Gene Summary

Gene:CD9; CD9 molecule
Aliases: MIC3, MRP-1, BTCC-1, DRAP-27, TSPAN29, TSPAN-29
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:VEGA, OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:CD9 antigen
Source:NCBIAccessed: 10 March, 2017


What does this gene/protein do?
Show (19)
Pathways:What pathways are this gene/protein implicaed in?
Show (1)

Cancer Overview

Research Indicators

Publications Per Year (1992-2017)
Graph generated 10 March 2017 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.

Tag cloud generated 10 March, 2017 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)

Lewitowicz P, Bernaczyk P, Horecka-Lewitowicz A, et al.
Ancient cardiac myxomas - another point of view in the light of tetraspanins.
Pol J Pathol. 2016; 67(1):69-77 [PubMed] Related Publications
Myxomas are the most common non-invasive but life-threatening cardiac neoplasms due to obstruction of heart chambers and risk of embolism in a manner resembling thromboembolism as well. They can occasionally disseminate via their detached fragments into the bloodstream to seed and grow as secondary still benign tumors. In this study we evaluated morphological and clinical aspects of 14 ancient, degenerated left or right-sided cardiac atrial myxomas with expression of CD9 and CD63, which are found to contribute to platelet activation, aggregation and, as a result, intratumoral thrombosis or fragmentation. The appearance of tumors varied from sessile to polypoid revealing that a higher rate of endocardial thrombosis was associated with sessile compared to polypoid myxomas and left-sided tumors compared to right-sided ones in our study. In the general aspect of ancient calcifications, amorphous calcification with intra-tumor thrombosis was noted more frequently in sessile tumors, while well-formed osseous metaplasia was usually a feature of polypoid tumors. In our material osseous metaplasia did not coexist with massive thrombosis and was found in polypoid, pedunculated myxomas. Most importantly, CD9 overexpression was recorded in every studied myxoma and CD63 gave a weak reaction in myxoma cells.

Garner JM, Herr MJ, Hodges KB, Jennings LK
The utility of tetraspanin CD9 as a biomarker for metastatic clear cell renal cell carcinoma.
Biochem Biophys Res Commun. 2016; 471(1):21-5 [PubMed] Related Publications
The use of tetraspanin CD9 as a biomarker for renal cell carcinomas (RCC) has been explored with minor conclusions. Identification of a biomarker that not only distinguishes between the different types of renal cell carcinomas, but also predicts the metastatic potential of these tumors would significantly advance diagnosis and prognosis of kidney cancers. We utilized established cell lines to better understand the contribution of CD9 to the metastatic potential of clear cell renal cell carcinomas, and then applied our findings to the TCGA database and immunohistochemical analysis of human samples based on tumor grading to determine the utility of CD9 as a biomarker for RCC. Clear cell renal cell carcinoma (ccRCC) cell expression of tetraspanin CD9 was compared to normal kidney cells and found to be elevated. Upon knockdown of CD9, ccRCC cells obtained a more metastatic phenotype. We found E-cadherin expression to be repressed and the endothelial to mesenchymal transition markers Snail, Twist1, and Zeb1 to be elevated upon CD9 knockdown. Upon observing these gene expression changes in the TCGA database and in 10 cases, we found that CD9 and E-cadherin expression was lowered in higher grade ccRCC tumors. There was a significant correlation between CD9 and either E-cadherin, Snail, or Zeb1 in these tumors. Collectively, using tetraspanin CD9 in tandem with E-cadherin as a biomarker in renal cell carcinoma will help to not only distinguish between types, but also predict the metastatic potential of RCC.

