Interaction between integrin alpha(5) and fibronectin is required for metastasis of B16F10 melanoma cells

Survivin enhances motility of melanoma cells by supporting Akt activation and {alpha}5 integrin upregulation

Survivin expression in melanoma is inversely correlated with patient survival. Transgenic mice harboring melanocyte-specific overexpression of survivin exhibit increased susceptibility to UV-induced melanoma and metastatic progression. To understand the mechanistic basis for metastatic progression, we investigated the effects of survivin on the motility of human melanocytes and melanoma cells. We found that survivin overexpression enhanced migration on fibronectin and invasion through Matrigel, whereas survivin knockdown under subapoptotic conditions blocked migration and invasion. In melanocytes, survivin overexpression activated the Akt and mitogen-activated protein kinase pathways. Akt phosphorylation was required for survivin-enhanced migration and invasion, whereas Erk phosphorylation was required only for enhanced invasion. In both melanocytes and melanoma cells, survivin overexpression was associated with upregulation of α5 integrin (fibronectin receptor component), the antibody-mediated blockade or RNA interference-mediated knockdown of which blocked survivin-enhanced migration. Knockdown of α5 integrin did not affect Akt activation, but inhibition of Akt phosphorylation prevented α5 integrin upregulation elicited by survivin overexpression. Together, our results showed that survivin enhanced the migration and invasion of melanocytic cells and suggested that survivin may promote melanoma metastasis by supporting Akt-dependent upregulation of α5 integrin.

CAV1 inhibits metastatic potential in melanomas through suppression of the integrin/Src/FAK signaling pathway

Caveolin-1 (CAV1) is the main structural component of caveolae, which are plasma membrane invaginations that participate in vesicular trafficking and signal transduction events. Although evidence describing the function of CAV1 in several cancer types has recently accumulated, its role in melanoma tumor formation and progression remains poorly explored. Here, by using B16F10 melanoma cells as an experimental system, we directly explore the function of CAV1 in melanoma tumor growth and metastasis. We first show that CAV1 expression promotes proliferation, whereas it suppresses migration and invasion of B16F10 cells in vitro. When orthotopically implanted in the skin of mice, B16F10 cells expressing CAV1 form tumors that are similar in size to their control counterparts. An experimental metastasis assay shows that CAV1 expression suppresses the ability of B16F10 cells to form lung metastases in C57Bl/6 syngeneic mice. Additionally, CAV1 protein and mRNA levels are found to be significantly reduced in human metastatic melanoma cell lines and human tissue from metastatic lesions. Finally, we show that following integrin activation, B16F10 cells expressing CAV1 display reduced expression levels and activity of FAK and Src proteins. Furthermore, CAV1 expression markedly reduces the expression of integrin β(3) in B16F10 melanoma cells. In summary, our findings provide experimental evidence that CAV1 may function as an antimetastatic gene in malignant melanoma.

PhosphoMARCKS drives motility of mouse melanoma cells

Phosphorylation of myristoylated alanine-rich C-kinase substrate (MARCKS) by protein kinase C alpha (PKC alpha) is known to trigger its release from the plasma membrane/cytoskeleton into the cytoplasm, thereby promoting actin reorganization during migration. This study shows that once released into the cytoplasm, phosphoMARCKS directly promotes motility of melanoma cells. Aggressively motile B16 F10 mouse melanoma cells express high levels of phosphoMARCKS, whereas in weakly motile B16 F1 cells it is undetectable. Following treatment with okadaic acid (OA) (a protein phosphatase inhibitor), F1 cells exhibited a dramatic increase in phosphoMARCKS that was co-incident with a 5-fold increase in motility. Both MARCKS phosphorylation and motility were substantially decreased when prior to OA addition, MARCKS expression was knocked out by a MARCKS-specific shRNA, thereby implicating MARCKS as a major component of the motility pathway. Decreased motility and phosphoMARCKS levels in OA-treated cells were observed with a PKC inhibitor (calphostin C), thus indicating that PKC actively phosphorylates MARCKS in F1 cells but that this reaction is efficiently reversed by protein phosphatases. The mechanistic significance of phosphoMARCKS to motility was further established with a pseudo-phosphorylated mutant of MARCKS-GFP in which Asp residues replaced Ser residues known to be phosphorylated by PKC alpha. This mutant localized to the cytoplasm and engendered three-fold higher motility in F1 cells. Expression of an unmyristoylated, phosphorylation-resistant MARCKS mutant that localized to the cytoplasm, blocked motility by 40-50% of both OA-stimulated F1 cells and intrinsically motile F10 cells. These results demonstrate that phosphoMARCKS contributes to the metastatic potential of melanoma cells, and reveal a previously undocumented signaling role for this cytoplasmic phospho-protein.

