Genomic organization of the melanoma-associated glycoprotein MUC18: implications for the evolution of the immunoglobulin domains

Melanoma Cell Adhesion Molecule (CD 146) in Endometrial Physiology and Disorder

The human endometrium, the innermost lining of the uterus, is the anatomic prerequisite for pregnancy. It is the only dynamic tissue that undergoes more than 400 cycles of regeneration throughout the reproductive life of women. Key to this function are endometrial stem cells as well as cell adhesion molecules. Melanoma cell adhesion molecule (MCAM/CD146/MUC18) is a membrane glycoprotein of the mucin family and a key cell adhesion protein, highly expressed by endometrial cells. CD146 is a significant molecule pivotal in endometrial physiology, assisting tissue regeneration and angiogenesis. Endometrium also acts as a culprit in causing several endometrial dysfunctions, such as endometriosis, endometrial hyperplasia, and endometrial carcinoma, due to interrupted molecular and functional mechanisms. Though most of the endometrial dysfunctions arise as a result of endocrine disturbance, it has a major pathological role associated with angiogenesis. It has already been proven that CD146 is a potential marker for the diagnosis of angiogenic dysfunctions and malignancy, including endometrial cancer. However, its mechanistic role in causing the pathology is a mystery. This chapter explores the role of CD146 in normal and pathological endometrial conditions and the therapeutic implications of CD146.

Mcam inhibits macrophage-mediated development of mammary gland through non-canonical Wnt signaling

While canonical Wnt signaling is well recognized for its crucial regulatory functions in cell fate decisions, the role of non-canonical Wnt signaling in adult stem cells remains elusive and contradictory. Here, we identified Mcam, a potential member of the non-canonical Wnt signaling, as an important negative regulator of mammary gland epithelial cells (MECs) by genome-scale CRISPR-Cas9 knockout (GeCKO) library screening. Loss of Mcam increases the clonogenicity and regenerative capacity of MECs, and promotes the proliferation, differentiation, and ductal morphogenesis of mammary epithelial in knockout mice. Mechanically, Mcam knockout recruits and polarizes macrophages through the Il4-Stat6 axis, thereby promoting secretion of the non-canonical Wnt ligand Wnt5a and its binding to the non-canonical Wnt signaling receptor Ryk to induce the above phenotypes. These findings reveal Mcam roles in mammary gland development by orchestrating communications between MECs and macrophages via a Wnt5a/Ryk axis, providing evidences for non-canonical Wnt signaling in mammary development.

CD146 as a prognostic marker in breast cancer: A meta-analysis

BACKGROUND

CD146, a cell adhesion molecule, was first discovered in melanoma. Since then, it has been established as a promoter of tumor progression and metastasis. Many recent clinical studies have associated CD146 overexpression with poor prognosis in various cancers. However, clinical relevance of CD146 in prognosis of breast cancer has been poorly studied.

METHODS

We performed meta-analysis of data of all clinical studies associated with the prognostic value of CD146 expression in breast cancer. Relevant studies were retrieved from PubMed database as per the inclusion and exclusion criteria, data were extracted independently and carefully by two reviewers with the help of standardized form, and meta-analysis was performed to correlate CD146 expression with molecular subtypes, lymph node metastasis, and overall survival in breast cancer.

RESULTS

Our findings suggest that CD146 expression is predominantly found in triple-negative breast cancer subtype (pooled odds ratio = 2.98, 95% confidence interval [CI] =2.19-4.05, P < .00001) and breast tumors overexpressing CD146 have a higher risk of lymph node metastasis (pooled relative risk = 1.64, 95% CI = 1.44-1.87, P < .00001). Furthermore, high expression of CD146 was associated with poor prognosis in breast cancer (pooled hazard ratio = 1.51, 95% CI = 1.21-1.87, P = .0002).

CONCLUSION

Overall results suggested that CD146 may be a potential prognostic marker to predict metastatic potential and disease outcomes in breast cancer and can be used as a therapeutic target.

The tendon interfascicular basement membrane provides a vascular niche for CD146+ cell subpopulations

Introduction: The interfascicular matrix (IFM; also known as the endotenon) is critical to the mechanical adaptations and response to load in energy-storing tendons, such as the human Achilles and equine superficial digital flexor tendon (SDFT). We hypothesized that the IFM is a tendon progenitor cell niche housing an exclusive cell subpopulation. Methods: Immunolabelling of equine superficial digital flexor tendon was used to identify the interfascicular matrix niche, localising expression patterns of CD31 (endothelial cells), Desmin (smooth muscle cells and pericytes), CD146 (interfascicular matrix cells) and LAMA4 (interfascicular matrix basement membrane marker). Magnetic-activated cell sorting was employed to isolate and compare in vitro properties of CD146+ and CD146- subpopulations. Results: Labelling for CD146 using standard histological and 3D imaging of large intact 3D segments revealed an exclusive interfascicular cell subpopulation that resides in proximity to a basal lamina which forms extensive, interconnected vascular networks. Isolated CD146+ cells exhibited limited mineralisation (osteogenesis) and lipid production (adipogenesis). Discussion: This study demonstrates that the interfascicular matrix is a unique tendon cell niche, containing a vascular-rich network of basement membrane, CD31+ endothelial cells, Desmin+ mural cells, and CD146+ cell populations that are likely essential to tendon structure and/or function. Contrary to our hypothesis, interfascicular CD146+ subpopulations did not exhibit stem cell-like phenotypes. Instead, our results indicate CD146 as a pan-vascular marker within the tendon interfascicular matrix. Together with previous work demonstrating that endogenous tendon CD146+ cells migrate to sites of injury, our data suggest that their mobilisation to promote intrinsic repair involves changes in their relationships with local interfascicular matrix vascular and basement membrane constituents.

MCAM/MUC18/CD146 as a Multifaceted Warning Marker of Melanoma Progression in Liquid Biopsy

Human malignant melanoma shows a high rate of mortality after metastasization, and its incidence is continuously rising worldwide. Several studies have suggested that MCAM/MUC18/CD146 plays an important role in the progression of this malignant disease. MCAM/MUC18/CD146 is a typical single-spanning transmembrane glycoprotein, existing as two membrane isoforms, long and short, and an additional soluble form, sCD146. We previously documented that molecular MCAM/MUC18/CD146 expression is strongly associated with disease progression. Recently, we showed that MCAM/MUC18/CD146 and ABCB5 can serve as melanoma-specific-targets in the selection of highly primitive circulating melanoma cells, and constitute putative proteins associated with disease spreading progression. Here, we analyzed CD146 molecular expression at onset or at disease recurrence in an enlarged melanoma case series. For some patients, we also performed the time courses of molecular monitoring. Moreover, we explored the role of soluble CD146 in different cohorts of melanoma patients at onset or disease progression, rather than in clinical remission, undergoing immune therapy or free from any clinical treatment. We showed that MCAM/MUC18/CD146 can be considered as: (1) a membrane antigen suitable for identification and enrichment in melanoma liquid biopsy; (2) a highly effective molecular "warning" marker for minimal residual disease monitoring; and (3) a soluble protein index of inflammation and putative response to therapeutic treatments.

