Coexpression of vimentin and keratins by human melanoma tumor cells: correlation with invasive and metastatic potential.

BACKGROUND: Several protein markers, including vimentin, have been used to diagnose human melanoma. Because melanoma often has metastasized by the time of diagnosis, early markers prognostic for metastatic potential need to be identified. Commonly, vimentin is found in mesenchymal cells, and keratins are present in epithelial cells, but recent studies report coexpression of vimentin and keratin(s) in epithelial and nonepithelial neoplasms, including some melanomas. PURPOSE: Our purpose was to determine whether coexpression of vimentin and keratin(s) is correlated with tumor cell invasion and metastatic behavior. METHODS: We evaluated nine human melanoma cell lines expressing vimentin and other markers of aggressive tumor behavior (HMB-45, S-100, HLA-ABC class I and HLA-DR class II histocompatibility antigens, and K8 and K18 keratins). Levels of K8 and K18 keratins were determined in the highly metastatic C8161 cell line, the poorly metastatic A375P line, and the moderately metastatic A375M line. To determine whether the presence of keratin affects migratory ability, we altered the conformational structure of keratin filaments in C8161 cells by transfection with a mutant K18 complementary DNA. We also determined messenger RNA levels of human type IV collagenase, an enzyme marker for invasion and metastasis. RESULTS: In A375P cells, two-dimensional electrophoresis with Coomassie-stained gels, immunoblotting, and immunofluorescence staining showed no detectable levels of K8 or K18. A375M cells showed low levels of K8 and K18 by Western and Northern blotting, with a distinctive fluorescent subpopulation of cells. In comparison, K8 and K18 levels in C8161 cells were high in all cells. Type IV collagenase messenger RNA levels were lowest in A375P cells and highest in C8161 cells, correlating with invasive ability in vitro and metastatic potential in athymic nude mice. The transfectant clones C1070-10 and C1070-14 derived from the C8161 parent line showed dramatic morphological changes, disrupted keratin filaments, and decreased invasive and metastatic potential directly correlated with a reduction in migratory activity. CONCLUSION: These findings show a correlation between the coexpression of vimentin with K8 and K18 keratins and the invasive and metastatic behavior of three representative human melanoma cell lines.     

Cloning efficiency of human melanoma cells is modulated after invasion through a reconstituted basement membrane

Three human malignant melanoma cell strains (C8146A, C8146C, and C83-2CY), three established human melanoma cell lines (A375P, A375M, and C8161), and one selected human melanoma subline (A375P-5) were studied to determine if invasion through a reconstituted basement membrane-coated filter (RBMF), which selects the most aggressively invasive cells, would also modulate the cloning efficiency of these cells in soft agar. With the use of the Membrane Invasion Culture System (MICS), all cell strains tested showed a significant increase in cloning efficiency (1.05-9.3-fold) following transit through the RBMF when compared to unmanipulated populations. The established cell lines (A375P, A375M, and C8161) and the A375P-5 subline showed either a decrease or unaltered status in cloning efficiency after invasion. However, all cells demonstrated a consistent decrease in clonogenicity following transit through an uncoated filter compared with RBMFs, thus suggesting the influence of the extracellular matrix on tumor cell clonogenic properties. In general, the established cell lines were more clonogenic before invasion of the RBMF compared with the cell strains, and no correlation was found between clonogenic potential and invasive or metastatic capability. These data may provide important insight into the underlying mechanisms of tumor cell invasion and the subsequent formation and dissemination of metastases in vivo.     

The role of human melanoma cell ICAM-1 expression on lymphokine activated killer cell-mediated lysis, and the effect of retinoic acid.

