CD9

Gene Summary

Gene:CD9; CD9 molecule
Aliases: MIC3, MRP-1, BTCC-1, DRAP-27, TSPAN29, TSPAN-29
Location:12p13.3
Summary:This gene encodes a member of the transmembrane 4 superfamily, also known as the tetraspanin family. Tetraspanins are cell surface glycoproteins with four transmembrane domains that form multimeric complexes with other cell surface proteins. The encoded protein functions in many cellular processes including differentiation, adhesion, and signal transduction, and expression of this gene plays a critical role in the suppression of cancer cell motility and metastasis. [provided by RefSeq, Jan 2011]
Databases:OMIM, VEGA, HGNC, Ensembl, GeneCard, Gene
Protein:CD9 antigen
HPRD
Source:NCBIAccessed: 17 March, 2015

Ontology:

What does this gene/protein do?
Show (19)
Pathways:What pathways are this gene/protein implicaed in?
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Cancer Overview

Research Indicators

Publications Per Year (1990-2015)
Graph generated 17 March 2015 using data from PubMed using criteria.

Literature Analysis

Mouse over the terms for more detail; many indicate links which you can click for dedicated pages about the topic.

  • Transduction
  • CD9 Antigen
  • Oncogene Fusion Proteins
  • Immunophenotyping
  • Gene Expression Profiling
  • Tumor Markers
  • Base Sequence
  • Chromosome 12
  • Karyotyping
  • Tumor Antigens
  • Acute Lymphocytic Leukaemia
  • Down-Regulation
  • Cancer RNA
  • Gene Expression
  • Cell Proliferation
  • Immunohistochemistry
  • Molecular Sequence Data
  • Neoplasm Metastasis
  • Chromosome Aberrations
  • Cell Differentiation
  • Flow Cytometry
  • Membrane Glycoproteins
  • Transfection
  • Cancer Gene Expression Regulation
  • Lung Cancer
  • Proto-Oncogene Proteins
  • Breast Cancer
  • Adolescents
  • Oligonucleotide Array Sequence Analysis
  • Leukaemia
  • Young Adult
  • Skin Cancer
  • Membrane Proteins
  • RTPCR
  • Esophageal Cancer
  • DNA Primers
  • Cell Movement
  • Neoplasm Proteins
  • Messenger RNA
  • Childhood Cancer
  • Promoter Regions
  • CD82
  • CD Antigens
Tag cloud generated 17 March, 2015 using data from PubMed, MeSH and CancerIndex

Specific Cancers (7)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: CD9 (cancer-related)

Hu X, Xuan H, Du H, et al.
Down-regulation of CD9 by methylation decreased bortezomib sensitivity in multiple myeloma.
PLoS One. 2014; 9(5):e95765 [PubMed] Free Access to Full Article Related Publications
Bortezomib therapy has been proven successful for the treatment of relapsed and/or refractory multiple myeloma (MM). However, both intrinsic and acquired resistance has already been observed. In this study, we explored the relationship between CD9 expression and bortezomib sensitivity in MM. We found that down-regulation of CD9 by methylation decreased bortezomib sensitivity in multiple myeloma. CD9 expression obviously increased bortezomib sensitivity through inducing apoptosis, significantly inhibiting U266 cells' adhesion to HS-5 and primary bone marrow stromal cells, but increasing U266 cells' adhesion to fibronectin. CD9 expression also significantly inhibited U266 cell migration. The mechanisms may include: the endoplasmic reticulum stress pathway, cell adhesion related signaling pathway and osteoclast differentiation related signaling pathway. Combination therapy with de-methylation reagent 5-Aza-2-deoxycytidine may prove useful to the development of novel strategies for the treatment of bortezomib-resistant MM patients.

Herr MJ, Longhurst CM, Baker B, et al.
Tetraspanin CD9 modulates human lymphoma cellular proliferation via histone deacetylase activity.
Biochem Biophys Res Commun. 2014; 447(4):616-20 [PubMed] Related Publications
Non-Hodgkin Lymphoma (NHL) is a type of hematological malignancy that affects two percent of the overall population in the United States. Tetraspanin CD9 is a cell surface protein that has been thoroughly demonstrated to be a molecular facilitator of cellular phenotype. CD9 expression varies in two human lymphoma cell lines, Raji and BJAB. In this report, we investigated the functional relationship between CD9 and cell proliferation regulated by histone deacetylase (HDAC) activity in these two cell lines. Introduction of CD9 expression in Raji cells resulted in significantly increased cell proliferation and HDAC activity compared to Mock transfected Raji cells. The increase in CD9-Raji cell proliferation was significantly inhibited by HDAC inhibitor (HDACi) treatment. Pretreatment of BJAB cells with HDAC inhibitors resulted in a significant decrease in endogenous CD9 mRNA and cell surface expression. BJAB cells also displayed decreased cell proliferation after HDACi treatment. These results suggest a significant relationship between CD9 expression and cell proliferation in human lymphoma cells that may be modulated by HDAC activity.

Kwon HJ, Min SY, Park MJ, et al.
Expression of CD9 and CD82 in clear cell renal cell carcinoma and its clinical significance.
Pathol Res Pract. 2014; 210(5):285-90 [PubMed] Related Publications
CD9 and CD82, members of the tetraspanin family, act as metastasis suppressors in many human malignant tumors, but the role of these molecules is not well known in clear cell renal cell carcinoma (CCRCC). This study was designed to evaluate the immunohistochemical expression of CD9 and CD82 in 644 cases of CCRCC and to determine the clinicopathologic and prognostic significance of their expression. The percentage of positive tumor cells was evaluated, and the expression was classified into 2 categories: low expression (less than 10% positive cells) or high expression (more than 10% positive cells) for CD9 expression and negative (no positive cells) or positive for CD82 expression. CD9 high expression was found in 303 (47.0%) patients, and CD82 positivity was found in 98 (15.2%) patients. High expression of CD9 was statistically associated with older patients (p=0.003). The cases showing positive immunoreactivity for CD82 exhibited a high stage (p<0.001) and high nuclear grade (p<0.001). The overall, cancer-specific and progression-free survival rates were significantly higher in patients with a CD82-negative profile compared to patients with a CD82-positive profile (p<0.001). Although the biological function of CD82 in CCRCC remains unclear, the CCRCC patients with CD82 positive expression show poor prognosis.

