF5 antibody reduced growth of TM4SF5 expressing cells and enhanced expression of E-cadherin and β-catenin. Using mouse colon cancer models, we then evaluated the in vivo anti-cancer effect of anti-TM4SF5 antibody. Injection of the antibody significantly reduced growth of tumors priorly established by subcutaneous injection of human colon cancer cells HT-29 in a xenograft setting. We obtained similar results with mouse colon cancer cell line CT-26 in an allograft setting. Therefore, we suggest that the TM4SF5-specific monoclonal antibody has a therapeutic effect against colon cancer.

Novel Anti-TM4SF1 Antibody-Drug Conjugates with Activity against Tumor Cells and Tumor Vasculature

Antibody-drug conjugates (ADC) represent a promising therapeutic modality for managing cancer. Here, we report a novel humanized ADC that targets the tetraspanin-like protein TM4SF1. TM4SF1 is highly expressed on the plasma membranes of many human cancer cells and also on the endothelial cells lining tumor blood vessels. TM4SF1 is internalized upon interaction with antibodies. We hypothesized that an ADC against TM4SF1 would inhibit cancer growth directly by killing cancer cells and indirectly by attacking the tumor vasculature. We generated a humanized anti-human TM4SF1 monoclonal antibody, v1.10, and armed it with an auristatin cytotoxic agent LP2 (chemical name mc-3377). v1.10-LP2 selectively killed cultured human tumor cell lines and human endothelial cells that express TM4SF1. Acting as a single agent, v1.10-LP2 induced complete regression of several TM4SF1-expressing tumor xenografts in nude mice, including non-small cell lung cancer and pancreas, prostate, and colon cancers. As v1.10 did not react with mouse TM4SF1, it could not target the mouse tumor vasculature. Therefore, we generated a surrogate anti-mouse TM4SF1 antibody, 2A7A, and conjugated it to LP2. At 3 mpk, 2A7A-LP2 regressed several tumor xenografts without noticeable toxicity. Combination therapy with v1.10-LP2 and 2A7A-LP2 together was more effective than either ADC alone. These data provide proof-of-concept that TM4SF1-targeting ADCs have potential as anticancer agents with dual action against tumor cells and the tumor vasculature. Such agents could offer exceptional therapeutic value and warrant further investigation. Mol Cancer Ther; 14(8); 1868-76. ©2015 AACR.

TM4SF1 as a prognostic marker of pancreatic ductal adenocarcinoma is involved in migration and invasion of cancer cells

The cell surface protein Transmembrane 4 L6 family member 1 (TM4SF1) has been detected in various tumors, and its expression on tumor cells is implicated in cancer cell metastasis and patient prognosis. The role of TM4SF1 in malignant tumors remains poorly understood, particularly in pancreatic cancer. We performed immunohistochemical staining to analyze the expression of TM4SF1 in resected pancreatic tissues and investigated the correlation between TM4SF1 expression and prognosis. The function of TM4SF1 in the invasion and migration of pancreatic cancer cells was analyzed in vitro using an RNA interference technique. In pancreatic cancer tissues, TM4SF1 expression was detected in cancer cells, and patients with high tumor levels of TM4SF1 showed longer survival times than those with low TM4SF1 levels (P=0.0332). In vitro, reduced TM4SF1 expression enhanced the migration (P<0.05) and invasion (P<0.05) of pancreatic cancer cells partially via decreased E-cadherin expression. TM4SF1 protein levels were also reduced after TGF-β1-induced epithelial-mesenchymal transition (EMT).TM4SF1 expression is associated with better prognosis in pancreatic cancer. Loss of TM4SF1 contributes to the invasion and migration of pancreatic cancer cells.

TM4SF5 suppression disturbs integrin α5-related signalling and muscle development in zebrafish

TM4SF5 suppression in zebrafish causes abnormal trunk morphology with aberrant translocation and organization of muscle cells, via altered fibronectin/integrin α5/FAK/vinculin/actin signalling. TM4SF5 controls muscle differentiation via alteration in integrin α5-related signalling.

