A novel anticancer mechanism of catfish (
Silurus asotus) egg lectin (SAL) was found to occur via the down-regulation of the membrane transopter
protein,
MRP1 (multidrug resistance associate
protein-1) on
Burkitt's lymphoma cells through Gb3(Galα1-4Galβ1-4Glc)-glycosphingolipid. Although SAL did not influence the viability of the cells directly, only 10 and 100 ng/mL of
vincristine and
etoposide, respectively induced anticancer effects when the
lectin was applied in conjunction with these drugs. These phenomena were specifically inhibited by the co-presence of the α-galactoside,
melibiose, which is a strong haptenic
sugar of SAL that mimicks Gb3. The degree of expression regulation of the transporter
proteins on the cells surface was investigated through the examination of the binding between SAL and Gb3-glycosphingolipid by immunological and molecular
biological procedures. PCR data showed that
MRP1 was more highly expressed when compared to another
ATP-binding cassette family, multi-
drug resistant
protein and the expression levels of
MRP1 on the cells were specifically dose- and time-dependently depleted by the addition of SAL. These results were also evaluated by immunological procedures using FACS and western-blotting.
Small interfering RNA coding a part of
MRP1 was transfected to Raji cells to knock down the
protein, and cell death was increased by 10% when
vincristine was administered at a concentration as low as 10 ng/mL compared to non-transfected cells. These results indicated that SAL possesses the potential to enhance the anticancer activites of low-concentrations of
vincristine by the down-regulating the
MRP1 gene expression to inhibit the multidrug resistance by binding to the target
ligand Gb3-glycosphingolipid on
Burkitt's lymphoma cells.