Bitter Sweetness of Malignant Melanoma: Deciphering the Role of Cell Surface Glycosylation in Tumour Progression and Metastasis

Malignant melanoma is the sixth most commonly diagnosed cancer in developed countries. Like in many cancers, survival rates are closely associated with the time of melanoma detection. Regrettably, most cases of melanoma are caught at diffuse state and methods used in clinical practice and experimental trials are not effective. Thus, there is a great interest in discovering biomarkers that could be used for screening those with melanoma, as prognostic and prediction factors as well as new potential targets for melanoma treatment. For this purpose, many groups have examined alteration in the structure and expression of carbohydrate part of glycoconjugates to identify changes that occur with melanoma. The observed changes include increased β1,6 branching correlating with higher abundance of polylactosamine extension, increased sialylation accompanied by differences in the position of sialic acid residues, increased fucosylation, higher levels of T and Tn antigens as well as changes in the expression of ganglioside structures. As a consequence of glycan modification, the loosened matrix adhesion, increased motility, higher invasive potential and metastasis formation have been observed. Growth and migration of melanoma cells have been also found to be stimulated by advanced glycation end products. Biomarker discovery is a multi-step process and the recent glycomic data on melanoma are mostly related to the discovery phase, as the first one leading to validation and standardisation steps

Cadherins and their Role in Malignant Transformation: Implications for Skin Cancer Progression

Cadherins are a large family of Ca2+dependent adhesion proteins. They are transmembrane or closely related to membrane glycoproteins localized in specialized adhesive junction. The expression of various cadherins may be concomitant with cancer progression steps and the term ‘cadherin switch’ has been created due to the observation of down-regulation of E-cadherin (suppressor of metastatic potential) and up-regulation of N-cadherin (promoter of metastatic potential) expression during tumour progression. These changes are thought to be closely related to epithelial-to-mesenchymal transition of cells of many different types of cancer including skin cancers, and accompany the increase of their motility and invasion abilities resulting in the metastasis formation. The cadherin polypeptide is a potential substrate for post-translational modification, for example, N-glycosylation, and its important role in the regulation of cadherin function has been described. The changed glycosylation of cadherins has been described in various skin cancers including melanoma and was consistent with cadherins’ role in epithelial-to-mesenchymal transition. The detailed analysis of cadherin expression and cadherin-related glycosylation changes taking place during malignant transformation could be a key for better understanding of the nature of this process and may open new opportunities for the creation of more effective anticancer therapeutics and diagnostic tools

Carbohydrate moieties of N-cadherin from human melanoma cell lines

Expression of N-cadherin an adhesion molecule of the cadherin family, in tumor cells is associated with their increased invasive potential. Many studies suggested the role of N-linked oligosaccharides as important factors that contribute to metastasis by influencing tumor cell invasion and adhesion. N-cadherin is a heavily glycosylated protein. We have analysed the carbohydrate profile of this protein synthesized in human melanoma cell lines: WM35 from the primary tumor site and WM239, WM9, and A375 from different metastatic sites. N-cadherin was immunoprecipitated with anti-human N-cadherin polyclonal antibodies. Characterisation of its carbohydrate moieties was carried out by SDS/PAGE electrophoresis and blotting, followed by immunochemical identification of the N-cadherin polypeptides and analysis of their glycans using highly specific digoxigenin or biotin labelled lectins. The positive reaction of N-cadherin from the WM35 cell line with Galanthus nivalis agglutinin (GNA), Datura stramonium agglutinin (DSA) and Sambucus nigra agglutinin (SNA) indicated the presence of high-mannose type glycans and biantennary complex type oligosaccharides with α2-6 linked sialic acid. N-cadherin from WM239, WM9, and A375 cell lines gave a positive reaction with Phaseolus vulgaris leukoagglutinin (L-PHA) and lotus Tetragonolobus purpureas agglutinin (LTA). This indicated the presence of tri- or tetra-antennary complex type glycans with α-fucose. In addition, N-cadherin from WM9 (lymphomodus metastatic site) and A375 (solid tumor metastatic site) contained complex type chains with α2-3 sialic acid (positive reaction with Maackia amurensis agglutinin - MAA). The results demonstrated that N-glycans of N-cadherin are altered in metastatic melanomas in a way characteristic for invasive tumor cells

The lectin-binding pattern of nucleolin and its interaction with endogenous galectin-3

Unlike nuclear nucleolin, surface-expressed and cytoplasmic nucleolin exhibit Tn antigen. Here, we show localization-dependent differences in the glycosylation and proteolysis patterns of nucleolin. Our results provide evidence for different paths of nucleolin proteolysis in the nucleus, in the cytoplasm, and on the cell surface. We found that full-length nucleolin and some proteolytic fragments coexist within live cells and are not solely the result of the preparation procedure. Extranuclear nucleolin undergoes N- and O-glycosylation, and unlike cytoplasmic nucleolin, membrane-associated nucleolin is not fucosylated. Here, we show for the first time that nucleolin and endogenous galectin-3 exist in the same complexes in the nucleolus, the cytoplasm, and on the cell surface of melanoma cells. Assessments of the interaction of nucleolin with galectin-3 revealed nucleolar co-localization in interphase, suggesting that galectin-3 may be involved in DNA organization and ribosome biogenesis

Innovative GenExpA software for selecting suitable reference genes for reliable normalization of gene expression in melanoma

The algorithms commonly used to select the best stable reference gene in RT-qPCR data analysis have their limitations. We showed that simple selection of the reference gene or pair of genes with the lowest stability value from the pool of potential reference genes—a commonly used approach—is not sufficient to accurately and reliably normalize the target gene transcript and can lead to biologically incorrect conclusions. For reliable assessment of changes in a target gene expression level, we propose our innovative GenExpA software, which works in a manner independent of the experimental model and the normalizer used. GenExpA software selects the best reference by combining the NormFinder algorithm with progressive removal of the least stable gene from the candidate genes in a given experimental model and in the set of daughter models assigned to it. The reliability of references is validated based on the consistency of the statistical analyses of normalized target gene expression levels through all models, described by the coherence score (CS). The use of the CS value imparts a new quality to qPCR analysis because it clarifies how low the stability value of reference must be in order for biologically correct conclusions to be drawn. We tested our method on qPCR data for the B4GALT genes family in melanoma, which is characterized by a high mutation rate, and in melanocytes. GenExpA is available at https://github.com/DorotaHojaLukowicz/GenExpA or https://www.sciencemarket.pl/baza-programow-open-source#oferty