Okamoto T, Iwata S, Yamazaki H, et al.
CD9 negatively regulates CD26 expression and inhibits CD26-mediated enhancement of invasive potential of malignant mesothelioma cells.
PLoS One. 2014; 9(1):e86671 [PubMed] Free Access to Full Article Related Publications
CD26/dipeptidyl peptidase IV is a cell surface glycoprotein which consists of multiple functional domains beside its ectopeptidase site. A growing body of evidence indicates that elevated expression of CD26 correlates with disease aggressiveness and invasive potential of selected malignancies. To further explore the molecular mechanisms involved in this clinical behavior, our current work focused on the interaction between CD26 and CD9, which were recently identified as novel markers for cancer stem cells in malignant mesothelioma. We found that CD26 and CD9 co-modulated and co-precipitated with each other in the malignant mesothelioma cell lines ACC-MESO1 and MSTO-211H. SiRNA study revealed that depletion of CD26 led to increased CD9 expression, while depletion of CD9 resulted in increased CD26 expression. Consistent with these findings was the fact that gene transfer of CD26 into CD26-negative MSTO-211H cells reduced CD9 expression. Cell invasion assay showed that overexpression of CD26 or gene depletion of CD9 led to enhanced invasiveness, while CD26 gene depletion resulted in reduced invasive potential. Furthermore, our work suggested that this enhanced invasiveness may be partly mediated by α5β1 integrin, since co-precipitation studies demonstrated an association between CD26 and α5β1 integrin. Finally, gene depletion of CD9 resulted in elevated protein levels and tyrosine phosphorylation of FAK and Cas-L, which are downstream of β1 integrin, while depletion of CD26 led to a reduction in the levels of these molecules. Collectively, our findings suggest that CD26 potentiates tumor cell invasion through its interaction with α5β1 integrin, and CD9 negatively regulates tumor cell invasion by reducing the level of CD26-α5β1 integrin complex through an inverse correlation between CD9 and CD26 expression. Our results also suggest that CD26 and CD9 serve as potential biomarkers as well as promising molecular targets for novel therapeutic approaches in malignant mesothelioma and other malignancies.

Liu T, Mendes DE, Berkman CE
Functional prostate-specific membrane antigen is enriched in exosomes from prostate cancer cells.
Int J Oncol. 2014; 44(3):918-22 [PubMed] Free Access to Full Article Related Publications
Developing simple and effective approaches to detect tumor markers will be critical for early diagnosis or prognostic evaluation of prostate cancer treatment. Prostate‑specific membrane antigen (PSMA) has been validated as an important tumor marker for prostate cancer progression including angiogenesis and metastasis. As a type II membrane protein, PSMA can be constitutively internalized from the cell surface into endosomes. Early endosomes can fuse with multivesicular bodies (MVB) to form and secrete exosomes (40-100 nm) into the extracellular environment. Herein, we tested whether some of the endosomal PSMA could be transferred to exosomes as an extracellular resource for PSMA. Using PSMA-positive LNCaP cells, the secreted exosomes were collected and isolated from the cultured media. The vesicular structures of exosomes were identified by electron microscopy, and exosomal marker protein CD9 and tumor susceptibility gene (TSG 101) were confirmed by western blot analysis. Our present data demonstrate that PSMA can be enriched in exosomes, exhibiting a higher content of glycosylation and partial proteolysis in comparison to cellular PSMA. An in vitro enzyme assay further confirmed that exosomal PSMA retains functional enzymatic activity. Therefore, our data may suggest a new role for PSMA in prostate cancer progression, and provide opportunities for developing non-invasive approaches for diagnosis or prognosis of prostate cancer.

Liu J, Sun H, Wang X, et al.
Increased exosomal microRNA-21 and microRNA-146a levels in the cervicovaginal lavage specimens of patients with cervical cancer.
Int J Mol Sci. 2014; 15(1):758-73 [PubMed] Free Access to Full Article Related Publications
Well-run screening programs for cervical cancer in the population at risk have been shown to result in a sharp decrease in the incidence and mortality of cervical cancer in a number of large populations. Expression patterns of a recently identified biomarker family, microRNA, appear to be characteristic of tumor type and developmental origin. Several tumors have been reported to actively release exosomes carrying microRNAs. The present study has determined the association of microRNAs with cervical cancer-derived exosomes. The cervical cancer-derived exosomes were enriched in the cervicovaginal lavages specimens and the abundance of exosomes and exosomal microRNAs was detected by electron microscopy, western blot analysis, RT-qPCR and microRNA target reporter vector. The microRNA-21 and microRNA-146a, which were up-regulated in cervical cancer patients, were associated with the high levels of cervical cancer-derived exosomes. In conclusion, we demonstrated the abundance of exosomes in the cervicovaginal lavage specimens of women with cervical cancer. Furthermore, our results indicated that abnormally high levels of microRNA-21 and microRNA-146a existed in the cervical cancer-derived exosomes and the two microRNAs were functional in 293T cells.

Behnan J, Isakson P, Joel M, et al.
Recruited brain tumor-derived mesenchymal stem cells contribute to brain tumor progression.
Stem Cells. 2014; 32(5):1110-23 [PubMed] Related Publications
The identity of the cells that contribute to brain tumor structure and progression remains unclear. Mesenchymal stem cells (MSCs) have recently been isolated from normal mouse brain. Here, we report the infiltration of MSC-like cells into the GL261 murine glioma model. These brain tumor-derived mesenchymal stem cells (BT-MSCs) are defined with the phenotype (Lin-Sca-1+CD9+CD44+CD166+/-) and have multipotent differentiation capacity. We show that the infiltration of BT-MSCs correlates to tumor progression; furthermore, BT-MSCs increased the proliferation rate of GL261 cells in vitro. For the first time, we report that the majority of GL261 cells expressed mesenchymal phenotype under both adherent and sphere culture conditions in vitro and that the non-MSC population is nontumorigenic in vivo. Although the GL261 cell line expressed mesenchymal phenotype markers in vitro, most BT-MSCs are recruited cells from host origin in both wild-type GL261 inoculated into green fluorescent protein (GFP)-transgenic mice and GL261-GFP cells inoculated into wild-type mice. We show the expression of chemokine receptors CXCR4 and CXCR6 on different recruited cell populations. In vivo, the GL261 cells change marker profile and acquire a phenotype that is more similar to cells growing in sphere culture conditions. Finally, we identify a BT-MSC population in human glioblastoma that is CD44+CD9+CD166+ both in freshly isolated and culture-expanded cells. Our data indicate that cells with MSC-like phenotype infiltrate into the tumor stroma and play an important role in tumor cell growth in vitro and in vivo. Thus, we suggest that targeting BT-MSCs could be a possible strategy for treating glioblastoma patients.