Podergajs N, Motaln H, Rajčević U, et al.
Transmembrane protein CD9 is glioblastoma biomarker, relevant for maintenance of glioblastoma stem cells.
Oncotarget. 2016; 7(1):593-609 [PubMed] Free Access to Full Article Related Publications
The cancer stem cell model suggests that glioblastomas contain a subpopulation of stem-like tumor cells that reproduce themselves to sustain tumor growth. Targeting these cells thus represents a novel treatment strategy and therefore more specific markers that characterize glioblastoma stem cells need to be identified. In the present study, we performed transcriptomic analysis of glioblastoma tissues compared to normal brain tissues revealing sensible up-regulation of CD9 gene. CD9 encodes the transmembrane protein tetraspanin which is involved in tumor cell invasion, apoptosis and resistance to chemotherapy. Using the public REMBRANDT database for brain tumors, we confirmed the prognostic value of CD9, whereby a more than two fold up-regulation correlates with shorter patient survival. We validated CD9 gene and protein expression showing selective up-regulation in glioblastoma stem cells isolated from primary biopsies and in primary organotypic glioblastoma spheroids as well as in U87-MG and U373 glioblastoma cell lines. In contrast, no or low CD9 gene expression was observed in normal human astrocytes, normal brain tissue and neural stem cells. CD9 silencing in three CD133+ glioblastoma cell lines (NCH644, NCH421k and NCH660h) led to decreased cell proliferation, survival, invasion, and self-renewal ability, and altered expression of the stem-cell markers CD133, nestin and SOX2. Moreover, CD9-silenced glioblastoma stem cells showed altered activation patterns of the Akt, MapK and Stat3 signaling transducers. Orthotopic xenotransplantation of CD9-silenced glioblastoma stem cells into nude rats promoted prolonged survival. Therefore, CD9 should be further evaluated as a target for glioblastoma treatment.

Arnaud MP, Vallée A, Robert G, et al.
CD9, a key actor in the dissemination of lymphoblastic leukemia, modulating CXCR4-mediated migration via RAC1 signaling.
Blood. 2015; 126(15):1802-12 [PubMed] Related Publications
CD9, a member of the tetraspanin family, has been implicated in hematopoietic and leukemic stem cell homing. We investigated the role of CD9 in the dissemination of B acute lymphoblastic leukemia (B-ALL) cells, by stably downregulating CD9 in REH and NALM6 cells. CD9 expression was associated with higher levels of REH cell adhesion to fibronectin and C-X-C motif chemokine receptor 4 (CXCR4)-mediated migration. Death occurred later in NOD/SCID mice receiving REH cells depleted of CD9 for transplantation than in mice receiving control cells. After C-X-C motif chemokine ligand 12 (CXCL12) stimulation, CD9 promoted the formation of long cytoplasmic actin-rich protrusions. We demonstrated that CD9 enhanced RAC1 activation, in both REH cells and blasts from patients. Conversely, the overexpression of a competing CD9 C-terminal tail peptide in REH cytoplasm decreased RAC1 activation and cytoplasmic extension formation in response to CXCL12. Finally, the inhibition of RAC1 activation decreased migration in vitro, and the depletion of RAC1 protein from transplanted REH cells increased mouse survival. Furthermore, a testis-conditioned medium induced the migration of REH and NALM6 cells, and this migration was impeded by an anti-CD9 antibody. The level of CD9 expression also influenced the homing of these cells in mouse testes. These findings demonstrate, for the first time, that CD9 plays a key role in the CXCR4-mediated migration and engraftment of B-ALL cells in the bone marrow or testis, through RAC1 activation.

Jeibmann A, Halama K, Witte HT, et al.
Involvement of CD9 and PDGFR in migration is evolutionarily conserved from Drosophila glia to human glioma.
J Neurooncol. 2015; 124(3):373-83 [PubMed] Related Publications
Platelet-derived growth factor receptor (PDGFR) signaling plays an important role in the biology of malignant gliomas. To investigate mechanisms modulating PDGFR signaling in gliomagenesis, we employed a Drosophila glioma model and genetic screen to identify genes interacting with Pvr, the fly homolog of PDGFRs. Glial expression of constitutively activated Pvr (λPvr) led to glial over migration and lethality at late larval stage. Among 3316 dsRNA strains crossed against the tester strain, 128 genes shifted lethality to pupal stage, including tetraspanin 2A (tsp2A). In a second step knockdown of all Drosophila tetraspanins was investigated. Of all tetraspanin dsRNA strains only knockdown of tsp2A partially rescued the Pvr-induced phenotype. Human CD9 (TSPAN29/MRP-1), a close homolog of tsp2A, was found to be expressed in glioma cell lines A172 and U343MG as well as in the majority of glioblastoma samples (16/22, 73 %). Furthermore, in situ proximity ligation assay revealed close association of CD9 with PDGFR α and β. In U343MG cells, knockdown of CD9 blocked PDGF-BB stimulated migration. In conclusion, modulation of PDGFR signaling by CD9 is evolutionarily conserved from Drosophila glia to human glioma and plays a role in glia migration.

