Tspan protein family: focusing on the occurrence, progression, and treatment of cancer

The Tetraspanins (Tspan) protein family, also known as the tetraspanin family, contains 33 family members that interact with other protein molecules such as integrins, adhesion molecules, and T cell receptors by forming dimers or heterodimers. The Tspan protein family regulates cell proliferation, cell cycle, invasion, migration, apoptosis, autophagy, tissue differentiation, and immune response. More and more studies have shown that Tspan proteins are involved in tumorigenesis, epithelial-mesenchymal transition, thrombosis, tumor stem cell, and exosome signaling. Some drugs and microRNAs can inhibit Tspan proteins, thus providing new strategies for tumor therapy. An in-depth understanding of the functions and regulatory mechanisms of the Tspan protein family, which can promote or inhibit tumor development, will provide new strategies for targeted interventions in the future.

The versatile roles of testrapanins in cancer from intracellular signaling to cell-cell communication: cell membrane proteins without ligands

The tetraspanins (TSPANs) are a family of four-transmembrane proteins with 33 members in mammals. They are variably expressed on the cell surface, various intracellular organelles and vesicles in nearly all cell types. Different from the majority of cell membrane proteins, TSPANs do not have natural ligands. TSPANs typically organize laterally with other membrane proteins to form tetraspanin-enriched microdomains (TEMs) to influence cell adhesion, migration, invasion, survival and induce downstream signaling. Emerging evidence shows that TSPANs can regulate not only cancer cell growth, metastasis, stemness, drug resistance, but also biogenesis of extracellular vesicles (exosomes and migrasomes), and immunomicroenvironment. This review summarizes recent studies that have shown the versatile function of TSPANs in cancer development and progression, or the molecular mechanism of TSPANs. These findings support the potential of TSPANs as novel therapeutic targets against cancer.

TSPAN1, a novel tetraspanin member highly involved in carcinogenesis and chemoresistance

The tetraspanin (TSPAN) family constitutes a poorly explored family of membrane receptors involved in various physiological processes, with relevant roles in anchoring multiple proteins, acting as scaffolding proteins, and cell signaling. Recent studies have increasingly demonstrated the involvement of TSPANs in cancer. In particular, tetraspanin 1 (also known as TSPAN1, NET-1, TM4C, C4.8 or GEF) has been implicated in cell survival, proliferation and invasion. Recently, our laboratory revealed a key role of TSPAN1 in the acquired resistance of tumor cells to conventional chemotherapy (e.g., cisplatin). In this review, we summarize and discuss the latest research on the physiological mechanisms of TSPANs in cancer and, in particular, on TSPAN1 regulating resistance to chemotherapy. A model of TSPAN1 action is proposed, and the potential of targeting TSPAN1 in anticancer therapeutic strategies is discussed.

Tetraspanins: Physiology, Colorectal Cancer Development, and Nanomediated Applications

Simple Summary

Considering the high incidence of colorectal cancer in adults, as well as the need for identifying novel therapies, we hereby explore the role of tetraspanins in the development of colorectal cancer. We have focused on variate aspects starting from the structure and general physiology and ending with the precise mechanisms involved in the dual reported role of tetraspanins (pro–tumoral and tumor suppressor key player element). Moreover, the present review focuses on the potential of tetraspanins as a target for nanotechnology-mediated therapies, also gathering the limited attempts towards this aim and their reported data.

Abstract

Tetraspanins are transmembrane proteins expressed in a multitude of cells throughout the organism. They contribute to many processes that surround cell–cell interactions and are associated with the progress of some diseases, including cancer. Their crucial role in cell physiology is often understated. Furthermore, recent studies have shown their great potential in being used as targeting molecules. Data have suggested the potential of tetraspanins as a targeting vector for nanomediated distribution and delivery for colorectal cancer applications. Our aim is to provide a review on the important part that tetraspanins play in the human organism and highlight their potential use for drug delivery systems using nanotechnology.