Intercellular adhesion molecule (ICAM-1) exists as a membrane-associated form (mICAM-1) on the surface of tumour cells as well as a soluble form (sICAM-1). This study analyses the ability of all-trans retinoic acid (RA) to alter both sICAM and mICAM-1 expression in C8161 and Hs294T human melanoma cell lines and investigates the involvement of ICAM-1 in the interaction between tumour and lymphokine-activated killer (LAK) cells using the Cr-51 release assay. Our data showed that 4-day pretreatment of the tumour cells with 10(-7) M RA and 10(-6) M RA induced an increase in lysis of both cell lines and also increased mICAM-1 expression without having any effect on sICAM-1 levels. Addition of blocking ICAM-1 antibody (10 microg ml(-1)) to the C8161 cells at an effector:tumour cell ratio of 40:1 caused a 2.3-fold reduction in lysis of tumour cells and a 3-fold reduction in lysis of RA-treated cells. Blocking ICAM-1 antibody at optimum concentrations of 5 microg ml(-1) reduced lysis 1.8-fold in control Hs294T cells and 1.3-fold in RA-treated cells. Blocking the HLA-ABC complex had no effect on lysis. The more highly metastatic C8161 cells were found to secrete 4-fold greater levels of sICAM-1 than the poorly metastatic Hs294T cells and addition of sICAM-1 to the assay failed to affect lysis of either cell line but did induce a 2-fold decrease in lysis of RA-treated C8161 cells. Collectively, these data provide further evidence for ICAM-1 involvement in the tumour/LAK cell response and indicates that the RA-induced increase in mICAM-1 levels are partly responsible for the increase in susceptibility of the tumour cells. sICAM-1 appears to be unimportant in evasion of the tumour cells from LAK cell lysis, but may play a role in evasion of RA-treated C8161 cells.     

Highly pigmented human melanoma variant which metastasizes widely in nude mice, including to skin and brain

The properties of a highly malignant human melanoma variant cell line which metastasizes in nude mice in a tissue-specific pattern are described. The variant, called 70-W, was isolated from the MeWo malignant melanoma by exposure of the latter to stepwise increasing concentrations of the toxic lectin, wheat germ agglutinin. After nine cycles of treatment a population of wheat germ agglutinin-resistant cells was obtained that manifested a 4-fold resistance to wheat germ agglutinin, a property which was found to be stable in culture for over 6 months in the absence of the lectin. Intravenous inoculation of 70-W cells into 4-6-week-old nude mice revealed remarkable differences in metastatic (organ colonization) behavior. Whereas the parent MeWo cells gave rise only to lung metastases, most of which were amelanotic, injection of the 70-W cells resulted in multiple skin (s.c.) and brain and, to a lesser extent, bone marrow, ovarian, mesenteric (gut-associated), muscle, and abdominal metastases all of which were highly melanotic. This is the first report of brain metastases of a human tumor in nude mice. They were found to be bilateral and confined to the deeper layers of the cerebral cortex. The unique malignant behavior of 70-W cells in nude mice should facilitate studies of host and tumor cell factors involved in human melanoma metastasis, melanogenesis, and development of new treatment strategies for disseminated human malignant melanoma.     

Altered methionine metabolism in metastatic variants of a human melanoma cell line

In order to identify the biochemical defect(s) responsible for the reduced levels of DNA 5-methylcytosine (5-mCyt) found within highly metastatic (in athymic "nude" mice) variants of the poorly metastatic human melanoma cell line MeWo, the ability of these cells to grow in culture medium devoid of exogenous methionine but containing either homocysteine (Hcy) or 5'-deoxy-5'-methylthioadenosine (MeSAdo) was determined. In contrast to the parental MeWo tumor line, many (but not all) of these malignant variants were completely unable to proliferate in methionine-free homocysteine-containing medium. Many of these malignant variants also exhibited a reduced ability to proliferate in methionine-free MeSAdo-containing medium. Cell lines established from "artificial" metastases of MeWo or its cloned sublines, exhibited no consistent reduction in their ability to grow in methionine-free medium containing either Hcy or MeSAdo. These observations suggest that alterations in S-adenosylmethionine(AdoMet)-dependent transmethylation reactions may contribute to "progression" of the MeWo tumor from a relatively benign to a highly autonomous and malignant state.     