Duijvesz D, Versluis CY, van der Fels CA, et al.
Immuno-based detection of extracellular vesicles in urine as diagnostic marker for prostate cancer.
Int J Cancer. 2015; 137(12):2869-78 [PubMed] Related Publications
Extracellular vesicles (including the subclass exosomes) secreted by cells contain specific proteins and RNA that could be of interest in determining new markers. Isolation/characterization of PCa-derived exosomes from bodily fluids enables us to discover new markers for this disease. Unfortunately, isolation with current techniques (ultracentrifugation) is labor intensive and other techniques are still under development. The goal of our study was to develop a highly sensitive time-resolved fluorescence immunoassay (TR-FIA) for capture/detection of PCa-derived exosomes. In our assay, biotinylated capture antibodies against human CD9 or CD63 were incubated on streptavidin-coated wells. After application of exosomes, Europium-labeled detection antibodies (CD9 or CD63) were added. Cell medium from 37 cell lines was taken to validate this TR-FIA. Urine was collected (after digital rectal exam) from patients with PCa (n = 67), men without PCa (n = 76). As a control, urine was collected from men after radical prostatectomy (n = 13), women (n = 16) and patients with prostate cancer without digital rectal exam (n = 16). Signal intensities were corrected for urinary PSA and creatinine. This TR-FIA can measure purified exosomes with high sensitivity and minimal background signals. Exosomes can be measured in medium from 37 cell lines and in urine. DRE resulted in a pronounced increase in CD63 signals. After DRE and correction for urinary PSA, CD9 and CD63 were significantly higher in men with PCa. This TR-FIA enabled us to measure exosomes with high sensitivity directly from urine and cell medium. This TR-FIA forms the basis for testing different antibodies directed against exosome membrane markers to generate disease-specific detection assays.

Huan J, Gao Y, Xu J, et al.
Overexpression of CD9 correlates with tumor stage and lymph node metastasis in esophageal squamous cell carcinoma.
Int J Clin Exp Pathol. 2015; 8(3):3054-61 [PubMed] Free Access to Full Article Related Publications
OBJECTIVE: Esophageal squamous cell carcinoma (ESCC) is one of the leading causes of cancer deaths worldwide. CD9 has been reported to play a critical role in cell motility, growth and metastasis of multiple cancers. The present study investigated the clinicopathological features of CD9, and its biological characteristics in ESCC.
METHODS: Fifteen normal esophageal tissue specimens, fifty-three ESCC adjacent tissues and one hundred and four ESCC tissues were included in this study. Using immunohistochemistry (IHC), the expression levels of CD9 were evaluated among different samples. And its clinicopathological parameters and its prognostic factors were analyzed. Western blotting was used to measure CD9 expression and colony formation was performed to determine the effect of CD9 on cell growth in ESCC TE-1 cells.
RESULTS: Compared with normal esophageal tissues and tumor adjacent tissues, CD9 expression level is significantly higher in ESCC tissues. CD9 expression correlated with tumor stage (P=0.022) and lymph node metastasis (P=0.019) in ESCC patients. Furthermore, the small interfering RNA-mediated silencing of CD9 expression in TE-1 cells resulted in increased proliferation as evidenced by increased colony number and colony size.
CONCLUSION: CD9 expression is upregulated in ESCC tissues and its expression is correlated with tumor stage and lymph node metastasis in ESCC patients. CD9 suppresses the proliferation of TE-1 cells. CD9 may present a potential in tumor progression in ESCC.