Herr MJ, Mabry SE, Jameson JF, Jennings LK
Pro-MMP-9 upregulation in HT1080 cells expressing CD9 is regulated by epidermal growth factor receptor.
Biochem Biophys Res Commun. 2013; 442(1-2):99-104 [PubMed] Related Publications
Degradation of the surrounding extracellular matrix (ECM) by matrix metalloproteinases (MMPs) drives invasion and metastasis of cancer cells. We previously demonstrated that tetraspanin CD9 expression upregulates pro-MMP-9 expression and release and promotes cellular invasion in a human fibrosarcoma cell line (HT1080). These events were dependent upon the highly functional second extracellular loop of CD9. We report here that the epidermal growth factor receptor (EGFR) tyrosine kinase expression and activity are involved in the CD9-mediated increase in pro-MMP-9 release and cellular invasion. Pro-MMP-9 expression was significantly decreased in a dose-dependent manner using first a broad spectrum receptor tyrosine kinase inhibitor and multiple specific EGFR inhibitors in CD9-HT1080 cells. Furthermore, gefitinib treatment of CD9-HT1080 cells reduced invasion through matrigel. EGFR knockdown using short interfering RNA resulted in decreased pro-MMP-9 expression and release into the media and subsequent cellular invasion without affecting CD9 expression or localization. Conclusively, this study points to EGFR as a key mediator between CD9-mediated pro-MMP-9 release and cellular invasion of HT1080 cells.

Nankivell P, Williams H, McConkey C, et al.
Tetraspanins CD9 and CD151, epidermal growth factor receptor and cyclooxygenase-2 expression predict malignant progression in oral epithelial dysplasia.
Br J Cancer. 2013; 109(11):2864-74 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Prognostic biomarkers aim to improve on the current inadequate method of histological assessment to identify patients with oral epithelial dysplasia at greatest risk of malignant transformation. We aimed to assess the prognostic ability of six protein biomarkers linked to the epidermal growth factor receptor (EGFR) pathway, including three tetraspanins, in a large multicentre oral dysplasia cohort.
METHODS: One hundred and forty-eight cases with varying degrees of epithelial dysplasia underwent immunohistochemical assessment for CD9, CD151, CD82, EGFR, Her-2, and COX-2. Scoring was performed independently by two observers. Univariate analyses using both logistic and Cox regression models and a multivariate regression were performed.
RESULTS: Malignant progression was significantly greater in those cases with decreased expression of CD9 (P=0.02), and increased expression of CD151 (P=0.02), EGFR (P=0.04), and COX-2 (P=0.003). Histological grade (P=0.0002) and morphology (P=0.03) were also prognostic, whereas smoking and alcohol were not. The optimal combination by backward-variable selection was of histological grade (hazard ratio (HR) 1.64; 95% CI 1.12, 2.40), COX-2 overexpression (HR 1.12; 1.02, 1.24) and CD9 underexpression (HR 0.88; 0.80, 0.97). CD82 and Her-2 demonstrated no prognostic ability.
CONCLUSION: This is the first study of the expression and prognostic potential of the tetraspanins in oral dysplasia. A combination of certain biomarkers with clinical factors appeared to improve the accuracy of determining the risk of malignancy in individuals with oral dysplasia. These findings may also offer potential new therapeutic approaches for this condition.

Yang H, Shen C, Zhang B, et al.
Expression and clinicopathological significance of CD9 in gastrointestinal stromal tumor.
J Korean Med Sci. 2013; 28(10):1443-8 [PubMed] Free Access to Full Article Related Publications
This study investigated the expression and clinicopathological significance of CD9 in gastrointestinal stromal tumor (GIST). Immunohistochemistry staining for CD9 was performed on tumor tissues from 74 GIST patients. The correlation with clinicopathological features, risk classification and prognosis was analyzed. CD9-positive staining comprised 59.5% (44/74) of the GIST patients. The CD9-positive expression rate of the sample was significantly associated with diameter (P = 0.028), mitotic counts (P = 0.035), risk classification (P = 0.018) and three-year recurrence-free survival (RFS) (P < 0.001). Cox proportional hazards regression (HR = 0.352; P = 0.015) showed that CD9 is an independent factor for post-operative RFS. The subgroup analysis showed that CD9 expression in gastric stromal tumor (GST) is significantly associated with diameter (P = 0.031), risk classification (P = 0.023) and three-year RFS (P = 0.001). The Cox proportional hazards regression (HR = 0.104; P = 0.006) also showed that CD9 is an independent factor for RFS of GST. However, CD9 expression does not have a statistically significant correlation with clinicopathological features, risk classification, and prognosis in non-GST. In conclusion, CD9 expression in GIST appears to be associated with the recurrence and/or metastasis of GIST patients, especially in GST, which may indicate the important role of CD9 in the malignant biological behavior and prognosis of GST.

Nagata M, Noman AA, Suzuki K, et al.
ITGA3 and ITGB4 expression biomarkers estimate the risks of locoregional and hematogenous dissemination of oral squamous cell carcinoma.
BMC Cancer. 2013; 13:410 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Molecular biomarkers are essential for monitoring treatment effects, predicting prognosis, and improving survival rate in oral squamous cell carcinoma. This study sought to verify the effectiveness of two integrin gene expression ratios as biomarkers.
METHODS: Gene expression analyses of integrin α3 (ITGA3), integrin β4 (ITGB4), CD9 antigen (CD9), and plakoglobin (JUP) by quantitative real-time PCR were conducted on total RNA from 270 OSCC cases. The logrank test, Cox proportional hazards model, and Kaplan-Meier estimates were performed on the gene expression ratios of ITGA3/CD9 and ITGB4/JUP and on the clinicopathological parameters for major clinical events.
RESULTS: A high rate (around 80%) of lymph node metastasis was found in cases with a high ITGA3/CD9 ratio (high-ITGA3/CD9) and invasive histopathology (YK4). Primary site recurrence (PSR) was associated with high-ITGA3/CD9, T3-4 (TNM class), and positive margin, indicating that PSR is synergistically influenced by treatment failure and biological malignancy. A high ITGB4/JUP ratio (high-ITGB4/JUP) was revealed to be a primary contributor to distant metastasis without the involvement of clinicopathological factors, suggesting intervention of a critical step dependent on the function of the integrin β4 subunit. Kaplan-Meier curves revealed positive margin as a lethal treatment consequence in high-ITGA3/CD9 and YK4 double-positive cases.
CONCLUSION: Two types of metastatic trait were found in OSCC: locoregional dissemination, which was reflected by high-ITGA3/CD9, and distant metastasis through hematogenous dissemination, uniquely distinguished by high-ITGB4/JUP. The clinical significance of the integrin biomarkers implies that biological mechanisms such as cancer cell motility and anchorage-independent survival are vital for OSCC recurrence and metastasis.