DNA methylating capacity in metastatic variants of a human melanoma cell line

Certain highly metastatic (in athymic immunosuppressed "nude" mice) variants of the poorly metastatic human melanoma cell line MeWo have been found to contain dramatically reduced levels of DNA 5-methylcytosine compared to the parental cell line. To identify the underlying biochemical defect which could be responsible for the reduced DNA methylation within these cells, the intracellular ratio of S-adenosylmethionine/S-adenosylhomocysteine and level of extractable DNA-methyltransferase were examined. No significant difference in the ratio of S-adenosylmethionine/S-adenosylhomocysteine or extractable DNA-methyltransferase activity were found between the highly malignant variants and the parental cell line. Thus, stable alterations in these cellular parameters are not likely responsible for the reduction in DNA 5-methylcytosine content which appears to occur during "progression" of the MeWo tumor line from a relatively benign to highly malignant state.     

Metastatic phenotype of mouse-human melanoma cell hybrids is associated with the presence of chromosome 17 from highly metastatic human melanoma cells

We have previously shown that in interspecific mouse-human melanoma cell hybrids obtained by fusion of nonmetastatic mouse with metastatic human melanoma cells, the metastatic phenotype predominates. The purpose of this study was to identify human chromosome(s) which could be responsible for conferring metastatic potential upon nonmetastatic mouse melanoma cells and therefore harbor the genes important for the metastatic properties of human melanoma cells. Seven mouse-human melanoma hybrids were examined; five were derived from the fusion of nonmetastatic (C19) and metastatic (C3) mouse K-1735 melanoma clones with highly metastatic clone (C15) of human melanoma A375 and the two others had as a human partner a nonmetastatic clone (Cls) of the A375 melanoma. The hybrids were examined during segregation of human chromosomes in vitro and in vivo for metastatic properties in nude mice and for the retaining human chromosomes. In the hybrid H7, which demonstrated the highest metastatic potential, the presence of human chromosomes was studied by GTG-banding and by fluorescence in situ hybridization (FISH) analysis. In the other hybrids, only FISH detection of human chromosomes was applied. All hybrids derived from nonmetastatic mouse and metastatic human melanoma cells demonstrated metastatic properties from early passages, when they contained the majority of the human chromosomes. Their metastatic phenotype remained stable during further segregation of most of the human chromosomes except for 17. Chromosome 17 was retained most consistently in all examined hybrids. However, the metastatic phenotype of the hybrids was associated only with the presence of chromosome 17 from the metastatic human donor cells. This chromosome was also found in almost 100% of cells recovered from lung metastases derived from the hybrid cells. In one lung metastasis developed from the H7 hybrid, chromosome 17 was detected as the sole human chromosome and these cells preserved the acquired high metastatic properties. Based on these results we conclude that human chromosome 17 from metastatic melanoma cells (A375 C15), when functional in the mouse genetic background, can be sufficient to render the recipient nonmetastatic mouse cells to a fully malignant phenotype. Additional data suggest that this ability might be related to the expression of the mutated human p53 gene.     

Silencing of tissue factor pathway inhibitor-2 gene in malignant melanomas

To identify tumor-suppressor genes inactivated by aberrant methylation of promoter CpG islands (CGIs) in human malignant melanomas, genes upregulated by treatment of cells with a demethylating agent, 5-aza-2'-deoxycytidine (5-aza-dC), were searched for using oligonucleotide microarrays in melanoma cell lines, HMV-I, MeWo and WM-115. Seventy-nine known genes with CGIs were identified as being upregulated (>or=16-fold), and 18 of them had methylation of their putative promoter CGIs in 1 or more of 8 melanoma cell lines. Among the 18 genes, TFPI-2, which is involved in repression of the invasive potential of malignant melanomas, was further analyzed. Its expression was repressed in a melanoma cell line with its complete methylation, and was restored by 5-aza-dC treatment. It was unmethylated in cultured neonatal normal epidermal melanocyte, and was induced by ultraviolet B. In surgical melanoma specimens, TFPI-2 methylation was detected in 5 of 17 metastatic site specimens (29%), while it was not detected in 20 primary site specimens (0%) (p=0.009). By immunohistochemistry, the 5 specimens with promoter methylation lacked immunoreactivity for TFPI-2. The results showed that TFPI-2 is silenced in human malignant melanomas by methylation of its promoter CGI and suggested that its silencing is involved in melanoma metastasis.     