Microphthalmia-Associated Transcription Factor-Dependent Melanoma Cell Adhesion Molecule Activation Promotes Peritoneal Metastasis of Ovarian Cancer

Ovarian cancer (OvCa) is one of the leading causes of death due to its high metastasis rate to the peritoneum. Recurrent peritoneal tumors also develop despite the use of conventional platinum-based chemotherapies. Therefore, it is still important to explore the factors associated with peritoneal metastasis, as these predict the prognosis of patients with OvCa. In this study, we investigated the function of microphthalmia-associated transcription factor (MITF), which contributes to the development of melanoma, in epithelial ovarian cancer (OvCa). High MITF expression was significantly associated with a poor prognosis in OvCa. Notably, MITF contributed to the motility and invasion of OvCa cells, and specifically with their peri-mesothelial migration. In addition, MITF-positive cells expressed the melanoma cell adhesion molecule (MCAM/CD146), which was initially identified as a marker of melanoma progression and metastasis, and MCAM expression was regulated by MITF. MCAM was also identified as a significant prognostic factor for poor progression-free survival in patients with OvCa. Collectively, our results suggest that MITF is a novel therapeutic target that potentially promotes peritoneal metastasis of OvCa.

CD146 (Cluster of Differentiation 146)

CD146 (cluster of differentiation 146) is an adhesion molecule that is expressed by different cells constituting vessels, particularly endothelial cells. The last 30 years of research in this field have shown that CD146 plays a key role in the control of several vessel functions. Three forms of CD146 have been described, including 2 transmembrane isoforms and a soluble protein that is detectable in the plasma. These CD146 forms mediate pleiotropic functions through homophilic and heterophilic interactions with proteins present on surrounding partners. Several studies used neutralizing antibodies, siRNA, or genetically modified mice to demonstrate the involvement of CD146 in the regulation of angiogenesis, vascular permeability, and leukocyte transmigration. In this review, we will focus on the current knowledge of the roles of CD146 in vascular homeostasis and diseases associated with endothelial dysfunction.

CD146 is highly expressed in glioma stem cells and acts as a cell cycle regulator

INTRODUCTION

CD146 is highly expressed in various malignant tumors and contributes to their malignancy phenotype, which involves metastatic and tumorigenic activity. However, studies on the expression and function of CD146 in brain tumors are limited.

METHODS

We over-expressed or knocked-down CD146 in both conventionally cultured glioma cells and tumor spheres (TS). The distribution of glioma cells and their stem cells in different cell cycle phases was analyzed by flow cytometry using the stem cell marker CD133 and the glial precursor marker A2B5. CD146 expression was immunohistochemically examined in glioma tissues.

RESULTS

The majority of glioma stem cells (GSCs) expressing CD133 were also CD146-positive. CD146 knockdown in GSCs significantly compromised cell growth. Cell cycle analysis revealed that most of the CD146 and CD133 double-positive cells were in the G2/M phase. Ectopic expression of CD146 in parental glioma cells resulted in cell cycle arrest of most differentiated cells in G0/G1 phase. In contrast, ectopic expression of CD146 in GSCs resulted in an increase in the number of CD133-positive cells in the G2/M phase. Furthermore, CD146 knockdown reduced the number of CD133-positive cells in the G2/M phase, which was consistent with effects of cell growth inhibition. Immunohistochemical analysis revealed that CD146 expression was significantly upregulated in World Health Organization (WHO) Grade III and IV glioma and positively correlated with CD133 expression.

CONCLUSIONS

CD146 is mainly expressed in dividing GSCs and may be a potential target for eradicating glioma stem cells.

CD146-mediated acquisition of stemness phenotype enhances tumour invasion and metastasis after EGFR-TKI resistance in lung cancer

INTRODUCTION

Tumours are more likely to metastasize after the development of resistance to EGFR-TKIs. CD146 is a multifunctional molecule and is implicated in tumour invasion and metastasis; however, its role in lung cancer has not been clearly established.

OBJECTIVE

Here, we aimed to explore the relationship between CD146 pathway and stem cell phenotype after EGFR-TKI resistance in lung cancer.

METHODS

EGFR-TKI-resistant cell lines were established by exposing parental cells to erlotinib/gefitinib. The CD146 level was measured by a western blot, RT-PCR and immunocytochemistry fluorescent. Cell migration was examined by the transwell assay and the scratch assay. Stemness phenotype genes were evaluated by RT-PCR and stem cell phenotype was observed by the microsphere formation assay.

RESULTS

CD146 and stemness phenotype genes increased while β-catenin decreased in acquired EGFR-TKI-resistant cell lines. CD146's over-expression induced the up-regulation of stemness-related genes and was inversely correlated with the β-catenin expression, which further increased the migration capability of resistant cancer cells. CD146's knockdown suppressed cell migration and stemness phenotype.

CONCLUSIONS

CD146 molecule contributes to the stemness phenotype and migration in EGFR-TKI-resistant cells. CD146 might be a potential therapeutic target for EGFR-TKI-resistant lung cancer or metastasis prevention.

Critical role of the MCAM-ETV4 axis triggered by extracellular S100A8/A9 in breast cancer aggressiveness

Metastatic breast cancer is the leading cause of cancer-associated death in women. The progression of this fatal disease is associated with inflammatory responses that promote cancer cell growth and dissemination, eventually leading to a reduction of overall survival. However, the mechanism(s) of the inflammation-boosted cancer progression remains unclear. In this study, we found for the first time that an extracellular cytokine, S100A8/A9, accelerates breast cancer growth and metastasis upon binding to a cell surface receptor, melanoma cell adhesion molecule (MCAM). Our molecular analyses revealed an important role of ETS translocation variant 4 (ETV4), which is significantly activated in the region downstream of MCAM upon S100A8/A9 stimulation, in breast cancer progression in vitro as well as in vivo. The MCAM-mediated activation of ETV4 induced a mobile phenotype called epithelial-mesenchymal transition (EMT) in cells, since we found that ETV4 transcriptionally upregulates ZEB1, a strong EMT inducer, at a very high level. In contrast, downregulation of either MCAM or ETV4 repressed EMT, resulting in greatly weakened tumor growth and lung metastasis. Overall, our results revealed that ETV4 is a novel transcription factor regulated by the S100A8/A9-MCAM axis, which leads to EMT through ZEB1 and thereby to metastasis in breast cancer cells. Thus, therapeutic strategies based on our findings might improve patient outcomes.

Therapeutic Targeting of CD146/MCAM Reduces Bone Metastasis in Prostate Cancer

Prostate Cancer is the most common cancer and the second leading cause of cancer-related death in males. When prostate cancer acquires castration resistance, incurable metastases, primarily in the bone, occur. The aim of this study is to test the applicability of targeting melanoma cell adhesion molecule (MCAM; CD146) with a mAb for the treatment of lytic prostate cancer bone metastasis. We evaluated the effect of targeting MCAM using in vivo preclinical bone metastasis models and an in vitro bone niche coculture system. We utilized FACS, cell proliferation assays, and gene expression profiling to study the phenotype and function of MCAM knockdown in vitro and in vivo. To demonstrate the impact of MCAM targeting and therapeutic applicability, we employed an anti-MCAM mAb in vivo. MCAM is elevated in prostate cancer metastases resistant to androgen ablation. Treatment with DHT showed MCAM upregulation upon castration. We investigated the function of MCAM in a direct coculture model of human prostate cancer cells with human osteoblasts and found that there is a reduced influence of human osteoblasts on human prostate cancer cells in which MCAM has been knocked down. Furthermore, we observed a strongly reduced formation of osteolytic lesions upon bone inoculation of MCAM-depleted human prostate cancer cells in animal model of prostate cancer bone metastasis. This phenotype is supported by RNA sequencing (RNA-seq) analysis. Importantly, in vivo administration of an anti-MCAM human mAb reduced the tumor growth and lytic lesions. These results highlight the functional role for MCAM in the development of lytic bone metastasis and suggest that MCAM is a potential therapeutic target in prostate cancer bone metastasis. IMPLICATIONS: This study highlights the functional application of an anti-MCAM mAb to target prostate cancer bone metastasis.

