Glycoconjugate profile and CD44 expression in human melanoma cell lines with different metastatic capacity

Rational Design of Polymeric Hybrid Micelles with Highly Tunable Properties to Co‐Deliver MicroRNA‐34a and Vismodegib for Melanoma Therapy

A polymeric hybrid micelle (PHM) system with highly tunable properties is reported to co‐deliver small molecule and nucleic acid drugs for cancer therapy; this system is structurally simple and easy‐to‐fabricate. The PHM consists of two amphiphilic diblock copolymers, polycaprolactone‐polyethylenimine (PCL‐PEI) and polycaprolactone‐polyethyleneglycol (PCL‐PEG). PHMs are rationally designed with different physicochemical properties by simply adjusting the ratio of the two diblock copolymers and the near neutral PHM‐2 containing a low ratio of PCL‐PEI achieves the optimal balance between high tumor distribution and subsequent cellular uptake after intravenous injection. Encapsulating Hedgehog (Hh) pathway inhibitor vismodegib (VIS) and microRNA‐34a (miR‐34a) into PHM‐2 generates the VIS/PHM‐2/34a co‐delivery system. VIS/PHM‐2/34a shows synergistic anticancer efficacy in murine B16F10‐CD44+ cells, a highly metastatic tumor model of melanoma. VIS/PHM‐2/34a synergistically attenuates the expression of CD44, a vital receptor indicating the metastasis of melanoma. Intriguingly, inhibiting Hh pathway by VIS is accompanied by downregulation of CD44 expression, revealing that Hh signaling might be an upstream regulator of CD44 expression in melanoma. Thus, co‐delivery of miR‐34a and VIS demonstrates great potential in cancer therapy, and PHM offers a structurally simple and highly tunable platform for the co‐delivery of small molecule and nucleic acid drugs in tumor combination therapy.

Whole Transcriptome Analysis (RNA Sequencing) of Peripheral Blood Mononuclear Cells of Vitiligo Patients

Vitiligo is an idiopathic disorder characterized by depigmented patches on the skin due to a loss of melanocytes. The cause of melanocyte destruction is not fully understood. The aim of this study was to detect the potential pathways involved in the vitiligo pathogenesis to further understand the causes and entity of vitiligo. For that the transcriptome of peripheral blood mononuclear cells of 4 vitiligo patients and 4 control subjects was analyzed using the SOLiD System platform and whole transcriptome RNA sequencing application. Altogether 2,470 genes were expressed differently and GRID2IP showed the highest deviation in patients compared to controls. Using functional analysis, altogether 993 associations between the gene groups and diseases were found. The analysis revealed associations between vitiligo and diseases such as lichen planus, limb-girdle muscular dystrophy type 2B, and facioscapulohumeral muscular dystrophy. Additionally, the gene groups with an altered expression pattern are participating in processes such as cell death, survival and signaling, inflammation, and oxidative stress. In conclusion, vitiligo is rather a systemic than a local skin disease; the findings from an enormous amount of RNA sequencing data support the previous findings about vitiligo and should be further analyzed.

MEL4B3, a novel mRNA is induced in skin tumors and regulated by TGF-beta and pro-inflammatory cytokines

Tumor-stroma interactions play a decisive role in the growth and metastasis of solid tumors, and involve signalling either by soluble mediators or direct cell-cell interaction. Here, we report the isolation and characterisation of a novel cDNA (MEL4B3), which is induced in cultured dermal fibroblasts exposed to supernatants of melanoma cell lines. MEL4B3 shares high homology with two predicted cDNA sequences for which no activity has so far been described. In situ hybridisation revealed the expression of MEL4B3 in malignant melanoma increasing with tumor depth; in basal cell carcinoma and in squamous cell carcinoma. MEL4B3 was barely detectable in normal skin or non-malignant melanocytic naevi. Furthermore, MEL4B3 was expressed at high level in the epidermis of psoriatic skin. In vitro, the expression of MEL4B3 was found to be induced by the exposure of human dermal fibroblasts to melanoma cell culture supernatants or to transforming growth factor-beta, interleukin-1 and tumor necrosis factor-alpha. The expression MEL4B3 therefore reflects closely cell activation occurring during tumor growth, metastasis and inflammation.

