CD151 enhances cell motility and metastasis of cancer cells in the presence of focal adhesion kinase

Impact of CD151 overexpression on prognosis and therapy in non-small cell lung cancer patients lacking EGFR mutations

This study investigates CD151, a protein linked to cancer progression, in non-small cell lung cancer (NSCLC) patients without epidermal growth factor receptor (EGFR) mutations. These patients often have limited treatment options. The study used retrospective analysis to examine 157 adenocarcinoma biopsy specimens and 199 patient cases from The Cancer Genome Atlas, correlating CD151 expression with patient survival. Cellular studies revealed that CD151 interacts with EGFR, influencing epidermal growth factor (EGF)-induced cell proliferation and the effectiveness of the EGFR inhibitor, erlotinib. A strong association was found between CD151 expression and EGFR mutation status. High CD151 expression in the absence of EGFR mutations is correlated with poorer survival outcomes. Biological assays showed that CD151 colocalizes and associates with EGFR, playing a crucial role in regulating EGF-induced cell proliferation via the AKT and ERK1/2 pathways. Importantly, CD151 expression was found to influence the anti-proliferative effects of the EGFR tyrosine kinase inhibitor, erlotinib. High CD151 expression, in the absence of EGFR mutations, was associated with poorer survival outcomes. It could serve as a potential prognostic marker and influence cellular responses to EGFR-targeted treatments. This study highlights CD151 as a potential novel target for therapeutic intervention in NSCLC, especially in populations lacking EGFR mutations.

CD151 enrichment in exosomes of luminal androgen receptor breast cancer cell line contributes to cell invasion

Breast cancer is the most common and highly heterogeneous disease in women worldwide. Given the challenges in the treatment of advanced metastatic breast cancer, it is necessary to understand the molecular mechanisms related to disease progression. Exosomes play various roles in the progression of tumors, including promoting the invasion and advancing the distant metastasis. To study the molecular mechanisms related to the progression of luminal androgen receptor (LAR) breast cancer, we first isolated exosomes of MDA-MB-453 cells, a representative cell line of LAR. Through quantitative proteomic analysis, we identified 180 proteins specifically enriched in exosomes after comparing with those in cells, microvesicles, and the 150K supernatant. Among these, CD151, a protein involved in the regulation of cell motility was the most enriched one. CD151-knockdown exosomes reduced the invasion ability of the recipient breast cancer cell and lowered the phosphorylation level of tyrosine-protein kinase Lck, indicating that the invasion of LAR breast cancer may be due to CD151-enriched exosomes. Our work reports for the first time that CD151 was highly abundant in the exosomes of MDA-MB-453 cells and expands the understanding of the development process of LAR subtype, suggesting CD151 may be a potential candidate for the treatment of LAR breast cancer.

CD151 in Respiratory Diseases

The tetraspanin, Cluster of Differentiation 151 (CD151), is ubiquitously expressed in adult tissue, especially in the lungs where it has been implicated in lung cancer, asthma, influenza, and idiopathic pulmonary fibrosis (IPF). CD151 interacts with laminin-binding integrins and growth factor receptors, and is reported in cancer-promoting processes such as tumor initiation, metastasis, and angiogenesis. In asthma, CD151 was shown to promote airways hyperresponsiveness through calcium signaling whereas in influenza, CD151 was shown to be a novel host factor for nuclear viral export signaling. Furthermore, CD151 was shown to be associated with increased disease severity and poorer survival outcome in asthma and lung cancer, respectively. In this review, we provide an update on the current understanding of CD151 with regards to its contribution to lung pathophysiology. We also summarize factors that have been shown to regulate CD151 expression and identify key areas that need to be taken into consideration for its utility as a screening or prognostic tool in disease management and/or as a therapeutic target for the treatment of lung diseases.

CD151 confers metastatic potential to clear cell sarcoma of the soft tissue in animal model

Cluster of differentiation 151 (CD151) is a potent therapeutic target for regulating tumor metastasis. In the present study, the role of CD151 in clear cell sarcoma of soft tissue was examined using a xenoplanted tumor model, which had high rates of metastasis. A clear cell sarcoma cell line, HS-MM, which was transplanted to the aponeuroses of the thighs, the most affected sites of human clear cell sarcoma, exhibited robust lymphatic invasion and nodal metastasis in SCID-beige mice. Serial in vivo passaging of peritoneally disseminated tumor cells accelerated the metastatic activity, which was accompanied by increased CD151 expression, and were designated as HS-MM^high. Notably, inoculation of anti-CD151 antibody significantly suppressed the lymphatic invasion, peritoneal dissemination and distant metastasis of the present clear cell sarcoma model without affecting local tumor growth at the transplantation site. Small interfering RNA (siRNA)-mediated downregulation of CD151 did not alter cell proliferation, but significantly inhibited Matrigel invasion activity of HS-MM^high cells. Downregulation of CD151 impaired matrix metalloproteinase-9 activity and phosphorylation of SMAD3 protein in HS-MM^high cells. The present results suggest that CD151 may contribute to invasion and metastasis of clear cell sarcoma of soft tissue. Therefore, CD151 may serve as a potent target to regulate metastasis of clear cell sarcoma.

CD151 promotes proliferation and migration of SK-NEP-1 cells via the GSK-3β/P21/cyclinD signaling pathway

Wilms'tumor is the most common malignant tumor with a poor clinical prognosis because of metastasis or recurrence among children worldwide. CD151, a member of transmembrane 4 superfamily, has now been confirmed to be involved in tumor progression including the proliferation, migration, invasion and metastasis of tumor cells. GSK-3β/P21/cyclinD signaling pathway plays a critical role in the cell cycle progression, regulating cellular proliferation. In this study, CD151 protein and mRNA levels were examined by western blot and RT-PCR. The proliferation of SK-NEP-1 cells was examined by CCK8 assay and the migration of SK-NEP-1 cells was detected with wound healing assay. Furthermore, p-GSK3β protein, GSK3β protein, p21protein and CyclinD protein were examined by western blot to verify whether CD151 could regulate the Wilms'tumor progression via the GSK-3β/P21/cyclinD signaling pathway. The RT-PCR and western blot results showed that CD151 protein was upregulated in Wilms'tumor cells compared with the control. The results by CCK8 assay and wound healing assay demonstrated that CD151 overexpression promoted the proliferation and migration in SK-NEP-1 cells and CD151 interference showed the opposite effects. Western blot assay revealed that CD151 activated the GSK-3β/P21/cyclinD signaling pathway and upregulated the expression of p-GSK3β protein, p21protein and CyclinD protein. It was also verified that CD151 promotes proliferation and migration of SK-NEP-1 cells through the GSK-3β/P21/cyclinD signaling pathway in this study. The specific aim of the study is to investigate and verify the role of CD151 in Wilm's tumor. Therefore, in-depth study on the molecular mechanisms will provide new strategies and methods for the treatment of Wilm's tumor.