Reduced CD146 expression promotes tumorigenesis and cancer stemness in colorectal cancer through activating Wnt/β-catenin signaling

Cancer stemness drives tumor progression and drug resistance, representing a challenge to cancer eradication. Compelling evidence indicates that cancer cells can reenter the stem cell state due to the reprogramming of self-renewal machinery. Here, we show that CD146 knockdown induces stem cell properties in colorectal cancer (CRC) cells through activating canonical Wnt signaling. shRNA-mediated CD146 knockdown in CRC cells facilitates tumor initiation in serial xenotransplantation experiments. Moreover, upon CD146 knockdown, CRC cells show elevated expression of specific cancer stem cell (CSC) markers, increased sphere and clone formation as well as drug resistance in vitro. Mechanistically, our findings provide evidence that CD146 expression negatively correlates with canonical Wnt/β-catenin activity in CRC cell lines and primary CRC specimens. Knockdown of CD146 results in inhibition of NF-κB/p65-initiated GSK-3β expression, subsequently promoting nuclear translocation and activation of β-catenin, and as a consequence restoring stem cell phenotypes in differentiated CRC cells. Together, our data strongly suggest that CD146 functions as a suppressor of tumorigenesis and cancer stemness in CRC through inactivating the canonical Wnt/β-catenin cascade. Our findings provide important insights into stem cell plasticity and the multifunctional role of CD146 in CRC progression.

A novel anti-CD146 antibody specifically targets cancer cells by internalizing the molecule

CD146 is an adhesion molecule present on many tumors (melanoma, kidney, pancreas, breast, ...). In addition, it has been shown to be expressed on vascular endothelial and smooth muscle cells. Generating an antibody able to specifically recognize CD146 in cancer cells (designated as tumor CD146), but not in normal cells, would thus be of major interest for targeting tumor CD146 without affecting the vascular system.

We thus generated antibodies against the extracellular domain of the molecule produced in cancer cells and selected an antibody that specifically recognizes tumor CD146. This antibody (TsCD146 mAb) was able to detect CD146-positive tumors in human biopsies and in vivo, by PET imaging, in a murine xenograft model. In addition, TsCD146 mAb antibody was able to specifically detect CD146-positive cancer microparticles in the plasma of patients. TsCD146 mAb displayed also therapeutic effects since it was able to reduce the growth of human CD146-positive cancer cells xenografted in nude mice. This effect was due to a decrease in the proliferation and an increase in the apoptosis of CD146-positive cancer cells after TsCD146-mediated internalization of the cell surface CD146.

Thus, TsCD146 mAb could be of major interest for diagnostic and therapeutic strategies against CD146-positive tumors in a context of personalized medicine.

Therapeutic and Diagnostic Antibodies to CD146: Thirty Years of Research on Its Potential for Detection and Treatment of Tumors

CD146 (MCAM, MUC18, S-Endo1) is a transmembrane glycoprotein belonging to both CAM and mucin families. It exists as different splice variants and is cleaved from the membrane by metalloproteases to generate a soluble form. CD146 is expressed by numerous cancer cells as well as being one of the numerous proteins expressed by the vascular endothelium. It has also been identified on smooth muscle cells, pericytes, and some immune cells. This protein was initially described as an actor involved in tumor growth and metastatic dissemination processes. Some recent works highlighted the role of CD146 in angiogenesis. Interestingly, this knowledge allowed the development of therapeutic and diagnostic tools specifically targeting the different CD146 variants. The first anti-CD146 antibody designed to study the function of this molecule, MUC18, was described by the Pr. J.P. Jonhson in 1987. In this review, we will discuss the 30 following years of research focused on the detection, study, and blocking of this protein in physiological and pathological processes.

Prognostic value of CD146 in solid tumor: A Systematic Review and Meta-analysis

CD146, also known as melanoma cell adhesion molecule, was initially identified as a marker of melanoma progression and metastasis. Recently many clinical studies investigated overexpression of CD146 predict poor prognosis of solid tumor, however, the results was inconclusive, partly due to small numbers of patients included. This present meta-analysis was therefore performed utilizing the results of all clinical studies concerned to determine the prognostic value of CD146 expression in solid tumors. Relevant articles were identified through searching the PubMed, Web of Science and Embase database. In this meta-analysis, 12 studies involving 2,694 participants were included, and we drew the conclusion that strong significant associations between CD146 expression and all endpoints: overall survival (OS) [hazard ratio (HR) = 2.496, 95% confidence interval (95% CI) 2.115–2.946], time to progression (TTP) (HR = 2.445, 95% CI 1.975–3.027). Furthermore, the subgroup analysis revealed that the associations between CD146 overexpression and the outcome endpoints (OS or TTP) were significant in Mongoloid patients and Caucasian patients, as well in patients with lung cancer and digestive system cancer. In conclusion, these results showed that high CD146 was associated with poor survival in human solid tumors. CD146 may be a valuable prognosis predictive biomarker; nevertheless, whether CD146 could be a potential therapeutic target in human solid tumors needs to be further studied.

Beneficial roles of melanoma cell adhesion molecule in spinal cord transection recovery in adult zebrafish

Melanoma cell adhesion molecule (MCAM) is a multifunctional protein involved in miscellaneous processes, including development and tumor angiogenesis. Here, spinal cord transection in adult zebrafish was used to investigate the effects of MCAM on spinal cord injury (SCI) and subsequent recovery. Expression of MCAM mRNA increased and co-localized with motoneurons in the spinal cord after SCI. With MCAM morpholino treatment, inhibition of MCAM retarded both axon regrowth and locomotor recovery in the spinal cord injured zebrafish. Furthermore, MCAM mRNA expression was also observed in fli1a:EGFP transgenic zebrafish, which specifically show labeled blood vessels. Inhibition of MCAM down-regulated the expression of angiogenesis-related factors, such as VEGFR-2, p-p38 and p-AKT, and the inflammatory factors TNF-α, IL-1β and IL-8. Taken together, these data suggest that MCAM may have a beneficial role in the recovery from SCI, via the promotion of neurogenesis and angiogenesis. In the context of adult zebrafish spinal cord injury, we proved that Melanoma cell adhesion molecule (MCAM) is beneficial to the recovery, possibly via mechanisms of angiogenensis and inflammation. MCAM promotes angiogenesis by adjusting VEGFR-2, p-p38 and p-AKT. MCAM affects inflammatory factors such as TNF-α, IL-1β and IL-8. Our results extend the beneficial role of MCAM in the regeneration of central nervous system.

The isolation and characterization of systemic sclerosis vascular smooth muscle cells: enhanced proliferation and apoptosis resistance

Background

Vascular dysfunction is a major pathologic component of systemic sclerosis (SSc). The role of vascular smooth muscle cells (vSMCs) in the development of vascular dysfunction is still unknown. In this study, we describe a method for isolation of dermal vSMCs from skin biopsies, and we outline their functional phenotype.