Rapamycin inhibits lung metastasis of B16 melanoma cells through down-regulating alphav integrin expression and up-regulating apoptosis signaling

Currently available data indicate the potential application of rapamycin and its analogues in the clinic as anticancer therapeutic agents through inhibiting tumor cell growth and tumor angiogenesis. However, whether rapamycin can directly suppress tumor metastasis remains unclear. In the present study, we demonstrated that rapamycin treatment results in reduced formation of metastatic nodules in the lung by B16 cells. This is due to two mechanisms. First, the expression of alphav integrin is down-regulated by rapamycin treatment, and subsequently, the phosphorylation of focal adhesion kinase (FAK) is reduced. Second, rapamycin promotes apoptosis by up-regulating the proapoptotic molecules Bid and Bax and down-regulating Bcl-xL. Blocking the apoptosis pathway by pan-caspase inhibitor zVAD partially reversed the suppression of rapamycin in B16 metastasis. Interestingly, rapamycin up-regulates Bax and Bid in B16 cells via the S6K1 pathway and down-regulates the expression of alphav integrin via other pathway(s). In addition, our data showed that autophagy was not involved in the mechanisms of rapamycin-mediated metastasis suppression. Our findings demonstrate a potential anti-metastatic effect of rapamycin via down-regulating alphav integrin expression and up-regulating apoptosis signaling, suggesting that rapamycin might be worthy of clinical evaluation as an antimetastatic agent.

Biomarkers for epithelial-mesenchymal transitions

Somatic cells that change from one mature phenotype to another exhibit the property of plasticity. It is increasingly clear that epithelial and endothelial cells enjoy some of this plasticity, which is easily demonstrated by studying the process of epithelial-mesenchymal transition (EMT). Published reports from the literature typically rely on ad hoc criteria for determining EMT events; consequently, there is some uncertainty as to whether the same process occurs under different experimental conditions. As we discuss in this Personal Perspective, we believe that context and various changes in plasticity biomarkers can help identify at least three types of EMT and that using a collection of criteria for EMT increases the likelihood that everyone is studying the same phenomenon - namely, the transition of epithelial and endothelial cells to a motile phenotype.

Role of the endothelium during tumor cell metastasis: is the endothelium a barrier or a promoter for cell invasion and metastasis?

The malignancy of cancer disease depends on the ability of the primary tumor to metastasize to distant organs. The process of the metastasis formation has largely been analyzed, but still main pathways regarding the extravasation step at the end of the metastasis formation process are controversially discussed. An agreement has been reached about the importance of the endothelium to promote metastasis formation either by enhancing the growth of the primary tumor or by homing (targeting) the tumor cells to blood or lymph vessels. The mechanical properties of the invading tumor cells become the focus of several studies, but the endothelial cell mechanical properties are still elusive. This paper describes the different roles of the endothelium in the process of metastasis formation and focuses on a novel role of the endothelium in promoting tumor cell invasion. It discusses how novel biophysical tools and in vivo animal models help to determine the role of the endothelium in the process of tumor cell invasion. Evidence is provided that cell mechanical properties, for example, contractile force generation of tumor cells, are involved in the process of tumor cell invasion.