Tang M, Yin G, Wang F, et al.
Downregulation of CD9 promotes pancreatic cancer growth and metastasis through upregulation of epidermal growth factor on the cell surface.
Oncol Rep. 2015; 34(1):350-8 [PubMed] Related Publications
The expression of CD9 has been shown to be inversely associated with pancreatic cancer metastasis but the underlying mechanism remains incompletely understood. Using the two closely associated pancreatic cancer cell lines, PaTu-8898s and PaTu-8898t, which are metastatic and non-metastatic, respectively, we showed that the PaTu-8988s cells expressed a lower level of CD9 but had higher proliferation and migration rates than the PaTu-8898t cells. An inverse correlation between CD9 expression and the cell surface level of epidermal growth factor receptor (EGFR) was observed in both cell lines. In the PaTu-8898s cells, overexpression of CD9 decreased the cell surface expression of EGFR, associated with increased expression of dynamin-2, whereas in the PaTu-8898t cells, knockdown of CD9 with RNA interference (RNAi) increased the cell surface expression of EGFR, associated with decreased expression of dynamin-2. However, the total EGFR level did not change by manipulation of CD9 expression, suggesting that CD9 plays a role in EGFR endocytosis. Furthermore, in the PaTu-8898ts cells, CD9 overexpression decreased the cell proliferation and migration, which were reversed by EGFR overexpression, whereas in the PaTu-8898t cells, CD9 knockdown enhanced the cell proliferation and migration which were blocked by EGFR RNAi both in vitro and in vivo. Thus, in pancreatic cancer cells, downregulation of CD9 may play a role in cancer growth and metastasis through, at least in part, enhancing cell surface expression of EGFR.

Murayama Y, Oritani K, Tsutsui S
Novel CD9-targeted therapies in gastric cancer.
World J Gastroenterol. 2015; 21(11):3206-13 [PubMed] Free Access to Full Article Related Publications
There are 33 human tetraspanin proteins, emerging as key players in malignancy, the immune system, fertilization, cellular signaling, adhesion, morphology, motility, proliferation, and tumor invasion. CD9, a member of the tetraspanin family, associates with and influences a variety of cell-surface molecules. Through these interactions, CD9 modifies multiple cellular events, including adhesion, migration, proliferation, and survival. CD9 is therefore considered to play a role in several stages during cancer development. Reduced CD9 expression is generally related to venous vessel invasion and metastasis as well as poor prognosis. We found that treatment of mice bearing human gastric cancer cells with anti-CD9 antibody successfully inhibited tumor progression via antiproliferative, proapoptotic, and antiangiogenic effects, strongly indicating that CD9 is a possible therapeutic target in patients with gastric cancer. Here, we describe the possibility of CD9 manipulation as a novel therapeutic strategy in gastric cancer, which still shows poor prognosis.

Rappa G, Green TM, Karbanová J, et al.
Tetraspanin CD9 determines invasiveness and tumorigenicity of human breast cancer cells.
Oncotarget. 2015; 6(10):7970-91 [PubMed] Free Access to Full Article Related Publications
Interaction of breast cancer cells (BCCs) with stromal components is critical for tumor growth and metastasis. Here, we assessed the role of CD9 in adhesion, migration and invasiveness of BCCs. We used co-cultures of BCCs and bone marrow-derived multipotent mesenchymal stromal cells (MSCs), and analyzed their behavior and morphology by dynamic total internal reflection fluorescence, confocal and scanning electron microscopy. 83, 16 and 10% of contacts between MDA-MB-231 (MDA), MA-11 or MCF-7 cells and MSCs, respectively, resulted in MSC invasion. MDA cells developed long magnupodia, lamellipodia and dorsal microvilli, whereas long microvilli emerged from MA-11 cells. MCF-7 cells displayed large dorsal ruffles. CD9 knockdown and antibody blockage in MDA cells inhibited MSC invasion by 95 and 70%, respectively, suggesting that CD9 is required for this process. Remarkably, CD9-deficient MDA cells displayed significant alteration of their plasma membrane, harboring numerous peripheral and dorsal membrane ruffles instead of intact magnupodium/lamellipodium and microvillus, respectively. Such modification might explain the delayed adhesion, and hence MSC invasion. In agreement with this hypothesis, CD9-knockdown suppressed the metastatic capacity of MDA cells in mouse xenografts. Our data indicate that CD9 is implicated in BCC invasiveness and metastases by cellular mechanisms that involve specific CD9+ plasma membrane protrusions of BCCs.