Methods

We obtained 4 mm punch-skin biopsies from three SSc patients and matched controls. After trypsin digestion, cells were cultured for 14 days. vSMCs were isolated by first depleting CD31+ cells (endothelial cells), followed by positive selection of CD146+ cells. The CD31- CD146+ cells were then cultured in media optimized for SMCs proliferation. We evaluated cell proliferation, viability and apoptosis in normal and in low serum culture conditions. Cytoplasmic and nuclear expression levels of β-catenin were also investigated.

Results

The CD31- CD146+ cell population expressed smooth muscle MYH11, Desmin and Vimentin but did not express NG2. Flow cytometry confirmed the high purity of CD31- CD146+ MYHC11+ cell population that was maintained for up to the eleventh passage. SSc-vSMCs exhibited increased cell proliferation and viability compared to control cells. Under serum starvation conditions, SSc-vSMCs exhibited more proliferative capacity, and resistance to apoptosis compared to control-vSMCs. Furthermore, a cytoplasmic to nuclear translocation of β-catenin was seen in SSc-vSMCs but not in control-vSMCs.

Conclusions

This is the first report of successful isolation and initial characterization of SSc-vSMCs. It is likely that increased proliferation of SSc-vSMCs in association with resistance to apoptosis can adversely impact the vascular lesion in SSc.

CD146 promotes metastasis and predicts poor prognosis of hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related mortality worldwide. Recurrence and metastasis after curative resection remain critical obstacles in HCC treatment. CD146 predicted poor prognosis of a variety of cancers including melanoma, breast tumors, prostate cancer, and gastric cancer. However, the role of CD146 in HCC has not yet been systematically explored.

METHODS

To investigate the role of CD146 in HCC, we evaluated its expression in HCC tissues and HCC cell lines using real-time PCR and western blotting (WB). Second, we established HCC cell lines that stably overexpressed and interfered CD146 and explored the function of CD146 in HCC in vitro and in vivo. Third, we conducted microarray analysis to investigate the potential mechanism by identifying differentially expressed genes. Last, follow ups were conducted to help uncover the connection of CD146 expression and the prognosis of HCC patients.

RESULTS

We found that CD146 was overexpressed in HCC tissues and that high CD146 expression predicted poor overall survival time and shorter recurrence period in HCC patients. In vitro and in vivo experiments indicated that CD146 promoted migration and invasion of HCC cell lines. Further study indicated that CD146 promoted epithelial mesenchymal transition (EMT), IL-8 upregulation, and STAT1 downregulation. CD146 was upregulated in HCC tissues and cell lines.

CONCLUSIONS

CD146 promoted metastasis of HCC cells and predicted poor prognosis of HCC patients. CD146 induced EMT, and IL-8 upregulation and STAT1 downregulation may be the potential underlying mechanism. The exact mechanism still needs further investigation.

Gene array analysis of neural crest cells identifies transcription factors necessary for direct conversion of embryonic fibroblasts into neural crest cells

Neural crest cells (NC cells) are multipotent cells that emerge from the edge of the neural folds and migrate throughout the developing embryo. Although the gene regulatory network for generation of NC cells has been elucidated in detail, it has not been revealed which of the factors in the network are pivotal to directing NC identity. In this study we analyzed the gene expression profile of a pure NC subpopulation isolated from Sox10-IRES-Venus mice and investigated whether these genes played a key role in the direct conversion of Sox10-IRES-Venus mouse embryonic fibroblasts (MEFs) into NC cells. The comparative molecular profiles of NC cells and neural tube cells in 9.5-day embryos revealed genes including transcription factors selectively expressed in developing trunk NC cells. Among 25 NC cell-specific transcription factor genes tested, SOX10 and SOX9 were capable of converting MEFs into SOX10-positive (SOX10+) cells. The SOX10+ cells were then shown to differentiate into neurons, glial cells, smooth muscle cells, adipocytes and osteoblasts. These SOX10+ cells also showed limited self-renewal ability, suggesting that SOX10 and SOX9 directly converted MEFs into NC cells. Conversely, the remaining transcription factors, including well-known NC cell specifiers, were unable to convert MEFs into SOX10+ NC cells. These results suggest that SOX10 and SOX9 are the key factors necessary for the direct conversion of MEFs into NC cells.

Summary: In this study, we identified the transcription factors specifically expressed in developing neural crest cells, and showed that SOX10 and SOX9 directly converted fibroblasts into neural crest cells.

Cell Adhesion Molecules and Ubiquitination-Functions and Significance

Cell adhesion molecules of the immunoglobulin (Ig) superfamily represent the biggest group of cell adhesion molecules. They have been analyzed since approximately 40 years ago and most of them have been shown to play a role in tumor progression and in the nervous system. All members of the Ig superfamily are intensively posttranslationally modified. However, many aspects of their cellular functions are not yet known. Since a few years ago it is known that some of the Ig superfamily members are modified by ubiquitin. Ubiquitination has classically been described as a proteasomal degradation signal but during the last years it became obvious that it can regulate many other processes including internalization of cell surface molecules and lysosomal sorting. The purpose of this review is to summarize the current knowledge about the ubiquitination of cell adhesion molecules of the Ig superfamily and to discuss its potential physiological roles in tumorigenesis and in the nervous system.

CRISPR-Cas9-mediated gene knockout in primary human airway epithelial cells reveals a proinflammatory role for MUC18

Targeted knockout of genes in primary human cells using CRISPR-Cas9 mediated genome-editing represents a powerful approach to study gene function and to discern molecular mechanisms underlying complex human diseases. We used lentiviral delivery of CRISPR-Cas9 machinery and conditional reprogramming culture methods to knockout the MUC18 gene in human primary nasal airway epithelial cells (AECs). Massively parallel sequencing technology was used to confirm that the genome of essentially all cells in the edited AEC populations contained coding region insertions and deletions (indels). Correspondingly, we found mRNA expression of MUC18 was greatly reduced and protein expression was absent. Characterization of MUC18 knockout cell populations stimulated with TLR2, 3 and 4 agonists revealed that IL-8 (a pro-inflammatory chemokine) responses of AECs were greatly reduced in the absence of functional MUC18 protein. Our results show the feasibility of CRISPR-Cas9 mediated gene knockouts in AEC culture (both submerged and polarized), and suggest a pro-inflammatory role for MUC18 in airway epithelial response to bacterial and viral stimuli.

Selection of scFv Antibody Fragments Binding to Human Blood versus Lymphatic Endothelial Surface Antigens by Direct Cell Phage Display

The identification of marker molecules specific for blood and lymphatic endothelium may provide new diagnostic tools and identify new targets for therapy of immune, microvascular and cancerous diseases. Here, we used a phage display library expressing human randomized single-chain Fv (scFv) antibodies for direct panning against live cultures of blood (BECs) and lymphatic (LECs) endothelial cells in solution. After six panning rounds, out of 944 sequenced antibody clones, we retrieved 166 unique/diverse scFv fragments, as indicated by the V-region sequences. Specificities of these phage clone antibodies for respective compartments were individually tested by direct cell ELISA, indicating that mainly pan-endothelial cell (EC) binders had been selected, but also revealing a subset of BEC-specific scFv antibodies. The specific staining pattern was recapitulated by twelve phage-independently expressed scFv antibodies. Binding capacity to BECs and LECs and differential staining of BEC versus LEC by a subset of eight scFv antibodies was confirmed by immunofluorescence staining. As one antigen, CD146 was identified by immunoprecipitation with phage-independent scFv fragment. This antibody, B6-11, specifically bound to recombinant CD146, and to native CD146 expressed by BECs, melanoma cells and blood vessels. Further, binding capacity of B6-11 to CD146 was fully retained after fusion to a mouse Fc portion, which enabled eukaryotic cell expression. Beyond visualization and diagnosis, this antibody might be used as a functional tool. Overall, our approach provided a method to select antibodies specific for endothelial surface determinants in their native configuration. We successfully selected antibodies that bind to antigens expressed on the human endothelial cell surfaces in situ, showing that BECs and LECs share a majority of surface antigens, which is complemented by cell-type specific, unique markers.

