Cancer cells very often display distinct oligosaccharides that are supposed to play a critical role in a tumor metastasis and an escape from immune response. The alteration of oligosaccharides can encompass both changes in their abundance and structural modifications. Many standard methods use lectins as probes in aim to detect carbohydrate’s structures. Lectins are proteins that recognize different types of oligosaccharides with very specific binding affinities comparable with those observed for enzyme–substrate or antigen–antibody interactions. They are commonly used in the characterization and isolation of simple and complex sugars and as histological reagents in many areas of diagnostic investigation, especially those related to changes in the expression of cell membrane glycans.
The expression of plasma membrane oligosaccharides of two human bladder cell lines was probed directly on a surface of living cell with the probing tip functionalized with three distinct lectins: concanavalin A (ConA), lectins from Sambucus Nigra (SNA) and from Phaseolus vulgaris (PHA-L). It was quantified based on the AFM measurements by the unbinding force giving the strength of interaction occurring between single pair of molecules and by the unbinding probability indicating the number of oligosaccharide’s ligands present on a surface of living bladder cells. The obtained results showed the differences of the oligosaccharide’s expression in cancer cells (T24) compared with the reference cells (HCV29). Both the number of a given glycan’s type and the distinct character of binding (i.e. formation of weak or strong bonds described by small or large unbinding force) were altered upon cancer transformation.
These results demonstrate the potential of AFM to directly probe the presence of molecules on a living cell surface, together with the quantitative description of their expression what can be used for detection of cancerous cells.
|