Immune Targeting of Tetraspanins Involved in Cell Invasion and Metastasis

Metastasis is the ultimate consequence of cancer progression and the cause of patients’ death across different cancer types. Patients with initial diagnosis of distant disease have a worst 5-year survival compared to patients with localized disease. Therapies that target primary tumors fail to eradicate distant dissemination of cancer. Recently, immunotherapies have improved the survival of patients with metastatic disease, such as melanoma and lung cancer. However, only a fraction of patients responds to immunotherapy modalities that target the host immune system. The need to identify new druggable targets that inhibit or prevent metastasis is, therefore, much needed. Tetraspanins have emerged as key players in regulating cell migration, invasion, and metastasis. By serving as molecular adaptors that cluster adhesion receptors, signaling molecules, and cell surface receptors; tetraspanins are involved in all steps of the metastatic cascade. They regulate cell proliferation, participate in EMT transition, modulate integrin-mediated cell adhesion, and participate in angiogenesis and invasion processes. Tetraspanins have also been shown to modulate metastasis indirectly through exosomes and by regulating cellular interactions in the immune system. Importantly, targeting individual tetraspanin with antibodies has impacted tumor progression. This review will focus on the contribution of tetraspanins to the metastatic process and their potential as therapeutic tumor targets.

Tetraspanin CD151 as an emerging potential poor prognostic factor across solid tumors: a systematic review and meta-analysis

Tetraspanin CD151, also known as PETA-3 or SFA-1, has been reported to predict prognosis in various solid tumors. Yet, the results of these studies remained inconclusive. Here, we performed this meta-analysis of relevant studies published on the topic to quantitatively evaluate the clinicopathological significance of CD151 in solid tumors. The relevant articles were identified via searching the PubMed, Web of Science and Embase database. The pooled hazard ratios (HRs) and corresponding 95% confidence intervals (CI) of overall survival (OS) and disease-free survival (DFS) were calculated to evaluate the prognostic value of CD151 expression in patients with solid tumors. A total of 19 studies involving 4, 270 participants were included in the study, we drew the conclusion that CD151 overexpression was associated with statistically significant poor OS (pooled HR = 1.498, 95% CI = 1.346-1.667, P<0.001) and poor DFS (pooled HR = 1.488, 95% CI = 1.314-1.685, P<0.001). Furthermore, the subgroup analysis revealed that the associations between CD151 overexpression and the outcome endpoints (OS or TTP) were significant within the Asian region and European, as well in patients with breast cancer or gastric cancer. Taken together, the incorporative HR showed CD151 overexpression was associated with poor survival in human solid tumors. CD151 could be a valuable prognosis biomarker or a potential therapeutic target of solid tumors.

CD151-mediated adhesion is crucial to osteosarcoma pulmonary metastasis

CD151, a tetraspanin family protein involved in cell-cell and cell-extracellular matrix interaction, is differentially expressed in osteosarcoma cell membranes. Thus, this study aimed to investigate the role of CD151 in osteosarcoma metastasis. We analyzed CD151 expression in patient tissue samples using immunohistochemistry. CD151 expression was also silenced with shRNA in osteosarcoma cells of high metastatic potential, and cell adhesion, migration and invasion were evaluated in vitro and pulmonary metastasis was investigated in vivo. Mediators of cell signaling pathways were also examined following suppression of CD151 expression. Overall survival for patients with low versus high CD151 expression level was 94 vs. 41 months (p=0.0451). CD151 expression in osteosarcoma cells with high metastatic potential was significantly higher than in those with low metastatic potential (p<0.001). shRNA-mediated silencing of CD151 did not influence cell viability or proliferation; however, cell adhesion, migration and invasion were all inhibited (all p<0.001). In mice inoculated with shRNA-transduced osteosarcoma cells, the number and size of lung metastatic lesions were reduced compared to the mice inoculated with control-shRNA transduced cells (p<0.001). In addition, CD151 knockdown significantly reduced Akt, p38, and p65 phosphorylation as well as focal adhesion kinase, integrin β1, p70s6, and p-mTOR levels. Taken together, CD151 induced osteosarcoma metastasis likely by regulating cell function through adhesion signaling. Further studies are necessary to fully explore the diagnostic and prognostic value of determining CD151 expression in osteosarcoma patients.

CD151 promotes cell metastasis via activating TGF-β1/Smad signaling in renal cell carcinoma

Tetraspanin CD151 has been identified as a tumor promoter, which is upregulated in various malignant cell types. However, the function of CD151 and its underlying mechanism in renal cell carcinoma is still unknown. In this study, we detected the expression of CD151 in RCC cells and tissues and explored its regulatory mechanism. We found that CD151 was upregulated in renal cell carcinoma tissues and cells and its expression was significantly associated with tumor stage (p=0.019) and survival (p=0.001) by analyzing tissue microarrays. After silencing of CD151 via lentivirus vector in Caki-1 and Caki-2 cells, reduced ability of migration and invasion were detected with downregulation of CD151. The opposite results were observed in cells with CD151 overexpression. Furthermore, western blotting was performed to investigate the influence of CD151 on epithelial-to-mesenchymal transition, matrix metalloproteinase 9 and TGF-β1/Smad signaling pathway in RCC. Subsequently, upregulating the protein level of transforming growth factor-β1 in cells with silencing of CD151 could rescue the malignant behaviors inhibited, which indicated that CD151 may play its promoting role in RCC partially by stimulating the expression of TGF-β1. Conclusively, CD151 might exhibit a prominent role in migration and invasion of RCC cells via activating TGF-β1/Smad signaling pathway.

Long-term Inflammation Transforms Intestinal Epithelial Cells of Colonic Organoids

BACKGROUND AND AIMS

Patients with ulcerative colitis [UC] are at an increased risk of developing colitis-associated cancer [CAC], suggesting that continuous inflammation in the colon promotes the transformation of colonic epithelial cells. However, the mechanisms underlying cell transformation in UC remain unknown. We therefore aimed to investigate the effect of long-term inflammation on intestinal epithelial cells [IECs] using organoid culture.

METHODS

IECs were isolated from mouse colon, and were cultured according to a method for a three-dimensional [3D] organoid culture. To mimic chronic inflammation, a mixture of cytokines and bacterial components were added to the medium for over a year. Cell signal intensity was assessed by 3D immunofluorescence. Cell transformation was assessed by microarray with gene set enrichment analysis.