Correlations between transmembrane 4 L6 family member 5 (TM4SF5), CD151, and CD63 in liver fibrotic phenotypes and hepatic migration and invasive capacities

Transmembrane 4 L6 family member 5 (TM4SF5) is overexpressed during CCl₄-mediated murine liver fibrosis and in human hepatocellular carcinomas. The tetraspanins form tetraspanin-enriched microdomains (TEMs) consisting of large membrane protein complexes on the cell surface. Thus, TM4SF5 may be involved in the signal coordination that controls liver malignancy. We investigated the relationship between TM4SF5-positive TEMs with liver fibrosis and tumorigenesis, using normal Chang hepatocytes that lack TM4SF5 expression and chronically TGFβ1-treated Chang cells that express TM4SF5. TM4SF5 expression is positively correlated with tumorigenic CD151 expression, but is negatively correlated with tumor-suppressive CD63 expression in mouse fibrotic and human hepatic carcinoma tissues, indicating cooperative roles of the tetraspanins in liver malignancies. Although CD151 did not control the expression of TM4SF5, TM4SF5 appeared to control the expression levels of CD151 and CD63. TM4SF5 interacted with CD151, and caused the internalization of CD63 from the cell surface into late lysosomal membranes, presumably leading to terminating the tumor-suppressive functions of CD63. TM4SF5 could overcome the tumorigenic effects of CD151, especially cell migration and extracellular matrix (ECM)-degradation. Taken together, TM4SF5 appears to play a role in liver malignancy by controlling the levels of tetraspanins on the cell surface, and could provide a promising therapeutic target for the treatment of liver malignancies.

Evidence showing that tetraspanins inhibit HIV-1-induced cell-cell fusion at a post-hemifusion stage

Human immunodeficiency virus type 1 (HIV-1) transmission takes place primarily through cell-cell contacts known as virological synapses. Formation of these transient adhesions between infected and uninfected cells can lead to transmission of viral particles followed by separation of the cells. Alternatively, the cells can fuse, thus forming a syncytium. Tetraspanins, small scaffolding proteins that are enriched in HIV-1 virions and actively recruited to viral assembly sites, have been found to negatively regulate HIV-1 Env-induced cell-cell fusion. How these transmembrane proteins inhibit membrane fusion, however, is currently not known. As a first step towards elucidating the mechanism of fusion repression by tetraspanins, e.g., CD9 and CD63, we sought to identify the stage of the fusion process during which they operate. Using a chemical epistasis approach, four fusion inhibitors were employed in tandem with CD9 overexpression. Cells overexpressing CD9 were found to be sensitized to inhibitors targeting the pre-hairpin and hemifusion intermediates, while they were desensitized to an inhibitor of the pore expansion stage. Together with the results of a microscopy-based dye transfer assay, which revealed CD9- and CD63-induced hemifusion arrest, our investigations strongly suggest that tetraspanins block HIV-1-induced cell-cell fusion at the transition from hemifusion to pore opening.

hsa-miR-141 downregulates TM4SF1 to inhibit pancreatic cancer cell invasion and migration

Expression of the transmembrane-4-L-six-family-1 (TM4SF1) is high in human pancreatic cancer cells, but the underlying mechanism remains unclear. In this study, we aimed to identify and characterize microRNAs that regulate TM4SF1 expression in PC cells. Western blot analysis and quantitative polymerase chain reaction were used to detect TM4SF1 and hsa-miR-141 levels in four PC cell lines. SW1990 and BxPc-3 cells were transfected with the inhibitor miR-141, the inhibitor negative control, the miR-141 mimic and the mimic negative control; and cell invasion, migration, proliferation, cell cycle progression and apoptosis were detected by Transwell, MTT and flow cytometry assays, respectively. The miR-141 levels negatively correlated with the TM4SF1 protein levels in PC cells. The TM4SF1 protein levels were lower in the 141M group but higher in the 141I group, although the TM4SF1 mRNA levels had no significant changes, compared to the negative controls. Luciferase assays demonstrated that hsa-miR-141 directly targeted the 3'-untranslated region of the TM4SF1 gene. In addition, miR-141 downregulated TM4SF1 expression to inhibit invasion and migration of PC cells but had no effects on cell proliferation, cell cycle progression or apoptosis. TM4SF1 is a direct target of miR-141. Our findings that TM4SF1 expression was inhibited by miR-141 provide new insights into the oncogenic mechanism of TM4SF1 and suggest that miR-141 represents a novel molecular target for PC therapy.