Isolation of a human melanoma adapted Newcastle disease virus mutant with highly selective replication patterns

The apathogenic Newcastle disease virus (NDV) strain Ulster has been used successfully as an adjuvant component for active specific immunotherapy of malignant mouse lymphoma, and in nude mice it was shown to be able to lead to retardation of the s.c. growth of xenotransplanted human melanoma cells. In order to improve in vivo effectiveness of virotherapy of human tumors without significantly increasing the risk of unspecific viral replication in host cells, we adapted the virus for growth in a human melanoma line (MeWo M). For this purpose NDV Ulster was mutagenized and a variant was selected which could replicate and reinfect the tumor line. The mutant (NDV 1E 10) performed late lysis on the melanoma line. Replication was found to be at least 100 times more efficient in MeWo M than in 6 of 8 other human tumor cell lines of different tissue origin. In 10 of 11 murine cell lines, NDV 1E 10 did not replicate via multicycles. Chick embryonic fibroblasts were permissive for nonlytic replication. Neither the virulent wild-type NDV Italian nor the avirulent strain NDV Ulster shared these specific replication properties with the new variant. We also established MeWo melanoma sublines with different metastatic capacities and tested them as targets for NDV 1E 10 infection. The MeWo subpopulations exhibited comparatively small differences in permissivity for multicyclic replication, but the more metastatic MeWo Met, like allogeneic melanoma lines, was more resistant to lysis. NDV Italian, in contrast, showed no differences in replication and lysis on any of the tested melanoma lines. Trypsin-activation experiments suggested an incomplete cleavage of mutant envelope glycoprotein F by the permissive cell line and, thus, mechanisms of specific infection and replication not requiring fully activated envelope glycoproteins.     

A small interfering CD147-targeting RNA inhibited the proliferation, invasiveness, and metastatic activity of malignant melanoma

CD147 plays a critical role in the invasive and metastatic activity of malignant melanoma cells by stimulating the surrounding fibroblasts to express matrix metalloproteinases and vascular endothelial growth factor. We developed a system that blocks CD147 in the human malignant melanoma cell line, A375, using RNA interference. By transfecting melanoma cells with the small interfering RNA (siRNA) that targets human CD147, we were able to establish two stable clones in which CD147 expression was significantly down-regulated. This resulted in the decreased proliferation and invasion of A375 cells in vitro. CD147 siRNA also down-regulated the expression of vascular endothelial growth factor in these cells and reduced the migration of vascular endothelial cells. The reduction in the CD147 level suppressed the size of s.c. tumors and the microvessel density in an A375 s.c. nude mouse xenograft model. In addition, the in vivo metastatic potential of A375 cells transfected with CD147 siRNA was suppressed in a nude mouse model of pulmonary metastasis.     

Malignant potential of cells isolated from lymph node or brain metastases of melanoma patients and implications for prognosis

We studied the correlation between the formation of brain metastasis and the malignant growth potential of seven human melanoma cell lines, isolated from lymph node metastases (A375-SM, TXM-1, DM-4) or from brain metastases (TXM-13, TXM-18, TXM-34, TXM-40), and the potential of three variants of the mouse K-1735 melanoma. Growth rates in different concentrations of fetal bovine serum and colony-forming efficiency in semisolid agarose were measured, and the tumorigenicity and metastatic ability were determined in nude mice (for the human melanoma cell lines) or in C3H/HeN mice (for the K-1735 variants). The ability to form brain metastasis was tested by injection of cells into the carotid artery. A high colony-forming efficiency in agarose, especially at concentrations of agarose greater than 0.6%, corresponded with high tumor take rates, rapid tumor growth rates, and metastatic colonization of the lungs of the recipient mice. For the human melanomas, the lymph node metastasis-derived cells were more tumorigenic and metastatic than the brain metastasis-derived cells. In the K-1735 mouse melanoma, the tumorigenic and metastatic behavior of the cells after i.v. and s.c. injection corresponded with growth in agarose cultures. However, for growth in the brain after intracarotid injection, the different melanoma cell lines showed similar frequencies of tumor take, regardless of tumorigenicity in other sites of the recipient mice, although mice given injections of brain metastasis-derived cells survived longer than mice given injections of lymph node metastasis (human melanoma) or lung metastasis (K-1735 M-2)-derived cell lines. The results from the human and mouse melanoma cell lines show that the brain metastasis-derived cell lines were not more malignant than the lymph node or lung metastasis-derived cells. These data imply that the production of brain metastasis is not always the final stage of a metastatic cascade.     