An ultrasensitive electrochemical immunosensor for the detection of CD146 based on TiO2 colloidal sphere laden Au/Pd nanoparticles

An ultrasensitive electrochemical immunosensor was developed for detecting CD146. rGO-TEPA enhanced the loading capacity of Ab₁ and facilitated the electron transfer. Au and Pd nanoparticles on the TiO₂ colloidal sphere facilitated the decomposition of H₂O₂. The immunosensor exhibited an extremely low detection limit of 1.6 pg mL⁻¹ for CD146.

MUC18 Differentially Regulates Pro-Inflammatory and Anti-Viral Responses in Human Airway Epithelial Cells

OBJECTIVE

MUC18 or CD146, a transmembrane glycoprotein, is mainly expressed by endothelial cells and smooth muscle cells where it serves as a cell-cell adhesion molecule. We have found MUC18 up-regulation in airway epithelial cells of patients with asthma and chronic obstructive pulmonary disease (COPD). However, the function of MUC18 in airway epithelial cells remains unclear. In the present study, we tested the hypothesis that MUC18 exerts a pro-inflammatory function during stimulation with a viral mimic polyI:C or human rhinovirus infection.

METHODS

Normal human primary airway epithelial cells were transduced with lentivirus encoding MUC18 cDNA to over-express MUC18 or with GFP (control), and treated with polyI:C or HRV for detection of pro-inflammatory cytokine IL-8 and anti-viral gene IFN-β. Additionally, we performed cell culture of human lung epithelial cell line NCIH292 cells to determine the mechanisms of MUC18 function.

RESULTS

We found that MUC18 over-expression promoted IL-8 production, while it inhibited IFN-β expression following polyI:C stimulation or HRV infection. Increased phosphorylation of MUC18 serines was observed in MUC18 over-expressing cells. Reduction of MUC18 serine phosphorylation by inhibiting ERK activity was associated with less production of IL-8 following polyI:C stimulation.

CONCLUSIONS

Our results for the first time demonstrate MUC18's pro-inflammatory and anti-viral function in human airway epithelial cells.

CD146 expression on mesenchymal stem cells is associated with their vascular smooth muscle commitment

Bone marrow mesenchymal stem cells (MSCs) are plastic adherent cells that can differentiate into various tissue lineages, including osteoblasts, adipocytes and chondrocytes. However, this progenitor property is not shared by all cells within the MSC population. In addition, MSCs vary in their proliferation capacity and expression of markers. Because of heterogeneity of CD146 expression in the MSC population, we compared CD146^−/Low and CD146^High cells under clonal conditions and after sorting of the non-clonal cell population to determine whether this expression is associated with specific functions. CD146^−/Low and CD146^High bone marrow MSCs did not differ in colony-forming unit-fibroblast number, osteogenic, adipogenic and chondrogenic differentiation or in vitro haematopoietic-supportive activity. However, CD146^−/Low clones proliferated slightly but significantly faster than did CD146^High clones. In addition, a strong expression of CD146 molecule was associated with a commitment to a vascular smooth muscle cell (VSMC) lineage characterized by a strong up-regulation of calponin-1 and SM22α expression and an ability to contract collagen matrix. Thus, within a bone marrow MSC population, certain subpopulations characterized by high expression of CD146, are committed towards a VSMC lineage.

Melanoma biomolecules: independently identified but functionally intertwined

The majority of patients diagnosed with melanoma present with thin lesions and generally these patients have a good prognosis. However, 5% of patients with early melanoma (<1 mm thick) will have recurrence and die within 10 years, despite no evidence of local or metastatic spread at the time of diagnosis. Thus, there is a need for additional prognostic markers to help identify those patients that may be at risk of recurrent disease. Many studies and several meta-analyses have compared gene and protein expression in melanocytes, naevi, primary, and metastatic melanoma in an attempt to find informative prognostic markers for these patients. However, although a large number of putative biomarkers have been described, few of these molecules are informative when used in isolation. The best approach is likely to involve a combination of molecules. We believe one approach could be to analyze the expression of a group of interacting proteins that regulate different aspects of the metastatic pathway. This is because a primary lesion expressing proteins involved in multiple stages of metastasis may be more likely to lead to secondary disease than one that does not. This review focuses on five putative biomarkers – melanoma cell adhesion molecule (MCAM), galectin-3 (gal-3), matrix metalloproteinase 2 (MMP-2), chondroitin sulfate proteoglycan 4 (CSPG4), and paired box 3 (PAX3). The goal is to provide context around what is known about the contribution of these biomarkers to melanoma biology and metastasis. Although each of these molecules have been independently identified as likely biomarkers, it is clear from our analyses that each are closely linked with each other, with intertwined roles in melanoma biology.

Mucins as diagnostic and prognostic biomarkers in a fish-parasite model: transcriptional and functional analysis

Mucins are O-glycosylated glycoproteins present on the apex of all wet-surfaced epithelia with a well-defined expression pattern, which is disrupted in response to a wide range of injuries or challenges. The aim of this study was to identify mucin gene sequences of gilthead sea bream (GSB), to determine its pattern of distribution in fish tissues and to analyse their transcriptional regulation by dietary and pathogenic factors. Exhaustive search of fish mucins was done in GSB after de novo assembly of next-generation sequencing data hosted in the IATS transcriptome database (www.nutrigroup-iats.org/seabreamdb). Six sequences, three categorized as putative membrane-bound mucins and three putative secreted-gel forming mucins, were identified. The transcriptional tissue screening revealed that Muc18 was the predominant mucin in skin, gills and stomach of GSB. In contrast, Muc19 was mostly found in the oesophagus and Muc13 was along the entire intestinal tract, although the posterior intestine exhibited a differential pattern with a high expression of an isoform that does not share a clear orthologous in mammals. This mucin was annotated as intestinal mucin (I-Muc). Its RNA expression was highly regulated by the nutritional background, whereas the other mucins, including Muc2 and Muc2-like, were expressed more constitutively and did not respond to high replacement of fish oil (FO) by vegetable oils (VO) in plant protein-based diets. After challenge with the intestinal parasite Enteromyxum leei, the expression of a number of mucins was decreased mainly in the posterior intestine of infected fish. But, interestingly, the highest down-regulation was observed for the I-Muc. Overall, the magnitude of the changes reflected the intensity and progression of the infection, making mucins and I-Muc, in particular, reliable markers of prognostic and diagnostic value of fish intestinal health.

MCAM expression is associated with poor prognosis in non-small cell lung cancer

BACKGROUND

MCAM has been recently identified as a biomarker for epithelial-mesenchymal transition (EMT) and is potentially involved in metastasis of cancer. The current study aimed at investigating the expression of MCAM in non-small-cell lung cancer (NSCLC) and its clinico-pathological significance.

METHODS

A follow-up analysis was performed on 118 patients with NSCLC resected by lobectomy or pneumectomy with systematic lymph node dissection. All patients were followed for 6-60 months. Immunostaining of tissue sections from primary tumors and their lymph node metastasis was performed and evaluated using monoclonal antibody against MCAM, E-cadherin, and vimentin. Correlations were investigated between MCAM immunostaining in primary tumors and E-cadherin, vimentin immunostaining, lymph node metastasis, and survival.