Zhang BH, Liu W, Li L, et al.
KAI1/CD82 and MRP1/CD9 serve as markers of infiltration, metastasis, and prognosis in laryngeal squamous cell carcinomas.
Asian Pac J Cancer Prev. 2013; 14(6):3521-6 [PubMed] Related Publications
OBJECTIVE: The current study explored the expression of KAI1/CD82 and MRP1/CD9 and its significance in laryngeal squamous cell carcinoma (LSCC).
METHODS: The expression levels of KAI1/CD82 and MRP1/CD9 in 100 LSCC tissue specimens, as well as in 30 para-LSCC non-carcinomatous tissue specimens randomly taken from the patients, were assessed using the quantitative polymerase chain reaction (Q-PCR) and immunohistochemistry and correlations with pathological parameters of LSCC and their influence on survival function were analyzed.
RESULTS: KAI1/CD82 and MRP1/CD9 showed basically consistent changes in both mRNA and protein expression. Their expression in the 30 LSCC specimens was significantly lower compared with that in the corresponding non-carcinous tissues (P < 0.01 or 0.05), notably correlating with TNM stage, differentiation degree, clinical stage, and lymphatic metastasis (P < 0.01 or 0.05), but not gender, age, and LSCC growth sites (P > 0.05). The median survival of patients with positive KAI1/CD82 and MRP1/CD9 protein expression was longer than that of patients with negative protein expression (P < 0.01 or 0.05). KAI1/CD82 protein expression negatively correlated with MRP1/CD9 protein expression in LSCC (χ(2) = 31.25, P < 0.01).
CONCLUSION: KAI1/CD82 and MRP1/CD9 may jointly participate in the development of LSCC. They may serve as the markers for judging the infiltration, metastasis, and prognosis of LSCC.

Herr MJ, Kotha J, Hagedorn N, et al.
Tetraspanin CD9 promotes the invasive phenotype of human fibrosarcoma cells via upregulation of matrix metalloproteinase-9.
PLoS One. 2013; 8(6):e67766 [PubMed] Free Access to Full Article Related Publications
Tumor cell metastasis, a process which increases the morbidity and mortality of cancer patients, is highly dependent upon matrix metalloproteinase (MMP) production. Small molecule inhibitors of MMPs have proven unsuccessful at reducing tumor cell invasion in vivo. Therefore, finding an alternative approach to regulate MMP is an important endeavor. Tetraspanins, a family of cell surface organizers, play a major role in cell signaling events and have been implicated in regulating metastasis in numerous cancer cell lines. We stably expressed tetraspanin CD9 in an invasive and metastatic human fibrosarcoma cell line (CD9-HT1080) to investigate its role in regulating tumor cell invasiveness. CD9-HT1080 cells displayed a highly invasive phenotype as demonstrated by matrigel invasion assays. Statistically significant increases in MMP-9 production and activity were attributed to CD9 expression and were not due to any changes in other key tetraspanin complex members or MMP regulators. Increased invasion of CD9-HT1080 cells was reversed upon silencing of MMP-9 using a MMP-9 specific siRNA. Furthermore, we determined that the second extracellular loop of CD9 was responsible for the upregulation of MMP-9 production and subsequent cell invasion. We demonstrated for the first time that tetraspanin CD9 controls HT1080 cell invasion via upregulation of an integral member of the MMP family, MMP-9. Collectively, our studies provide mounting evidence that altered expression of CD9 may be a novel approach to regulate tumor cell progression.

Gustafson-Wagner E, Stipp CS
The CD9/CD81 tetraspanin complex and tetraspanin CD151 regulate α3β1 integrin-dependent tumor cell behaviors by overlapping but distinct mechanisms.
PLoS One. 2013; 8(4):e61834 [PubMed] Free Access to Full Article Related Publications
Integrin α3β1 potently promotes cell motility on its ligands, laminin-332 and laminin-511, and this may help to explain why α3β1 has repeatedly been linked to breast carcinoma progression and metastasis. The pro-migratory functions of α3β1 depend strongly on lateral interactions with cell surface tetraspanin proteins. Tetraspanin CD151 interacts directly with the α3 integrin subunit and links α3β1 integrin to other tetraspanins, including CD9 and CD81. Loss of CD151 disrupts α3β1 association with other tetraspanins and impairs α3β1-dependent motility. However, the extent to which tetraspanins other than CD151 are required for specific α3β1 functions is unclear. To begin to clarify which aspects of α3β1 function require which tetraspanins, we created breast carcinoma cells depleted of both CD9 and CD81 by RNA interference. Silencing both of these closely related tetraspanins was required to uncover their contributions to α3β1 function. We then directly compared our CD9/CD81-silenced cells to CD151-silenced cells. Both CD9/CD81-silenced cells and CD151-silenced cells showed delayed α3β1-dependent cell spreading on laminin-332. Surprisingly, however, once fully spread, CD9/CD81-silenced cells, but not CD151-silenced cells, displayed impaired α3β1-dependent directed motility and altered front-rear cell morphology. Also unexpectedly, the CD9/CD81 complex, but not CD151, was required to promote α3β1 association with PKCα in breast carcinoma cells, and a PKC inhibitor mimicked aspects of the CD9/CD81-silenced cell motility defect. Our data reveal overlapping, but surprisingly distinct contributions of specific tetraspanins to α3β1 integrin function. Importantly, some of CD9/CD81's α3β1 regulatory functions may not require CD9/CD81 to be physically linked to α3β1 by CD151.