Phosphatase of regenerating liver-3 localizes to cyto-membrane and is required for B16F1 melanoma cell metastasis in vitro and in vivo

Background

Phosphatase of regenerating liver-3 (PRL-3) is a member of the novel phosphatases of regenerating liver family, characterized by one protein tyrosine phosphatase active domain and a C-terminal prenylation (CCVM) motif. Though widely proposed to facilitate metastasis in many cancer types, PRL-3's cellular localization and the function of its CCVM motif in metastatic process remain unknown.

Methodology/Principal Findings

In the present study, a series of Myc tagged PRL-3 wild type or mutant plasmids were expressed in B16F1 melanoma cells to investigate the relationship between PRL-3's cellular localization and metastasis. With immuno-fluorescence microcopy and cell adhesion/migration assay in vitro, and an experimental passive metastasis model in vivo, we found that CCVM motif is critical for the localization of PRL-3 on cell plasma membrane and the lung metastasis of melanoma. In particular, Cystine170 is the key site for prenylation in this process.

Conclusions/Significance

These results suggest that cellular localization of PRL-3 is highly correlated with its function in tumor metastasis, and inhibition of PRL-3 prenylation might be a new approach to cancer therapy.

Volociximab, a chimeric monoclonal antibody that specifically binds alpha5beta1 integrin: a phase I, pharmacokinetic, and biological correlative study

PURPOSE

This study aimed to assess the safety and feasibility of administering volociximab, a chimeric monoclonal antibody that specifically binds to alpha(5)beta(1) integrin, and to determine the pharmacokinetics, pharmacodynamics, and preliminary evidence of antitumor activity.

EXPERIMENTAL DESIGN

Patients with advanced solid malignancies were treated with escalating doses of volociximab i.v. administered over 60 minutes. Blood samples were assayed to determine plasma pharmacokinetic parameters, detect human antichimeric antibody formation, and determine the saturation of alpha5beta1 sites on peripheral blood monocytes.

RESULTS

Twenty-one patients received 223 infusions of volociximab at doses ranging from 0.5 to 15 mg/kg i.v. on days 1, 15, 22, 29, and 36; and weekly thereafter. Treatment was well tolerated, and dose-limiting toxicity was not identified over the range examined. Mild (grade 1 or 2), reversible fatigue was the principal toxicity of volociximab at the highest dose levels of 10 and 15 mg/kg. Nausea, fever, anorexia, headache, vomiting, and myalgias were mild and infrequent, and there was no hematologic toxicity. Volociximab had biexponential distribution; clearance was inversely related to increasing dose, and the half-life at 15 mg/kg was estimated as being 30 days. Three patients tested positive for anti-volociximab antibodies. Saturation of monocyte alpha5beta1 integrin sites was dose-dependent up to 15 mg/kg. There was one minor response (renal, 7 months) and one durable stable disease (melanoma, 14 months).

CONCLUSIONS

Volociximab can be safely administered at 15 mg/kg i.v. per week. The absence of severe toxicities and preliminary activity at the highest dose level warrants further disease-directed studies.

Stimulation of lung carcinoma cell growth by fibronectin-integrin signalling

Throughout many countries, lung cancer will kill more people this year than malignancies related to breast, prostate, colon, liver, kidney and melanoma combined. Despite recent advances in understanding the molecular biology of lung carcinoma and the introduction of multiple new chemotherapeutic agents for its treatment, its dismal five-year survival rate (<15%) has not changed substantially. The lack of advancement in this area reflects the limited knowledge available concerning the factors that promote oncogenic transformation and proliferation of carcinoma cells in the lung. Malignant transformation plays a key role in tumor growth and invasion; however, other factors such as the surrounding stroma, local growth factors, vascularity, and systemic hormones are important contributors as well. We believe that the composition of the lung extracellular matrix is also important due to its ability to affect malignant cell behavior in vitro. The matrix glycoprotein fibronectin, for example, is highly expressed in chronic lung disorders where most lung carcinomas are identified. This document reviews information that implicates fibronectin in the stimulation of lung carcinoma cell growth. Data available to date indicate that by binding to specific integrin receptors expressed on the surface of tumor cells, fibronectin stimulates intracellular signals implicated in the pathobiology of lung carcinogenesis and lung tumor chemoresistance including mitogen-activated protein kinases, GTPases, and the PI3-kinase/Akt/mTOR pathway. Thus, integrin-mediated signals triggered by fibronectin in tumor cells represent promising targets for the development of novel anti-cancer strategies.