RESULTS

MCAM protein expression was found in 46.61 % of squamous cell carcinomas and 37.47 % of adenocarcinomas; MCAM expression positively correlated with vimentin, but inversely with E-cadherin (both P values <0.05). There were significant correlations between the MCAM immunostaining score in primary tumors and in their lymph node metastasis (P = 0.03). According to the Kaplan-Meier survival estimate, the level of MCAM expression in primary tumors was a statistically significant prognostic factor (P < 0.05).

CONCLUSIONS

MCAM expression in surgically treated NSCLC is clearly associated with lymph node metastasis and poor prognosis.

CD146, a multi-functional molecule beyond adhesion

CD146 is a cell adhesion molecule (CAM) that is primarily expressed at the intercellular junction of endothelial cells. CD146 was originally identified as a tumor marker for melanoma (MCAM) due to its existence only in melanoma but not in the corresponding normal counterpart. However CD146 is not just a CAM for the inter-cellular and cell-matrix adhesion. Recent evidence indicates that CD146 is actively involved in miscellaneous processes, such as development, signaling transduction, cell migration, mesenchymal stem cells differentiation, angiogenesis and immune response. CD146 has increasingly become an important molecule, especially identified as a novel bio-marker for angiogenesis and for cancer. Here we have reviewed the dynamic research of CD146, particularly newly identified functions and the underlying mechanisms of CD146.

CD146 expression in human breast cancer cell lines induces phenotypic and functional changes observed in Epithelial to Mesenchymal Transition

BACKGROUND

Metastasis is an important step in tumor progression leading to a disseminated and often incurable disease. First steps of metastasis include down-regulation of cell adhesion molecules, alteration of cell polarity and reorganization of cytoskeleton, modifications associated with enhanced migratory properties and resistance of tumor cells to anoikis. Such modifications resemble Epithelial to Mesenchymal Transition (EMT). In breast cancer CD146 expression is associated with poor prognosis and enhanced motility.

METHODOLOGY/PRINCIPAL FINDINGS

On 4 different human breast cancer cell lines, we modified CD146 expression either with shRNA technology in CD146 positive cells or with stable transfection of CD146 in negative cells. Modifications in morphology, growth and migration were evaluated. Using Q-RT-PCR, we analyzed the expression of different EMT markers. We demonstrate that high levels of CD146 are associated with loss of cell-cell contacts, expression of EMT markers, increased cell motility and increased resistance to doxorubicin or docetaxel. Experimental modulation of CD146 expression induces changes consistent with the above described characteristics: morphology, motility, growth in anchorage independent conditions and Slug mRNA variations are strictly correlated with CD146 expression. These changes are associated with modifications of ER (estrogen receptor) and Erb receptors and are enhanced by simultaneous and opposite modulation of JAM-A, or exposure to heregulin, an erb-B4 ligand.

CONCLUSIONS

CD146 expression is associated with an EMT phenotype. Several molecules are affected by CD146 expression: direct or indirect signaling contributes to EMT by increasing Slug expression. CD146 may also interact with Erb signaling by modifying cell surface expression of ErbB3 and ErbB4 and increased resistance to chemotherapy. Antagonistic effects of JAM-A, a tight junction-associated protein, on CD146 promigratory effects underline the complexity of the adhesion molecules network in tumor cell migration and metastasis.

MCAM is a novel metastasis marker and regulates spreading, apoptosis and invasion of ovarian cancer cells

Melanoma cell adhesion molecule (MCAM) is a cell adhesion molecule that is abnormally expressed in a variety of tumours and is closely associated with tumour metastasis. The role of MCAM in ovarian cancer development has not been fully studied. In this study, through immunohistochemical staining of ovarian cancer tissue samples and RNA interference to silence MCAM in ovarian cancer cells, we examined the impact of MCAM on the biological functions of ovarian cancer cells and attempted to reveal the role of MCAM in ovarian cancer development. Our results showed that MCAM expression was particularly high in metastatic ovarian cancers compared with other pathological types of ovarian epithelial tissues. After MCAM silencing in the MCAM high-expression ovarian cancer cell line SKOV-3, the cell apoptosis was increased, whereas the cell spreading and invasion were significantly reduced, which may be related with dysregulation of small RhoGTPase (RhoA and Cdc42).These results suggest that MCAM expression in ovarian cancer is highly correlated with the metastatic potential of the cancer. MCAM is likely to participate in the regulation of the Rho signalling pathway to protect ovarian cancer cells from apoptosis and promote their malignant invasion and metastasis. Therefore, MCAM can be used not only as a molecular marker to determine the prognosis of ovarian cancer but also as a therapeutic target in metastatic ovarian cancer.

Coexpression of CCR6 and CD146 (MCAM) is a marker of effector memory T-helper 17 cells

Effector memory T (T(EM)) cells are a subpopulation of memory T cells that express receptors mediating migration to inflamed tissues and produce various cytokines. Effector memory T-helper (Th)17 (Th17(EM)) cells are thought to be essential for inflammation in Th17-mediated diseases, but have not been studied in detail. To identify superior surface markers to isolate a homogeneous population of Th17(EM) cells from peripheral blood, CD4(+) T cells were isolated from the peripheral blood of healthy donors based on the expression of CCR7, CCR6 and CD146 using six-color flow cytometry. After 4days of culture in the presence of anti-CD3/28 beads, intracellular cytokines were determined by flow cytometric analysis. To investigate the relevance of Th17(EM) cells in Th17-mediated disease, the frequencies of T(EM) -cell subsets in psoriasis were quantified using six-color flow cytometry. An enzyme-linked immunosorbent assay was performed to confirm the interleukin (IL)-17-producing capacity of T(EM) -cell subsets from the peripheral blood of a patient with psoriasis. CCR6(+) CD146(+) T(EM) (CD4(+) CD45RA(-) CCR7(-)) cells had a greater capacity to produce IL-17 than CCR6(+) CD146(-) or CCR6(-) CD146(+) T(EM) cells. Although the percentage of CCR6(+) CD146(+) cells in T(EM) cells was not significantly different between patients with psoriasis and controls, three of eight patients had a higher percentage of CCR6(+) CD146(+) T(EM) cells than the mean +5 standard deviations of the controls. Coexpression of CCR6 and CD146 is a useful marker for Th17(EM) cells. Increasing the number of CCR6(+) CD146(+) Th17(EM) cells in peripheral blood may facilitate estimation of systemic Th17-cell activity in Th17-mediated diseases.

PKCθ synergizes with TLR-dependent TRAF6 signaling pathway to upregulate MUC5AC mucin via CARMA1

CARD-containing MAGUK protein 1 (CARMA1) plays a crucial role in regulating adaptive immune responses upon T-cell receptor (TCR) activation in T cells. Its role in regulating host mucosal innate immune response such as upregulation of mucin remains unknown. Here we show that CARMA1 acts as a key signaling mediator for synergistic upregulation of MUC5AC mucin by bacterium nontypeable Haemophilus influenzae (NTHi) and phorbol ester PMA in respiratory epithelial cells. NTHi-induced TLR-dependent TRAF6-MKK3-p38 MAPK signaling pathway synergizes with PKCθ-MEK-ERK signaling pathway. CARMA1 plays a crucial role in mediating this synergistic effect via TRAF6, thereby resulting in synergistic upregulation of MUC5AC mucin. Thus our study unveils a novel role for CARMA1 in mediating host mucosal innate immune response.