Molecular cloning, sequence characterization and expression analysis of a CD63 homologue from the coleopteran beetle, Tenebrio molitor

CD63, a member of the tetraspanin membrane protein family, plays a pivotal role in cell growth, motility, signal transduction, host-pathogen interactions and cancer. In this work, the cDNA encoding CD63 homologue (TmCD63) was cloned from larvae of a coleopteran beetle, Tenebrio molitor. The cDNA is comprised of an open reading frame of 705 bp, encoding putative protein of 235 amino acid residues. In silico analysis shows that the protein has four putative transmembrane domains and one large extracellular loop. The characteristic “Cys-Cys-Gly” motif and “Cys188” residues are highly conserved in the large extracellular loop. Phylogenetic analysis of TmCD63 revealed that they belong to the insect cluster with 50%–56% identity. Analysis of spatial expression patterns demonstrated that TmCD63 mRNA is mainly expressed in gut and Malphigian tubules of larvae and the testis of the adult. Developmental expression patterns of CD63 mRNA showed that TmCD63 transcripts are detected in late larval, pupal and adult stages. Interestingly, TmCD63 transcripts are upregulated to the maximum level of 4.5 fold, in response to DAP-type peptidoglycan during the first 6 h, although other immune elicitors also caused significant increase to the transcript level at later time-points. These results suggest that CD63 might contribute to T. molitor immune response against various microbial pathogens.

Tetraspanin CD63 promotes vascular endothelial growth factor receptor 2-β1 integrin complex formation, thereby regulating activation and downstream signaling in endothelial cells in vitro and in vivo

CD63 is a member of the transmembrane-4 glycoprotein superfamily (tetraspanins) implicated in the regulation of membrane protein trafficking, leukocyte recruitment, and adhesion processes. We have investigated the involvement of CD63 in endothelial cell (EC) signaling downstream of β1 integrin and VEGF. We report that silencing of CD63 in primary ECs arrested capillary sprouting and tube formation in vitro because of impaired adhesion and migration of ECs. Mechanistically, CD63 associated with both β1 integrin and the main VEGF receptor on ECs, VEGFR2. Our data suggest that CD63 serves to bridge between β1 integrin and VEGFR2 because CD63 silencing disrupted VEGFR2-β1 integrin complex formation identified using proximity ligation assays. Signaling downstream of β1 integrin and VEGFR2 was attenuated in CD63-silenced cells, although their cell surface expression levels remained unaffected. CD63 was furthermore required for efficient internalization of VEGFR2 in response to VEGF. Importantly, systemic delivery of VEGF failed to potently induce VEGFR2 phosphorylation and downstream signaling in CD63-deficient mouse lungs. Taken together, our findings demonstrate a previously unrecognized role for CD63 in coordinated integrin and receptor tyrosine kinase signaling in vitro and in vivo.

Prophylactic effect of a peptide vaccine targeting TM4SF5 against colon cancer in a mouse model

Expression of transmembrane 4 superfamily member 5 protein (TM4SF5) was implicated in hepatocellular carcinoma (HCC) and colon cancer. Previously, we have shown that immunization with TM4SF5 peptide-CpG-DNA-liposome complex induces production of TM4SF5-specific antibodies and protects mice from HCC progression in an allograft model. Here, we confirmed expression of TM4SF5 in the mouse colon cancer cell line CT-26 and found that anti-TM4SF5 antibody inhibits growth of CT-26 cells. We then immunized mice with TM4SF5 peptide-CpG-DNA-liposome complex and transplanted CT-26 cells to investigate the vaccination effects. Robust production of TM4SF5-specific antibodies was induced by challenge with CT-26 cells and the tumor growth was significantly suppressed in the immunized mice. The peptide vaccine targeting TM4SF5 consequently showed a prophylactic effect against colon cancer development in a mouse model. These results suggest that the peptide vaccine can be potentially applied in humans to treat colon cancer.