Proteoglycan control of cell movement during wound healing and cancer spreading

By virtue of their multifunctional nature, proteoglycans (PGs) are thought to govern the process of cell movement in numerous physiological and pathological contexts, spanning from early embryonic development to tumour invasion and metastasis. The precise mode by which they influence this process is still fragmentary, but evidence is accruing that they may affect it in a multifaceted manner. PGs bound to the plasma membrane mediate the polyvalent interaction of the cell with matrix constituents and with molecules of the neighbouring cells' surfaces; they modulate the activity of receptors implicated in the recognition of these components; and they participate in the perception and convergence of growth- and motility-promoting cues contributed by soluble factors. Through some of these interactions several PGs transduce to pro-motile cells crucial intracellular signals that are likely to be essential for their mobility. A regulated shedding of certain membrane-intercalated PGs seems to provide an additional level of control of cell movement. Coincidentally, matrix-associated PGs may govern cell migration by structuring permissive and non-permissive migratory paths and, when directly secreted by the moving cells, may alternatively create favourable or hostile microenvironments. To exert this latter, indirect effect on cell movement, matrix PGs strongly rely upon their primary molecular partners, such as hyaluronan, link proteins, tenascins, collagens and low-affinity cell surface receptors, whereas a further finer control is provided by a highly regulated proteolytic processing of the PGs accounted by both the migrating cells themselves and cells of their surrounding tissues. Overall, PGs seem to play an important role in determining the migratory phenotype of a cell by initiating, directing and terminating cell movement in a spatio-temporally controlled fashion. This implies that the "anti-adhesive and/or "anti-migratory" properties that have previously been assigned to certain PGs may be re-interpreted as being a means by which these macromolecules elaborate haptotaxis-like mechanisms imposing directionality upon the moving cells. Since these conditions would allow cells to be led to given tissue locations and become immobilized at these sites, a primary function may be ascribed to PGs in the dictation of a "stop or go" choice of the migrating cells.

Tumor cell-induced deactivation of human monocytes

Although blood monocytes exhibit significant cytotoxic activity against tumor cells, the function of tumor infiltrating macrophages (TIM) is depressed in cancer patients. This study addresses the question of how the antitumor response of human monocytes, assessed by production of cytokines (tumor necrosis factor alpha, TNF; IL-10; IL-12p40) and cytotoxicity, is altered by exposure to cancer cells. Tumor cell--pre-exposed monocytes restimulated with tumor cells showed significantly decreased production of TNF, IL-12, increased IL-10 (mRNA and release) and inhibition of IL-1 receptor-associated kinase-1 (IRAK-1) expression. This down-regulation of cytokine production was selective, as the response of pre-exposed monocytes to lipopolysaccharide (LPS) was unaffected. Treatment of tumor cell--pre-exposed monocytes with hyaluronidase (HAase) improved their depressed production of TNF, while HAase-treated cancer cells did not cause monocyte dysfunction. The response of hyaluronan (HA)--pre-exposed monocytes to stimulation with tumor cells was also inhibited. Cytotoxic activity of monocytes pretreated with cancer cells was also decreased. This study shows that tumor cells selectively deactivate monocytes and suggests that tumor cell-derived HA by blocking CD44 on monocytes inhibits their antitumor response. These observations may provide some explanation for the depressed function of TIM in human malignancy.

CD44s adhesive function spontaneous and PMA-inducible CD44 cleavage are regulated at post-translational level in cells of melanocytic lineage

Adhesion between the CD44s receptor and hyaluronic acid plays an important role in cell migration, tumour growth and progression. Although the alternative splicing of CD44 variant exons represents the principal regulatory mechanism of CD44-mediated functions, CD44v spliced variants are scantily expressed in melanoma cells. For this reason, we have investigated the possibility that post-translational modifications of the CD44 standard receptor could play a pivotal role in regulating CD44-mediated functions in melanoma. Using metabolic inhibitors of N- and O-glycosylation, as well as melanoma transfectants expressing CD44s O-glycosylation site-specific mutants, we performed structural and functional analysis of N- and O-deglycosylated CD44s molecules expressed in melanoma cells. We discovered that complete N- and O-glycosylation is not required by CD44s to be correctly expressed on the melanoma cell surface. Indeed, variably glycosylated and functionally different CD44s molecules were constitutively expressed in primary and metastatic lesions. Furthermore, we observed that changes in N- and O-glycosylation of CD44s could modulate its cleavage. In fact, spontaneous CD44s shedding was dependent on the presence of partial or complete O-glycosylation of four serine-glycine motifs localized in the membrane-proximal CD44 ectodomain. Mutation of these serine residues, as well as an extensive metabolic O-deglycosylation, strongly impaired spontaneous CD44 shedding. Furthermore, an O-glycosylation-independent mechanism of CD44 cleavage has been identified. This alternative mechanism of receptor cleavage is phorbol 12-myristate-13-acetate (PMA) inducible, mediated by metalloproteinase and requires the presence of N-linked sugar residues. Our findings demonstrate that the post-translational modification of CD44s represents the principal regulatory mechanism of CD44s-mediated functions in melanoma.

Effect of transforming growth factor-beta1, insulin-like growth factor-I, and hepatocyte growth factor on proteoglycan production and regulation in canine melanoma cell lines

OBJECTIVE

To identify extracellular proteoglycans produced by canine melanoma cell lines and analyze the effect of transforming growth factor-beta1 (TGF-beta1), insulin-like growth factor-I (IGF-I), and hepatocyte growth factor (HGF) on these proteoglycans.

SAMPLE POPULATION

3 canine melanoma cell lines (ie, CML-1, CML-6M, and CML-10c2).

PROCEDURE

Extracellular proteoglycans were analyzed by use of metabolic labeling and western immunoblot analysis. The effect of TGF-beta1 on cell proliferation was determined by incorporation of 5-bromo-2'-deoxyuridine.