A cancer terminator virus eradicates both primary and distant human melanomas

The prognosis and response to conventional therapies of malignant melanoma inversely correlate with disease progression. With increasing thickness, melanomas acquire metastatic potential and become inherently resistant to radiotherapy and chemotherapy. These harsh realities mandate the design of improved therapeutic modalities, especially those targeting metastases. To develop an approach to effectively treat this aggressive disease, we constructed a conditionally replication-competent adenovirus in which expression of the adenoviral E1A gene, necessary for replication, is driven by the cancer-specific promoter of progression-elevated gene-3 (PEG-3) and which simultaneously expresses mda-7/IL-24 in the E3 region of the adenovirus (Ad.PEG-E1A-mda-7), a cancer terminator virus (CTV). This CTV produces large quantities of MDA-7/IL-24 protein as a function of adenovirus replication uniquely in cancer cells. Infection of Ad.PEG-E1A-mda-7 (CTV) in normal human immortal melanocytes and human melanoma cells demonstrates cancer cell-selective adenoviral replication, mda-7/IL-24 expression, growth inhibition and apoptosis induction. Injecting Ad.PEG-E1A-mda-7 CTV into xenografts derived from MeWo human metastatic melanoma cells in athymic nude mice completely eliminated not only primary treated tumors but also distant non-treated tumors (established in the opposite flank), thereby implementing a cure. These provocative findings advocate potential therapeutic applications of this novel virus for treating patients with advanced melanomas with metastases.     

Neutrophils influence melanoma adhesion and migration under flow conditions

We have studied human melanoma cell (C8161) adhesion and migration in response to stimulation by soluble collagen IV (CIV) using a modified Boyden chamber. In this modified chamber, shear flow can be introduced over the cell-substrate interface, affecting tumor cell chemotactic migration through a microporous filter. A relatively high level of intercellular adhesion molecule-1 (ICAM-1) was found on C8161 cells. In contrast, levels of beta(2)-integrins (e.g., LFA-1 and Mac-1), the molecules that would be necessary for C8161 stable adhesion to the endothelium substrate, were found to be very low on these melanoma cells. As a result, C8161 transendothelial migration under a flow condition of 4 dyn/cm(2) decreased by 70% as compared to static migration. When human neutrophils (PMNs) were present in the tumor cell suspension, C8161 migration recovered by 85% over C8161 cells alone under the 4 dyn/cm(2) flow condition. Blocking ICAM-1 on C8161 cells or Mac-1 on PMNs significantly inhibited C8161-PMN adhesion and subsequent C8161 migration through the endothelium under flow conditions. In addition, increased interleukin-8 production and Mac-1 expression by PMNs were detected when they were co-cultured with C8161 melanoma cells. These results suggest that transmigration of C8161 cells under flow conditions can be influenced by PMNs, mediated by Mac-1/ICAM-1 adhesive interactions and enhanced by altered cytokine production.     

Soluble intercellular adhesion molecule 1 is released by human melanoma cells and is associated with tumor growth in nude mice.