Integrin-dependent translational control: Implication in cancer progression

The importance of translational control in cancer progression has been underscored by a number of recent studies. However, little is known how cancer cells maintain their high efficiency of translation. Here, we summarize studies that support the role of integrins in translational control, especially at the initiation step, and discuss the various mechanisms by which integrins regulate the recruitment of translational machinery. This review also examines the hypothesis that integrins contribute to various aspects of cancer progression such as proliferation, survival, angiogenesis, and invasion through translational control.

Tissue transgluaminase 2 expression in meningiomas

Meningiomas are common intracranial tumors that occur in extra-axial locations, most often over the cerebral convexities or along the skull-base. Although often histologically benign these tumors frequently present challenging clinical problems. Primary clinical management of patients with symptomatic tumors is surgical resection. Radiation treatment may arrest growth or delay recurrence of these tumors, however, meningioma cells are generally resistant to apoptosis after treatment with radiation. Tumor cells are known to alter their expression of proteins that interact in the ECM to provide signals important in tumor progression. One such protein, fibronectin, is expressed in elevated levels in the ECM in a number of tumors including meningiomas. We recently reported that levels of both extracellular fibronectin and tissue transglutaminase 2 (TG2) were increased in glioblastomas. We examined the expression of fibronectin and its association TG2 in meningiomas. Both fibronectin and TG2 were strongly expressed in all meningiomas studied. TG2 activity was markedly elevated in meningiomas, and TG2 was found to co-localize with fibronectin. Treatment of meningiomas with the small molecule TG2 inhibitor, KCC009, inhibited the binding of TG2 to fibronectin and blocked disposition of linear strands of fibronectin in the ECM. KCC009 treatment promoted apoptosis and enhanced radiation sensitivity both in cultured IOMM-Lee meningioma cells and in meningioma tumor explants. These findings support a potential protective role for TG2 in meningiomas.

Galectin-9 suppresses tumor metastasis by blocking adhesion to endothelium and extracellular matrices

We previously described an inverse correlation between galectin-9 (Gal-9) expression and metastasis in patients with malignant melanoma and breast cancer. This study verified the ability of Gal-9 to inhibit lung metastasis in experimental mouse models using highly metastatic B16F10 melanoma and Colon26 colon cancer cells. B16F10 cells transfected with a secreted form of Gal-9 lost their metastatic potential. Intravenous Gal-9 administration reduced the number of metastases of both B16F10 and Colon26 cells in the lung, indicating that secreted Gal-9 suppresses metastasis. Analysis of adhesive molecule expression revealed that B16F10 cells highly express CD44, integrin alpha1, alpha 4, alpha V, and beta1, and that Colon26 cells express CD44, integrin alpha2, alpha 5, alpha V, and beta1, suggesting that Gal-9 may inhibit the adhesion of tumor cells to vascular endothelium and the extracellular matrix (ECM) by binding to such adhesive molecules. Indeed, Gal-9 suppressed the binding of hyaluronic acid to CD44 on both B16F10 and Colon26 cells, and also suppressed the binding of vascular cell adhesion molecule-1 to very late antigen-4 on B16F10 cells. Furthermore, Gal-9 inhibited the binding of tumor cells to ECM components, resulting in the suppression of tumor cell migration. The present results suggest that Gal-9 suppresses both attachment and invasion of tumor cells by inhibiting the binding of adhesive molecules on tumor cells to ligands on vascular endothelium and ECM.