RESULTS

The CML-1 and CML-6M melanoma cell lines produced 2 main extracellular proteoglycans. One of them was identified as versican, a proteoglycan found in undifferentiated human melanoma cell lines. The CML-10c2 cells produced a small amount of extracellular proteoglycans. Addition of TGF-beta1 (1.25 to 6.25 ng/ml) increased the release of sulfated proteoglycans into the medium. The TGF-beta1 had mainly a posttranslational effect, because it increased the molecular mass of the sulfated bands. Addition of IGF-I (50 ng/ml) slightly increased production of proteoglycans in the CML-6M cell line, whereas HGF (50 ng/ml) did not have any effect on proteoglycan production.

CONCLUSIONS AND CLINICAL RELEVANCE

The proteoglycan content and response toTGF-beta1 treatment for CML-1 and CML-6M canine melanoma cell lines are similar to that for undifferentiated human melanoma cell lines. In contrast, CML-10c2 cells produced a low amount of proteoglycans with high molecular weight. Because these extracellular proteoglycans are involved in the control of cell adhesion, proliferation, and migration, they may play an important role in the progression of melanomas in dogs.

Myxoid melanoma: immunohistochemical studies and a review of the literature

Malignant myxoid melanoma (MMM) is a rarely reported variant of malignant melanoma, which can often be confused with other mucin-containing neoplasms. A retrospective study of 3 cases of MMM and a review of the English-language literature was performed. MMM affects an older population and is frequently misdiagnosed. The major pathologic features are atypical spindle cells embedded in a myxoid stroma. Immunohistochemistry analysis of the tumor shows uniform staining of the spindle cells with S-100. In our 3 cases, there were noticeably more mast cells that could be detected with Giemsa stain and with antibody against transforming growth factor. The prognosis appears to be equivalent to other primary melanomas. Diagnosing MMM requires a high index of suspicion. We hypothesize that mast cells and secretion of transforming growth factor beta stimulates fibroblast secretion of mucin, which contributes to the tumor's invasive potential.

Cross-talk between human monocytes and cancer cells during reactive oxygen intermediates generation: the essential role of hyaluronan

Human monocytes exhibit considerable cytocidal activity against tumor (but not normal cells) associated, at least partly, with the generation of reactive oxygen intermediates (ROIs). The present study examined the role of surface determinants and hyaluronan (HA) in the induction of ROI production by human monocytes stimulated with cancer cells, as measured by luminol-enhanced chemiluminescence (CL). The inhibitory effect of monoclonal antibodies (MAbs) indicated the engagement of CD18, CD29 and CD44 adhesion molecules. Preincubation of monocytes and tumor cells, expressing CD44 determinants, with either anti-CD44 MAb or HA inhibited CL generation. Addition of HA to monocytes decreased the expression of CD44 and induced CL response. Supernatants from the cultures of tumor cells stimulated CL response of monocytes, an effect that was abolished by treatment of the supernatants with hyaluronidase (HAase) or by preincubation of monocytes with an anti-CD44 MAb. These results indicate that several surface molecules of monocytes, including CD44, are required to trigger the generation of ROI after their contact with tumor cells, whereas HA overexpressed on some cancer cells may allow monocytes (via CD44) to distinguish between transformed and normal cells. However, blocking of CD44 on monocytes by free HA dampens their response to tumor cells. Taken together, these observations suggest that the presence of HA in the tumor stroma may modulate effector functions of infiltrating macrophages and their interactions with cancer cells in situ.

The pattern of metastasis of human melanoma to the central nervous system is not influenced by integrin alpha(v)beta(3) expression

We investigated the effect of integrin alpha(v)beta(3) expression on the metastatic pattern of human melanoma cells in the central nervous system (CNS). For this purpose, we developed a hematogenous CNS melanoma metastasis model in nude mice using a modified internal carotid artery infusion technique. This protocol revealed 2 different patterns of CNS metastasis. The integrin alpha(v)beta(3)-expressing melanoma lines Mel57 and Zkr nearly exclusively produced metastases in the brain parenchyma, whereas cells of the BLM and MV3 lines, devoid of integrin alpha(v)beta(3) expression, preferentially metastasized to dura mater and leptomeninges. Treatment with hyaluronidase to obtain single BLM cell suspensions did not influence the metastatic pattern, indicating that this was not simply the result of entrapment of tumor cell aggregates in large-sized leptomeningeal vessels. The role of integrin alpha(v)beta(3) expression in the process of metastasis was tested by transfection of BLM, but did not lead to an altered pattern of metastasis. We did observe, however, slower growth of the transfected tumors, although the in vitro growth rate was unaltered, indicating a reduction in tumorigenicity. We conclude from our findings that CNS metastasis of melanoma cells in the mouse xenograft model occurs in at least 2 different but very reproducible patterns. Although it is predicted that adhesion of tumor cells to endothelial cells plays a role in this phenomenon, tumor cell integrin alpha(v)beta(3) expression per se does not explain the difference in metastatic behavior in the CNS. We assume that other, as yet unknown factors, must be involved.