Chitadze G, Lettau M, Bhat J, et al.
Shedding of endogenous MHC class I-related chain molecules A and B from different human tumor entities: heterogeneous involvement of the "a disintegrin and metalloproteases" 10 and 17.
Int J Cancer. 2013; 133(7):1557-66 [PubMed] Related Publications
The interaction of the MHC class I-related chain molecules A and B (MICA and MICB) with the corresponding natural killer group 2, member D (NKG2D) receptor triggers cytotoxic effector activity of natural killer cells and certain T-cell subsets and provides a costimulatory signal for cytokine production. Thus, the presence of MICA/B on transformed cells contributes to tumor immunosurveillance. Consequently, the proteolytic cleavage of MICA/B is regarded as an important immune escape mechanism of various cancer cells. To investigate the molecular machinery responsible for the shedding of endogenous MICA/B, we analyzed different human tumor entities including mammary, pancreatic and prostate carcinomas. Flow cytometry and enzyme-linked immunosorbent assay (ELISA) revealed that all tested tumor cells constitutively expressed MICA and MICB on the cell surface and also released NKG2D ligands into the supernatant. We demonstrate that the "a disintegrin and metalloproteases" (ADAMs) 10 and 17 are largely responsible for the generation of soluble MICA/B. Pharmacological inhibition of metalloproteases reduced the level of released MICA/B and increased cell surface expression. Studies using RNA interference not only revealed a prominent role of ADAM10 and ADAM17 in NKG2D ligand shedding but also a tumor cell-specific role of ADAM10 and/or ADAM17 in shedding of MICA or MICB. Moreover, we report that in the prostate carcinoma cell line PC-3, MICA was not shed at all but rather was secreted in exosomes. These data indicate that the release of NKG2D ligands from individual tumor entities is by far more complex than suggested in previously reported MICA/B transfection systems.

Kischel P, Bellahcene A, Deux B, et al.
Overexpression of CD9 in human breast cancer cells promotes the development of bone metastases.
Anticancer Res. 2012; 32(12):5211-20 [PubMed] Related Publications
BACKGROUND: Bone is a preferred target for circulating metastatic breast cancer cells. We found that the CD9 protein was up-regulated in the B02 osteotropic cell line, derived from the aggressive parental MDA-MB-231 breast cancer cell line. Here, we investigated the putative relationship between CD9 expression and the osteotropic phenotype.
MATERIALS AND METHODS: Overexpression of CD9 was analyzed by immunoblotting in different cell lines. Immunohistochemistry was used to assess CD9 expression in primary tumors and metastatic lesions. In vivo experiments were conducted in mice using a monoclonal antibody against CD9.
RESULTS: CD9 overexpression was confirmed in osteotropic cells. CD9 was significantly overexpressed in bone metastases versus primary tumors and visceral metastatic lesions. Finally, in vivo experiments showed that an antibody against CD9 delays homing of B02 cells in bone marrow, slowing down bone destruction.
CONCLUSION: Our study reveals a potential implication of CD9 in the formation of bony metastases from breast cancer cells.

Iwasaki T, Takeda Y, Maruyama K, et al.
Deletion of tetraspanin CD9 diminishes lymphangiogenesis in vivo and in vitro.
J Biol Chem. 2013; 288(4):2118-31 [PubMed] Free Access to Full Article Related Publications
Tetraspanins have emerged as key players in malignancy and inflammatory diseases, yet little is known about their roles in angiogenesis, and nothing is known about their involvement in lymphangiogenesis. We found here that tetraspanins are abundantly expressed in human lymphatic endothelial cells (LEC). After intrathoracic tumor implantation, metastasis to lymph nodes was diminished and accompanied by decreased angiogenesis and lymphangiogenesis in tetraspanin CD9-KO mice. Moreover, lymphangiomas induced in CD9-KO mice were less pronounced with decreased lymphangiogenesis compared with those in wild-type mice. Although mouse LEC isolated from CD9-KO mice showed normal adhesion, lymphangiogenesis was markedly impaired in several assays (migration, proliferation, and cable formation) in vitro and in the lymphatic ring assay ex vivo. Consistent with these findings in mouse LEC, knocking down CD9 in human LEC also produced decreased migration, proliferation, and cable formation. Immunoprecipitation analysis demonstrated that deletion of CD9 in LEC diminished formation of functional complexes between VEGF receptor-3 and integrins (α5 and α9). Therefore, knocking down CD9 in LEC attenuated VEGF receptor-3 signaling, as well as downstream signaling such as Erk and p38 upon VEGF-C stimulation. Finally, double deletion of CD9/CD81 in mice caused abnormal development of lymphatic vasculature in the trachea and diaphragm, suggesting that CD9 and a closely related tetraspanin CD81 coordinately play an essential role in physiological lymphangiogenesis. In conclusion, tetraspanin CD9 modulates molecular organization of integrins in LEC, thereby supporting several functions required for lymphangiogenesis.

Amatya VJ, Takeshima Y, Aoe K, et al.
CD9 expression as a favorable prognostic marker for patients with malignant mesothelioma.
Oncol Rep. 2013; 29(1):21-8 [PubMed] Free Access to Full Article Related Publications
CD9 is involved in cell growth, adhesion and motility and its expression is reported to be of prognostic significance in various types of human malignancies. We found increased cell migration in the mesothelioma cell lines MSTO-211H and TUM1 following in vitro shRNA-mediated knockdown of CD9 expression. We investigated CD9 expression in 112 malignant pleural mesotheliomas. CD9 expression was observed in 62 of 71 epithelioid, 13 of 20 biphasic and only 1 of 21 sarcomatoid mesotheliomas. Among the epithelioid mesotheliomas (EMs), CD9 expression was observed in all of the 33 cases with a differentiated type (EM-D) and in 29 of the 38 cases with a less-differentiated type (EM-LD). Patients with CD9 expression showed higher 1- and 2-year survival rates (63 and 25%) compared to the patients without CD9 expression (39 and 11%). Univariate analysis revealed that patients with CD9 expression demonstrated a more favorable survival (P=0.0025) along with other clinicopathological factors, including age younger than 60 years, IMIG stage I-II, epithelioid histology, EM-D and patients who underwent extrapleural pneumonectomy or received chemotherapy. Multivariate analysis identified CD9 expression as an independent prognostic factor with a hazard ratio (HR) of 1.99 in the analysis of all mesotheliomas (P=0.0261) and an HR of 2.60 in the analysis of EMs (P=0.0376). CD9 expression is an independent favorable prognostic marker of malignant mesothelioma.