Weighted Gene Co-expression Network Analysis Identified a Novel Thirteen-Gene Signature Associated With Progression, Prognosis, and Immune Microenvironment of Colon Adenocarcinoma Patients

Colon adenocarcinoma (COAD) is one of the most common malignant tumors and has high migration and invasion capacity. In this study, we attempted to establish a multigene signature for predicting the prognosis of COAD patients. Weighted gene co-expression network analysis and differential gene expression analysis methods were first applied to identify differentially co-expressed genes between COAD tissues and normal tissues from the Cancer Genome Atlas (TCGA)-COAD dataset and GSE39582 dataset, and a total of 309 overlapping genes were screened out. Then, our study employed TCGA-COAD cohort as the training dataset and an independent cohort by merging the GES39582 and GSE17536 datasets as the testing dataset. After univariate and multivariate Cox regression analyses were performed for these overlapping genes and overall survival (OS) of COAD patients in the training dataset, a 13-gene signature was constructed to divide COAD patients into high- and low-risk subgroups with significantly different OS. The testing dataset exhibited the same results utilizing the same predictive signature. The area under the curve of receiver operating characteristic analysis for predicting OS in the training and testing datasets were 0.789 and 0.868, respectively, which revealed the enhanced predictive power of the signature. Multivariate Cox regression analysis further suggested that the 13-gene signature could independently predict OS. Among the 13 prognostic genes, NAT1 and NAT2 were downregulated with deep deletions in tumor tissues in multiple COAD cohorts and exhibited significant correlations with poorer OS based on the GEPIA database. Notably, NAT1 and NAT2 expression levels were positively correlated with infiltrating levels of CD8+ T cells and dendritic cells, exhibiting a foundation for further research investigating the antitumor immune roles played by NAT1 and NAT2 in COAD. Taken together, the results of our study showed that the 13-gene signature could efficiently predict OS and that NAT1 and NAT2 could function as biomarkers for prognosis and the immune response in COAD.

RNA Interference and Nanotechnology: A Promising Alliance for Next Generation Cancer Therapeutics

Cancer is a significant health hazard of the 21st century, and GLOBOCAN predicts increasing cancer incidence in the coming decades. Though several conventional treatment modalities exist, most of them end up causing off-target and debilitating effects, and drug resistance acquisition. Advances in our understanding of tumor molecular biology offer alternative strategies for precise, robust, and potentially less toxic treatment paradigms for circumventing the disease at the cellular and molecular level. Several deregulated molecules associated with tumorigenesis have been developed as targets in RNA interference (RNAi) based cancer therapeutics. RNAi, a post-transcriptional gene regulation mechanism, has significantly gained attention because of its precise multi-targeted gene silencing. Although the RNAi approach is favorable, the direct administration of small oligonucleotides has not been fruitful because of their inherent lower half-lives and instability in the biological systems. Moreover, the lack of an appropriate delivery system to the primary site of the tumor that helps determine the potency of the drug and its reach, has limited the effective medical utilization of these bio-drugs. Nanotechnology, with its unique characteristics of enhanced permeation and better tumor-targeting efficiency, offers promising solutions owing to the various possibilities and amenability for modifications of the nanoparticles to augment cancer therapeutics. Nanoparticles could be made multimodal, by designing and synthesizing multiple desired functionalities, often resulting in unique and potentially applicable biological structures. A small number of Phase I clinical trials with systemically administered siRNA molecules conjugated with nanoparticles have been completed and the results are promising, indicating that, these new combinatorial therapies can successfully and safely be used to inhibit target genes in cancer patients to alleviate some of the disease burden. In this review, we highlight different types of nano-based delivery strategies for engineering Nano-RNAi-based bio drugs. Furthermore, we have highlighted the insights gained from current research that are entering the preclinical evaluation and information about initial clinical developments, shaping the future for next generation cancer therapeutics.

