Metastasis accounts for the majority of mortality associated with melanoma, as limited treatment options exist for advanced disease stages. The identification of prognostic markers for advanced melanoma is of great importance as currently the survival rate for patients at this stage of disease is highly variable.
One avenue that has been underexplored in melanoma research is protein glycosylation. Glycans attached to proteins, produced by cancer cells are known to play an important role in cancer progression and are promising melanoma biomarker targets.
The melanoma cell adhesion molecule (MCAM) is a cell surface glycoprotein, which is expressed in approximately 90% of lymph node metastases. MCAM is also associated with a poorer outcome in patients. However, to date the glycosylation status of this heavily N-glycosylated prognostic marker is still largely unknown.
Here, we investigate the relationship between cell surface glycosylation, metastatic phenotypes, and patient prognosis. We report the first in-depth glycan characterisation of cell surface proteins and evaluate the prognostic potential of glycosylation signatures for disease management.
Glycans released from melanoma cell surface proteins were characterised using a porous graphitized carbon liquid chromatography mass spectrometry glycomics platform. Structures were fully assigned using MS/MS fragmentation patterns and retention behaviours. The glycosylation profile of cell lines and tissue from different patient subgroups including disease stage were investigated to identify subtype-associated glycan features. In addition, the glycosylation profile of cultured cells was compared to patient tissue.
Global glycomics identified differences in structural features including branching, sialylation and fucosylation between individual patient samples. Patient tissue also exhibited a more complex glycosylation profile than cultured cells. The use of our orthogonal analytical workflow provided valuable structural information including confirmation of sialic acid linkage and the presence of polylactosamine chains. MCAM-specific glycosylation showed signatures that clearly change in abundance between patients including epitopes that have not been previously reported in metastatic melanoma.
This study contributes to our understanding of glycosylation alterations in melanoma metastasis, towards using specific glycosylation changes as novel biomarkers for monitoring metastasis and predicting prognosis.