RESULTS

Stimulation with cytokines resulted in a significant induction of target genes for the nuclear factor [NF]-κB pathway in colonic organoids. Following 60 weeks of continuous stimulation, cell differentiation was suppressed. Continuous stimulation also resulted in significant amplification of NF-κB signalling. Amplified NF-κB signalling by long-term stimulation remained in colonic organoids even 11 weeks after the removal of all cytokines. Some genes were specifically upregulated only in colonic organoids after the removal all cytokines following long-term stimulation.

CONCLUSIONS

Colonic organoids stimulated with cytokines for a prolonged period were established as in vitro model to assess long-term epithelial responses to inflammatory cytokines. Chronic inflammation led to sustained NF-κB signalling activation in colonic organoids, resulting in cell transformation that might be related to the carcinogenesis of CAC in UC.

EMP1, EMP 2, and EMP3 as novel therapeutic targets in human cancer

The epithelial membrane protein genes 1, 2, and 3 (EMP1, EMP2, and EMP3) belong to the peripheral myelin protein 22-kDa (PMP22) gene family, which consists of at least seven members: PMP22, EMP1, EMP2, EMP3, PERP, brain cell membrane protein 1, and MP20. This review addresses the structural and functional features of EMPs, detailing their tissue distribution and functions in the human body, their expression pattern in a variety of tumors, and highlighting the underlying mechanisms involved in carcinogenesis. The implications in cancer biology, patient prognosis prediction, and potential application in disease therapy are discussed. For example, EMP1 was reported to be a biomarker of gefitinib resistance in lung cancer and contributes to prednisolone resistance in acute lymphoblastic leukemia patients. EMP2 functions as an oncogene in human endometrial and ovarian cancers; however, characteristics of EMP2 in urothelial cancer fulfill the criteria of a suppressor gene. Of particular interest, EMP3 overexpression in breast cancer is significantly related to strong HER-2 expression. Co-expression of HER-2 and EMP3 is the most important indicator of progression-free and metastasis-free survival for patients with urothelial carcinoma of the upper urinary tract. Altogether, discovery of pharmacological inhibitors and/or regulators of EMP protein activity could open novel strategies for enhanced therapy against EMP-mediated human diseases.

CD151 mediates netrin-1-induced angiogenesis through the Src-FAK-Paxillin pathway

Crosstalk between the nervous and vascular systems is important during development and in response to injury, and the laminin-like axonal guidance protein netrin-1 has been studied for its involvement in angiogenesis and vascular remodelling. In this study, we examined the role of netrin-1 in angiogenesis and explored the underlying mechanisms. The effect of netrin-1 on brain tissues and endothelial cells was examined by immunohistochemistry and western blotting in a middle cerebral artery occlusion model and in human umbilical vein endothelial cells. Cell proliferation and cell cycle progression were assessed by the MTT assay and flow cytometry, and the Transwell and tube formation assays were used to examine endothelial cell motility and function. Netrin-1 up-regulated CD151 and VEGF concomitant with the activation of focal adhesion kinase (FAK), Src and Paxillin in vitro and in vivo and the induction of cell proliferation, migration and tube formation in vitro. Silencing of CD151 abolished the effects of netrin-1 on promoting cell migration and tube formation mediated by the activation of FAK/Src signalling. Netrin-1 promoted angiogenesis in vitro and in vivo by activating the FAK/Src/Paxillin signalling pathway through a mechanism dependent on the expression of the CD151 tetraspanin, suggesting the existence of a netrin-1/FAK/Src/CD151 signalling axis involved in the modulation of angiogenesis.

CD151-α3β1 integrin complexes are prognostic markers of glioblastoma and cooperate with EGFR to drive tumor cell motility and invasion

Glioblastoma, one of the most aggressive forms of brain cancer, is featured by high tumor cell motility and invasiveness, which not only fuel tumor infiltration, but also enable escape from surgical or other clinical interventions. Thus, better understanding of how these malignant traits are controlled will be key to the discovery of novel biomarkers and therapies against this deadly disease. Tetraspanin CD151 and its associated α3β1 integrin have been implicated in facilitating tumor progression across multiple cancer types. How these adhesion molecules are involved in the progression of glioblastoma, however, remains largely unclear. Here, we examined an in-house tissue microarray-based cohort of 96 patient biopsies and TCGA dataset to evaluate the clinical significance of CD151 and α3β1 integrin. Functional and signaling analyses were also conducted to understand how these molecules promote the aggressiveness of glioblastoma at molecular and cellular levels. Results from our analyses showed that CD151 and α3 integrin were significantly elevated in glioblastomas at both protein and mRNA levels, and exhibited strong inverse correlation with patient survival (p < 0.006). These adhesion molecules also formed tight protein complexes and synergized with EGF/EGFR to accelerate tumor cell motility and invasion. Furthermore, disruption of such complexes enhanced the survival of tumor-bearing mice in a xenograft model, and impaired activation of FAK and small GTPases. Also, knockdown- or pharmacological agent-based attenuation of EGFR, FAK or Graf (ARHGAP26)/small GTPase-mediated pathways markedly mitigated the aggressiveness of glioblastoma cells. Collectively, our findings provide clinical, molecular and cellular evidence of CD151-α3β1 integrin complexes as promising prognostic biomarkers and therapeutic targets for glioblastoma.

CD151 expression is frequent but unrelated to clinical outcome in head and neck cancer

OBJECTIVES

CD151 is a plasma membrane protein belonging to the tetraspanin family. CD151 represents a putative therapeutic target and has been suggested as a prognostic marker in several cancer types. The present study aims to investigate the prognostic relevance of immunohistochemical CD151 expression in head and neck squamous cell carcinoma (HNSCC).

MATERIALS AND METHODS

Tissue microarray (TMA) sections containing samples from 667 cancers of oral cavity, oro- and hypopharynx and larynx, for which follow-up data were available, were analyzed for CD151 expression by immunohistochemistry.

RESULTS

Membranous CD151 immunostaining was recorded in 269 (60.3 %) of 446 analyzable cases. Staining was considered weak in 129 (28.9 %), moderate in 98 (22.0 %), and strong in 42 (9.4 %) of cancers. CD151 expression was unrelated to histological grade, tumor stage, nodal status, or surgical margin. There was a tendency towards a somewhat lower prevalence of CD151 expression in tumors of the oral cavity (52.9 % positive) as compared to cancers of the oro-hypopharynx (62.1 %) and larynx (63.3 %; p = 0.0100). CD151 expression had no impact on patient survival.

CLINICAL RELEVANCE

In summary, immunohistochemical analysis of CD151 lacks prognostic utility in HNSCC. The high prevalence of CD151 expression in HNSCC emphasizes its putative relevance as a therapeutic target for further development of anti-CD151 drugs.