CD44 is the principal mediator of hyaluronic-acid-induced melanoma cell proliferation

Interactions of the extracellular matrix component hyaluronic acid and its cellular receptors CD44 and RHAMM/IHABP have been linked to tumor progression and metastasis formation. We investigated the expression and hyaluronic-acid-dependent functions of CD44 and RHAMM/IHABP in human melanoma. Immunohistochemistry of tumor specimens at different stages of melanoma progression revealed an increased expression of CD44 and RHAMM/IHABP. High mRNA expression of CD44 was found in three highly tumorigenic melanoma cell lines compared with less tumorigenic melanoma cells or nontransformed melanocytes. RHAMM/IHABP expression was upregulated in all cell lines analyzed but not in melanocytes. In contrast to the cell surface localization of CD44, RHAMM/IHABP was detected exclusively within the cytoplasm of melanoma cells. Binding and adhesion of melanoma cells to hyaluronic acid is mainly CD44 dependent as it was inhibited to 60%--80% by an anti-CD44 monoclonal antibody whereas anti-RHAMM/IHABP sera had no effect. Culture of melanoma cells in the presence of hyaluronic acid resulted in a dose-dependent, CD44-mediated increase of melanoma cell proliferation and enhanced release of basic fibroblast growth factor and transforming growth factor beta 1. We conclude that (i) the expression of CD44 and RHAMM/IHABP is increased during melanoma progression, (ii) CD44 is the principal hyaluronic acid surface receptor on melanoma cells, and (iii) the hyaluronic-acid-induced increase of the proliferative capacity of melanoma cells is mainly dependent on CD44--hyaluronic acid interactions.

Reduced level of CD44 and hyaluronan associated with unfavorable prognosis in clinical stage I cutaneous melanoma

The cell surface glycoprotein CD44 and its ligand, hyaluronan (HA), enhance growth and metastatic capacity of melanoma cells in vitro, but their clinical significance in primary cutaneous melanoma is still unclear. Therefore, we studied whether the levels of CD44 and HA associate with disease progression and survival of cutaneous melanoma. A series of 292 clinical stage I cutaneous melanomas was analyzed by immunohistochemistry using an anti-CD44H antibody (clone 2C5). HA was demonstrated histochemically using a biotinylated HA-specific affinity probe (bHABC). The reduced staining levels of CD44 and HA were associated with each other and indicators of progressive disease. Reduced CD44 and HA level, high tumor thickness, high pT category, high Clark's level, bleeding, and male gender predicted short univariate recurrence free survival (RFS) and overall survival (OS). In Cox's multivariate analysis (N: = 251), the decreased level of CD44, high tumor thickness, and bleeding predicted independently short RFS. High tumor thickness and bleeding were associated with short OS. We conclude that the reduced cell surface CD44 and HA levels associate with poor prognosis in clinical stage I cutaneous melanoma. The notion that the decreased level of CD44 independently predicts short RFS suggests that reduced cell surface CD44 enhances the spreading potential in localized cutaneous melanoma and that quantification of CD44 offers a prognostic tool for its clinical evaluation.

Functional hierarchy of simultaneously expressed adhesion receptors: integrin alpha2beta1 but not CD44 mediates MV3 melanoma cell migration and matrix reorganization within three-dimensional hyaluronan-containing collagen matrices

Haptokinetic cell migration across surfaces is mediated by adhesion receptors including beta1 integrins and CD44 providing adhesion to extracellular matrix (ECM) ligands such as collagen and hyaluronan (HA), respectively. Little is known, however, about how such different receptor systems synergize for cell migration through three-dimensionally (3-D) interconnected ECM ligands. In highly motile human MV3 melanoma cells, both beta1 integrins and CD44 are abundantly expressed, support migration across collagen and HA, respectively, and are deposited upon migration, whereas only beta1 integrins but not CD44 redistribute to focal adhesions. In 3-D collagen lattices in the presence or absence of HA and cross-linking chondroitin sulfate, MV3 cell migration and associated functions such as polarization and matrix reorganization were blocked by anti-beta1 and anti-alpha2 integrin mAbs, whereas mAbs blocking CD44, alpha3, alpha5, alpha6, or alphav integrins showed no effect. With use of highly sensitive time-lapse videomicroscopy and computer-assisted cell tracking techniques, promigratory functions of CD44 were excluded. 1) Addition of HA did not increase the migratory cell population or its migration velocity, 2) blocking of the HA-binding Hermes-1 epitope did not affect migration, and 3) impaired migration after blocking or activation of beta1 integrins was not restored via CD44. Because alpha2beta1-mediated migration was neither synergized nor replaced by CD44-HA interactions, we conclude that the biophysical properties of 3-D multicomponent ECM impose more restricted molecular functions of adhesion receptors, thereby differing from haptokinetic migration across surfaces.