Adenovirus-mediated delivery of siRNA targeting TM4SF4 attenuated liver cancer cell growth in vitro and in vivo

Gene targeting using short interfering RNA (siRNA) has become a common strategy to explore gene function because of its prominent efficacy and specificity. The human transmembrane 4 superfamily member 4 (TM4SF4) was originally identified in intestine and liver as a cell proliferation-related gene. Recently, it showed an increased expression in the hepatocellular carcinoma (HCC) tissues. In this study, we developed an adenoviral vector harboring an effective siRNA targeting TM4SF4 (AdSiTM4SF4) and identified its function in suppression of tumor cell growth. It was confirmed that TM4SF4 was overexpressed in HCC tissues compared with its paired non-tumor tissues by western blot analysis and immunohistochemistry. Remarkably, it was more abundant on the cell surface of HCC cells. The signals of ectopically expressed TM4SF4 in four cell lines dramatically localized in the plasma membrane, slightly in the cytoplasm, and absent in the nucleus, demonstrating that TM4SF4 is a membrane protein. Targeting TM4SF4 by AdSiTM4SF4 successfully exerted a gene knockdown effect. The QGY-7701 and SMMC-7721 HCC cells infected with AdSiTM4SF4 displayed remarkably attenuated growth potential. Moreover, intratumoral injection of AdSiTM4SF4 significantly suppressed tumor growth in a xenograft mouse model using SMMC-7721 hepatoma cells. Our results indicated that targeting TM4SF4 might be a promising modality for inhibition of HCC.

PTK7 marks the first human developmental EMT in vitro

Epithelial to mesenchymal transitions (EMTs) are thought to be essential to generate diversity of tissues during early fetal development, but these events are essentially impossible to study at the molecular level in vivo in humans. The first EMT event that has been described morphologically in human development occurs just prior to generation of the primitive streak. Because human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs) are thought to most closely resemble cells found in epiblast-stage embryos prior to formation of the primitive streak, we sought to determine whether this first human EMT could be modeled in vitro with pluripotent stem cells. The data presented here suggest that generating embryoid bodies from hESCs or hiPSCs drives a procession of EMT events that can be observed within 24–48 hours after EB generation. These structures possess the typical hallmarks of developmental EMTs, and portions also display evidence of primitive streak and mesendoderm. We identify PTK7 as a novel marker of this EMT population, which can also be used to purify these cells for subsequent analyses and identification of novel markers of human development. Gene expression analysis indicated an upregulation of EMT markers and ECM proteins in the PTK7+ population. We also find that cells that undergo this developmental EMT retain developmental plasticity as sorting, dissociation and re-plating reestablishes an epithelial phenotype.

Induction of immunological memory response by vaccination with TM4SF5 epitope-CpG-DNA-liposome complex in a mouse hepatocellular carcinoma model

The innovation of a peptide vaccine strategy may contribute to the development of efficacious and convenient cancer vaccines. Recently, we formulated an efficacious peptide vaccine without carriers using the natural phosphodiester bond CpG-DNA and a special liposome complex [Lipoplex(O)]. The peptide vaccine targeting a tumor antigen, transmembrane 4 superfamily member 5 protein (TM4SF5), was confirmed to have preventive and therapeutic effects in a mouse hepatocellular carcinoma (HCC) model. In this study, we demonstrated that the isotype-switched (IgM(-)IgD(-)) B cell population increased after immunization and that the functional memory response persisted for at least 70 days after the final immunization of mice. Delayed implantation of BNL-HCC cells significantly induced the peptide-specific IgG2a production in the immunized mice. Accordingly, tumor growth was inhibited and the survival rate increased. These results suggest that our peptide vaccine induces memory response, which is essential for cancer vaccine application.