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

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

LINKED ARTICLES

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

Tetraspanins in cell migration

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

CD151-A Striking Marker for Cancer Therapy

Cluster of differentiation 151 (CD151) is a member of the mammalian tetraspanin family, which is involved in diverse functions such as maintaining normal cellular integrity, cell-to-cell communication, wound healing, platelet aggregation, trafficking, cell motility and angiogenesis. CD151 also supports de novo carcinogenesis in human skin squamous cell carcinoma (SCC) and tumor metastasis. CD151 interacts with α3β1 and α6β4 integrins through palmitoylation where cysteine plays an important role in the association of CD151 with integrins and non-integrin proteins. Invasion and metastasis of cancer cells were diminished by decreasing CD151 association with integrins. CD151 functions at various stages of cancer, including metastatic cascade and primary tumor growth, thus reinforcing the importance of CD151 as a target in oncology. The present review highlights the role of CD151 in tumor metastasis and its importance in cancer therapy.

Involvement of activation of C-met signaling pathway in CD151-induced HUVECs angiogenesis

CD151 is a member of the tetraspanin family that is implicated as a promoter of pathological or physiological angiogenesis. C-Met is expressed on a variety of cells including vascular endothelial cells (VECs) and up-regulated during angiogenesis. In this study, we investigated whether CD151 regulated migration, proliferation, tube formation and angiogenesis of human umbilical VECs (HUVECs) with activation of C-Met. Moreover, we studied whether CD151 could affect the angiogenic molecules such as nitric oxide (NO), vascular cell adhesion molecule-1 (VCAM-1) and vascular endothelial growth factor (VEGF). The expression of CD151 was determined by Western blotting. The cell proliferation assay was performed using the cell counting kit-8 (CCK-8) method and cell migration was assessed in microchemotaxis chambers by using fetal bovine serum (FBS) as the chemotactic stimulus. The angiogenic molecules were evaluated using ELISA. The NO level was detected using NO detection kit. The potential involvement of various signaling pathways was explored using relevant antibodies. We found that proliferation, migration and tube formation of HUVECs were promoted by CD151 with activation of C-Met, FAK and CDC42, while they were suppressed with CD151 knockdown by RNAi. Similarly, the levels of NO, VCAM-1 and VEGF in HUVECs were increased by CD151, but they were inhibited with CD151 knockdown by RNAi. These data suggested that CD151 could promote migration, proliferation, tube formation and angiogenesis of HUVECs, which was possibly related to the C-Met signaling pathways.

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

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

Effect of an anti-human Co-029/tspan8 mouse monoclonal antibody on tumor growth in a nude mouse model

New therapeutic agents are needed in digestive tract tumors. Co-029/tspan8 is a tetraspanin frequently expressed on human colorectal tumors, In this work, we report the effects of the monoclonal antibody Ts29.2, targeting Co-029/tspan8, on colorectal tumor cells in vitro and after implantation in nude mice. HT29, Isreco1 and SW480 colorectal tumor cell lines were used for this study. HT29 has a strong endogenous expression of Co-029/tspan8, whereas Isreco1 cells don't express Co-029/tspan8 and SW480 has only a weak expression. Isreco1 and SW480 were transduced to express Co-029/tspan8 at the same level as HT29. In order to check the specificity of the effect of monoclonal antibody Ts29.2, low Co-029/tspan8 expressing SW480 cells were injected simultaneously with transduced cells in the back, on the left and right sides of the mice. With an early treatment, Ts29.2 mAb inhibited growth of tumors expressing Co-029/tspan8 up to 70%, whereas a delayed treatment was less efficient. No effect of the antibody on cell proliferation or apoptosis induction was detected in vitro. No increase of activated caspase 3 labeling was observed in vivo and areas occupied by vessels were not significantly different between treated mice and controls. This suggests that the action of Ts29.2 is linked neither to cellular toxicity nor to the inhibition of the previously reported angiogenic properties of Co-029/tspan8. An inhibition of cell proliferation in vivo is demonstrated by a reduction of the mitotic index in HT29 tumors of Ts29.2 treated mice. The discrepancy between in vitro and in vivo data on cell proliferation suggests that the binding of Ts29.2 to tumor cells may modify their response to signals issued from the microenvironment. Given the restricted pattern of tissue expression of the tetraspanin Co-029/tspan8, these preliminary results put forth for consideration the antibody targeting of this tetraspanin in further investigations for therapeutic applications.

Reduced CD151 expression is related to advanced tumour stage in urothelial bladder cancer

AIMS

CD151 belongs to the group of tetraspanins and is aberrantly expressed in different tumours and differential expression has been associated with prognosis. The aim of this study was to clarify the relationship of CD151 expression with tumour phenotype and clinical outcome in bladder cancer.

METHODS

A bladder cancer tissue microarray containing samples from 686 urothelial bladder cancers was analysed by immunohistochemistry.

RESULTS

Membranous CD151 immunostaining was recorded in 409 (66.0%) of 620 analysable cases. High CD151 expression was seen in normal urothelium and in most non-invasive tumours. Low CD151 expression levels were associated with a more unfavourable tumour phenotype. CD151 staining was seen in 71.5% of 284 pTa, 62.1% of 145 pT1 and 60.4% of 187 pT2-4 cancers (p = 0.0033). CD151 staining was detectable in 77.3% of 75 grade 1, 71.1% of 273 grade 2 and 57.7% of 272 grade 3 cancers (p < 0.0001). CD151 expression status was not associated with overall or tumour-specific survival in muscle-invasive cancers (pT2-4), tumour progression in pT1 and recurrences in pTa tumours.

CONCLUSION

On the basis of our data we conclude that loss of CD151 may contribute to bladder cancer progression through attenuation of cell adhesion. In clinically defined subgroups CD151 expression does not provide additional prognostic information.

Tetraspanin proteins promote multiple cancer stages

An abundance of evidence shows supporting roles for tetraspanin proteins in human cancer. Many studies show that the expression of tetraspanins correlates with tumour stage, tumour type and patient outcome. In addition, perturbations of tetraspanins in tumour cell lines can considerably affect cell growth, morphology, invasion, tumour engraftment and metastasis. This Review emphasizes new studies that have used de novo mouse cancer models to show that select tetraspanin proteins have key roles in tumour initiation, promotion and metastasis. This Review also emphasizes how tetraspanin proteins can sometimes participate in tumour angiogenesis. These recent data build an increasingly strong case for tetraspanins as therapeutic targets.