Calcium- and calmodulin-dependent PMA-activation of the CD44 adhesion molecule

The ability of the CD44 adhesion molecule to interact with its ligand hyaluronic acid (HA) is tightly regulated. CD44-positive mouse LB lymphoma cells are unable to bind HA unless activated by the tumor promoter phorbol 12-myristate 13-acetate (PMA). PMA causes a dose-dependent increase in both CD44 expression level and HA-binding capacity, with the binding of HA observed only above a threshold amount of CD44 molecules. This induction of HA-binding as well as the increase in CD44 expression are prevented by cycloheximide, suggesting a requirement for new additional CD44 molecules on the cell surface and/or cooperating proteins. In the present study, we have investigated which of the signal transduction pathways activated by PMA leads to the increased CD44 expression with subsequent acquisition of HA-binding capacity. By comparing the influence of each inhibitory agent on PMA-activated LB lymphoma cells versus that on a constitutive HA-binder cell line derived from LB cells (designated HA9 cells), we could distinguish between an effect on the PMA-activation phase and a one on the HA-binding phase. Our data show that the PMA-induced HA-binding could not be blocked by agents inhibiting protein kinase C (PKC) (staurosporine, sphingosine, polymyxin B, quercetin) or genestein, an inhibitor of tyrosine protein kinases. However, this PMA response was strongly inhibited by calmodulin antagonists (chlorpromazine, trifluoperazine, W-7) and the calcium blocker verapamil. The calmodulin antagonists inhibited the PMA-induced increase in CD44 expression on LB cells, but had no influence on the ability of the constitutive HA-binder HA9 cell line to interact with HA, indicating an effect on the PMA induction phase rather than on the binding itself. Verapamil also blocked the PMA-induced increase in CD44 expression on LB cells, but in addition it slightly reduced the ability of the HA9 cells to bind HA without affecting their CD44 expression level. In conclusion, our data suggest that CD44 activation by PMA is calcium and calmodulin dependent, rather than mediated by protein kinase C.

Induction of reactive oxygen intermediates in human monocytes by tumour cells and their role in spontaneous monocyte cytotoxicity

The present study examined the ability of human monocytes to produce reactive oxygen intermediates after a contact with tumour cells. Monocytes generated oxygen radicals, as measured by luminol-enhanced chemiluminescence and superoxide anion production, after stimulation with the tumour, but not with untransformed, cells. The use of specific oxygen radical scavengers and inhibitors, superoxide dismutase, catalase, dimethyl sulphoxide and deferoxamine as well as the myeloperoxidase inhibitor 4-aminobenzoic acid hydrazide, indicated that chemiluminescence was dependent on the production of superoxide anion and hydroxyl radical and the presence of myeloperoxidase. The tumour cell-induced chemiluminescent response of monocytes showed different kinetics from that seen after activation of monocytes with phorbol ester. These results indicate that human monocytes can be directly stimulated by tumour cells for reactive oxygen intermediate production. Spontaneous monocyte-mediated cytotoxicity towards cancer cells was inhibited by superoxide dismutase, catalase, deferoxamine and hydrazide, implicating the role of superoxide anion, hydrogen peroxide, hydroxyl radical and hypohalite. We wish to suggest that so-called 'spontaneous' tumoricidal capacity of freshly isolated human monocytes may in fact be an inducible event associated with generation of reactive oxygen intermediates and perhaps other toxic mediators, resulting from a contact of monocytes with tumour cells.

CD44 expression in sinonasal melanomas: is loss of isoform expression associated with advanced tumour stage?

The expression of the adhesion molecule CD44 was examined in 14 primary sinonasal melanomas (SMs), aggressive neoplasms with short survival times, as CD44 overexpression has been linked to poor survival in human cancers. Immunohistochemistry was performed on formalin-fixed, paraffin-embedded sections with CD44 isoform-specific monoclonal antibodies to the CD44 standard (s) and variant isoforms (v) v5 and v6. CD44s, v5, and v6 were strongly expressed in a membranous pattern in SM in situ, early invasive SM, and in uninvolved respiratory/squamous epithelium. In invasive SM, membranous CD44s expression was identified in a large proportion of melanoma cells. Membranous staining of CD44v5 and v6 was lost in invasive SM, independently of the histological subtype. Diffuse cytoplasmic staining was observed focally in invasive SM and loss of cytoplasmic expression of CD44v6 and v5 was associated with advanced tumour stage in the linear-by-linear association test (p = 0.042 and 0.066, respectively). CD44s may not be important for malignant transformation, as it is expressed in both benign and malignant melanocytes. Loss of membranous CD44 isoform expression in widely invasive SM suggests that loss of cellular adhesion facilitates matrix and vascular infiltration and dissemination of sinonasal melanoma cells.

Expression of the NG2 proteoglycan enhances the growth and metastatic properties of melanoma cells

The human homologue of NG2, the human melanoma proteoglycan (HMP), is expressed on most human melanomas. To investigate the role of this proteoglycan in melanoma progression, we have attempted to identify functionally important molecular ligands for NG2. Immunohistochemical analysis of cell lines that endogenously express NG2/HMP suggests that NG2/HMP associates with CD44 and alpha4beta1 integrin, two molecules previously implicated in melanoma progression. Transfection of rat NG2 into the NG2-negative B16 mouse melanoma cell line also resulted in a highly colocalized pattern of expression between the transfected rat NG2 and the endogenously expressed mouse CD44 and alpha4beta1 integrin molecules. In functional assays, expression of NG2 decreased the adhesion of B16 melanoma cells to CD44 monoclonal antibodies, hyaluronic acid, the C-terminal 40-kDa fibronectin fragment, and the CS1 fibronectin peptide, suggesting that NG2 may negatively modulate CD44- and alpha4beta1-mediated binding events. Expression of NG2 increased the proliferation of melanoma cells in culture and increased tumorigenicity in vivo. Moreover, NG2 expression led to increased lung metastasis of B16F1 and B16F10 melanoma cells in experimental metastasis studies. Together, these studies demonstrate that NG2 is capable of modulating the adhesion, proliferation, and metastatic potential of melanoma cells.