We have studied the cytokine regulation of cell surface and soluble intercellular adhesion molecule 1 (ICAM-1) expression on the human melanoma cell line A375M. Unstimulated cells express ICAM-1 on their cell surface but do not secrete significant levels of soluble ICAM-1. Interleukin 1, interleukin 6, tumor necrosis factor, and gamma-interferon all increased cell surface expression of ICAM-1. Tumor necrosis factor, interleukin 1, and gamma-interferon also caused the release of soluble ICAM-1. The serum of melanoma patients has been reported to contain elevated levels of soluble ICAM-1; however, the source of this ICAM-1 is unclear. The serum from nude mice bearing s.c. human melanoma tumors was found to contain soluble human ICAM-1. ICAM-1 levels showed a positive correlation with tumor weight. The release of ICAM-1 from melanoma tumors, in response to host-derived cytokines, may have relevance to immune recognition of the tumor.     

Effect of interleukin-1-beta on metastasis formation in different tumor systems

Experiments were done to determine the effect of interleukin-1-beta (IL-1 beta) on metastasis formation in different tumor systems. Intravenous administration of 1 microgram of human recombinant IL-1 beta given 1 hour before tumor cell injection augmented lung colony formation (experimental metastases) by the human A375 melanoma variants, the human HT-29M colon carcinoma, the SN12-K1 renal carcinoma in nude mice, the murine B16 melanoma variants, and the murine UV-2237M fibrosarcoma in syngeneic recipients. The same treatment did not induce lung colony formation by a human rectal carcinoma (HCC-P2988) or by a murine reticulum cell sarcoma (M5076), both of which are not metastatic to the lung. Spontaneous metastases were studied in C57BL/6 mice bearing the B16-BL6 melanoma (metastatic to the lung) in their footpad and the M5076 reticulum cell sarcoma (metastatic to the liver) subcutaneously. Daily intraperitoneal treatment with 1 microgram of IL-1 beta increased lung and liver metastases. These findings indicate that treatment of mice with IL-1 beta can increase the number of artificial or spontaneous metastases and that this effect is not limited to a single tumor type or to a specific organ.     

A new Mr 55,000 surface protein implicated in melanoma progression: association with a metastatic phenotype

Emergence of the invasive phenotype is a key event in the progression of human melanoma from benign proliferative lesions to malignant lesions. Recently we successfully selected in vivo from a poorly metastatic M4Beu. human melanoma cell line two variants (7GP and T1P26) that generate a higher frequency of spontaneous metastases to the lungs into immune-suppressed neonatal rats. Both cell lines showed no significant differences in the integrin profile of the subunits analyzed except for beta3, which was reduced to a background level in metastatic variants. To investigate how these variant sublines of human melanomas manage to sustain growth in the absence of alpha(v)beta3, a subtractive immunization approach was used to elicit host antibody response against cell surface proteins expressed on metastatic variants. In this study, a new monoclonal antibody (MoAb), LY1, that is highly specific for the 7GP and T1P26 variants, was isolated. LY1 identifies a membrane protein of Mr 55,000 on melanoma variants with epitopes that were resistant to sugar-cleaving enzymes. Immunostaining cells from variants by LY1 showed that staining is distributed to the cell periphery with high labeling intensity at the cell-to-cell contact points. This MoAb significantly inhibited invasion of metastatic variants through a reconstituted basement membrane (Matrigel) in vitro. Moreover, tumor growth of melanoma variants was dramatically affected in vivo with this MoAb. In vitro studies indicate that the LY1 MoAb does not inhibit chemotactic migration of the metastatic variants, the adhesion of tumor cells to vitronectin, collagen IV, fibronectin, and laminin, or cell proliferation. Expression of this antigen is high in human striated muscle, heart, spleen, brain, and lung and absent in kidney, liver, and pancreas. Using 59 fixed, paraffin-embedded archival tissues of human melanomas and nevi, LY1-reactive cells were not observed in melanocytes, nevi, or radial growth phase primary melanomas. In sharp contrast, LY1 selectively stained melanocytes derived from the vertical growth phase of many primary melanomas and metastatic melanomas. These results provide evidence that the Mr 55,000 protein expressed by selected variants with increased metastatic properties in vivo plays a functionally important role in determining metastasis. This molecule may represent a new metastatic risk marker in human melanoma and may be of biological importance in the identification of fatal metastatic subpopulations that have acquired competence for metastasis production.