Tetraspanin 1 promotes endometriosis leading to ovarian clear cell carcinoma

Ovarian clear cell carcinoma (OCCC) reportedly develops from endometriosis. However, the molecular mechanism underlying its malignant progression to OCCC remains elusive. This study aimed to identify an essential gene in the malignant transformation of endometriosis to OCCC. We performed RNA sequencing in formalin‐fixed, paraffin‐embedded (FFPE) tissues of endometriosis (n = 9), atypical endometriosis (AtyEm) (n = 18), adjacent endometriosis to OCCC (AdjEm) (n = 7), and OCCC (n = 17). We found that tetraspanin 1 (TSPAN1) mRNA level was significantly increased by 2.4‐ (DESeq2) and 3.4‐fold (edgeR) in AtyEm and by 80.7‐ (DESeq2) and 101‐fold (edgeR) in OCCC relative to endometriosis. We confirmed that TSPAN1 protein level was similarly overexpressed in OCCC tissues and cell lines. In immortalized endometriosis cell lines, TSPAN1 overexpression enhanced cell growth and invasion. Mechanistically, TSPAN1 triggered AMP‐activated protein kinase (AMPK) activity, promoting endometriosis and cell growth. Upregulated levels of TSPAN1 are considered an early event in the development of high‐risk endometriosis that could progress to ovarian cancer. Our study suggests the potential of TSPAN1 as a screening candidate for high‐risk endometriosis.

miR-573 suppresses pancreatic cancer cell proliferation, migration, and invasion through targeting TSPAN1

PURPOSE

To explore whether miR-573 can suppress pancreatic cancer cell proliferation, migration, and invasion by targeting TSPAN1.

METHODS

The expression of miR-573 and TSPAN1 in pancreatic cancer tissues and cells lines was analyzed using RT-qPCR. The human pancreatic cancer cell line PANC‑1 was transfected with miR-573 mimic, pcDNA3.1-TSPAN1, or genOFFTM st-h-TSPAN1. The effects of miR-573 and TSPAN1 on cell proliferation, colony formation, migration, and invasion were analyzed by CCK‑8, colony formation, transwell migration, and invasion assay, respectively. Target genes of miR-573 were screened using bioinformatics tools and confirmed by dual-luciferase reporter assay and real-time PCR. The effects of miR-573 in vivo were observed using tumor xenografts.

RESULTS

We found that miR-573 is downregulated and TSPAN1 is upregulated in pancreatic cancer tissues and cells lines. Function assays demonstrated that overexpression of miR-573 inhibited cell proliferation, colony formation, migration, and invasion of pancreatic cancer cells, as well as suppressing tumor growth in vivo. Target genes of miR-573 were predicted using bioinformatics tools and confirmed by dual-luciferase reporter assay and RT-qPCR or western blotting. Downregulation of TSPAN1 also inhibited cell proliferation, colony formation, migration, and invasion of pancreatic cancer cells. Furthermore, overexpression of TSPAN1 attenuated miR-573-induced inhibition of pancreatic cancer cell proliferation and migration.

CONCLUSION

Our findings indicated that miR-573 suppresses pancreatic cancer cell proliferation, migration, and invasion through targeting TSPAN1. TSPAN1 targeted by miR-573 might be a potential therapeutic target for clinical treatment of pancreatic cancer.

Restoration of KMT2C/MLL3 in human colorectal cancer cells reinforces genome-wide H3K4me1 profiles and influences cell growth and gene expression

BACKGROUND

The histone 3 lysine 4 (H3K4) monomethylase KMT2C is mutated across several cancer types; however, the effects of mutations on epigenome organization, gene expression, and cell growth are not clear. A frequently recurring mutation in colorectal cancer (CRC) with microsatellite instability is a single nucleotide deletion within the exon 38 poly-A(9) repeat (c.8390delA) which results in frameshift preceding the functional carboxy-terminal SET domain. To study effects of KMT2C expression in CRC cells, we restored one allele to wild type KMT2C in the two CRC cell lines RKO and HCT116, which both are homozygous c.8390delA mutant.