Blockade of metastasis formation by CD44-receptor globulin

CD44 standard as well as variant isoforms have been frequently reported to be involved in the process of metastasis formation. Whereas in the rat system, but also in some human tumours, the variant exon v6 is of importance in the lymphatic spread of carcinomas, in human malignant melanoma CD44s and, possibly, CD44v10 appear to facilitate local invasion and haematogenous spread. This has been tested in the B16F10 murine melanoma model by treating B16F10-bearing C57BL/6 mice either with a CD44s-/ CD44v10-specific antibody, or with receptor globulins (Rg) containing the extracellular part of CD44s or CD44v10 linked to the constant region of the immunoglobulin kappa light chain. Prior characterization of the CD44s and CD44v10 Rg had shown that both Rgs bound to components of the extracellular matrix, CD44s in particular to hyaluronic acid. Immunohistological screening of organ sections from adult C57BL/6 mice revealed additional evidence for both Rgs binding to elements of the extracellular matrix, particularly in bone marrow, intestine and lung. In the absence of any further treatment, the CD44s Rg reduced the number of lung colonies by 70%, while application of the CD44v10 Rg resulted in 60% reduction. CD44-specific antibodies were equally efficient with regard to B16F10 settlement in the lung. However, only the CD44 Rgs prevented spread and settlement of melanoma cells in distant organs. The finding confirms the involvement of both CD44s and CD44v10 in melanoma progression, and is suggestive for the use of Rgs as therapeutic reagents.

Hyaluronan-independent lodgment of CD44+ lymphoma cells in lymphoid organs

We previously found that monoclonal antibodies (MAbs) directed against the constant region of the CD44 molecule block lymph node infiltration of a mouse LB T-cell lymphoma, suggesting a role for this glycoprotein in the LB cell dissemination process. In the present study, we investigated whether LB cells in the local tumor must undergo a change in the CD44 phenotype to be able to migrate to and invade the remote lymph nodes, and if hyaluronic acid (HA), the principal ligand of activated CD44, functions as a mediator in this process. We compared the in vivo behavior of a non-HA-binder LB cell line with that of a constitutive HA-binder HA9 subline. Our results show that the lymphoid organ-infiltrating LB cells express similar levels of pan-CD44 and V4- and V6-containing CD44 variants, as the corresponding cells in the local growth and the cultured LB cells. The tested CD44 phenotype of HA9 cells also remained unchanged during the metastatic process. Even after lymph node infiltration, LB cells remained incapable of binding HA, whereas the HA9 cells retained an efficient HA-binding capacity. The constitutive HA-binder HA9 cells that expressed an approximately 10-fold higher level of pan-CD44 than did the parental LB cells, as well as an elevated level of the V4 and V6 exon products formed a local tumor and invaded both lymph nodes and spleen, as did the parental LB cells, albeit at a much slower rate. Our finding indicates that there is no direct correlation between the amount of CD44 expressed on the cell surface, the HA-binding capacity and tumorigenicity. Moreover, interaction with HA is not obligatory for LB cell localization in the lymphoid organs, and a tight cell-HA interaction, as observed in HA9 cells, does not prevent tumor cell dissemination, although it may retard tumor spread.

CD44 and the adhesion of neoplastic cells

CD44 is a family of transmembrane glycoproteins that act mainly as a receptor for hyaluronan. It can also bind some other extracellular matrix ligands (chondroitin sulphate, heparan sulphate, fibronectin, serglycin, osteopontin) with lower affinity. CD44 is encoded by a single gene containing 20 exons, 10 of which (v1-v10) are variant exons inserted by alternative splicing. The standard, ubiquitously expressed isoform of CD44, does not contain sequences encoded by these variant exons. Numerous variant isoforms of CD44 containing different combinations of exons v1-v10 inserted into the extracellular domain can be expressed in proliferating epithelial cells and activated lymphocytes. CD44 plays a significant role in lymphocyte homing. Both alternative splicing and glycosylation influence receptor function of the molecule, usually reducing its affinity to hyaluronan. The cytoplasmic domain of CD44 communicates with the cytoskeleton via ankyrin and proteins belonging to the ezrin-moesin-radixin family. Relatively little is known about the intracellular events following interactions of CD44 with its ligands. Some variant isoforms, especially those containing sequences encoded by v6-v10, are overexpressed in both human and animal neoplasms. In a rat pancreatic adenocarcinoma model one of the variant CD44 isoforms was proved to be determinant in the metastatic process. For some human neoplasms (carcinomas of the digestive tract, non-Hodgkin's lymphomas, thyroid carcinomas, and others) correlations have been made between the particular pattern of CD44 variants produced by neoplastic cells and clinicopathological parameters of tumours, such as grade, stage, presence of metastases, and survival. In vitro studies indicate that modifications of CD44 expression result in different ligand recognition and influence cell motility, invasive properties, and metastatic potential of experimental tumours. Investigation of CD44 neoexpression can be useful both in early cancer diagnosis and in predicting tumour behaviour. It can also contribute to better understanding of molecular mechanisms leading to neoplastic transformation.