Wang GP, Han XF
CD9 modulates proliferation of human glioblastoma cells via epidermal growth factor receptor signaling.
Mol Med Rep. 2015; 12(1):1381-6 [PubMed] Related Publications
The tetraspanin CD9 has previously been shown to be involved in various cellular activities, including proliferation and migration. In addition, CD9 has been shown to be associated with epidermal growth factor receptor (EGFR). A common characteristic of glioblastoma multiforme histology is EGFR amplification, which affects signal transduction processes. The anti-proliferative effects of CD9 have been linked to EGFR signaling pathways, including phosphorylation of phosphoinositide-3-kinase (PI3K)/Akt and activation of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated protein kinase (Erk). The present study demonstrated that CD9 decreased the phosphorylation of EGFR at specific sites. In addition, CD9 attenuated EGFR signaling of PI3K/Akt and MAPK/Erk, which was associated with cell growth and proliferation. Conversely, small hairpin RNA-mediated knockdown of CD9 expression enhanced the activation of EGFR signal transduction pathways, including PI3K/Akt and MAPK/Erk. These results suggested that the mechanism underlying CD9-induced suppression of cell proliferation may involve the inhibition of phosphorylation of EGFR and the activity of PI3K/Akt and MAPK/Erk signaling pathways.

Hu Q, Fu J, Luo B, et al.
OY-TES-1 may regulate the malignant behavior of liver cancer via NANOG, CD9, CCND2 and CDCA3: a bioinformatic analysis combine with RNAi and oligonucleotide microarray.
Oncol Rep. 2015; 33(4):1965-75 [PubMed] Related Publications
Given its tumor-specific expression, including liver cancer, OY-TES-1 is a potential molecular marker for the diagnosis and immunotherapy of liver cancers. However, investigations of the mechanisms and the role of OY-TES-1 in liver cancer are rare. In the present study, based on a comprehensive bioinformatic analysis combined with RNA interference (RNAi) and oligonucleotide microarray, we report for the first time that downregulation of OY-TES-1 resulted in significant changes in expression of NANOG, CD9, CCND2 and CDCA3 in the liver cancer cell line BEL-7404. NANOG, CD9, CCND2 and CDCA3 may be involved in cell proliferation, migration, invasion and apoptosis, yet also may be functionally related to each other and OY-TES-1. Among these molecules, we identified that NANOG, containing a Kazal-2 binding motif and homeobox, may be the most likely candidate protein interacting with OY-TES-1 in liver cancer. Thus, the present study may provide important information for further investigation of the roles of OY-TES-1 in liver cancer.

Wang HX, Sharma C, Knoblich K, et al.
EWI-2 negatively regulates TGF-β signaling leading to altered melanoma growth and metastasis.
Cell Res. 2015; 25(3):370-85 [PubMed] Free Access to Full Article Related Publications
In normal melanocytes, TGF-β signaling has a cytostatic effect. However, in primary melanoma cells, TGF-β-induced cytostasis is diminished, thus allowing melanoma growth. Later, a second phase of TGF-β signaling supports melanoma EMT-like changes, invasion and metastasis. In parallel with these "present-absent-present" TGF-β signaling phases, cell surface protein EWI motif-containing protein 2 (EWI-2 or IgSF8) is "absent-present-absent" in melanocytes, primary melanoma, and metastatic melanoma, respectively, suggesting that EWI-2 may serve as a negative regulator of TGF-β signaling. Using melanoma cell lines and melanoma short-term cultures, we performed RNAi and overexpression experiments and found that EWI-2 negatively regulates TGF-β signaling and its downstream events including cytostasis (in vitro and in vivo), EMT-like changes, cell migration, CD271-dependent invasion, and lung metastasis (in vivo). When EWI-2 is present, it associates with cell surface tetraspanin proteins CD9 and CD81 - molecules not previously linked to TGF-β signaling. Indeed, when associated with EWI-2, CD9 and CD81 are sequestered and have no impact on TβR2-TβR1 association or TGF-β signaling. However, when EWI-2 is knocked down, CD9 and CD81 become available to provide critical support for TβR2-TβR1 association, thus markedly elevating TGF-β signaling. Consequently, all of those TGF-β-dependent functions specifically arising due to EWI-2 depletion are reversed by blocking or depleting cell surface tetraspanin proteins CD9 or CD81. These results provide new insights into regulation of TGF-β signaling in melanoma, uncover new roles for tetraspanins CD9 and CD81, and strongly suggest that EWI-2 could serve as a favorable prognosis indicator for melanoma patients.

