Characterisation of the Helix pomatia agglutinin binding glycoproteins of colorectal cancer cell lines and tissue samples

Colorectal cancer (CRC) is one of the most common malignancies in the US and Western Europe and metastatic dissemination after CRC is a leading cause of mortality. New markers predictive of cancer cell behaviour are actively sought both as targets and as a means of predicting patient prognosis. The lectin from the Roman snail Helix pomatia (HPA) has attracted interest as tool for the detection of metastatic colorectal cancer but the HPA binding partners have remained poorly characterised. We established an in vitro model using human colorectal cancer cell lines ranging from HPA negative, non metastatic, to HPA positive and metastatic. Confocal microscopy was used to assess the HPA binding pattern in the cell lines and the monosaccharides N-acetylgalactosamine, N-acetylglucosamine, and sialic acid were used to inhibit the interaction between the lectin and the cancer cells.
A proteomic approach based on cell membrane isolation, pre-fractionation using lectin affinity chromatography, followed by 2-dimensional electrophoresis and MALDI-TOF-MS enabled the identification of the HPA binding proteins in the metastatic cancer cell line HT29. The proteins that eluted in the HPA binding fraction were present either by virtue of their ability to bind directly to HPA or as protein complexes of HPA binding partners and included molecules involved in cell adhesion / migration (integrin a6, integrin aV, annexins) re-modeling (filament proteins including oc tubulin, Ptubulin, cytokeratins, actin) and anti-apoptotic pathways (Hsp-70, Hsp-90, Hsp-96 and TNFR-1). Although many of these proteins have previously been described as altered in cancer, we are not aware of a single reagent like HPA which will concurrently bind all of these molecules.