RESULTS

Gene editing resulted in increased KMT2C expression, increased H3K4me1 levels, altered gene expression profiles, and subtle negative effects on cell growth, where higher dependence and stronger effects of KMT2C expression were observed in RKO compared to HCT116 cells. Surprisingly, we found that the two RKO and HCT116 CRC cell lines have distinct baseline H3K4me1 epigenomic profiles. In RKO cells, a flatter genome-wide H3K4me1 profile was associated with more increased H3K4me1 deposition at enhancers, reduced cell growth, and more differential gene expression relative to HCT116 cells when KMT2C was restored. Profiling of H3K4me1 did not indicate a highly specific regulation of gene expression as KMT2C-induced H3K4me1 deposition was found globally and not at a specific enhancer sub-set in the engineered cells. Although we observed variation in differentially regulated gene sets between cell lines and individual clones, differentially expressed genes in both cell lines included genes linked to known cancer signaling pathways, estrogen response, hypoxia response, and aspects of immune system regulation.

CONCLUSIONS

Here, KMT2C restoration reduced CRC cell growth and reinforced genome-wide H3K4me1 deposition at enhancers; however, the effects varied depending upon the H3K4me1 status of KMT2C deficient cells. Results indicate that KMT2C inactivation may promote colorectal cancer development through transcriptional dysregulation in several pathways with known cancer relevance.

Silencing Tspan1 inhibits migration and invasion, and induces the apoptosis of human pancreatic cancer cells

Pancreatic cancer (PCC) is one of the most dangerous types of tumor as it is very difficult to treat and its 5-year survival rate is <6%. To date, there have been no effective therapeutic strategies to treat PCC, thus, novel effective therapeutic methods are required. Tetraspanin 1 (Tspan1) is a novel member of the tetraspanins superfamily and is highly expressed in a variety of types of cancer, including gastric, hepatocellular and colonic carcinomas. However, the detailed functional role of Tspan1 in pancreatic cancer cells is still unclear and further investigation is required to uncover its therapeutic potential for the treatment of different tumor types. The purpose of the present study was to investigate the expression of Tspan1 in human PCC tissues and cells, and explore the effect of Tspan1 silencing on invasion, migration, cell survival and apoptosis in human PCC to clarify its function. Expression levels of Tspan1 were analyzed in human pancreatic cancer tissues and the cell lines Capan-2 and SW1990 using immunohistochemistry staining, reverse transcription-quantitative polymerase chain reaction and western blotting. The effects of downregulation of Tspan1 expression on cell survival, apoptosis, invasion and migration were investigated viaTspan1-small interfering (si)RNA transfection into human PCC cell lines. The results indicated that Tspan1 expression was increased in human PCC tissues compared with the adjacent normal pancreatic tissues. Tspan1 was highly expressed in the human PCC cell lines Capan-2 and SW1990 when compared with the normal pancreatic cell line HPC-Y5. In addition, transfection with siRNA-targeting Tspan1 significantly reduced cell migration and invasion, and increased the cell apoptosis of Capan-2 and SW1990. The present findings highlighted the important role of Tspan1 in human PCC cell migration, invasion and apoptosis. Thus, Tspan1 RNA interference may serve as a potential therapeutic strategy to treat human PCC.

Decreased TSPAN1 promotes prostate cancer progression and is a marker for early biochemical recurrence after radical prostatectomy

Patients with prostate cancer (PCa) have a variable prognosis. It is challenging to recognize the progressive disease. In this study, we focused on TSPAN1, a new member of the tetraspanin family. Its expression was decreased in progressive PCa and was an independent prognosis factor of biochemical recurrence after radical prostatectomy. In vitro, knockdown and overexpression of TSPAN1 in PCa cell lines showed that TSPAN1 could inhibit cell proliferation and migration. TSPAN1 was positive related to PTEN in both clinical specimen and mouse models. The combination of these two markers could increase their prognosis value especially in low risk patients. In vitro TSPAN1 knockdown resulted in increased Akt phosphorylation and caused evident cell cycle transition from G1 to S phase. Our data suggests that TSPAN1 is a valuable marker to recognize more progressive PCa.