CD151 in cancer progression and metastasis: a complex scenario

Originally identified as a molecular organizer of interacting proteins into tetraspanin-enriched microdomains, the tetraspanin CD151 has now been shown to be involved in tumour progression. Increasing evidence emerging from in vitro, in vivo and clinical analyses implicates this tetraspanin in supporting growth of various types of tumours at different levels. It affects both cell autonomous behavior and communication with neighboring cells and the microenvironment. CD151 regulates post-adhesion events, that is, cell spreading, migration and invasion including subsequent intravasation and formation of metastasis. Present on both neoplastic and endothelial cells, CD151 is engaged in promotion of tumour neovascularization. The molecular mechanism of CD151 in cancer is based on its ability to organize distribution and function of interacting proteins, ie, laminin-binding integrins (α3β1, α6β1 and α6β4), receptors for growth factors (HGFR, EGFR and TGF-β1R) and matrix metalloproteinases (MMP-7, MMP-2 and MMP-9), which indicates its importance in disease development. Results of clinical analyses of CD151 expression in different types of cancer and a large number of in vivo models demonstrate its impact on tumour growth and invasion and implicate CD151 as a valuable diagnostic and prognostic marker as well as a potential target for anti-cancer therapy.

Systematic review of protein biomarkers of invasive behavior in glioblastoma

Glioblastoma (GBM) is an aggressive and incurable brain tumor with a grave prognosis. Recurrence is inevitable even with maximal surgical resection, in large part because GBM is a highly invasive tumor. Invasiveness also contributes to the failure of multiple cornerstones of GBM therapy, including radiotherapy, temozolomide chemotherapy, and vascular endothelial growth factor blockade. In recent years there has been significant progress in the identification of protein biomarkers of invasive phenotype in GBM. In this article, we comprehensively review the literature and survey a broad spectrum of biomarkers, including proteolytic enzymes, extracellular matrix proteins, cell adhesion molecules, neurodevelopmental factors, cell signaling and transcription factors, angiogenic effectors, metabolic proteins, membrane channels, and cytokines and chemokines. In light of the marked variation seen in outcomes in GBM patients, the systematic use of these biomarkers could be used to form a framework for better prediction, prognostication, and treatment selection, as well as the identification of molecular targets for further laboratory investigation and development of nascent, directed therapies.

Knockdown of cathepsin B and uPAR inhibits CD151 and α3β1 integrin-mediated cell adhesion and invasion in glioma

Glioma is a highly complex brain tumor characterized by the dysregulation of proteins and genes that leads to tumor metastasis. Cathepsin B and uPAR are overexpressed in gliomas and they are postulated to play central roles in glioma metastasis. In this study, efficient downregulation of cathepsin B and uPAR by siRNA treatments significantly reduced glioma cell adhesion to laminin as compared to vitronectin, fibronectin, or collagen I in U251 and 4910 glioma cell lines. Brain glioma tissue array analysis showed high expression of CD151 in clinical samples when compared with normal brain tissue. Cathepsin B and uPAR siRNA treatment led to the downregulation of CD151 and laminin-binding integrins α3 and β1. Co-immunoprecipitation experiments revealed that downregulation of cathepsin B and uPAR decreased the interaction of CD151 with uPAR cathepsin B, and α3β1 integrin. Studies on the downstream signaling cascade of uPAR/CD151/α3β1 integrin have shown that phosphorylation of FAK, SRC, paxillin, and expression of adaptor cytoskeletal proteins talin and vinculin were reduced with knockdown of cathepsin B, uPAR, and CD151. Treatment with the bicistronic construct reduced interactions between uPAR and CD151 as well as lowering α3β1 integrin, talin, and vinculin expression levels in pre-established glioma tumors of nude mice. In conclusion, our results show that downregulation of cathepsin B and uPAR alone and in combination inhibit glioma cell adhesion by downregulating CD151 and its associated signaling molecules in vitro and in vivo. Taken together, the results of the present study show that targeting the uPAR-cathepsin B system has possible therapeutic potential.

Tetraspanin CD9 promotes the invasive phenotype of human fibrosarcoma cells via upregulation of matrix metalloproteinase-9

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.

Prognostic significance of CD151 overexpression in non-small cell lung cancer

The overexpression of tetraspanin CD151 - a transmembrane protein that promotes tumor invasion and metastasis - is associated with poor prognosis in various cancers. However, its clinical significance in non-small cell lung cancers (NSCLCs) has not been fully elucidated. We investigated CD151 expression status by immunohistochemical analysis in paraffin-embedded specimens obtained from 380 patients with surgically resected NSCLCs (245 squamous cell carcinomas [SCCs] and 135 adenocarcinomas [ADCs]) between 1994 and 2001. High CD151 expression was detected in 28.7% NSCLCs (20.8% of SCCs and 42.9% of ADCs) and was significantly associated with male gender, smokers, and ADCs. Moreover, elevated CD151 levels were correlated with reduced overall (OS) and disease-free survival (DFS), and were an independent negative prognostic factor for OS in NSCLC. According to histological type, high CD151 expression was an independent prognostic factor for lower OS in ADC, although not in each subtype, and the elevated CD151 expression levels were more common in solid-predominant tumors (48.3%). In contrast, there was no prognostic correlation in SCC. High CD151 expression appeared to correlate with aggressive behavior in NSCLC, suggesting that it may be a useful prognostic marker for lung ADC patients and a potential molecular target for NSCLC treatment.

Normal viability of Kai1/Cd82 deficient mice

The KAI1/CD82 tetraspanin is a widely expressed cell surface molecule thought to organize diverse cellular signaling processes. KAI1/CD82 suppresses metastasis but not tumorigenicity, establishing it as one of a class of metastasis suppressor genes. In order to further assess its functions, we have characterized the phenotypic properties of Kai1/Cd82 deleted mice, including viability, fertility, lymphocyte composition, blood chemistry and tissue histopathology, and of their wild-type and heterozygote littermates. Interestingly, Kai1/Cd82(-/-) showed no obvious genotype associated defects in any of these processes and displayed no genotype associated histopathologic abnormalities after 12 or 18 months of life. Expression profiles of non-immortal, wild-type and Kai1/Cd82(-/-) mouse embryo fibroblast (MEFs) indicated distinct sex-specific and genotype-specific profiles. These data identify 191 and 1,271 differentially expressed transcripts (by twofold at P < 0.01) based on Kai1/CD82 genotype status in female and male MEFs, respectively. Differentially expressed genes in male MEFs were surprisingly enriched for cell division related processes, suggesting that Kai1/Cd82 may functionally affect these processes. This suggests that Kai/Cd82 has an unappreciated role in the early establishment of proliferation and division when challenged with a new environment that might play a role in adaptability to new metastatic sites.