Chiba M, Kimura M, Asari S
Exosomes secreted from human colorectal cancer cell lines contain mRNAs, microRNAs and natural antisense RNAs, that can transfer into the human hepatoma HepG2 and lung cancer A549 cell lines.
Oncol Rep. 2012; 28(5):1551-8 [PubMed] Free Access to Full Article Related Publications
Exosomes are microvesicles that are released from various cells into the extracellular space. It has been reported that the components within exosomes vary according to the type of secreted cell. In the present study, we investigated the tetraspanin family proteins CD63, CD9 and CD81 as useful collection markers of exosomes derived from the three colorectal cancer (CRC) cell lines HCT-15, SW480 and WiDr. In addition, we aimed to detect the mRNAs, microRNAs and natural antisense RNAs within the exosomes secreted from the three CRC cell lines. Furthermore, we examined whether exosomes containing their RNAs were transferred into the hepatoma cell line HepG2 and lung cancer cell line A549. CD81 was detected in exosomes secreted from the three CRC cell lines. This result indicates that CD81 can be a collection marker of exosomes derived from the three CRC cell lines. When the RNA species within exosomes derived from the three CRC cell lines were examined, the mRNAs of housekeeping genes such as ACTB and GAPDH, the microRNAs such as miR-21, miR-192 and miR-221, and the natural antisense RNAs of LRRC24, MDM2 and CDKN1A genes, were detected. We discovered their natural antisense RNAs within exosomes for the first time in the present study. Furthermore, PKH67-labeled exosomes derived from the CRC cell lines were taken up into HepG2 and A549 cells. These findings indicate that the intracellular RNAs enclosed within exosomes are secreted to the outside, and exosomes derived from the CRC cell lines are transferred into HepG2 and A549 cells. In conclusion, we reveal that exosomes derived from the CRC cell lines contain mRNAs, microRNAs and natural antisense RNAs, and can be delivered into HepG2 and A549 cells. These findings indicate that exosomal RNAs can shuttle between cells, and may be involved in the regulation of gene expression in recipient cells.

Atanackovic D, Hildebrandt Y, Templin J, et al.
Role of interleukin 16 in multiple myeloma.
J Natl Cancer Inst. 2012; 104(13):1005-20 [PubMed] Related Publications
BACKGROUND: Multiple myeloma is a malignancy characterized by the expansion of a plasma cell clone that localizes to the human bone marrow. Myeloma cells and bone marrow stromal cells produce soluble factors that promote the survival and progression of multiple myeloma. Interleukin 16 (IL-16) is involved in regulating the migration and proliferation of normal leukocytes. However, the role of IL-16 in human cancers, including multiple myeloma, is unclear.
METHODS: We investigated IL-16 expression in cell lines (n = 10) and in the bone marrow of myeloma patients (n = 62) and healthy bone marrow donors (n = 12) by quantitative reverse transcription-polymerase chain reaction, immunoblot analysis, enzyme-linked immunosorbent assay, flow cytometry, and immunohistochemistry. Transfection of two human multiple myeloma cell lines with small interfering RNAs was used to examine the effect of IL-16 gene silencing on apoptosis by flow cytometry, on proliferation by bromodeoxyuridine incorporation, and on colony formation. Protein neutralization assays were performed by treating multiple myeloma cells with a monoclonal antibody against the carboxyl-terminal fragment of IL-16. All statistical tests were two-sided.
RESULTS: IL-16 was strongly overexpressed in the bone marrow of myeloma patients compared with healthy donors. Myeloma cell lines as well as primary tumor cells from myeloma patients constitutively expressed IL-16 and its receptors CD4 and/or CD9 and spontaneously secreted soluble IL-16. Silencing of IL-16 reduced the proliferative activity of myeloma cells by approximately 80% compared with untreated cells (mean relative proliferative activity IL-16 siRNA vs untransfected cells, EJM cells: 20.1%, 95% confidence interval [CI] = 14.3% to 26.0%, P = .03; KMS-12-BM cells: 22.8%, 95% CI = 5.5% to 40.0%, P = .04), and addition of a recombinant carboxyl-terminal IL-16 peptide reversed that effect. A monoclonal antibody directed against IL-16 or its receptors had a comparably strong growth-inhibiting effect on the tumor cells.
CONCLUSIONS: IL-16 is an important growth-promoting factor in multiple myeloma and a candidate for novel diagnostic, prognostic, and therapeutic applications for this incurable human malignancy.

Zou Q, Xiong L, Yang Z, et al.
Expression levels of HMGA2 and CD9 and its clinicopathological significances in the benign and malignant lesions of the gallbladder.
World J Surg Oncol. 2012; 10:92 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: The objective of this study was to investigate CD9 and HMGA2 expression and its clinicopathological significance in benign and malignant lesion tissues of the gallbladder.
METHODS: The resected specimens of 108 cases of gallbladder adenocarcinoma, 46 cases of adjacent tissue, 15 cases of polyps and 35 cases of chronic cholecystitis were made into conventional paraffin-embedded sections, using the method of EnVision immunohistochemistry to stain HMGA2 and CD9.
RESULTS: HMGA2 expression of gallbladder adenocarcinoma was significantly higher than that of adenocarcinoma adjacent tissues (= 16.13, P <0.01), polyps (= 8.19, P <0.01) and chronic cholecystitis (= 21.41, P <0.01); but CD9 expression was the opposite (P <0.05 or P <0.01). The positive rate of HMGA2 expression from the cases that had well-differentiated adenocarcinoma, with the largest tumor diameter <2 cm, and without lymph node metastasis, and that did not invade the surrounding tissue was significantly lower than that of HMGA2 expression from the cases that had poorly differentiated adenocarcinoma, with the largest tumor diameter ≥2 cm, lymph node metastasis, and that invaded the surrounding tissues (P <0.05 or P <0.01). The positive rate of CD9 expression from the cases that had well-differentiated adenocarcinoma, with the largest tumor diameter <2 cm, and without lymph node metastasis, and that did not invade the surrounding tissue was significantly higher than that of CD9 expression from the cases that had poorly differentiated adenocarcinoma, with the largest tumor diameter ≥2 cm, lymph node metastasis, and which invaded the surrounding tissues (P <0.05 or P <0.01). The Kaplan-Meier survival analysis showed that after surgery, the survival period of HMGA2 expression-positive cases was significantly lower than that of HMGA2 expression-negative cases (P = 0.020), but the survival period of CD9 expression-positive cases was significantly higher than that of cases with CD9 expression-negative (P = 0.019). Cox multivariate regression analysis showed that the HMGA2 positive expression and/or CD9 negative expression was an important indicator reflecting the poor prognosis of gallbladder cancer.
CONCLUSION: The expression of HMGA2 and/or CD9 might be closely related to the carcinogenesis, clinical biological behaviors and prognosis of gallbladder adenocarcinoma.