Chronic occupational exposure to arsenic induces carcinogenic gene signaling networks and neoplastic transformation in human lung epithelial cells

Chronic arsenic exposure remains a human health risk; however a clear mode of action to understand gene signaling-driven arsenic carcinogenesis is currently lacking. This study chronically exposed human lung epithelial BEAS-2B cells to low-dose arsenic trioxide to elucidate cancer promoting gene signaling networks associated with arsenic-transformed (B-As) cells. Following a 6month exposure, exposed cells were assessed for enhanced cell proliferation, colony formation, invasion ability and in vivo tumor formation compared to control cell lines. Collected mRNA was subjected to whole genome expression microarray profiling followed by in silico Ingenuity Pathway Analysis (IPA) to identify lung carcinogenesis modes of action. B-As cells displayed significant increases in proliferation, colony formation and invasion ability compared to BEAS-2B cells. B-As injections into nude mice resulted in development of primary and secondary metastatic tumors. Arsenic exposure resulted in widespread up-regulation of genes associated with mitochondrial metabolism and increased reactive oxygen species protection suggesting mitochondrial dysfunction. Carcinogenic initiation via reactive oxygen species and epigenetic mechanisms was further supported by altered DNA repair, histone, and ROS-sensitive signaling. NF-κB, MAPK and NCOR1 signaling disrupted PPARα/δ-mediated lipid homeostasis. A 'pro-cancer' gene signaling network identified increased survival, proliferation, inflammation, metabolism, anti-apoptosis and mobility signaling. IPA-ranked signaling networks identified altered p21, EF1α, Akt, MAPK, and NF-κB signaling networks promoting genetic disorder, altered cell cycle, cancer and changes in nucleic acid and energy metabolism. In conclusion, transformed B-As cells with their whole genome expression profile provide an in vitro arsenic model for future lung cancer signaling research and data for chronic arsenic exposure risk assessment.

Prevention and therapy of hepatocellular carcinoma by vaccination with TM4SF5 epitope-CpG-DNA-liposome complex without carriers

Although peptide vaccines have been actively studied in various animal models, their efficacy in treatment is limited. To improve the efficacy of peptide vaccines, we previously formulated an efficacious peptide vaccine without carriers using the natural phosphodiester bond CpG-DNA and a special liposome complex (Lipoplex(O)). Here, we show that immunization of mice with a complex consisting of peptide and Lipoplex(O) without carriers significantly induces peptide-specific IgG2a production in a CD4⁺ cells- and Th1 differentiation-dependent manner. The transmembrane 4 superfamily member 5 protein (TM4SF5) has gained attention as a target for hepatocellular carcinoma (HCC) therapy because it induces uncontrolled growth of human HCC cells via the loss of contact inhibition. Monoclonal antibodies specific to an epitope of human TM4SF5 (hTM4SF5R2-3) can recognize native mouse TM4SF5 and induce functional effects on mouse cancer cells. Pre-immunization with a complex of the hTM4SF5R2-3 epitope and Lipoplex(O) had prophylactic effects against tumor formation by HCC cells implanted in an mouse tumor model. Furthermore, therapeutic effects were revealed regarding the growth of HCC when the vaccine was injected into mice after tumor formation. These results suggest that our improved peptide vaccine technology provides a novel prophylaxis measure as well as therapy for HCC patients with TM4SF5-positive tumors.

Production of human tetraspanin proteins in Escherichia coli

Tetraspanins are found in multicellular eukaryotes and are generally thought to act as scaffolding proteins, localizing multiple proteins to a specific region of the cell membrane. Activities for tetraspanins have been identified in several fundamental processes such as motility, cell adhesion, proliferation and viral entry. Tetraspanins are also key players in cancer development and progression. However, structural and biochemical information on tetraspanins is decidely limited, due in no small part to the difficulties associated with expressing eukaryotic membrane proteins. In this study, we have used GFP fusions of a library of human tetraspanin proteins to identify growth conditions for expression in Escherichia coli. Three tetraspanin-GFP proteins could be produced at high enough levels to allow subsequent purification, paving the way for future structural and biochemical studies.