A novel role for sox7 in Xenopus early primordial germ cell development: mining the PGC transcriptome

Xenopus primordial germ cells (PGCs) are determined by the presence of maternally derived germ plasm. Germ plasm components both protect PGCs from somatic differentiation and begin a unique gene expression program. Segregation of the germline from the endodermal lineage occurs during gastrulation, and PGCs subsequently initiate zygotic transcription. However, the gene network(s) that operate to both preserve and promote germline differentiation are poorly understood. Here, we utilized RNA-sequencing analysis to comprehensively interrogate PGC and neighboring endoderm cell mRNAs after lineage segregation. We identified 1865 transcripts enriched in PGCs compared with endoderm cells. We next compared the PGC-enriched transcripts with previously identified maternal, vegetally enriched transcripts and found that ∼38% of maternal transcripts were enriched in PGCs, including sox7 PGC-directed sox7 knockdown and overexpression studies revealed an early requirement for sox7 in germ plasm localization, zygotic transcription and PGC number. We identified pou5f3.3 as the most highly expressed and enriched POU5F1 homolog in PGCs. We compared the Xenopus PGC transcriptome with human PGC transcripts and showed that 80% of genes are conserved, underscoring the potential usefulness of Xenopus for understanding human germline specification.

The cancer-associated cell migration protein TSPAN1 is under control of androgens and its upregulation increases prostate cancer cell migration

Cell migration drives cell invasion and metastatic progression in prostate cancer and is a major cause of mortality and morbidity. However the mechanisms driving cell migration in prostate cancer patients are not fully understood. We previously identified the cancer-associated cell migration protein Tetraspanin 1 (TSPAN1) as a clinically relevant androgen regulated target in prostate cancer. Here we find that TSPAN1 is acutely induced by androgens, and is significantly upregulated in prostate cancer relative to both normal prostate tissue and benign prostate hyperplasia (BPH). We also show for the first time, that TSPAN1 expression in prostate cancer cells controls the expression of key proteins involved in cell migration. Stable upregulation of TSPAN1 in both DU145 and PC3 cells significantly increased cell migration and induced the expression of the mesenchymal markers SLUG and ARF6. Our data suggest TSPAN1 is an androgen-driven contributor to cell survival and motility in prostate cancer.

Tspan9 inhibits the proliferation, migration and invasion of human gastric cancer SGC7901 cells via the ERK1/2 pathway

Tetraspanins are a heterogeneous group of 4-transmembrane proteins that recruit other cell surface receptors and signaling proteins into tetraspanin-enriched microdomains (TEMs). TEMs of various types are involved in the regulation of cell growth, migration and invasion of several tumor cell types, both as suppressors or promotors. Tetraspanin 9 (Tspan9, NET-5, PP1057), a member of the transmembrane 4 superfamily (TM4SF) of tetraspanins, reportedly regulates platelet function in concert with other platelet tetraspanins and their associated proteins. Our previous study demonstrated that Tspan9 is also expressed in gastric cancer (GC), but the role of Tspan9 in GC has not been well characterized. In this study, we investigated the influence of Tspan9 on proliferation, migration and invasion of human gastric cancer SGC7901 cells using CCK-8 assay, cell cycle analysis, wound-healing assay and Transwell assay. Western blot analysis and ELISA assay were also performed to identify the potential mechanisms involved. The proliferation, migration and invasion of human gastric cancer SGC7901 cells were significantly inhibited by overexpression of Tspan9. In addition, Tspan9 downregulated the phosphorylation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) and the secretion levels of proteins related to tumor metastasis, such as matrix metalloproteinase-9 (MMP-9) and urokinase plasminogen activator (uPA). Our study indicated that Tspan9 inhibited SGC7901 cell proliferation, migration and invasion through the ERK1/2 pathway.