Zhang S, Kodys K, Babcock GJ, Szabo G
CD81/CD9 tetraspanins aid plasmacytoid dendritic cells in recognition of hepatitis C virus-infected cells and induction of interferon-alpha.
Hepatology. 2013; 58(3):940-9 [PubMed] Related Publications
UNLABELLED: Recognition of hepatitis C virus (HCV)-infected hepatocyes and interferon (IFN) induction are critical in antiviral immune response. We hypothesized that cell-cell contact between plasmacytoid dendritic cells (pDCs) and HCV-infected cells was required for IFN-α induction through the involvement of cell-surface molecules. Coculture of human peripheral blood mononuclear cells (PBMCs) with genotype 1a full-length (FL) HCV genomic replicon cells or genotype 2a Japanese fulminant hepatitis type 1 (JFH-1) virus-infected hepatoma cells (JFH-1), and not with uninfected hepatoma cells (Huh7.5), induced IFN-α production. Depletion of pDCs from PBMCs attenuated IFN-α release, and purified pDCs produced high levels of IFN-α after coculture with FL replicons or JFH-1-infected cells. IFN-α induction by HCV-containing hepatoma cells required viral replication, direct cell-cell contact with pDCs, and receptor-mediated endocytosis. We determined that the tetraspanin proteins, CD81 and CD9, and not other HCV entry receptors, were required for IFN-α induction in pDCs by HCV-infected hepatoma cells. Disruption of cholesterol-rich membrane microdomains, the localization site of CD81, or inhibition of the CD81 downstream molecule, Rac GTPase, inhibited IFN-α production. IFN-α induction involved HCV RNA and Toll-like receptor (TLR) 7. IFN-α production by HCV-infected hepatoma cells was decreased in pDCs from HCV-infected patients, compared to healthy controls. We found that preexposure of healthy PBMCs to HCV viral particles attenuated IFN-α induction by HCV-infected hepatoma cells or TLR ligands, and this inhibitory effect could be prevented by an anti-HCV envelope glycoprotein 2-blocking antibody.
CONCLUSION: Our novel data show that recognition of HCV-infected hepatoma cells by pDCs involves CD81- and CD9-associated membrane microdomains and induces potent IFN-α production.

Pellinen T, Rantala JK, Arjonen A, et al.
A functional genetic screen reveals new regulators of β1-integrin activity.
J Cell Sci. 2012; 125(Pt 3):649-61 [PubMed] Related Publications
β1 integrins constitute a large group of widely distributed adhesion receptors, which regulate the ability of cells to interact with their surroundings. This regulation of the expression and activity of integrins is crucial for tissue homeostasis and development and contributes to inflammation and cancer. We report an RNA interference screen to uncover genes involved in the regulation of β1-integrin activity using cell spot microarray technology in cancer cell lines. Altogether, ten cancer and two normal cell lines were used to identify regulators of β1 integrin activity. Cell biological analysis of the identified β1-integrin regulatory genes revealed that modulation of integrin activity can influence cell invasion in a three-dimensional matrix. We demonstrate with loss-of-function and rescue experiments that CD9 activates and MMP8 inactivates β1 integrins and that both proteins associate with β1 integrins in cells. Furthermore, CD9 and MMP8 regulate cancer cell extravasation in vivo. Our discovery of new regulators of β1-integrin activity highlight the complexity of integrin activity regulation and provide a set of new genes involved in regulation of integrin function.

Blumenthal A, Giebel J, Ummanni R, et al.
Morphology and migration of podocytes are affected by CD151 levels.
Am J Physiol Renal Physiol. 2012; 302(10):F1265-77 [PubMed] Related Publications
CD151, a member of the tetraspanin family of membrane proteins, is crucially involved in the formation of the glomerular filtration barrier in humans and mice. However, the role of CD151 in podocytes has not been investigated so far. In the present study, we utilized a conditionally immortalized mouse podocyte cell line to characterize CD151 in podocytes and to examine the consequences of manipulating CD151 expression levels. Mouse podocytes endogenously express CD151 as determined by RT-PCR and Western blotting. GFP-CD151 fusion protein localized to the cell membrane, to cell protrusions and cell-cell contacts, colocalizing with actin, β(1)-integrin, zonula occludens-1, and CD9. The expression of GFP-CD151 in cultured podocytes resulted in a marked increase in the presence of thin arborized protrusions (TAPs). TAPs are distinct from filopodia by increased length, protein composition, branched morphology, and slower dynamics. Furthermore, the migration rate of pEGFP-CD151-transfected podocytes was reduced in a wound assay. Fluorescence recovery after photo bleaching measurements revealed a half-time of 3 s for GFP-CD151 consistent with a high mobility of CD151 in the membrane and cytosol. CD151 knockdown in podocytes reduced β(1)-integrin expression and podocyte cell area, indicating diminished adherence and/or spreading. Our results indicate that CD151 importantly modulates podocyte function.

Chapman MH, Tidswell R, Dooley JS, et al.
Whole genome RNA expression profiling of endoscopic biliary brushings provides data suitable for biomarker discovery in cholangiocarcinoma.
J Hepatol. 2012; 56(4):877-85 [PubMed] Free Access to Full Article Related Publications
BACKGROUND & AIMS: Molecular analyses of biliary brushings using microarray and qPCR have the potential to provide valuable information on the biology of biliary diseases. Microarray analysis of biliary strictures has rarely been applied to endoscopic biliary brushings.
METHODS: Biliary brushings were obtained from patients with benign and malignant biliary disease at the time of ERCP. Microarray analysis of mRNA isolated using brushings from 10 patients was validated for a selection of genes by qPCR using the same source mRNA and a second fresh set of nine biliary brushings as well as surgical resection tissue. Cultured cholangiocytes were used to assess the impact of bile or X-ray contrast solution on RNA quality.
RESULTS: RNA was of variable quantity (100-1500 ng) and poor quality (Agilent RNA Integrity Number (RIN)<5, estimated to be fragments 100 to 600 base pairs long). Reliable qPCR results required primer pairs designed to produce amplicons <130 bp. Differential gene expression by microarray analysis identified 1140 up-regulated genes and 1001 down-regulated genes between benign and malignant biliary strictures. The trends in a selection of 45 up-regulated genes, including various HOX genes, collagens, PVT1, MUC4, MUC5AC, and LEF1, were validated by qPCR using RNA from biliary strictures with a moderate to strong correlation coefficient between microarray and qPCR (r=0.41 to r=0.57). Immunohistochemistry of surgical resection tissues (n=23) showed elevated CD9, SERPINA3, and PNMA2 protein expression in cancer samples.
CONCLUSIONS: RNA isolated from biliary brushings is suitable for molecular analysis of biliary diseases using qPCR and microarray.

