CD44 and variants in melanocytic skin neoplasms

CD44 and HCELL: preventing hematogenous metastasis at step 1

Despite great strides in our knowledge of the genetic and epigenetic changes underlying malignancy, we have limited information on the molecular basis of metastasis. Over 90% of cancer deaths are caused by spread of tumor cells from a primary site to distant organs and tissues, highlighting the pressing need to define the molecular effectors of cancer metastasis. Mounting evidence suggests that circulating tumor cells (CTCs) home to specific tissues by hijacking the normal leukocyte trafficking mechanisms. Cancer cells characteristically express CD44, and there is increasing evidence that hematopoietic cell E-/L-selectin ligand (HCELL), a sialofucosylated glycoform of CD44, serves as the major selectin ligand on cancer cells, allowing interaction of tumor cells with endothelium, leukocytes, and platelets. Here, we review the structural biology of CD44 and of HCELL, and present current data on the function of these molecules in mediating organ-specific homing/metastasis of CTCs.

HGF-promoted motility in primary human melanocytes depends on CD44v6 regulated via NF-kappa B, Egr-1, and C/EBP-beta

The regulation of CD44v6, a variant of the CD44 family of glycosylated adhesion molecules, through hepatocyte growth factor (HGF) has implications for motility in primary human melanocytes. We show that exposure of primary human melanocytes to HGF results in an increase of CD44v6 expression. Immunostaining of melanocytic lesions revealed low cytoplasmic positivity of CD44v6 in some nevi but high membranous expression in primary cutaneous melanomas, and cutaneous and lymph node metastases. HGF-dependent CD44v6 regulation in melanocytes is NF-kappaB dependent because BAY 11-7082, an inhibitor of NF-kappaB activation, but not interference with the mitogen-activated protein kinase or phosphatidylinositol 3-kinase cascade, antagonized HGF-induced CD44v6 expression. NF-kappaB-mediated transcriptional regulation of CD44v6 involves the transcription factors Egr-1 and CCAAT enhancer-binding protein-beta (C/EBP-beta). In gel shift assays, the initial binding of p100/p52 NF-kappaB, C/EBP-beta, and Egr-1 to the CD44 promoter experienced reshuffling toward increased affinity of C/EBP-beta after HGF stimulation. A blocking antibody to CD44v6 decreased HGF-induced c-Met phosphorylation as well as enhanced random- and site-directed migration. Our data show that HGF-induced motility in primary human melanocytes depends on c-Met-CD44v6 interaction, and that HGF-enhanced CD44v6 expression is required for motility and transcriptional upregulation of CD44v6, presumably mediated through a complex comprising NF-kappaB/C/EBP-beta and Egr-1.

Tumor necrosis is associated with increased alphavbeta3 integrin expression and poor prognosis in nodular cutaneous melanomas

Background

Tumor necrosis and apoptotic activity are considered important in cancer progression, but these features have not been much studied in melanomas. Our hypothesis was that rapid growth in cutaneous melanomas of the vertical growth phase might lead to tissue hypoxia, alterations in apoptotic activity and tumor necrosis. We proposed that these tumor characteristics might be associated with changes in expression of cell adhesion proteins leading to increased invasive capacity and reduced patient survival.

Methods

A well characterized series of nodular melanoma (originally 202 cases) and other benign and malignant melanocytic tumors (109 cases) were examined for the presence of necrosis, apoptotic activity (TUNEL assay), immunohistochemical expression of hypoxia markers (HIF-1 α, CAIX, TNF-α, Apaf-1) and cell adhesion proteins (α_vβ₃ integrin, CD44/HCAM and osteopontin). We hypothesized that tumor hypoxia and necrosis might be associated with increased invasiveness in melanoma through alterations of tumor cell adhesion proteins.

Results

Necrosis was present in 29% of nodular melanomas and was associated with increased tumor thickness, tumor ulceration, vascular invasion, higher tumor proliferation and apoptotic index, increased expression of α_vβ₃ integrin and poor patient outcome by multivariate analysis. Tumor cell apoptosis did also correlate with reduced patient survival. Expression of TNF-α and Apaf-1 was significantly associated with tumor thickness, and osteopontin expression correlated with increased tumor cell proliferation (Ki-67).

Conclusion

Tumor necrosis and apoptotic activity are important features of melanoma progression and prognosis, at least partly through alterations in cell adhesion molecules such as increased α_vβ₃ integrin expression, revealing potentially important targets for new therapeutic approaches to be further explored.