Rab25 associates with alpha5beta1 integrin to promote invasive migration in 3D microenvironments

Here, we report a direct interaction between the beta1 integrin cytoplasmic tail and Rab25, a GTPase that has been linked to tumor aggressiveness and metastasis. Rab25 promotes a mode of migration on 3D matrices that is characterized by the extension of long pseudopodia, and the association of the GTPase with alpha5beta1 promotes localization of vesicles that deliver integrin to the plasma membrane at pseudopodial tips as well as the retention of a pool of cycling alpha5beta1 at the cell front. Furthermore, Rab25-driven tumor-cell invasion into a 3D extracellular matrix environment is strongly dependent on ligation of fibronectin by alpha5beta1 integrin and the capacity of Rab25 to interact with beta1 integrin. These data indicate that Rab25 contributes to tumor progression by directing the localization of integrin-recycling vesicles and thereby enhancing the ability of tumor cells to invade the extracellular matrix.

Engineering tumors with 3D scaffolds

Microenvironmental conditions control tumorigenesis and biomimetic culture systems that allow for in vitro and in vivo tumor modeling may greatly aid studies of cancer cells' dependency on these conditions. We engineered three-dimensional (3D) human tumor models using carcinoma cells in polymeric scaffolds that recreated microenvironmental characteristics representative of tumors in vivo. Strikingly, the angiogenic characteristics of tumor cells were dramatically altered upon 3D culture within this system, and corresponded much more closely to tumors formed in vivo. Cells in this model were also less sensitive to chemotherapy and yielded tumors with enhanced malignant potential. We assessed the broad relevance of these findings with 3D culture of other tumor cell lines in this same model, comparison with standard 3D Matrigel culture and in vivo experiments. This new biomimetic model may provide a broadly applicable 3D culture system to study the effect of microenvironmental conditions on tumor malignancy in vitro and in vivo.

PRL-3 siRNA inhibits the metastasis of B16-BL6 mouse melanoma cells in vitro and in vivo

Phosphatase of regenerating liver-3 (PRL-3) has been proposed to promote the invasion of tumor cells to metastasis sites. However, the effect of PRL-3 on spontaneous metastasis has not been clearly demonstrated, and whether PRL-3 could become a new therapeutic target in malignant tumor is still unknown. In this study, we used PRL-3 siRNA as a molecular medicine to specifically reduce the expression of PRL-3 in B16-BL6 cells, a highly metastatic melanoma cell line. In vitro, PRL-3 siRNA significantly inhibited cell adhesion and migration, but had no effect on cell proliferation. In the spontaneous metastatic tumor model in vivo, PRL-3 siRNA treatment remarkably inhibited the proliferation of primary tumor, prevented tumor cells from invading the draining lymph nodes, and prolonged the life span of mice. Therefore, our results indicate that PRL-3 plays a critical role in promoting the whole process of spontaneous metastasis and tumor growth initiation, and that inhibiting PRL-3 will improve malignant tumor therapy.

Effect of RGD-disintegrins on melanoma cell growth and metastasis: involvement of the actin cytoskeleton, FAK and c-Fos

The effects and molecular mechanisms of RGD-disintegrins isolated from snake venoms on the growth and metastatic potential of B16F10-melanoma cells were investigated. Jarastatin (JT) from Bothrops jararaca is a ligand of alpha(5)beta(1), alpha(v)beta(3) and alpha(m)beta(2) integrins, flavoridin (FL) from Trimeresurus flavoridis binds preferentially to alpha(5)beta(1) and kistrin (KR) from Calloselasma rhodostoma is a selective ligand of alpha(v)beta(3). When injected simultaneously with melanoma cells in mice, the three disintegrins significantly reduced tumor lung colonization. On the other hand, JT and FL, but not KR, inhibited B16F10 cell growth in vitro. Interaction of JT or FL with melanoma cells induced actin cytoskeleton rearrangement, increasing actin polymerization and FAK phosphorylation. The effect of FL correlates with the decrease in the constitutively high nuclear content of c-Fos, whereas JT interfered with NF-kappaB translocation in melanoma cells. None of the disintegrins produced alterations in the nuclear Erk-2. The results provide further evidence to suggest RGD-disintegrins as potent anti-metastatic agents in vivo, and indicate that their interaction with alpha(5)beta(1) integrin interfere with integrin-couple signaling, down-regulating transcription factors and negatively modulating cell proliferation. These effects may contribute to inhibition of melanoma cell invasion in vivo.