The L6 domain tetraspanin Tm4sf4 regulates endocrine pancreas differentiation and directed cell migration

The homeodomain transcription factor Nkx2.2 is essential for pancreatic development and islet cell type differentiation. We have identified Tm4sf4, an L6 domain tetraspanin family member, as a transcriptional target of Nkx2.2 that is greatly upregulated during pancreas development in Nkx2.2(-/-) mice. Tetraspanins and L6 domain proteins recruit other membrane receptors to form active signaling centers that coordinate processes such as cell adhesion, migration and differentiation. In this study, we determined that Tm4sf4 is localized to the ductal epithelial compartment and is prominent in the Ngn3(+) islet progenitor cells. We also established that pancreatic tm4sf4 expression and regulation by Nkx2.2 is conserved during zebrafish development. Loss-of-function studies in zebrafish revealed that tm4sf4 inhibits α and β cell specification, but is necessary for ε cell fates. Thus, Tm4sf4 functional output opposes that of Nkx2.2. Further investigation of how Tm4sf4 functions at the cellular level in vitro showed that Tm4sf4 inhibits Rho-activated cell migration and actin organization in a ROCK-independent fashion. We propose that the primary role of Nkx2.2 is to inhibit Tm4sf4 in endocrine progenitor cells, allowing for delamination, migration and/or appropriate cell fate decisions. Identification of a role for Tm4sf4 during endocrine differentiation provides insight into islet progenitor cell behaviors and potential targetable regenerative mechanisms.

TM4SF1, a novel primary androgen receptor target gene over-expressed in human prostate cancer and involved in cell migration

BACKGROUND

The Androgen Receptor (AR) plays a key role in controlling prostate gland homeostasis and contributes to prostate carcinogenesis. The identification of its target genes should provide new candidates that may be implicated in cancer initiation and progression.

METHODS

Transcriptomic experiments and chromatin immunoprecipitation were combined to identify direct androgen regulated genes. Real-time quantitative PCR (RT-qPCR) analyses were performed to measure TM4SF1 mRNA levels in prostate cancer and benign prostatic hyperplasia (BPH) specimens. Immunohistochemical methods were used to compare TM4SF1 protein expression profiles in the same cohort. A targeted siRNAs knockdown strategy was used, prior to wound healing assays, to analyze the role of TM4SF1 in cell migration in vitro.

RESULTS

We demonstrate for the first time that TM4SF1 is a direct target gene of the AR, a transcription factor of the steroid nuclear receptor family. A functional androgen response element was identified in the promoter region of the gene. In addition, TM4SF1 mRNA expression was higher in cancer samples compared to BPH tissues. The TM4SF1 protein mediates cell motility of prostate cancer cells where it is predominantly localized in the cytoplasm, in contrast to its apical membrane localization in normal prostate epithelial cells.

CONCLUSIONS

Our results reveal a novel function for TM4SF1 in AR signaling. The TM4SF1 mRNA expression is higher in prostate cancer tissues as compared to BPH samples. Inhibition of cell migration after targeted knockdown of TM4SF1 protein expression suggests its contribution to prostate cancer cell metastasis.

CD63 is an essential cofactor to leukocyte recruitment by endothelial P-selectin

The activation of endothelial cells is critical to initiating an inflammatory response. Activation induces the fusion of Weibel-Palade Bodies (WPB) with the plasma membrane, thus transferring P-selectin and VWF to the cell surface, where they act in the recruitment of leukocytes and platelets, respectively. CD63 has long been an established component of WPB, but the functional significance of its presence within an organelle that acts in inflammation and hemostasis was unknown. We find that ablating CD63 expression leads to a loss of P-selectin-dependent function: CD63-deficient HUVECs fail to recruit leukocytes, CD63-deficient mice exhibit a significant reduction in both leukocyte rolling and recruitment and we show a failure of leukocyte extravasation in a peritonitis model. Loss of CD63 has a similar phenotype to loss of P-selectin itself, thus CD63 is an essential cofactor to P-selectin.