Genetic ablation of the tetraspanin CD151 reduces spontaneous metastatic spread of prostate cancer in the TRAMP model

Tetraspanins are integral membrane proteins that associate with motility-related molecules such as integrins. Experimental studies have indicated that they may be important regulators of tumor invasion and metastasis, and high expression of the tetraspanin CD151 has been linked to poor prognosis in a number of cancers. Here, we show for the first time that genetic ablation of CD151 inhibits spontaneous metastasis in a transgenic mouse model of de novo tumorigenesis. To evaluate the effects of CD151 on de novo prostate cancer initiation and metastasis, a Cd151(-/-) (KO) murine model was crossed with the Transgenic Adenocarcinoma of Mouse Prostate (TRAMP) model. Mice were analyzed for initiation of prostate tumor by palpation and primary tumors were analyzed by immunohistochemistry. Liver and lungs were examined for incidence and size of spontaneous metastatic lesions by histopathology. Knocking-out Cd151 had no significant effect on prostate cancer initiation or on expression of markers of proliferation, apoptosis, or angiogenesis in primary tumors. However, it did significantly decrease metastasis in a site-specific fashion, notably to the lungs but not the liver. Thus, CD151 acts principally as promoter of metastasis in this model. Prostate cancer is the second highest cause of cancer-related deaths in men in most Western countries, with the majority of deaths attributed to late-stage metastatic disease. CD151 may prove to be a valuable prognostic marker for treatment stratification and is a possible antimetastatic target.

Prognostic significance of tetraspanin CD151 in newly diagnosed glioblastomas

BACKGROUND

Tetraspanin CD151 is a positive effector of cancer invasion and metastasis.

METHODS

We investigated the expression of CD151 by immunohistochemistry in 211 cases of grade I to IV gliomas. Additionally, we performed O6-methylguanin-DNA methyltransferase (MGMT) methylation analysis using real-time methylation-specific PCR in 36 patients with glioblastoma, and the prognostic significance of these biomarkers in glioblastomas was evaluated.

RESULTS

Overexpression of CD151 was observed in a significant proportion (55.6%) of glioblastomas, while CD151 was rarely overexpressed in most of grade I to III glial tumors. CD151 overexpression was closely associated with MGMT methylation (P = 0.014), and it was a prognostic factor for predicting worse overall survival (OS; P = 0.002) and progression-free survival (PFS; P = 0.043). We also found that combination of CD151 overexpression and MGMT methylation better stratified the patients' OS (P = 0.001) and PFS (P = 0.009). In multivariate analysis, CD151 overexpression was an independent prognostic factor for predicting OS over MGMT methylation (P = 0.012).

CONCLUSIONS

CD151 seems to have a critical role for high-grade progression in astroglial tumors. Furthermore, CD151 is a good tissue marker that can be used easily in a daily practice for predicting worse prognosis in patients with glioblastoma.

Targeting tetraspanins in cancer

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

Tetraspanin CD151 stimulates adhesion-dependent activation of Ras, Rac, and Cdc42 by facilitating molecular association between β1 integrins and small GTPases

Tetraspanin CD151 associates with laminin-binding α(3)β(1)/α(6)β(1) integrins in epithelial cells and regulates adhesion-dependent signaling events. We found here that CD151 plays a role in recruiting Ras, Rac1, and Cdc42, but not Rho, to the cell membrane region, leading to the formation of α(3)β(1)/α(6)β(1) integrin-CD151-GTPases complexes. Furthermore, cell adhesion to laminin enhanced CD151 association with β(1) integrin and, thereby, increased complex formation between the β(1) family of integrins and small GTPases, Ras, Rac1, and Cdc42. Adhesion receptor complex-associated small GTPases were activated by CD151-β(1) integrin complex-stimulating adhesion events, such as α(3)β(1)/α(6)β(1) integrin-activating cell-to-laminin adhesion and homophilic CD151 interaction-generating cell-to-cell adhesion. Additionally, FAK and Src appeared to participate in this adhesion-dependent activation of small GTPases. However, engagement of laminin-binding integrins in CD151-deficient cells or CD151-specific siRNA-transfected cells did not activate these GTPases to the level of cells expressing CD151. Small GTPases activated by engagement of CD151-β(1) integrin complexes contributed to CD151-induced cell motility and MMP-9 expression in human melanoma cells. Importantly, among the four tetraspanin proteins that associate with β(1) integrin, only CD151 exhibited the ability to facilitate complex formation between the β(1) family of integrins and small GTPases and stimulate β(1) integrin-dependent activation of small GTPases. These results suggest that CD151 links α(3)β(1)/α(6)β(1) integrins to Ras, Rac1, and Cdc42 by promoting the formation of multimolecular complexes in the membrane, which leads to the up-regulation of adhesion-dependent small GTPase activation.

Comparison of LanthaScreen Eu kinase binding assay and surface plasmon resonance method in elucidating the binding kinetics of focal adhesion kinase inhibitors

An understanding of the dynamics of drug-target interactions is important in the drug discovery process. Information related to the binding kinetics of a drug toward its target or off-target aids in determining the efficacy or toxicity of a drug. Biophysical techniques such as surface plasmon resonance (SPR) have been available for over 20 years, but have been predominantly utilized to characterize protein-protein interactions. With improvements in instrument sensitivity and data analysis software, interactions between proteins (such as kinases) and small molecules have been successfully evaluated. More recently, the LanthaScreen Eu kinase binding assay for characterizing kinase inhibitors has been described. This assay monitors displacement of an Alexa Fluor 647-labeled tracer from the ATP-binding site of an epitope-tagged kinase by a test compound. Such behavior results in a decrease in time-resolved fluorescence energy transfer signal. In this report, a side-by-side comparison of the LanthaScreen Eu kinase binding assay and the SPR method was performed using inhibitors of focal adhesion kinase. The two methods yielded comparable results and identified compounds with time-dependent inhibition and relatively slow dissociation.

CD151 promotes proliferation and migration of PC3 cells via the formation of CD151-integrin α3/α6 complex

Over-expression of CD151 was found to be associated with metastasis and poor prognosis of prostatic carcinoma. This study was designed to examine the mechanism by which CD151 promotes the proliferation and migration of prostatic cancer cells. The pAAV-CD151, pAAV-GFP and pAAV-CD151-AAA mutant plasmids were constructed and used to transiently transfect PC3 cells (a prostatic carcinoma 3 cell line) by the mediation of Fugene HD. Then, the cells were assigned to control group, pAAV-GFP group, pAAV-CD151 group, and pAAV-CD151-AAA group respectively. Cell proliferation was evaluated by using the 3-[4,5-dimet-hylthiazol-2-yl]-2,5, diphenyltetrazolium bromide (MTT) method. Cell migration assay was performed by using Boyden chambers. The formation of CD151-integrin α3/α6 complex was determined by the method of co-immunoprecipitation. The protein expression levels of CD151 and extracellular signal-regulated kinase (ERK) were measured by Western blotting. The results showed that transfection of pAAV-CD151 or pAAV-CD151-AAA mutant increased the expression of CD151 protein in PC3 cells. Co-immunoprecipitation showed that more CD151-integrin α3/α6 complex was formed in the pAAV-CD151 group than in the control group, the pAAV-GFP group and the pAAV-CD151-AAA mutant group. Furthermore, the proliferative and migrating capacity of PC3 cells was substantially increased in the pAAV-CD151 group but inhibited in the pAAV-CD151-AAA mutant group. CD151 transfection increased the expression of phospho-ERK. Taken together, it was concluded that CD151 promotes the proliferation and migration of PC3 cells through the formation of CD151-integrin complex and the activation of phosphorylated ERK.