Hwang JR, Jo K, Lee Y, et al.
Upregulation of CD9 in ovarian cancer is related to the induction of TNF-α gene expression and constitutive NF-κB activation.
Carcinogenesis. 2012; 33(1):77-83 [PubMed] Related Publications
Ovarian cancer is a gynecological cancer with a high death rate. We utilized global gene expression profiles of ovarian carcinomas obtained by complementary DNA (cDNA) microarray to identify ovarian cancer-specific proteins. CD9 was upregulated in ovarian carcinomas, and overexpression of the CD9 protein was detected in ovarian carcinomas by immunohistochemistry. CD9 was also overexpressed in several cancer cell lines, including ovarian cancer cells. In order to elucidate the biological significance of highly expressed CD9 in cancer cells, functional studies of CD9 were performed by ectopic expression, knockdown of CD9 using small interfering RNA (siRNA) and blockage of CD9 activity using the CD9-specific monoclonal antibody ALB6. Ectopic CD9 induced cell survival. In order to identify signaling pathways related to CD9, the gene expressions of CD9/SKOV3 cells were analyzed by cDNA microarray. Among the many upregulated genes, tumor necrosis factor (TNF)-α was induced in CD9/SKOV3 cells. The effect of overexpressed CD9 on the downstream signaling events of TNF-α was further investigated. In CD9/SKOV3 cells, the nuclear factor-kappaB (NF-κB)-signaling pathway was constitutively activated. Knockdown of CD9 by siRNA and blockage of CD9 activity by ALB6 in ovarian cancer cells demonstrated that constitutive activation of NF-κB is CD9 dependent and that CD9 is involved in anti-apoptosis. A CD9 functional study was performed in an ovarian cancer-xenograft mouse by injecting ALB6 into the peritoneum. ALB6 resulted in reduced tumor weight compared with that of control IgG(1). Collectively, these results demonstrate that CD9 functions as an oncogene and represents a target for the development of cancer-specific therapeutics.

Yamazaki H, Xu CW, Naito M, et al.
Regulation of cancer stem cell properties by CD9 in human B-acute lymphoblastic leukemia.
Biochem Biophys Res Commun. 2011; 409(1):14-21 [PubMed] Related Publications
Although the prognosis of acute lymphoblastic leukemia (ALL) has improved considerably in recent years, some of the cases still exhibit therapy-resistant. We have previously reported that CD9 was expressed heterogeneously in B-ALL cell lines and CD9(+) cells exhibited an asymmetric cell division with greater tumorigenic potential than CD9(-) cells. CD9(+) cells were also serially transplantable in immunodeficient mice, indicating that CD9(+) cell possess self-renewal capacity. In the current study, we performed more detailed analysis of CD9 function for the cancer stem cell (CSC) properties. In patient sample, CD9 was expressed in the most cases of B-ALL cells with significant correlation of CD34-expression. Gene expression analysis revealed that leukemogenic fusion proteins and Src family proteins were significantly regulated in the CD9(+) population. Moreover, CD9(+) cells exhibited drug-resistance, but proliferation of bulk cells was inhibited by anti-CD9 monoclonal antibody. Knockdown of CD9 remarkably reduced the leukemogenic potential. Furthermore, gene ablation of CD9 affected the expression and tyrosine-phosphorylation of Src family proteins and reduced the expression of histone-deubiquitinase USP22. Taken together, our results suggest that CD9 links to several signaling pathways and epigenetic modification for regulating the CSC properties of B-ALL.

Chen Z, Gu S, Trojanowicz B, et al.
Down-regulation of TM4SF is associated with the metastatic potential of gastric carcinoma TM4SF members in gastric carcinoma.
World J Surg Oncol. 2011; 9:43 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: The aim of this study was to clarify the clinical significance of TM4SF members CD9, CD63 and CD82 in human gastric carcinoma.
METHODS: By employing RT-PCR and immunohistochemistry, we studied the expression of CD9, CD63 and CD82 in 49 paired tissue specimens of normal gastric mucosa and carcinoma. All tissues were obtained from patients who underwent curative surgery.
RESULTS: All normal gastric epithelium and gastric ulcer tissues strongly expressed transcripts and proteins of CD9, CD63 and CD82 as compared with corresponding controls. We found a significant correlation between CD63 mRNA level and different pM statuses (P = 0.036). Carcinomas in M0 stage revealed a stronger expression of CD63 than carcinomas in M1 stage. Expression of CD9 protein was found significantly stronger in pN0, pM0 than in advanced pN stages (P = 0.03), pM1 (P = 0.013), respectively. We found the relationship between CD63 expression, gender (p = 0.09) and nodal status (p = 0.028), respectively. Additionally, advanced and metastasized tumor tissues revealed significantly down-regulated CD82 protein expression (p = 0.033 and p = 0, respectively), which correlated with the tumor pTNM stage (p = 0.001).
CONCLUSION: The reduction of CD9, CD63 and CD82 expression are indicators for the metastatic potential of gastric carcinoma cells. Unlike their expression in other tumor types, the constitutive expression of CD63 may indicate that this factor does play a direct role in human gastric carcinogenesis.

Powner D, Kopp PM, Monkley SJ, et al.
Tetraspanin CD9 in cell migration.
Biochem Soc Trans. 2011; 39(2):563-7 [PubMed] Related Publications
Tetraspanin CD9 is associated with integrin adhesion receptors and it was reported that CD9 regulates integrin-dependent cell migration and invasion. Pro- and anti-migratory effects of CD9 have been linked to adhesion-dependent signalling pathways, including phosphorylation of FAK (focal adhesion kinase) and activation of phosphoinositide 3-kinase, p38 MAPK (mitogen-activated protein kinase) and JNK (c-Jun N-terminal kinase). In the present paper, we describe a novel mechanism whereby CD9 specifically controls localization of talin1, one of the critical regulators of integrin activation, to focal adhesions: CD9-deficiency leads to impaired localization of talin1 to focal adhesions and correlates with increased motility of breast cancer cells.

Wang HX, Li Q, Sharma C, et al.
Tetraspanin protein contributions to cancer.
Biochem Soc Trans. 2011; 39(2):547-52 [PubMed] Related Publications
Among the 33 human tetraspanin proteins, CD151, CD9 and Tspan12 play particularly important roles in cancer. Tetraspanin CD151, in partnership with integrins α6β1 and α6β4, modulates tumour cell growth, invasion, migration, metastasis, signalling and drug sensitivity. Tetraspanin CD9 has suppressor functions in multiple tumour cell types. Major CD9 partner proteins, such as EWI-2 and EWI-F, may modulate these tumour-suppressor functions. Tetraspanin Tspan12 mutations are linked to a human disease called familial exudative vitreoretinopathy. In addition, as a regulator of the metalloprotease ADAM10 (a disintegrin and metalloprotease 10) maturation and function, Tspan12 probably contributes to the pro-tumorigenic functions of ADAM10.

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