huBC1-IL12, an immunocytokine which targets EDB-containing oncofetal fibronectin in tumors and tumor vasculature, shows potent anti-tumor activity in human tumor models

IL-12 is a cytokine which showed anti-tumor effects in clinical trials, but also produced serious toxicity. We describe a fusion protein, huBC1-IL12, designed to achieve an improved therapeutic index by specifically targeting IL-12 to tumor and tumor vasculature. huBC-1 is a humanized antibody that targets a cryptic sequence of the human ED-B-containing fibronectin isoform, B-FN, present in the subendothelial extracellular matrix of most aggressive tumors. B-FN is oncofetal and angiogenesis-associated, and is undetectable in most normal adult tissues. The original murine BC-1 antibody has been used successfully for immunoscintigraphy to image brain tumor mass in glioblastoma patients. In huBC1-IL12, each of the IgG heavy chains is genetically fused to the N-terminus of the IL-12 p35 subunit, which in turn is disulfide-bonded to the p40 subunit, resulting in a hexameric molecule of MW of approximately 300 kDa. Since human IL-12 has no biological activity in mice, we produced huBC1-muIL12 as a surrogate molecule for animal tumor models. Despite the relatively poor PK profile of this molecule in mice and the apparent drawbacks of xenogeneic models in SCID mice, which lack T and B cells, one cycle of treatment with huBC1-muIL12 was efficacious in the PC3mm2, A431, and HT29 subcutaneous tumor models and PC3mm2 lung metastasis model. This molecule also was found to have surprisingly low toxicity in immunocompetent mice. A fusion protein that contains human IL-12 (huBC1-huIL12), which is a suitable molecule for investigation as a therapeutic, has also been produced. This protein has been shown to have a longer serum half-life than huBC1-muIL12 in mice, and retains both antigen binding and IL-12 activity in in vitro assays.

Distinct roles for LINE-1 and HERV-K retroelements in cell proliferation, differentiation and tumor progression

Transformed cells express high levels of non-telomeric reverse-transcriptase (RT) activity of retrotransposon and endogenous retrovirus origin. We previously reported that RT inhibition, either pharmacological or through transient silencing of RT-encoding LINE-1 (L1) elements by RNA interference (RNAi), reduced proliferation, induced differentiation and reprogrammed gene expression in human tumorigenic cell lines. Moreover, the antiretroviral drug efavirenz antagonized tumor progression in animal models in vivo. To get insight into the role of retroelements in tumorigenesis, we have now produced two cell lines derived from A-375 melanoma, in which the expression of either L1 retrotransposon, or HERV-K endogenous retrovirus, was stably suppressed by RNAi. Compared to the parental A-375 cell line, cells with stably interfered L1 expression show a lower proliferation rate, a differentiated morphology and lower tumorigenicity when inoculated in nude mice. L1 silencing modulates expression of several genes and, unexpectedly, also downregulates HERV-K expression. In HERV-K interfered cells, instead, L1 expression was unaffected, and cell proliferation and differentiation remained unchanged compared to parental A-375 cells. In vivo, however, their tumorigenic potential was found to be reduced after inoculation in nude mice. These results suggest that L1 and HERV-K play specific and distinct roles in cell transformation and tumor progression.