Expression of CD44 isoforms and beta 1,6-branched oligosaccharides in human malignant melanoma is correlated with tumor progression but not with metastatic potential

CD44, a family of closely related glycoproteins generated by alternative splicing, as well as the increased beta 1,6-branching of Asn-linked oligosaccharides (beta 1,6-branches), have been implicated in tumor progression and metastasis. We have investigated the expression of CD44 standard (CD44s), various CD44 splice variants (CD44v3, -v4, -v5, -v6 and -v9), and of beta 1,6-branches in a total of 37 paraffin-embedded human primary melanomas and metastases. Out of the 28 studied primary melanomas, 27 were positive for CD44s, 21 for CD44v5 (cytoplasmic staining) and 26 for beta 1,6 branches. Furthermore, superficial spreading melanomas showed a significant (p = 0.004) stronger staining for CD44s than the thick (> 1.5 mm) nodular melanomas, whereas no significant difference was found with regard to staining for CD44v5 and beta 1,6-branches. Eight of the 9 studied melanoma metastases were positive for CD44s, 6 for CD44v5 (cytoplasmic staining) and 7 for beta 1,6-branches. No CD44v3, -v4, -v6 and -v9 could be detected in any of the tumors. On average, metastases as compared to primary tumors, exhibited a significant (p = 0.002) weaker staining for CD44s. However, metastasizing melanomas could not be distinguished from non-metastasizing ones based on CD44 immunostaining.

Detection of CD44 splice variants in formalin-fixed, paraffin-embedded specimens of human skin cancer

The standard form of CD44 (CD44s) and CD44 isoforms, containing sequences encoded by one or several of 10 different variant CD44 exons (v1-v10), are thought to play a crucial role in the growth and metastasis of certain human tumors. Recently, monoclonal antibodies (mAbs) directed against all CD44 isoforms (panCD44), or against epitopes encoded by specific variant exons (CD44v) have been developed, which unfortunately only stain cryopreserved tissues. We wished to develop a technique to unmask chemically CD44s and CD44v epitopes in paraffin-embedded specimens of human skin cancers, so that they would be accessible for these mAbs. To address this issue, CD44s and CD44v expression was compared in cryopreserved and in formalin-fixed, paraffin-embedded biopsies obtained from the same basal cell carcinomas (BCC), squamous cell carcinomas (SCC), primary malignant melanomas (PMM) and metastatic malignant melanomas (MMM). Formalin-fixed tumors were deparaffinized and treated briefly with an antigen retrieval fluid (TUFTM) at 95 degrees C or left untreated. In untreated paraffin-embedded tissues, no CD44s or CD44v staining was detected. In contrast, in antigen retrieval fluid-treated biopsies CD44s and CD44v expression was identical to that in cryopreserved specimens of the same tumor with the exception of mAbs detecting v7/8 and v10. We conclude that antigen retrieval unmasks certain epitopes in formalin-fixed, paraffin-embedded tissues, thus facilitating future research on the relevance of CD44s and CD44v expression for human skin carcinogenesis.

Migration of highly aggressive melanoma cells on hyaluronic acid is associated with functional changes, increased turnover and shedding of CD44 receptors

Recent evidence indicates that CD44, a multifunctional adhesion receptor involved in cell-cell as well as in cell-matrix interactions, plays an important role in local progression and metastasis of malignant tumors. We have studied a set of human melanoma cell lines differing in their metastatic potential in nude mice as well as in normal melanocytes for changes in CD44 expression and function. All melanocytes and melanoma cell lines tested highly expressed the CD44 standard form (CD44s, 85 kDa) but variants at low levels only. With respect to one of the CD44-associated functions primarily involved in tumor progression we found that two highly metastatic tumor cell lines, MV3 and BLM, showed fivefold higher migration rates towards hyaluronate than melanomas with low metastatic potential and normal melanocytes. Moreover, the highly metastatic cell lines expressed four- to sixfold higher levels of the CD44 epitope involved in hyaluronic acid-binding (monoclonal antibody Hermes-1) than less aggressive melanomas and melanocytes. Hermes-1 efficiently blocked haptotaxis to hyaluronate, supporting the functional relevance of this epitope. In contrast, expression levels of other CD44s epitopes recognized by seven different anti-CD44 monoclonal antibodies were unchanged, suggesting that the migratory behaviour of the cells depends on the formation of the hyaluronate-binding Hermes-1 epitope rather than on the overall CD44s surface expression, which was virtually identical in all melanoma and melanocyte cell lines tested. Differences in the accessibility of the hyaluronate-binding epitope defined by Hermes-1 correlated with the phosphorylation state of CD44s, probably reflecting different activation states of the receptor. Furthermore, immunoprecipitation and pulse/chase studies revealed a three- to fivefold increase in CD44 synthesis in the highly aggressive melanoma cells as compared to the other cell lines and the melanocytes, indicating a reduction of CD44 half-life and up-regulation of turnover. Moreover, highly aggressive melanoma cell lines were found to shed significant amounts of CD44 from the cell surface and to secrete its ligand hyaluronic acid, which may refer to an “autocrine' mechanism mediating melanoma cell motility.