Expression of Id-1 is regulated by MCAM/MUC18: a missing link in melanoma progression

The acquisition of the metastatic melanoma phenotype is associated with increased expression of the melanoma cell adhesion molecule MCAM/MUC18 (CD146). However, the mechanism by which MUC18 contributes to melanoma metastasis remains unclear. Herein, we stably silenced MUC18 expression in two metastatic melanoma cell lines, A375SM and C8161, and conducted cDNA microarray analysis. We identified and validated that the transcriptional regulator, inhibitor of DNA binding-1 (Id-1), previously shown to function as an oncogene in several malignancies, including melanoma, was downregulated by 5.6-fold following MUC18 silencing. Additionally, we found that MUC18 regulated Id-1 expression at the transcriptional level via ATF-3, which itself was upregulated by 6.9-fold in our cDNA microarray analysis. ChIP analysis showed increased binding of ATF-3 to the Id-1 promoter after MUC18 silencing. To complement these studies, we rescued the expression of MUC18, which reversed the expression patterns of Id-1 and ATF-3. Moreover, we showed that MUC18 promotes melanoma invasion through Id-1, as overexpression of Id-1 in MUC18-silenced cells resulted in increased MMP-2 expression and activity. To our knowledge, this is the first demonstration that MUC18 is involved in cell signaling regulating the expression of Id-1 and ATF-3, thus contributing to melanoma metastasis.

Up-regulation of MUC18 in airway epithelial cells by IL-13: implications in bacterial adherence

Airway bacterial infections are a major problem in lung diseases, including asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis. Increased Th2 cytokines, such as IL-13, are observed in lung diseases and may contribute to bacterial infections. How Th2 cytokines affect bacterial infection remains unknown. MUC18, an adhesion molecule shown to be involved in the pathogenesis of malignant melanoma, has been recently identified in airway epithelial cells of patients with COPD. We investigated MUC18 regulation by IL-13 and the role of MUC18 in bacterial adherence to epithelial cells. Human airway tissues, brushed bronchial epithelial cells from normal subjects and subjects with asthma, and epithelial cell lines (e.g., HEK293 cells) were used to study the regulation of MUC18 by IL-13 and the involvement of MUC18 in bacterial (e.g., Mycoplasma pneumoniae [Mp] and nontypeable Haemophilus influenzae [NTHi]) adherence to epithelial cells. Asthmatic bronchial epithelium expressed higher levels of MUC18 than normal bronchial epithelium. IL-13 increased MUC18 in cultured bronchial epithelial cells from normal subjects and particularly from subjects with asthma. IL-13-induced MUC18 expression may be modulated in part through transcription factor specificity protein 1. Overexpression of human MUC18 in HEK293 cells increased cell-associated Mp and NTHi levels. Moreover, MUC18 was shown to directly interact with Mp and NTHi. These results for the first time show that an allergic airway milieu (e.g., IL-13) increases MUC18 expression, which may contribute to increased bacterial infection/colonization in asthma and other lung diseases.

Transcriptional control of melanoma metastasis: the importance of the tumor microenvironment

The molecular changes associated with the transition of melanoma cells from radial growth phase (RGP) to vertical growth phase (VGP) and the metastatic phenotype are not very well defined. However, some of the genes involved in this process and their transcriptional regulation are beginning to be elucidated. For example, the switch from RGP to VGP and the metastatic phenotype is associated with loss of the AP-2α transcription factor. AP-2α regulates the expression of c-KIT, MMP-2, VEGF, and the adhesion molecule MCAM/MUC18. Recently, we reported that AP-2α also regulates two G-protein coupled receptors (GPCRs) PAR-1 and PAFR. In turn, the thrombin receptor, PAR-1, regulates the expression of the gap junction protein Connexin-43 and the tumor suppressor gene Maspin. Activation of PAR-1 also leads to overexpression and secretion of proangiogenic factors such as IL-8, uPA, VEGF, PDGF, as well certain integrins. PAR-1 also cooperates with PAFR to regulate the expression of the MCAM/MUC18 via phosphorylation of CREB. The ligands for these GPCRs, thrombin and PAF, are secreted by stromal cells, emphasizing the importance of the tumor microenvironment in melanoma metastasis. The metastatic phenotype of melanoma is also associated with overexpression and function of CREB/ATF-1. Loss of AP-2α and overexpression of CREB/ATF-1 results in the overexpression of MCAM/MUC18 which by itself contributes to melanoma metastasis by regulating the inhibitor of DNA binding-1 (Id-1). CREB/ATF-1 also regulates the angiogenic factor CYR-61. Our recent data indicate that CREB/ATF-1 regulates the expression of AP-2α, thus, supporting the notion that CREB is an important "master switch" in melanoma progression.

Soluble CD146 is generated by ectodomain shedding of membrane CD146 in a calcium-induced, matrix metalloprotease-dependent process

CD146 is a cell adhesion molecule localized at the endothelial junction and is involved in the control of cell-cell cohesion. In this study, we showed that calcium influx in human microvascular lung endothelial cells results in the loss of surface CD146 and the release of soluble CD146. This calcium-induced CD146 shedding could be prevented with inhibitors of matrix metalloproteases indicating a central role of matrix metalloproteases in this process. We also investigated if CD146 shedding influences vascular permeability. Endothelial cell monolayers cultured on filter membranes showed an increased permeability for albumin when stimulated with ionomycin. This calcium-induced increase in permeability was inhibited when CD146 shedding was prevented by a matrix metalloprotease inhibitor. Our data indicate that surface CD146 plays a central role in the regulation of vascular permeability and demonstrate that CD146 and matrix metalloproteases are potential targets to modify endothelial barrier function.

Identification of MCAM/CD146 as the target antigen of a human monoclonal antibody that recognizes both epithelioid and sarcomatoid types of mesothelioma

The prognosis for patients diagnosed with mesothelioma is generally poor, and currently available treatments are usually ineffective. Therapies that specifically target tumor cells hold much promise for the treatment of cancers that are resistant to current approaches. We have previously selected phage antibody display libraries on mesothelioma cell lines to identify a panel of internalizing human single chain (scFv) antibodies that target mesothelioma-associated, clinically represented cell surface antigens and further exploited the internalizing function of these scFvs to specifically deliver lethal doses of liposome-encapsulated small molecule drugs to both epithelioid and sarcomatous subtypes of mesothelioma cells. Here, we report the identification of MCAM/MUC18/CD146 as the surface antigen bound by one of the mesothelioma-targeting scFvs using a novel cloning strategy based on yeast surface human proteome display. Immunohistochemical analysis of mesothelioma tissue microarrays confirmed that MCAM is widely expressed by both epithelioid and sarcomatous types of mesothelioma tumor cells in situ but not by normal mesothelial cells. In addition, quantum dot-labeled anti-MCAM scFv targets primary meosthelioma cells in tumor fragment spheroids cultured ex vivo. As the first step in evaluating the therapeutic potential of MCAM-targeting antibodies, we performed single-photon emission computed tomography studies using the anti-MCAM scFv and found that it recognizes mesothelioma organotypic xenografts in vivo. The combination of phage antibody library selection on tumor cells and rapid target antigen identification by screening the yeast surface-displayed human proteome could be a powerful method for mapping the targetable tumor cell surface epitope space.