Aoki Y, Watanabe T, Saito Y, et al.
Identification of CD34+ and CD34- leukemia-initiating cells in MLL-rearranged human acute lymphoblastic leukemia.
Blood. 2015; 125(6):967-80 [PubMed] Free Access to Full Article Related Publications
Translocation of the mixed-lineage leukemia (MLL) gene with AF4, AF9, or ENL results in acute leukemia with both lymphoid and myeloid involvement. We characterized leukemia-initiating cells (LICs) in primary infant MLL-rearranged leukemia using a xenotransplantation model. In MLL-AF4 patients, CD34(+)CD38(+)CD19(+) and CD34(-)CD19(+) cells initiated leukemia, and in MLL-AF9 patients, CD34(-)CD19(+) cells were LICs. In MLL-ENL patients, either CD34(+) or CD34(-) cells were LICs, depending on the pattern of CD34 expression. In contrast, in patients with these MLL translocations, CD34(+)CD38(-)CD19(-)CD33(-) cells were enriched for normal hematopoietic stem cells (HSCs) with in vivo long-term multilineage hematopoietic repopulation capacity. Although LICs developed leukemic cells with clonal immunoglobulin heavy-chain (IGH) rearrangement in vivo, CD34(+)CD38(-)CD19(-)CD33(-) cells repopulated recipient bone marrow and spleen with B cells, showing broad polyclonal IGH rearrangement and recipient thymus with CD4(+) single positive (SP), CD8(+) SP, and CD4(+)CD8(+) double-positive (DP) T cells. Global gene expression profiling revealed that CD9, CD32, and CD24 were over-represented in MLL-AF4, MLL-AF9, and MLL-ENL LICs compared with normal HSCs. In patient samples, these molecules were expressed in CD34(+)CD38(+) and CD34(-) LICs but not in CD34(+)CD38(-)CD19(-)CD33(-) HSCs. Identification of LICs and LIC-specific molecules in primary human MLL-rearranged acute lymphoblastic leukemia may lead to improved therapeutic strategies for MLL-rearranged leukemia.

Orchard-Webb DJ, Lee TC, Cook GP, Blair GE
CUB domain containing protein 1 (CDCP1) modulates adhesion and motility in colon cancer cells.
BMC Cancer. 2014; 14:754 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Deregulated expression of the transmembrane glycoprotein CDCP1 (CUB domain-containing protein-1) has been detected in several cancers including colon, lung, gastric, breast, and pancreatic carcinomas. CDCP1 has been proposed to either positively or negatively regulate tumour metastasis. In this study we assessed the role of CDCP1 in properties of cells that are directly relevant to metastasis, namely adhesion and motility. In addition, association between CDCP1 and the tetraspanin protein CD9 was investigated.
METHODS: CDCP1 and CD9 protein expression was measured in a series of colon cancer cell lines by flow cytometry and Western blotting. Adhesion of Colo320 and SW480 cells was determined using a Matrigel adhesion assay. The chemotactic motility of SW480 cells in which CDCP1 expression had been reduced by RNA interference was analysed using the xCELLigence system Real-Time Cell Analyzer Dual Plates combined with 8 μm pore filters. Detergent-resistant membrane fractions were generated following density gradient centrifugation and the CDCP1 and CD9 protein composition of these fractions was determined by Western blotting. The potential association of the CDCP1 and CD9 proteins was assessed by co-immunoprecipitation.
RESULTS: Engineered CDCP1 expression in Colo320 cells resulted in a reduction in cell adhesion to Matrigel. Treatment of SW480 cells with CDCP1 siRNA reduced serum-induced chemotaxis. CDCP1 and CD9 cell-surface protein and mRNA levels showed a positive correlation in colon cancer cell lines and the proteins formed a low-level, but detectable complex as judged by co-sedimentation of detergent lysates of HT-29 cells in sucrose gradients as well as by co-immunoprecipitation in SW480 cell lysates.
CONCLUSIONS: A number of recent studies have assigned a potentially important role for the cell-surface protein CDCP1 in invasion and metastasis of a several types of human cancer cells. In this study, CDCP1 was shown to modulate cell-substratum adhesion and motility in colon cancer cell lines, with some variation depending on the colon cancer cell type. CDCP1 and CD9 were co-expressed at the mRNA and protein level and we obtained evidence for the presence of a molecular complex of these proteins in SW480 colon cancer cells.