Metastatic potential of human melanoma cells in nude mice--characterisation of phenotype, cytokine secretion and tumour-associated antigens

Incidence and mortality of human malignant melanoma has risen rapidly over recent decades. Although the notorious resistance to treatment is characteristic for metastatic malignant melanoma, only a few experimental models have been established to study the metastatic cascade or to test new alternative treatment modalities. Thus, new human models are wanted. Here, we describe the metastatic behaviour of seven human melanoma cell lines derived from two primary cutaneous melanomas (WM 98-1, WM 1341) and five metastases established from liver (UKRV-Mel-4), skin (M7, M13), pleural effusion (UKRV-Mel-2) and lymph node (MV3). All cell lines were analysed for their capacity to grow in nude mice after s.c. and i.v. administration. M13 cells developed liver metastases spontaneously after s.c. injection, and subsequent passages of M13 and M7 melanoma cells caused liver metastases after i.v. injection, whereas MV3 and WM98-1 gave rise to lung metastases, using the same inoculation route. In contrast, WM 1341, UKRV-Mel-2 and UKRV-Mel-4 grew only very slowly in nude mice after s.c. injection and did not cause any metastases after i.v. or s.c. administration. The pattern of metastases or growth kinetics did not correlate with the interleukin 8 or tumour necrosis factor secretion of cell lines. Adhesion molecules and growth factor receptor expression on the cell lines differed widely, as determined by flow cytometry, with the low metastatic cell lines (UKRV-Mel-2, UKRV-Mel-4 and WM 1341) demonstrating a marked reduction in VLA-1 and VLA-5 expression compared with the metastatic lines (M7, M13, MV3 and WM 98-1). Expression of pigment-related proteins such as tyrosinase, TRP-1, TRP-2, Melan-A/MART-1, gp100, MAGE1 or MAGE-3 was not associated with growth and metastatic characteristics of the melanoma cell lines analysed. In conclusion, the established human melanoma cell lines exhibited diverse growth behaviour in nude mice in congruence with some early established prognostic markers such as VLA-1 and VLA-5. The xenografts provide good models for further study of metastatic processes as well as for evaluation of alternative treatment modalities including new pharmaceutical drugs and gene therapeutic targeting using tissue-specific gene regulatory elements for gene targeting.

CD44 expression on epidermal melanocytes

We examined CD44 expression on melanocytes to begin to understand what role CD44 might have in the normal behavior of melanocytes and to provide a basis for comparing CD44 expression in melanoma cells. CD44 was expressed on the entire surface of melanocytes and accentuated at the tips of dendritic processes. Two predominant forms of CD44 are expressed on cultured human foreskin melanocytes. One form has the covalent addition of chondroitin sulfate, whereas the other form has no chondroitin sulfate. Both use the hematopoietic, or CD44H, core protein. Using polymerase chain reaction primers that span the site where alternative splicing of CD44 occurs, we found only the cDNA coding CD44H. 12-O-Tetradecanoylphorbol 13-acetate increases the size of the chondroitin sulfate chain(s) attached to CD44 but not the proportion of CD44 molecules that carry chondroitin sulfate. Ninety percent of proteoglycans on melanocytes are chondroitin sulfate proteoglycans, and the CD44 chondroitin sulfate proteoglycan represented 10% of that total. These data show that CD44H is expressed as a "part-time" chondroitin sulfate proteoglycan on normal cultured melanocytes.

CD44 and melanocytic tumors: a possible role for standard CD44 in the epidermotropic spread of melanoma

CD44 is a polymorphic family of cell membrane glycoproteins that mediate cell-matrix and cell-cell interactions involved in the mechanisms of tumor invasion and metastasis, and are subject to differential regulation during normal and malignant cell growth. We have investigated immunohistochemically the expression of CD44S and the variant isoforms CD44v3 and CD44v6 in paraffin-embedded tissue from 5 Spitz nevi, 3 compound melanocytic nevi, 2 blue nevi, 6 primary melanomas, 15 cutaneous metastases (three epidermotropic, nine dermal and three ulcerated) and 10 lymph node metastases of melanoma. Melanocytes were extensively positive for CD44S in primary melanomas and benign melanocytic proliferations. Among 15 cases of cutaneous metastases of melanoma, the three epidermotropic metastases, as well as one of the three ulcerated ones were positive for CD44S. CD44S expression was diminished or totally absent in six of the nine dermal metastases, in two of the ulcerated metastases and in seven of the ten lymph node metastases. CD44v3 and CD44v6 melanocytic expression was absent in all the lesions studied. According to our results, selective retention of CD44S expression by melanocytes in epidermotropic metastases of melanoma seems to indicate that preservation of CD44S may contribute to the intraepidermal spread of melanoma.