Structural and inhibitory properties of a plant proteinase inhibitor containing the RGD motif

Purified from Bauhinia rufa seeds, BrTI is a Kunitz proteinase inhibitor that contains the RGD sequence. BrTI inhibits trypsin (K(iapp) 2.9 nM) and human plasma kallikrein (K(iapp) 14.0 nM) but not other related enzymes. The synthetic peptide YLEPVARGDGGLA-NH(2) (70 microM) inhibited the adhesion to fibronectin of B16F10 (high-metastatic B16 murine mouse melanoma cell line) and of Tm5 (murine melanoma cell lines derived from a non-tumorigenic lineage of pigmented murine melanocytes, melan-a). YLEPVARGEGGLA-NH(2) in which Asp(9) was changed into Glu does not affect the cell attachment. Moreover, this peptide was functional only when the sequence present in the native protein was preserved, since YLIPVARGDGGLA-NH(2) in which Glu(3) was changed into Ile does not interfere with B16F10 and was less effective on Tm5 cell line adhesion. Neither YLEPVARGDGGLA-NH(2), YLIPVARGDGGLA-NH(2) or YLEPVARGEGGLA-NH(2) inhibit the interaction of RAEC (endothelial cell line from rabbit aorta) with fibronectin.

Carba analogs of cyclic phosphatidic acid are selective inhibitors of autotaxin and cancer cell invasion and metastasis

Autotaxin (ATX, nucleotide pyrophosphate/phosphodiesterase-2) is an autocrine motility factor initially characterized from A2058 melanoma cell-conditioned medium. ATX is known to contribute to cancer cell survival, growth, and invasion. Recently ATX was shown to be responsible for the lysophospholipase D activity that generates lysophosphatidic acid (LPA). Production of LPA is sufficient to explain the effects of ATX on tumor cells. Cyclic phosphatidic acid (cPA) is a naturally occurring analog of LPA in which the sn-2 hydroxy group forms a 5-membered ring with the sn-3 phosphate. Cellular responses to cPA generally oppose those of LPA despite activation of apparently overlapping receptor populations, suggesting that cPA also activates cellular targets distinct from LPA receptors. cPA has previously been shown to inhibit tumor cell invasion in vitro and cancer cell metastasis in vivo. However, the mechanism governing this effect remains unresolved. Here we show that 3-carba analogs of cPA lack significant agonist activity at LPA receptors yet are potent inhibitors of ATX activity, LPA production, and A2058 melanoma cell invasion in vitro and B16F10 melanoma cell metastasis in vivo.

The monoclonal antibody SM5-1 recognizes a fibronectin variant which is widely expressed in melanoma

Background

Previously we have generated the monoclonal antibody SM5-1 by using a subtractive immunization protocol of human melanoma. This antibody exhibits a high sensitivity for primary melanomas of 99% (248/250 tested) and for metastatic melanoma of 96% (146/151 tested) in paraffin embedded sections. This reactivity is superior to the one obtained by HMB-45, anti-MelanA or anti-Tyrosinase and is comparable to anti-S100. However, as compared to anti-S100, the antibody SM5-1 is highly specific for melanocytic lesions since 40 different neoplasms were found to be negative for SM5-1 by immunohistochemistry. The antigen recognized by SM5-1 is unknown.

Methods

In order to characterize the antigen recognized by mAb SM5-1, a cDNA library was constructed from the metastatic human melanoma cell line SMMUpos in the Uni-ZAP lambda phage and screened by mAb SM5-1. The cDNA clones identified by this approach were then sequenced and subsequently analyzed.

Results

Sequence analysis of nine independent overlapping clones (length 3100–5600 bp) represent fibronectin cDNA including the ED-A, but not the ED-B region which are produced by alternative splicing. The 89aa splicing variant of the IIICS region was found in 8/9 clones and the 120aa splicing variant in 1/9 clones, both of which are included in the CS1 region of fibronectin being involved in melanoma cell adhesion and spreading.

Conclusion

The molecule recognized by SM5-1 is a melanoma associated FN variant expressed by virtually all primary and metastatic melanomas and may play an important role in melanoma formation and progression. This antibody is therefore not only of value in immunohistochemistry, but potentially also for diagnostic imaging and immunotherapy.