Rappa G, Green TM, Lorico A
The nuclear pool of tetraspanin CD9 contributes to mitotic processes in human breast carcinoma.
Mol Cancer Res. 2014; 12(12):1840-50 [PubMed] Related Publications
UNLABELLED: Tetraspanin-29 (CD9) is an integral membrane protein involved in several fundamental cell processes and in cancer metastasis. Here, characterization of a panel of breast cancer cells revealed a nuclear pool of CD9, not present in normal human mammary epithelial cells. Antibody binding to surface CD9 of breast cancer cells resulted in increased nuclear CD9 fluorescence. CD9 was also found, along with a plasma membrane-associated pool, in the nuclei of all primary ductal breast carcinoma patient specimens analyzed. In all patients, about 40% of the total CD9 cellular fluorescence was nuclear. CD9 colocalized at the nuclear level with CEP97, a protein implicated in centrosome function, and with the IGSF8, an established CD9 partner in the plasma membrane. Co-immunoprecipitation of CEP97 and IGSF8 with CD9 was shown in nuclear extracts from breast cancer cells expressing a CD9-GFP fusion protein. However, by fluorescence resonance energy transfer (FRET) analysis, no direct binding of CD9 with either protein was observed, suggesting that CD9 is part of a larger nuclear protein complex. CD9 depletion or exposure of parental breast cancer cells to anti-CD9 mAb resulted in polynucleation and multipolar mitoses. These data indicate that the nuclear CD9 pool has an important role in the mitotic process.
IMPLICATIONS: The discovery of a nuclear pool of CD9 has prognostic and/or therapeutic potential for patients with ductal carcinoma of the breast.

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.

Yoshioka Y, Kosaka N, Konishi Y, et al.
Ultra-sensitive liquid biopsy of circulating extracellular vesicles using ExoScreen.
Nat Commun. 2014; 5:3591 [PubMed] Free Access to Full Article Related Publications
Cancer cells secrete small membranous extracellular vesicles (EVs) into their microenvironment and circulation. Although their potential as cancer biomarkers has been promising, the identification and quantification of EVs in clinical samples remains challenging. Here we describe a sensitive and rapid analytical technique for profiling circulating EVs directly from blood samples of patients with colorectal cancer. EVs are captured by two types of antibodies and are detected by photosensitizer-beads, which enables us to detect cancer-derived EVs without a purification step. We also show that circulating EVs can be used for detection of colorectal cancer using the antigen CD147, which is embedded in cancer-linked EVs. This work describes a new liquid biopsy technique to sensitively detect disease-specific circulating EVs and provides perspectives in translational medicine from the standpoint of diagnosis and therapy.

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.

Yin M, Soikkeli J, Jahkola T, et al.
Osteopontin promotes the invasive growth of melanoma cells by activating integrin αvβ3 and down-regulating tetraspanin CD9.
Am J Pathol. 2014; 184(3):842-58 [PubMed] Related Publications
Overexpression of osteopontin (OPN) is strongly associated with the invasiveness/metastasis of many cancers, including melanomas. However, the molecular mechanisms of OPN in these processes remain poorly understood. We found that forced expression of OPN in early vertical-growth-phase melanoma cells dramatically increased their migration/invasion and growth/survival in a three-dimensional collagen I gel. Neutralizing antibodies to OPN, integrin β1, and integrin αvβ3, but not to CD44, negated the effects of OPN. Conversely, knocking down OPN in metastatic melanoma cells abrogated the invasive growth. OPN overexpression activated and OPN knockdown inactivated αvβ3 and αvβ5 integrins, negligibly affecting their expression. We further found OPN expression to inversely correlate with tetraspanin CD9 expression. Early-stage melanoma cells displayed low OPN and high CD9 expression, and conversely, metastatic cells displayed high OPN and low CD9 expression. Overexpression of OPN in vertical-growth-phase melanoma cells induced down-regulation of CD9, and knockdown of OPN in metastatic melanoma cells up-regulated CD9. Reversion of these CD9 changes abolished the effects of OPN. Furthermore, knockdown of CD9 in early-stage melanoma cells stimulated their invasive capacity in three-dimensional collagen. Similarly, microarray analyses of benign nevi and primary melanomas from different stages revealed an inverse correlation between OPN and CD9. These data suggest that OPN promotes melanoma cell invasion by activating integrin αvβ3 and down-regulating CD9, a putative metastasis suppressor.

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.

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