The molecular basis of melanomagenesis and the metastatic phenotype

The last two decades have seen spectacular advances in our understanding of the biology of melanoma and, in particular, have elucidated the mechanisms operative in disease initiation and progression. With respect to the former, the genetics of melanoma and in particular the impact of genetic defects on dysregulation of the cell cycle are key issues in malignant transformation and are a major focus of this review. With respect to the latter, consideration also is given to the acquisition of growth factor autonomy and the capacity for invasion and metastasis from the standpoint of cell adhesion, motility, and matrix digestion. These events have specific morphologic correlates that will be briefly addressed. Where relevant, we will address certain of the modern pharmacogenetic strategies that flow from these novel observations concerning melanoma biology.

Comparative Histopathology of Grey-Horse-Melanoma and Human Malignant Melanoma

Equine melanoma shows striking features particularly with regard to clinical development in grey horses: in contrast to malignant melanoma in humans and in solid coloured horses that are characterized by early onset of metastasis, pigment cell tumours display almost benign clinical features in ageing grey horses. Through evolution, grey horses appear to be in a favourable position in regard to the biological behaviour of melanomas. Yet unknown factors inhibiting or retarding early melanoma metastasis may be responsible for this phenomenon. In this study, immunostaining profiles and histopathologic patterns of equine vs. human melanotic tumours were compared. In addition, the expression of melanoma markers currently used in human melanoma detection and characterization were evaluated for their applicability in equine melanoma diagnosis. Immunohistopathologic investigations revealed that benign grey horse melanomas share common features with human blue nevi and with human malignant desmoplastic melanomas, whereas their resemblance to other types of human cutaneous malignant melanomas is less pronounced. Our data equally underline that S-100, proliferating cell nuclear antigen (PCNA), HMB-45, Ki-67, T-311 and CD44 can serve as reliable markers for horse melanomas. Further investigations aiming at identifying factors retarding metastasis in affected grey horses are needed, as they may contribute to the development of novel treatment strategies for human malignant melanoma.

Differential Expression of CD44 in Canine Melanocytic Tumours

CD44, the main cell surface receptor for hyaluronan (HA), is often overexpressed in tumour cells, and its presence has been related to cell proliferation and migration. Many of the functions of CD44 are mediated through its interaction with hyaluronan. This study investigated the expression of CD44 in CML-1 and CML-10c2 canine melanoma cell lines and melanoma biopsies, and the production of hyaluronan and versican by the canine melanoma cell lines. Versican is an extracellular proteoglycan that binds hyaluronan, forming a tridimensional pericellular coat surrounding the cells. Both canine melanoma cell lines expressed CD44 and produced HA, but only CML-1 produced versican. Cells expressing all three components (CD44, HA and versican) formed abundant extracellular matrices as demonstrated by a particle exclusion assay. CD44 was present within benign and malignant melanomas, but its expression was more intense in malignant melanomas (P < 0.01). In high CD44-expressing tumours, CD44 tended to be present in the periphery of malignant melanomas, whereas its expression was homogeneous in benign melanomas.

CD44 in cancer

CD44 is a multistructural and multifunctional cell surface molecule involved in cell proliferation, cell differentiation, cell migration, angiogenesis, presentation of cytokines, chemokines, and growth factors to the corresponding receptors, and docking of proteases at the cell membrane, as well as in signaling for cell survival. All these biological properties are essential to the physiological activities of normal cells, but they are also associated with the pathologic activities of cancer cells. Experiments in animals have shown that targeting of CD44 by antibodies, antisense,and CD44-soluble proteins markedly reduces the malignant activities of various neoplasms, stressing the therapeutic potential of anti-CD44 agents. Furthermore, because alternative splicing and posttranslational modifications generate many different CD44 sequences, including, perhaps, tumor-specific sequences, the production of anti-CD44 tumor-specific agents may be a realistic therapeutic approach. However, in many cancers (renal cancer and non-Hodgkin's lymphomas are exceptions), a high level of CD44 expression is not always associated with an unfavorable outcome. On the contrary, in some neoplams CD44 upregulation is associated with a favorable outcome. Even worse, in many cases different research grows analyzing the same neoplastic disease reached contradictory conclusions regarding the correlation between CD44 expression and disease prognosis, possibly due to differences in methodology. These problems must be resolved before applying anti-CD44 therapy to human cancers.

Immunohistochemical markers of melanocytic lesions: a review of their diagnostic usefulness

We critically reviewed recent literature reports of 25 melanocytic immunohistochemical markers. This review organizes and summarizes the many new studies of old and novel melanocytic markers and identifies the most promising diagnostic immunohistochemical markers that can be used to distinguish melanocytic from nonmelanocytic lesions and benign melanocytic from malignant melanocytic lesions.

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.