CD151 restricts the α6 integrin diffusion mode

Laminin-binding integrins (α3β1, α6β1, α6β4, α7β1) are almost always expressed together with tetraspanin CD151. In every coexpressing cell analyzed to date, CD151 makes a fundamental contribution to integrin-dependent motility, invasion, morphology, adhesion and/or signaling. However, there has been minimal mechanistic insight into how CD151 affects integrin functions. In MDA-MB-231 mammary cells, tetraspanin CD151 knockdown impairs α6 integrin clustering and functions without decreasing α6 integrin expression or activation. Furthermore, CD151 knockdown minimally affects the magnitude of α6 integrin diffusion, as measured using single particle tracking. Instead, CD151 knockdown has a novel and unexpected dysregulating effect on the mode of α6 integrin diffusion. In control cells α6 integrin shows mostly random-confined diffusion (RCD) and some directed motion (DMO). In sharp contrast, in CD151-knockdown cells α6 integrin shows mostly DMO. In control cells α6 diffusion mode is sensitive to actin disruption, talin knockdown and phorbol ester stimulation. By contrast, CD151 knockdown cell α6 integrin is sensitive to actin disruption but desensitized to talin knockdown or phorbol ester stimulation, indicating dysregulation. Both phorbol ester and EGF stimulate cell spreading and promote α6 RCD in control cells. By contrast, CD151-ablated cells retain EGF effects but lose phorbol-ester-stimulated spreading and α6 RCD. For α6 integrins, physical association with CD151 promotes α6 RCD, in support of α6-mediated cable formation and adhesion. By comparison, for integrins not associated with CD151 (e.g. αv integrins), CD151 affects neither diffusion mode nor αv function. Hence, CD151 support of α6 RCD is specific and functionally relevant, and probably underlies diverse CD151 functions in skin, kidney and cancer cells.

Clinical significance of CD151 overexpression in subtypes of invasive breast cancer

Background:

CD151 is a member of the tetraspanin family, which interacts with laminin-binding integrins and other tetraspanins. This protein is implicated in motility, invasion, and metastasis of cancer cells, but the prevalence of CD151 expression in subtypes of breast cancers and its influence on clinical outcome remains to be evaluated.

Methods and results:

The immunohistochemistry-based tissue microarray analysis showed that 127 (14.3%) cases overexpressed CD151 among 886 breast cancer patients. CD151 overexpression was found to be significantly associated with larger tumour size, higher nodal stage, advanced stage, absence of oestrogen receptor and progesterone receptor, and human epidermal growth factor receptor 2 overexpression. CD151 overexpression resulted in poorer overall survival (OS) (P<0.001) and disease-free survival (P=0.02), and stage II and III patients with CD151 overexpression demonstrated substantially poorer OS (P=0.0474 and 0.0169). In the five subtypes analyses, CD151 overexpression retained its adverse impact on OS in the Luminal A (P=0.0105) and quintuple-negative breast cancer (QNBC) subtypes, one subgroup of triple-negative breast cancer (P=0.0170). Multivariate analysis that included stage, subtype, and adjuvant chemotherapy showed that CD151 overexpression was independently associated with poor OS in invasive breast cancer.

Conclusion:

CD151 overexpression may be a potential molecular therapeutic target for breast cancer, especially in QNBC subtype and more advanced stages of breast cancer.

Tetraspanin CD151 as a target for antibody-based cancer immunotherapy

CD151 is a plasma membrane protein belonging to the tetraspanin superfamily which is expressed on normal cells such as endothelial cells and platelets and frequently overexpressed on cancer cells. It is known to be functionally linked to cancer metastasis. In humans, increased expression of CD151 is indicative of a poor prognosis in different cancer types. Whereas its mechanism of action remains obscure, CD151 was shown to regulate cell motility and adhesion through association with laminin-binding integrins such as α3β1 or α6β4. Several anti-CD151 mAbs (monoclonal antibodies) have been shown to display anti-metastatic activity in vivo. Inhibition of metastasis was not attributed to any effect of these mAbs on tumour cell growth, but was essentially attributed to inhibition of cell motility. We have generated anti-CD151 mAbs which can inhibit the tumoral growth in different xenograft cancer models. As expected, these mAbs were also able to inhibit metastasis in orthotopic cancer models. These data suggest that CD151 could function at multiple cancer stages, including not only metastasis cascade steps, but also earlier steps of primary tumour growth, thus reinforcing the interest of this innovative target in oncology. mAbs targeting CD151 may be of significant interest for cancer biotherapy.

CD151 expression can predict cancer progression in clear cell renal cell carcinoma

AIMS

CD151 is known to be implicated in cancer progression and metastasis. The aim was to evaluate the expression of CD151 in clear cell renal cell carcinoma (CCRCC) and to assess its prognostic significance.

METHODS AND RESULTS

The expression of CD151 was evaluated in 489 cases of CCRCC by immunohistochemistry. Immunoreactivity was classified into four categories (minimal, 0-10% positive cells; focal, 10-50% positive cells; diffuse moderate, >50% positive cells with moderate staining intensity; diffuse strong, >50% positive cells with strong staining). To determine the statistical significance of CD151 expression in CCRCC, all cases were divided into two groups based on their CD151 expression level: a CD151-low group (n=257; minimal and focal) and a CD151-high group (n=232; diffuse). Expression of CD151 was correlated positively with pT, pN, pM categories, pathological tumour-node-metastasis (pTNM) stage, nuclear grade, tumour size and patient's age. The CD151-high group had significantly shorter cancer-specific survival (P<0.001) and progression-free survival (P<0.001) times. Furthermore, multivariate analysis showed that CD151 expression was an independent predictor for tumour progression in patients with CCRCC (P=0.040).

CONCLUSIONS

High CD151 expression is associated with advanced stage and high nuclear grade in CCRCC. CD151 is a prognostic marker for tumour progression in CCRCC patients.