Towards understanding the mode of action of the multifaceted cell adhesion receptor CD146

CD146, also known as melanoma cell adhesion molecule or MCAM, is a key cell adhesion protein in vascular endothelial cell activity and angiogenesis. CD146 promotes tumor progression of many cancers including melanoma and prostate. Strikingly, its expression is frequently lost in breast carcinoma cells, and it may act as a suppressor of breast cancer progression. While upstream mechanisms regulating CD146 are well documented, our understanding of the downstream molecular events underlying its mode of action remains to be elucidated. This review aims to focus on the progress in understanding the signaling mechanisms and the functional relevance of CD146, a multifaceted molecule, in cancer with particular emphasis on its role in inhibiting breast cancer progression.

CD146 expression is associated with a poor prognosis in human breast tumors and with enhanced motility in breast cancer cell lines

Introduction

Metastasis is a complex process involving loss of adhesion, migration, invasion and proliferation of cancer cells. Cell adhesion molecules play a pivotal role in this phenomenon by regulating cell–cell and cell–matrix interactions. CD146 (MCAM) is associated with an advanced tumor stage in melanoma, prostate cancer and ovarian cancer. Studies of CD146 expression and function in breast cancer remain scarce except for a report concluding that CD146 could act as a tumor suppressor in breast carcinogenesis.

Methods

To resolve these apparent discrepancies in the role of CD146 in tumor cells, we looked at the association of CD146 expression with histoclinical features in human primary breast cancers using DNA and tissue microarrays. By flow cytometry, we characterized CD146 expression on different breast cancer cell lines. Using siRNA or shRNA technology, we studied functional consequences of CD146 downmodulation of MDA-MB-231 cells in migration assays. Wild-type, mock-transfected and downmodulated transfected cells were profiled using whole-genome DNA microarrays to identify genes whose expression was modified by CD146 downregulation.

Results

Microarray studies revealed the association of higher levels of CD146 with histoclinical features that belong to the basal cluster of human tumors. Expression of CD146 protein on epithelial cells was detected in a small subset of cancers with histoclinical features of basal tumors. CD146⁺ cell lines displayed a mesenchymal phenotype. Downmodulation of CD146 expression in the MDA-MB-231 cell line resulted in downmodulation of vimentin, as well as of a set of genes that include both genes associated with a poor prognosis in a variety of cancers and genes known to promote cell motility. In vitro functional assays revealed decreased migration abilities associated with decreased CD146 expression.

Conclusions

In addition to its expression in the vascular compartment, CD146 is expressed on a subset of epithelial cells in malignant breast. CD146 may directly or indirectly contribute to tumor aggressiveness by promoting malignant cell motility. Changes in molecular signatures following downmodulation of CD146 expression suggest that CD146 downmodulation is associated with the reversal of several biological characteristics associated with epithelial to mesenchymal transition, and the phenomenon associated with the metastatic process.

Hypermethylation of MCAM gene is associated with advanced tumor stage in prostate cancer

BACKGROUND

DNA methylation has emerged as a promising biomarker for prostate cancer detection. In this report, we screened 36 candidate genes generated by a bioinformatic analysis of the human genome, and found that the melanoma cell adhesion molecule (MCAM) was an excellent candidate for cancer-specific methylation in prostate cancer.

METHODS

Direct sequencing of bisulfite-treated genomic DNA, conventional methylation-specific PCR (MSP), real-time quantitative methylation-specific PCR, immunohistochemistry, colony formation assay, and statistical analysis.

RESULTS

We found that the melanoma cell adhesion molecule (MCAM) gene promoter was specifically methylated in prostate cancer cell lines and primary prostate cancer (PCa) but not in non-neoplastic prostate (BPH) tissues by direct sequencing of bisulfite-treated genomic DNA and conventional methylation-specific PCR (MSP). Further analysis with quantitative MSP showed greater hypermethylation of the MCAM promoter (80%, 70/88) in primary prostate cancer compared to 12.5% (3/24) in BPH. Prostatic intraepithelial neoplasias (PIN), potential precursors of prostate carcinoma, showed an intermediate methylation rate of 23% (7/30). We further observed that MCAM promoter methylation was directly correlated with tumor stage (pT3+pT4) (P = 0.001) and Gleason score (P = 0.018) in primary prostate carcinoma.

CONCLUSIONS

Our results suggest that MCAM promoter hypermethylation deserves further attention as a potential diagnostic prostatic DNA marker in human prostate cancer.

Murine CD146 is widely expressed on endothelial cells and is recognized by the monoclonal antibody ME-9F1

The endothelium plays an important role in the exchange of molecules, but also of immune cells between blood and the underlying tissue. The endothelial molecule S-Endo 1 antigen (CD146) is preferentially located at endothelial junctions and has been claimed to support endothelial integrity. In this study we show that the monoclonal antibody ME-9F1 recognizes the extracellular portion of murine CD146. Making use of ME-9F1 we found CD146 highly expressed and widely spread on endothelial cells in the analyzed murine tissues. In contrast to humans that express CD146 also on T cells or follicular dendritic cells, murine CD146 albeit at low levels was only found on a subset of NK1.1+ cells. The antibody against murine CD146 is useful for immunomagnetic sorting of primary endothelial cells not only from the liver but from various other organs. In vitro, no evidence was seen that the formation and integrity of endothelial monolayers or the transendothelial migration of T cells was affected by antibody binding to CD146 or by crosslinking of the antigen. This makes the antibody ME-9F1 an excellent tool especially for the ex vivo isolation of murine endothelial cells intended to be used in functional studies.

Dual role of melanoma cell adhesion molecule (MCAM)/CD146 in lymphocyte endothelium interaction: MCAM/CD146 promotes rolling via microvilli induction in lymphocyte and is an endothelial adhesion receptor

The melanoma cell adhesion molecule (MCAM)/CD146 is expressed as two isoforms differing by their cytoplasmic domain (MCAM long (MCAM-l) and MCAM short (MCAM-s)). MCAM being expressed by endothelial cells and activated T cells, we analyzed its involvement in lymphocyte trafficking. The NK cell line NKL1 was transfected by MCAM isoforms and submitted to adhesion on both the endothelial cell monolayer and recombinant molecules under shear stress. MCAM-l transfection reduced rolling velocity and increased NKL1 adhesion on the endothelial cell monolayer and VCAM-1. Scanning electron microscopy revealed that MCAM-l induced microvilli formation and extension. In contrast, MCAM short or mock transfection had no effect on adhesion of NKL1 cells and microvilli formation. As shown by mutagenesis, serine 32 of the MCAM-l cytoplasmic tail, belonging to a putative protein kinase C phosphorylation site, was necessary for MCAM-l-actin cytoskeleton interaction and microvilli induction. Accordingly, chelerythrine chloride, a protein kinase C inhibitor, abolished MCAM-l-induced microvilli and rolling of MCAM-l-transfected NKL1 cells. Inhibition of adhesion under shear stress by anti-MCAM Abs suggested that both lymphoid MCAM-l and endothelial MCAM were also directly involved in lymphocyte endothelium interaction. MCAM-l-transfected NKL1 and activated CD4 T cells adhered to rMCAM under shear stress whereas anti-MCAM Ab treatment inhibited this process. Taken together, these data establish that MCAM is involved in the initial steps of lymphocyte endothelium interaction. By promoting the rolling on the inflammation marker VCAM-1 via microvilli induction and displaying adhesion receptor activity involving possible homophilic MCAM-l-MCAM-l interactions, MCAM might be involved in the recruitment of activated T cells to inflammation sites.