Tetraspanin 1 is involved in survival, proliferation and carcinogenesis of pancreatic cancer

Pancreatic cancer (PCC) is one of the most difficult cancers to treat and the 10th leading cause of cancer-related death in worldwide. Studies have demonstrated that the tetraspanin 1 (Tspan1) is overexpressed in various cancers and may be a potential therapeutic strategy for the treatment of different cancers. However, the possible role of Tspan1 in PCC is still unknown. In the present study, our data revealed that the increased Tspan1 in PCC tissues was associated with the clinicopathological features and survival rate of PCC patient. We also investigated the effects of Tspan1 gene knockdown on the biological behavior of human PCC. The expression of Tspan1 (detected by immunohistochemistry, qRT-PCR and western blot analysis) derived from human PCC tissues and cell lines (AsPC-1 and PANC-1), were significantly elevated compared with those of the control (P<0.05). Transfection with siRNA-targeting Tspan1 significantly decreased proliferation, increased the apoptosis and reduced migration and invasion of AsPC-1 and PANC-1 cells. The present study demonstrated that Tspan1 plays an important role in PCC carcinogenic progression, including migration and invasion. The siRNA targeting of Tspan1 may be a potential therapeutic strategy for the treatment of PCC.

Tetraspanins as regulators of the tumour microenvironment: implications for metastasis and therapeutic strategies

One of the hallmarks of cancer is the ability to activate invasion and metastasis. Cancer morbidity and mortality are largely related to the spread of the primary, localized tumour to adjacent and distant sites. Appropriate management and treatment decisions based on predicting metastatic disease at the time of diagnosis is thus crucial, which supports better understanding of the metastatic process. There are components of metastasis that are common to all primary tumours: dissociation from the primary tumour mass, reorganization/remodelling of extracellular matrix, cell migration, recognition and movement through endothelial cells and the vascular circulation and lodgement and proliferation within ectopic stroma. One of the key and initial events is the increased ability of cancer cells to move, escaping the regulation of normal physiological control. The cellular cytoskeleton plays an important role in cancer cell motility and active cytoskeletal rearrangement can result in metastatic disease. This active change in cytoskeletal dynamics results in manipulation of plasma membrane and cellular balance between cellular adhesion and motility which in turn determines cancer cell movement. Members of the tetraspanin family of proteins play important roles in regulation of cancer cell migration and cancer-endothelial cell interactions, which are critical for cancer invasion and metastasis. Their involvements in active cytoskeletal dynamics, cancer metastasis and potential clinical application will be discussed in this review. In particular, the tetraspanin member, CD151, is highlighted for its major role in cancer invasion and metastasis.

LINKED ARTICLES

This article is part of a themed section on Cytoskeleton, Extracellular Matrix, Cell Migration, Wound Healing and Related Topics. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-24.

Tetraspanins in cell migration

Tetraspanins are a superfamily of small transmembrane proteins that are expressed in almost all eukaryotic cells. Through interacting with one another and with other membrane and intracellular proteins, tetraspanins regulate a wide range of proteins such as integrins, cell surface receptors, and signaling molecules, and thereby engage in diverse cellular processes ranging from cell adhesion and migration to proliferation and differentiation. In particular, tetraspanins modulate the function of proteins involved in all determining factors of cell migration including cell-cell adhesion, cell-ECM adhesion, cytoskeletal protrusion/contraction, and proteolytic ECM remodeling. We herein provide a brief overview of collective in vitro and in vivo studies of tetraspanins to illustrate their regulatory functions in the migration and trafficking of cancer cells, vascular endothelial cells, skin cells (keratinocytes and fibroblasts), and leukocytes. We also discuss the involvement of tetraspanins in various pathologic and remedial processes that rely on cell migration and their potential value as targets for therapeutic intervention.