TM4SF1: a tetraspanin-like protein necessary for nanopodia formation and endothelial cell migration

Transmembrane-4-L-six-family-1 (TM4SF1) is a tetraspanin-like membrane protein that is highly and selectively expressed by cultured endothelial cells (EC) and, in vivo, by EC lining angiogenic tumor blood vessels. TM4SF1 is necessary for the formation of unusually long (up to a 50 μm), thin (~100-300 nm wide), F-actin-poor EC cell projections that we term 'nanopodia'. Immunostaining of nanopodia at both the light and electron microsopic levels localized TM4SF1 in a regularly spaced, banded pattern, forming TM4FS1-enriched domains. Live cell imaging of GFP-transduced HUVEC demonstrated that EC project nanopodia as they migrate and interact with neighboring cells. When TM4SF1 mRNA levels in EC were increased from the normal ~90 mRNA copies/cell to ~400 copies/cell through adenoviral transduction, EC projected more and longer nanopodia from the entire cell circumference but were unable to polarize or migrate effectively. When fibroblasts, which normally express TM4SF1 at ~5 copies/cell, were transduced to express TM4SF1 at EC-like levels, they formed typical TM4SF1-banded nanopodia, and broadened, EC-like lamellipodia. Mass-spectrometry demonstrated that TM4SF1 interacted with myosin-10 and β-actin, proteins involved in filopodia formation and cell migration. In summary, TM4SF1, like genuine tetraspanins, serves as a molecular organizer that interacts with membrane and cytoskeleton-associated proteins and uniquely initiates the formation of nanopodia and facilitates cell polarization and migration.

Phosphatidylserine increases IKBKAP levels in familial dysautonomia cells

Familial Dysautonomia (FD) is an autosomal recessive congenital neuropathy that results from abnormal development and progressive degeneration of the sensory and autonomic nervous system. The mutation observed in almost all FD patients is a point mutation at position 6 of intron 20 of the IKBKAP gene; this gene encodes the IκB kinase complex-associated protein (IKAP). The mutation results in a tissue-specific splicing defect: Exon 20 is skipped, leading to reduced IKAP protein expression. Here we show that phosphatidylserine (PS), an FDA-approved food supplement, increased IKAP mRNA levels in cells derived from FD patients. Long-term treatment with PS led to a significant increase in IKAP protein levels in these cells. A conjugate of PS and an omega-3 fatty acid also increased IKAP mRNA levels. Furthermore, PS treatment released FD cells from cell cycle arrest and up-regulated a significant number of genes involved in cell cycle regulation. Our results suggest that PS has potential for use as a therapeutic agent for FD. Understanding its mechanism of action may reveal the mechanism underlying the FD disease.

Tetraspanins regulate cell-to-cell transmission of HIV-1

BACKGROUND

The presence of the tetraspanins CD9, CD63, CD81 and CD82 at HIV-1 budding sites, at the virological synapse (VS), and their enrichment in HIV-1 virions has been well-documented, but it remained unclear if these proteins play a role in the late phase of the viral replication cycle. Here we used overexpression and knockdown approaches to address this question.

RESULTS

Neither ablation of CD9, CD63 and/or CD81, nor overexpression of these tetraspanins was found to affect the efficiency of virus release. However, confirming recently reported data, tetraspanin overexpression in virus-producing cells resulted in the release of virions with substantially reduced infectivity. We also investigated the roles of these tetraspanins in cell-to-cell transmission of HIV-1. Overexpression of CD9 and CD63 led to reduced cell-to-cell transmission of this virus. Interestingly, in knockdown experiments we found that ablation of CD63, CD9 and/or CD81 had no effect on cell-free infectivity. However, knockdown of CD81, but not CD9 and CD63, enhanced productive particle transmission to target cells, suggesting additional roles for tetraspanins in the transmission process. Finally, tetraspanins were found to be downregulated in HIV-1-infected T lymphocytes, suggesting that HIV-1 modulates the levels of these proteins in order to maximize the efficiency of its transmission within the host.