Targeted delivery of small interfering RNA using reconstituted high-density lipoprotein nanoparticles

RNA interference holds tremendous potential as a therapeutic approach, especially in the treatment of malignant tumors. However, efficient and biocompatible delivery methods are needed for systemic delivery of small interfering RNA (siRNA). To maintain a high level of growth, tumor cells scavenge high-density lipoprotein (HDL) particles by overexpressing its receptor: scavenger receptor type B1 (SR-B1). In this study, we exploited this cellular characteristic to achieve efficient siRNA delivery and established a novel formulation of siRNA by incorporating it into reconstituted HDL (rHDL) nanoparticles. Here, we demonstrate that rHDL nanoparticles facilitate highly efficient systemic delivery of siRNA in vivo, mediated by the SR-B1. Moreover, in therapeutic proof-of-concept studies, these nanoparticles were effective in silencing the expression of two proteins that are key to cancer growth and metastasis (signal transducer and activator of transcription 3 and focal adhesion kinase) in orthotopic mouse models of ovarian and colorectal cancer. These data indicate that an rHDL nanoparticle is a novel and highly efficient siRNA carrier, and therefore, this novel technology could serve as the foundation for new cancer therapeutic approaches.

E-cadherin/p120-catenin and tetraspanin Co-029 cooperate for cell motility control in human colon carcinoma

Tumor invasion and metastasis are major obstacles to clinical treatment that rely on cell migration. Here, we elucidate a mechanism of colon carcinoma cell migration that is supported by the cell surface tetraspanin Co-029 (tspan8), which is known to favor tumor progression and metastasis. This mechanism is unmasked by silencing of E-cadherin or its associated adapter molecule p120-catenin (p120ctn), and it involves a switch in signaling between the collagen-binding integrins α(1)β(1) and α(2)β(1). Direct interaction between E-cadherin and Co-029 was documented by chemical cross-linking and immunohistologic analysis of colon carcinomas. High expression of Co-029 and cytoplasmic delocalization of p120ctn were each associated with poor prognosis. Cell motility was reduced severely by antibody-mediated disruption of Co-029 only when p120ctn was silenced, suggesting that tumor progression may be hindered by Co-029 targeting. Our findings define a function for tetraspanin Co-029 as a modifier of cancer cell motility and reveal an adhesion signaling network implicated in progression and metastasis.

Dual targeting of EphA2 and ER restores tamoxifen sensitivity in ER/EphA2-positive breast cancer

Overexpression and altered function of EphA2 receptor tyrosine kinase are critical in the progression of breast cancer and provide a target for breast cancer therapy. We have previously demonstrated that EphA2 overexpression decreases estrogen dependence and Tamoxifen sensitivity both in vitro and in vivo. EA5, a novel monoclonal antibody that mimicks the binding of ephrin A to EphA2, reverses the effect of EphA2 overexpression and restores Tamoxifen sensitivity in EphA2-transfected MCF-7 cells in vitro. To explore the role of EphA2 overexpression on ER-dependent mechanisms, we used two different ER+/EphA2-transfected cell line models (MCF-7(neo)/MCF-7(EphA2) and T47D(neo)/T47D(EphA2)). EA5 inhibits primary tumor growth and restores Tamoxifen sensitivity in the MCF-7(EphA2) xenografts. Using the T47D(EphA2) in vitro model, we verified that EphA2 decreases ER activation in response to E2 stimulation consistent with our earlier results in MCF-7(EphA2) model. We found no direct interaction between ER and EphA2 and no difference in expression of canonical ER-dependent proteins or ER co-regulators. However, E2 stimulation phosphorylates FAK(Tyr925) only in ER+/EphA2+ cell lines. Treatment of T47D(EphA2) cells with EA5 and Tamoxifen leads to dephosphorylation of FAK(Tyr925) in response to E2. Our data demonstrate that dual targeting of EphA2 and ER is a promising approach for delaying resistance to Tamoxifen. The data support our hypothesis that EphA2 impacts ER function via a FAK dependent pathway.

HLA ligand profiles of primary renal cell carcinoma maintained in metastases

In recent years, several approaches have been taken in the peptide-based immunotherapy of metastatic renal cell carcinoma (RCC), although little is known about HLA presentation on metastases compared to primary tumor and normal tissue of RCC. In this study we compared primary tumor, normal tissue and metastases with the aim of identifying similarities and differences between these tissues. We performed this comparison for two RCC patients on the level of the HLA ligandome using mass spectrometry and for three patients on the level of the transcriptome using oligonucleotide microarrays. The quantitative results show that primary tumor is more similar to metastasis than to normal tissue, both on the level of HLA ligand presentation and mRNA. We were able to characterize a total of 142 peptides in the qualitative analysis of HLA-presented peptides. Six of them were significantly overpresented on metastasis, among them a peptide derived from CD151; fourteen were overpresented on both primary tumor and metastasis compared to normal tissue, among them an HLA ligand derived from tumor protein p53. Thus, we could demonstrate that peptide-based immunotherapy might affect tumor as well as metastasis of RCC, but not healthy kidney tissue. Furthermore we were able to identify several peptides derived from tumor-associated antigens that are suitable for vaccination of metastatic RCC.

Tetraspanin CD151 regulates RhoA activation and the dynamic stability of carcinoma cell-cell contacts

Tetraspanins regulate integrin-dependent tumor cell interactions with the extracellular matrix. Here we show that tetraspanin CD151, which plays critical roles in regulating the adhesion and motility of individual tumor cells, is also an important regulator of collective tumor cell migration. Near total silencing of CD151 destabilizes E-cadherin-dependent carcinoma cell-cell junctions and enhances the collective migration of intact tumor cell sheets. This effect does not depend on reduced E-cadherin cell-surface expression or intrinsic adhesivity, or on obvious disruptions in the E-cadherin regulatory complex. Instead, the loss of CD151 causes excessive RhoA activation, loss of actin organization at cell-cell junctions, and increased actin stress fibers at the basal cell surface. Cell-cell contacts within CD151-silenced monolayers display a nearly threefold increase in remodeling rate and a significant reduction in lifespan as compared to cell-cell contacts within wild-type monolayers. CD151 re-expression restores junctional stability, as does acute treatment of CD151-silenced cells with a cell-permeable RhoA inhibitor. However, a CD151 mutant with impaired association with α3β1 integrin fails to restore junctional organization. These data reveal that, in addition to its roles in regulating tumor cell-substrate interactions, CD151 is also an important regulator of the stability of tumor cell-cell interactions, potentially through its interaction with α3β1 integrin. This could help to explain the phenotypes in human patients and mice lacking CD151.