TSPAN1 functions as an oncogene in gastric cancer and is downregulated by miR-573

Tetraspanin 1 (TSPAN1) has been reported to be upregulated in gastric cancer (GC). However, whilst TSPAN1 is positively correlated with clinical stage and negatively correlated with survival rates, its function in GC remains elusive. Here we show that expression of TSPAN1 is significantly higher in GC tissues compared to non-cancerous tissues. Furthermore, we demonstrate that RNAi-mediated down-regulation of TSPAN1 expression markedly blocks GC cell proliferation, cell cycle progression and invasive activity. We identified TSPAN1 as a novel target gene of miR-573. Overexpression of miR-573 suppressed proliferation and invasion of GC cells by down-regulation of TSPAN1 expression. Restoration of TSPAN1 rescued the effects of miR-573 overexpression. Therefore, our findings suggest that the miR-573/TSPAN1 axis is important in the control of gastric carcinogenesis.

MicroRNA-638 inhibits cell proliferation, invasion and regulates cell cycle by targeting tetraspanin 1 in human colorectal carcinoma

The expression of miR-638 was found downregulated in colorectal carcinoma (CRC) in our previous study. However, the role of miR-638 in CRC remains unknown. The aim of this study was to determine the function and mechanism of miR-638 in CRC. Here, we verified that miR-638 was frequently downregulated in CRC tissues compared with corresponding noncancerous tissues (NCTs) in an expanded CRC cohort, and survival analysis showed that the downregulation of miR-638 in CRC was associated with poor prognoses. The ectopic expression of miR-638 inhibited CRC cell proliferation, invasion and arrest the cell cycle in G1 phase, whereas the repression of miR-638 significantly promoted CRC cell growth, invasion and cell cycle G1/S transition. Subsequent mechanism analyses revealed that miR-638 inhibited CRC cell growth, invasion and cell cycle progression by targeting TSPAN1. TSPAN1 protein levels were upregulated in CRC samples and were inversely correlated with miR-638 levels. More importantly, high TSPAN1 expression levels in CRC tissues predicted poor overall survival, and appears to be an independent prognostic factor for CRC survival. Furthermore, CpG island methylation analyses revealed that the miR-638 promoter was hypermethylated in CRC and that attenuating promoter methylation was sufficient to restore miR-638 expression in CRC cells. Taken together, our current data demonstrate that miR-638 functions as a tumor suppressor in human CRC by inhibiting TSPAN1, and that TSPAN1 is a potential prognostic factor for CRC.

MiR-200a enhances the migrations of A549 and SK-MES-1 cells by regulating the expression of TSPAN1

MicroRNA-200a (miR-200a) has been reported to regulate tumour progression in several tumours; however, little is known about its role in non-small cell lung cancer cells (NSCLCs). Here, we found that miR-200a was up-regulated in A549 and SK-MES-1 cells compared with normal lung cells HELF. By a series of gain-of-function and loss-offunction studies, over-expression of miR-200a was indicated to enhance cells migration, and its knock-down inhibited migration of cells in NSCLC cell lines. Furthermore, miR-200a was identified to induce TSPAN1 expression which was related to migration. TSPAN1 was proved to induce migration, and so up-regulation of TSPAN1 by miR-200a may explain why over-expressing miR-200a promotes NSCLC cells migration.

RNA interference in the treatment of colon cancer

Colorectal cancer is the third most common cancer in both men and women and has shown a progressive increase over the past 20 years. Current chemotherapy has major limitations, and a novel therapeutic approach is required. Given that neoplastic transformation of colon epithelial cells is a consequence of genetic and epigenetic alterations, RNA interference (RNAi) has been proposed as a new therapeutic strategy that offers important advantages over conventional treatments, with high specificity and potency and low toxicity. RNAi has been employed as an effective tool to study the function of genes, preventing their expression and leading to the development of new approaches to cancer treatment. In malignancies, including colon cancer, RNAi is being used for "silencing" genes that are deregulated by different processes such as gene amplification, mutation, or overexpression and may be the cause of oncogenesis. This strategy not only provides information on the involvement of certain genes in colon cancer, but also opens up a new perspective for its treatment. However, most studies have used adenovirus or lentivirus vectors to transport RNAi into tumor cells or tumors in animal models, because several technical obstacles must be overcome before RNAi can be used in the clinical setting. The aim of this study was to review current knowledge on the use of RNAi techniques in the treatment of colon cancer.