CONCLUSION

Altogether, these results establish an active role of tetraspanins in HIV-1 producer cells.

The L6 protein TM4SF1 is critical for endothelial cell function and tumor angiogenesis

Transmembrane-4-L-six-family-1 (TM4SF1) was originally described as a cancer cell protein. Here, we show that it is highly expressed in the vascular endothelium of human cancers and in a banded pattern in the filopodia of cultured endothelial cells (EC). TM4SF1 knockdown prevented filopodia formation, inhibited cell mobility, blocked cytokinesis, and rendered EC senescent. Integrin-alpha5 and integrin-beta1 subunits gave a similar staining pattern and interacted constitutively with TM4SF1, whereas integrin subunits often associated with angiogenesis (alphaV, beta3, beta5) interacted with TM4SF1 only after vascular endothelial growth factor (VEGF)-A or thrombin stimulation. TM4SF1 knockdown substantially inhibited maturation of VEGF-A(164)-induced angiogenesis. Thus, TM4SF1 is a key regulator of EC function in vitro and of pathologic angiogenesis in vivo and is potentially an attractive target for antiangiogenesis therapy.

Cooperation between integrin alpha5 and tetraspan TM4SF5 regulates VEGF-mediated angiogenic activity

Tetraspan TM4SF5 is highly expressed in a diverse number of tumor types. Here we explore the mechanistic roles of TM4SF5 in angiogenesis. We found that TM4SF5 overexpression correlates with vascular endothelial growth factor (VEGF) expression in SNU449 hepatocytes and with vessel formation in clinical hepatocarcinoma samples. Conditioned media from TM4SF5-expressing cells enhanced viability and tube formation of primary human umbilical vein endothelial cells, and outgrowth of endothelial cells from aorta ring segments, which was abolished by treatment with an anti-VEGF antibody. TM4SF5 retained integrin alpha(5) on the cell surface for VEGF induction, and preincubation with anti-integrin alpha(5) antibody abolished TM4SF5-mediated VEGF expression and secretion. TM4SF5-mediated effects required integrin alpha(5), c-Src, and signal transducer and activator of transcription 3 (STAT3). In addition, tumors from nude mice injected with TM4SF5-expressing cells and from clinical human hepatocarcinoma tissues showed enhanced integrin alpha(5) expression, vessel formation, and signaling activity, which were inhibited by administration of anti-integrin alpha(5) or -VEGF antibody. This study suggests that TM4SF5 facilitates angiogenesis of neighboring endothelial cells through VEGF induction, mediated by cooperation between TM4SF5 and integrin alpha(5) of epithelial cells.

Trafficking and function of the tetraspanin CD63

Tetraspanins comprise a large superfamily of cell surface-associated membrane proteins characterized by four transmembrane domains. They participate in a variety of cellular processes, like cell activation, adhesion, differentiation and tumour invasion. At the cell surface, tetraspanins form networks with a wide diversity of proteins called tetraspanin-enriched microdomains (TEMs). CD63 was the first characterized tetraspanin. In addition to its presence in TEMs, CD63 is also abundantly present in late endosomes and lysosomes. CD63 at the cell surface is endocytosed via a clathrin-dependent pathway, although recent studies suggest the involvement of other pathways as well and we here present evidence for a role of caveolae in CD63 endocytosis. In late endosomes, CD63 is enriched on the intraluminal vesicles, which by specialized cells are secreted as exosomes through fusion of endosomes with the plasma membrane. The complex localization pattern of CD63 suggests that its intracellular trafficking and distribution must be tightly regulated. In this review we discuss the latest insights in CD63 trafficking and its emerging function as a transport regulator of its interaction partners. Finally, the involvement of CD63 in cancer will be discussed.