Expression and function of NET-1 in human skin squamous cell carcinoma

To evaluate the clinicopathological significance of NET-1 in human skin squamous cell carcinoma (SSCC). The expression of NET-1 and Ki67 protein was detected using immunostaining from 60 SSCC cases, 50 SIN samples and ten normal skin tissues. The vectors expressing NET-1, siRNA NET-1 and shRNA NET-1 were constructed, as well as negative controls (target-off). In transfected A431 cells, the expression of NET-1 was detected by qRT-PCR, Western blot and immunofluorescence staining; the proliferation and migration of cells was evaluated by MTT, flow cytometry, wound healing and transwell chamber assays. The stable cell lines transfected with shRNANET-1 was inoculated in nude mice for in vivo study. (1) The levels of NET-1 were significantly higher in SSCC (96.67 %) and SIN III (93.75 %) than that in SIN I and II (41.18 %), (P < 0.05). NET-1 expression was significantly enhanced in spindle-cell SSCC (75 %) versus other histological types (P < 0.05). (2) The expression of NET-1 in A431 cells transfected with siRNANET-1 or shRNANET-1 was significantly decreased; the proliferation and migration of these cells were obviously inhibited as compared to controls (P < 0.05). (3) The growth of subcutaneous tumors was significantly inhibited associated with reduction in the expression of NET-1 vs. the negative control or untreated group (P < 0.05). The overexpression of NET-1 in tumor cells may be closely related to the malignant phenotype of SSCC. NET-1 RNAi used in this study can specifically and effectively downregulate NET-1 gene expression; thus SSCC proliferation, invasion and tumor growth were attenuated. NET-1 might be one of the potential targets for SSCC therapy.

Inhibition of hepatocellular carcinoma growth and angiogenesis by dual silencing of NET-1 and VEGF

Simultaneous silencing of multiple up-regulated genes is an attractive and viable strategy to treat many incurable diseases including cancer. Herein we used dual gene targeted siRNA (DGT siRNA) conjugate composed of NET-1 and VEGF siRNA sequences in the same backbone could inhibit growth and angiogenesis HCC. DGT siRNA showed a further down regulation on VEGF mRNA and protein levels compared with NET-1 siRNA or VEGF siRNA, but not on NET-1 expression. It also exhibited greater suppression on proliferation and trigger of apoptosis in HepG2 cells than NET-1 siRNA or VEGF siRNA; this could be explained by the significant down regulation of cyclin D1 and Bcl-2. A lower level of ANG2 mRNA and protein was detected in HUVEC cultured with supernatant of HepG2 cells treated with DGT siRNA than that of VEGF siRNA or NET-1 siRNA, resulting in much more inhibited angiogenesis of HUVEC. Tumor growth was inhibited and microvessel density dropped in the xenograft tumor models compared to the untreated controls. NET-1 and VEGF silencing play a key role in inhibiting hepatocellular cell proliferation, promoting apoptosis, and reducing angiogenesis. Simultaneous silencing of NET-1 and VEGF using DGT siRNA construct may provide an advantageous alternative in development of therapeutics for Hepatocellular carcinoma.

Targeting tetraspanins in cancer

INTRODUCTION

Tetraspanins are a family of small proteins that cross the membrane four times and form complexes by interacting between themselves and with a variety of transmembrane and cytosolic proteins, building a network of interactions referred to as tetraspanin web or tetraspanin enriched microdomains (TEMs). These domains provide a signaling platform involved in many important cellular functions and malignant processes.

AREAS COVERED

The authors describe the methods and the rationale for targeting tetraspanins in the therapy of cancer in this review.

EXPERT OPINION

Targeting tetraspanins in cancer may be a promising therapy due to the importance of tetraspanins in several steps of tumor formation, communication with the environment, dissemination, and metastasis.